This PDF file contains the front matter associated with SPIE Proceedings Volume 7650, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

This paper compares and contrasts one-dimensional (1D) and three-dimensional (3D) scanning laser Doppler vibrometer (LDV) measurements of Lamb waves generated by lead zirconate titanate (PZT) transducers. Due to the large cost and capability differences between the previously mentioned systems, this study is provided to highlight differences between these systems. 1D measurements are defined here as measurements of only out-of-plane velocities which are well-suited for studying anti-symmetric Lamb wave modes. 3D measurements provide both in- and out-of-plane velocities, which are especially important when studying both symmetric and anti-symmetric Lamb wave modes. The primary reason for using scanning LDVs is that these systems can make non-contact, accurate surface velocity measurements over a spatially-dense grid providing relatively high resolution image sequences of wave propagation. These scans can result in a clear understanding of Lamb waves propagating in plate-like structures and interacting with structural variations.

In this paper, the use of time domain data from piezoelectric active-sensing techniques is investigated for structural health monitoring (SHM) applications. Piezoelectric transducers have been increasingly used in SHM because of their proven advantages. Especially, the use of known and repeatable inputs at high frequency ranges makes the development of SHM signal processing algorithm easier and more efficient. However, to date, most of these techniques have been based on frequency domain analyses, such as impedance-based or high-frequency response functions (FRF) -based SHM techniques. Even with Lamb wave propagations, most researchers adopt frequency domain or wavelets analysis for damage-sensitive feature extraction. This process usually requires excessive averaging to reduce measurement noise and more computational resources, which is not ideal from both memory and power consumption standpoints. Therefore in this study, we investigate the use of autoregressive models with exogenous inputs (ARX) with the measured time series data from piezoelectric active-sensors. The test structure considered in this study is a composite plate, where several damage conditions were manually imposed. The performance of this technique is compared to that of traditional autoregressive models, traditionally used in low-frequency passive sensing SHM applications, and that of FRF-based analysis, and its superior capability for SHM is demonstrated.

This contribution is concerned with the hardware design of a structural health monitoring (SHM) system for continuous delamination detection in carbon fiber reinforced polymer components. The component is equipped with an integrated actuator array of eight piezoelectric patches which are driven by miniaturized high frequency power amplifiers. The phased line array is capable of emitting directional guided Lamb waves with a frequency of several hundreds of kilohertz and with user-selectable waveform pattern and directivity angle into the continuum. The directivity of the Lamb wave depends on the phase difference between the individual actuator signals. A special milling technique allows to create phased array stripes of arbitrary size and shape of the electrodes with high precision and reduce the placing and time complexity. A laser scanning Doppler vibrometer is used to visualize the propagation of the corresponding Lamb waves, as well as reflections which are caused by delamination defects. The results of the measurements can be evaluated to characterize the damage and the material properties. The hardware platform provides a portable system for the investigation of real world components, e.g. aircraft CFRP structures.

Metal-core piezoelectric fibers (MPF) are a new type of piezoelectric ceramic device with small size, and have great potential to be used as structurally integrated transducers for guided-wave (GW) structural health monitoring. The response of surface-bonded metal-core piezoelectric fiber (MPF) sensors to Lamb-wave fields is introduced. The interaction of Lamb waves with damage, e.g. the reflection of the waves at defects, allows the detection of damage in structures by monitoring the Lamb wave propagation characteristics. The good directional properties of MPF are used to determine the direction of the reflected Lamb waves by mounting three MPF sensors in a rosette configuration. Two suitably spaced rosettes are used to locate the source of reflection, i.e., the damage, by taking the intersection of the directional lines given by the two rosettes. The performance of the sensor for Lamb wave sensing and damage localization is validated on an aluminum plate.

Many studies have demonstrated for composite structures such as aerospace components the peak force of impacts can be correlated to damage. Hence, techniques able to estimate the impact forces are being investigated. The present paper deals specifically with the inverse problem of identification of impact forces on isotropic and composite panels given the dynamic response of Macro Fiber Composite (MFC) sensors bonded to the components. First a Semi Analytical Finite Element (SAFE) approach is employed to predict the frequency response and time history response of the MFC sensors assuming an impulse force excitation. Subsequently, the impact force is estimated updating the force time history assumed in the SAFE by minimizing the difference between numerical and experimental signals from MFC sensors. Such procedure has been used in isotropic and composite plates. Impact forces generated using impact hammers and different ice projectiles launched with gas cannon on panels have been identified.

Wireless sensor networks (WSN) are proving to be a good fit where real time monitoring of multiple physical parameters is required. In many applications such as structural health monitoring, patient data monitoring, traffic accident monitoring and analysis, sensor networks may involve interface with conventional P2P systems and it is challenging to handle heterogeneous network systems. Heterogeneous deployments will become increasingly prevalent as it allows for systems to seamlessly integrate and interoperate especially when it comes to applications involving monitoring of large infrastructures. Such networks may have wireless sensor network overlaid on a conventional computer network to pick up data from one distant location and carry out the analysis after relaying it over to another distant location. This paper discusses monitoring of bridges using WSN. As a test bed, a heterogeneous network of WSN and conventional P2P together with a combination of sensing devices (including vibration and strain) is to be used on a bridge model. Issues related to condition assessment of the bridge for situations including faults, overloads, etc., as well as analysis of network and system performance will be discussed. When conducted under controlled conditions, this is an important step towards fine tuning the monitoring system for recommendation of permanent mounting of sensors and collecting data that can help in the development of new methods for inspection and evaluation of bridges. The proposed model, design, and issues therein will be discussed, along with its implementation and results.

Bridge structural health monitoring system is a typical multi-sensor measurement system due to the multi-parameters of bridge structure collected from the monitoring sites on the river-spanning bridges. Bridge structure monitored by multi-sensors is an entity, when subjected to external action; there will be different performances to different bridge structure parameters. Therefore, the data acquired by each sensor should exist countless correlation relation. However, complexity of the correlation relation is decided by complexity of bridge structure. Traditionally correlation analysis among monitoring sites is mainly considered from physical locations. unfortunately, this method is so simple that it cannot describe the correlation in detail. The paper analyzes the correlation among the bridge monitoring sites according to the bridge structural data, defines the correlation of bridge monitoring sites and describes its several forms, then integrating the correlative theory of data mining and signal system to establish the correlation model to describe the correlation among the bridge monitoring sites quantificationally. Finally, The Chongqing Mashangxi Yangtze river bridge health measurement system is regards as research object to diagnosis sensors fault, and simulation results verify the effectiveness of the designed method and theoretical discussions.

Acoustic stress waves can be guided to follow pre-determined paths in solids, using elastic anisotropy. Recently, there has been intense interest to design materials and structures that can shield specific regions within the material by redirecting the incident stress-waves along desired paths. Some of the proposed techniques involve variable mass density and stiffness. We have designed a material with isotropic mass density but highly anisotropic elasticity that can guide incident waves along desired trajectories. Harmonic excitations are imposed, and it is shown that the stress-wave energy would travel around a protected central region. The model is also evaluated using numerical simulations, which confirm that majority of the stress-wave energy is guided around the central cavity and is delivered exactly to the opposing face in a location corresponding to the incident excitation location.

The wave speed in an anisotropic plate is dependent on the direction of propagation and therefore the conventional triangulation technique does not work for the prediction of the impact point. A method based on the optimization technique was proposed by Kundu et al. to detect the point of impact in an anisotropic plate. They defined an objective function that uses the time of flight information of the ultrasonic signals to the passive transducers attached to the plate and the wave propagation direction (θ) from the impact point to the receiving sensors. This function is very sensitive to the arrival times. A small variation in any one arrival time results in a significant change in the impact point prediction. This shortcoming is overcome here by modifying the objective function and following a new algorithm. Both old and new objective functions (denoted as functions 1 and 2) are used in the new algorithm. This algorithm uses different sets of transducers and identifies the common predictions from different sets. The proposed algorithm is less sensitive to the arrival time variation and thus is capable of predicting the impact point correctly even when the measured arrival time has some error. The objective function 2 is simpler, so the computer code run time is reduced and it is less likely to converge to the local minima when using the simplex or other optimization techniques. The theoretical predictions are compared with experimental results.

Transducer arrangements including specially designed electronic drive and detection circuitry are presented, suitable to distinguish between the orthogonal symmetric and anti-symmetric Lamb wave modes. Whereas transducers mounted on both surfaces have already been introduced for this task, novel schemes based on transducers mounted single sided can also be exemplified in combination with advanced electronic schemes providing alignment with respect to the orthogonality of the separated modes. Detail of the developed scheme is exemplified together with experimental results which are compared to the expectations based on established modeling.

This work focuses on the detection, localization, and quantification of damage in the form of loose bolts on an isogrid satellite structure. In the process of rapid satellite development and deployment, it is necessary to quickly complete several levels of validation tests. Structural Health Monitoring methods are being investigated as a means for reducing the number of validation tests required. This method for detecting loose bolts enables quick confirmation of proper assembly, and verification that structural fasteners are still intact after validation testing. Within this testing framework, feature selection is presented as well as a localization methodology. Quantification of fastener torque is also developed. Locating damage in an isogrid structure is complicated by the directionally dependent dispersion characteristics caused by a propagating wave passing through ribs and holes. For this reason, an actuation frequency with the best first wave arrival clarity is selected. A methodology is presented in which a time map is constructed for each actuator-sensor pair which establishes times of flight for each location on the sample. Differences in time between healthy and damaged sensor signals are then extracted and used to create a map of possible damage locations. These resulting solution maps are merged yielding a final damage position. Fastener torque is correlated to a damage parameter, and the loose bolt position is calculated within 3 cm.

A novel time-frequency procedure is presented in this paper for guided wave (GW) propagation analysis in structure health monitoring (SHM) applications.The proposed approach combines the Warped Frequency Transform (WFT) with a Basis Pursuit algorithm to generate a sparse yet accurate time-frequency representation of the acquired signals even in the case of multi-modal dispersive propagation associated to broadband excitation of the waveguide. This is obtained through over complete dictionaries composed by optimized atoms which are designed to match the spectro-temporal structure of the various propagating modes.The Warped Basis Pursuit (W-BP) decomposition of several acquired waveforms results in distance signals that can be combined through classical beamforming techniques for imaging purposes. This approach is tested on experimental data obtained by broadband GW excitation in a 1 mm thick aluminum plate with an artificially introduced through crack, followed by multiple waveguide displacement recording through a scanning laser Doppler vibrometer. Dispersion compensation and high-resolution source as well as defect imaging is demonstrated even in domain regions that are not directly accessible for measurement.

The transmissibility between two response measurements is a widely-used feature for damage detection and localization in vibration-based, structural health monitoring applications. In this paper, we investigate two features computed from transmissibility measurement changes to quantify connection stiffness loss: root-mean-square error and dot-product difference. In real practice, noise contaminates the measurements, and this noise can lead to reduced sensitivity in the transmissibility as a damage-sensitive feature and increase false-positive (Type-I) errors. This work establishes a model to investigate the effect of noise and establishes statistical confidence limits on the transmissibility estimate. We make the assumption that the system is stationary, the signal channels are optimized, and the signal-to-noise ratios are balanced. The analytical expressions of the biased error and variation are given in terms of coherence estimation, and the confidence bounds of the transmissibility with corresponding level of confidence are estimated.

This paper presents a conjugate-pair decomposition (CPD) method for offline damage inspection and online health monitoring of dynamical systems. Responses of damaged dynamical systems are often nonlinear and nonstationary. For a nonlinear non-stationary signal, empirical mode decomposition (EMD) uses the apparent time scales revealed by the signal's local maxima and minima to sequentially sift intrinsic mode functions (IMFs) of different time-varying scales, starting from high- to low-frequency ones. For offline detailed damage inspection, CPD uses one or more pairs of windowed adaptive harmonics and function orthogonality to track time-varying frequency and amplitude of each IMF. Because CPD processes only time-domain data, it is free from the edge effect caused by Gibbs' phenomenon and other mathematical and numerical problems caused by the use of Hilbert transform. Hence, results from CPD are valuable for accurate identification of dynamical systems. For parametric identification, one can compare the time-varying frequency and amplitude from CPD with those from perturbation analysis to determine the type and order of nonlinearity and system parameters. For online health monitoring, CPD tracks the instantaneous frequency of an arbitrary signal without signal decomposition by processing three or more most recent data to estimate its instantaneous frequency and amplitude. Numerical results show that CPD is versatile for system identification, damage inspection, and health monitoring of different linear/nonlinear dynamical systems.

On the basis of first principle approaches as used for lattice dynamics basic features of the dependence of the time-offlight of acoustic waves on elongation under stress are treated and exemplified for a linear chain. The chain is constructed from point masses connected by mass free springs acting instantaneously. The microscopic approach is used to exemplify the nature of the effects involved in stress or load detection by monitoring the time-of-flight of ultrasonic waves. Whereas the effects caused by anharmonicity lead to an increase in the monitored time-of-flight, tension can also lead to a decrease if geometric effects are present, leading to a stiffening under tension. In the absence of geometrical stiffening, which is not present in a linear chain for longitudinal polarized waves, the time-of-flight in a harmonic chain with forces transferred instantly is independent of tension.

The acoustic emission (AE) technique is a promising tool for monitoring the integrity of structural members while they are in service. The major obstacle in deploying this technique is the presence of noise from extraneous sources that generate false positives. Identification and separation of noise from crack related signals are of interest. Friction induced AE is a prominent source of noise in structural members. When a structural member having riveted or bolted joints is subjected to cyclic loading, the mating parts of the surfaces experience very small relative motion that results in a localized rubbing process usually termed as "fretting". The fretting process is a prolific source of AE signals. As signals from crack growth as well as fretting emanates from the same region in riveted joints, it is difficult to discriminate crack related AE from fretting related AE, unless the distinct characteristics of the two signals are well understood. However, fretting related AE signals are also of noteworthy interest in tribological applications as they contain significant information about the surface conditions. To understand friction induced AE signals, numerically simulated fretting signals are analyzed. Greenwood and Williamson's multiple asperity contact model is used to generate fretting signals numerically. The results are also compared with experimentally obtained fretting signals.

The development of effective damage imaging and characterization tools is a challenging task because of the dispersive and multi-modal nature of Lamb waves. An additional problem is the need for baseline data that is required by a number of existing techniques. This paper presents the development of imaging algorithms applied to filtered wavefield data received from piezoelectric disc sources. Frequency-wavenumber filtering is used to separate incident/backscattered waves and individual wave modes. Filtered data are provided as input to imaging algorithms that detect damage and estimate its location. The implementation of incident and backscattered waves separation procedures avoids the need for a baseline, while mode separation permits the analysis of modes that are most sensitive to damage. The proposed algorithm is verified experimentally for damage detection on an aluminum plate.

Lamb waves are being explored for structural health monitoring (SHM) due to their capability of detecting relatively small damage within reasonably large inspection areas. However, Lamb wave behavior is fairly complex, and therefore, various computational techniques, including finite element analysis (FEA), have been utilized to design appropriate SHM systems. Validation of these computational models is often based on a limited number of measurements made at discrete locations on the structure. For example, models of pitch-catch of Lamb waves may be validated by comparing predicted waveform time histories at a sensor to experimentally measured results. The use of laser Doppler vibrometer (LDV) measurements offers the potential to improve model validation. One-dimensional (1D) LDV scans provide detailed out-of-plane measurements over the entire scanned region, and checks at discrete sensor locations can still be performed. The use of three-dimensional (3D) laser vibrometer scans further expands the data available for correlation by providing in- and out-of-plane velocity components over the entire scanned region. This paper compares the use of 1D and 3D laser vibrometer data for qualitatively and quantitatively validating models of healthy metallic and composite plates.

Guided waves generated by a spatially distributed array of piezoelectric are being evaluated by many researchers for structural health monitoring applications. These surface-mounted transducers, which are typically Lead Zirconate Titanate (PZT), are generally assumed to be both undamaged and properly bonded to the host structure during usage. However, this assumption may not be valid, particularly after long term operation under realistic conditions. Existing transducer diagnosis techniques often identify PZT defects by comparing current data to baseline data previously measured from the pristine condition of the bonded transducers. This baseline-dependent approach can result in false alarms because of its susceptibility to operational, structural and environmental variations. In this study, a methodology for PZT transducer diagnosis is developed to identify damaged or poorly bonded transducers by quantifying the degree of linear reciprocity for waves propagating between pairs of surface-mounted transducers on metallic structures. The proposed method does not require direct comparisons of signals to baselines, and also is independent of wave mode(s), excitation signal, structural complexity and edge reflections. The efficacy of the proposed diagnostic technique is evaluated via experiments with PZT transducers instrumented on an aluminum plate under varying environmental and structural conditions and also on a complex structure.

This paper describes a method based on Ultrasonic Guided Waves (UGWs) for the detection of cracks in sign support structures. The method combines the advantages of UGWs with the extraction of defect-sensitive features aimed at performing a multivariate diagnosis of damage. The general frame work presented in this paper is applied to ultrasonic data collected from a dimantled overhead sign support structure tested at the University of Pittsburgh. The probing hardware consists of a National Instruments-PXI platform that controls the generation and detection of the ultrasonic signals by means of the piezoelectric transducers made of Lead Zirconate Titanate. The effectiveness of the proposed approach to diagnose the presence of defects as small as a few percent of the waveguide cross-sectional are is demonstrated.

In this study, the feasibility of using a scanning laser vibrometer for detecting hidden delamination in multi-layer composites is explored. First, Lamb waves are excited by Lead Zirconate Titanate (PZT) transducers mounted on the surface of a composite plate, and the out-of-plane ultrasonic velocity field is measured using a 1D scanning laser vibrometer. From the scanned time signals, wave field images are constructed and processed to study the interaction of Lamb waves with hidden delamination. In order to highlight the defect area in the image, the performance of different image processing tools were investigated. In particular, the Laplacian image filter was found to accentuate the visual indications of the ultrasound-defect interaction by suppressing the presence of incident waves in the wave field images. The performance of the proposed scheme is investigated using experimental data collected from a 1.8 mm thick multilayer composite plate and a 10 mm thick composite wing structure.

Impedance-based structural health monitoring (SHM) has been of great interest to many researchers. In general, conventional impedance-based damage detection techniques identify damage by comparing "current" impedance signals with "baseline" ones obtained from the pristine condition of a structure. However, structures in field are often subject to changing environmental and operational conditions that affect the measured impedance signals and these ambient variations can often cause false-alarms. In this paper, a new reference-free impedance method, which does not require direct comparison with baseline impedance signals, is employed for crack detection in a plate-like structure. This method utilizes a single pair of PZTs collocated on the both surfaces of a structure to detect mode conversion caused by the presence of crack damage. A new statistical damage classifier is developed for instantaneous damage classification based on decomposed impedance signatures containing mode conversion information. Experimental tests, particularly under varying temperature and loading conditions are presented to demonstrate the applicability of the proposed method to crack detection.

A new ultrasonic guided wave modal analysis technique (UMAT) is being studied to bridge the gap between ultrasonic guided wave methods and lower frequency vibration modal analysis methods for Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM). The new technique provides improved defect detection sensitivity superior to modal analysis alone, and, at the same time, reduces the number of inspection positions required by the guided wave techniques for a complete coverage of the structures being inspected. Instead of focusing on the transient structural response to a guided wave input, the proposed UMAT puts the emphasis on the long time structural response to a specifically defined ultrasonic guided wave input. Since different guided wave modes and frequencies yield good sensitivities to different kinds of defects, the specified guided wave input which is selected to target on a certain defect type provides a special sensitivity to the defect type. By varying the input guided wave modes and frequencies, good sensitivities to all different kinds of defects can be achieved. In UMAT, the defect information is extracted through modal analyses on the long time structural responses to the controlled guided wave inputs. Thanks to the fact that the long time structural responses result from multiple reflections and scatterings of the input guided wave energy, an overall coverage of the structure can be reached from a very limited number of tests. UMAT is also capable of inspecting odd shaped parts with different attachment considerations or boundary conditions and even hidden, coated, or insulated parts as long as a small section is accessible.

An effective in-service health monitoring system is needed for steam pipes to track through their wall the condensation of water in real-time at high temperatures. The system is required to measure the height of the condensed water inside the pipe while operating at temperatures that are as high as 250°C. The system needs to be able to make time measurements while accounting for the effects of water flow and cavitation. For this purpose, ultrasonic waves were used to perform data acquisition of reflected signals in pulse-echo and via autocorrelation the data was processed to determine the water height. Transmitting and receiving the waves is done by piezoelectric transducers. There are transducers with Curie temperatures that are significantly higher than the required for this task offering the potential to sustain the conditions of the pipe over extended operation periods. This paper reports the progress of the current feasibility study that is intended to establish the foundations for such health monitoring systems.

Concrete pipelines are one of the most popular underground lifelines used for the transportation of water resources. Unfortunately, this critical infrastructure system remains vulnerable to ground displacements during seismic and landslide events. Ground displacements may induce significant bending, shear, and axial forces to concrete pipelines and eventually lead to joint failures. In order to understand and model the typical failure mechanisms of concrete segmented pipelines, large-scale experimentation is necessary to explore structural and soil-structure behavior during ground faulting. This paper reports on the experimentation of a reinforced concrete segmented concrete pipeline using the unique capabilities of the NEES Lifeline Experimental and Testing Facilities at Cornell University. Five segments of a full-scale commercial concrete pressure pipe (244 cm long and 37.5 cm diameter) are constructed as a segmented pipeline under a compacted granular soil in the facility test basin (13.4 m long and 3.6 m wide). Ground displacements are simulated through translation of half of the test basin. A dense array of sensors including LVDT's, strain gages, and load cells are installed along the length of the pipeline to measure the pipeline response while the ground is incrementally displaced. Accurate measures of pipeline displacements and strains are captured up to the compressive and flexural failure of the pipeline joints.

The durability of concrete pavement to freeze/thaw cycles is mainly dependent on the air void system. Air entraining admixtures are used to provide a beneficial air void system. Large entrapped air voids reduce strength and make it insufficient to simply characterize the porosity by the air content; void spacing and specific surface parameters are also important. Ability to perform quality assurance testing - nondestructive evaluation - of concrete pavement soon after placement is highly desirable. Thus, laboratory experiments have been conducted to investigate Rayleigh surface waves for characterization of porosity in fresh concrete. A mediator mounted onto a Plexiglas wedge is used to introduce waves from an ultrasonic transducer onto the surface of the concrete. The challenges are that fresh concrete is highly attenuative and that the material properties evolve as the concrete sets. Rayleigh wave speed is shown to be sensitive to porosity by simple micromechanical modeling, and results are presented for normal concrete with large aggregate, sieved concrete, and mortar. Wave speeds are significantly less (10-22% depending on time after placement) for concrete with approximately 5% porosity relative to concrete with no air entrainment admixture.

Soil liquefaction in Northeast Arkansas (NEA) is expected to result in substantial damage during seismic events. Insitu shear wave velocity (V_s) profile of the subsurface, to a depth of at least 30-meters (according to the International Building Code or IBC), is necessary for determining the "Site Class", which is subsequently used in the structural analysis of buildings, and can be used as a screening tool to evaluate the depth and thickness of potentially liquefiable soil layers. Shear wave velocity profiles at 3 sites in Craighead County, AR were determined utilizing simplified equipment by means of a non-invasive technique. The results indicated good agreement with previous work performed by other researchers. These profiles were used to evaluate the liquefaction resistance at these sites using the simplified procedure by Seed and Idriss (V_s approach). The liquefaction resistance was also evaluated using the Standard Penetration Test (SPT approach) results from the geotechnical investigations that were conducted by others. The equipment and procedure should allow governmental agencies and engineering professional to determine the shear wave velocity profiles of the upper soil zones at relatively low cost. These profiles can aid different agencies in mapping areas of interest and assessing seismic hazard potential during planning future development or evaluating current facilities.

Concrete piles are widely used in the construction of civil infrastructures and it is important to perform the health monitoring of concrete piles for safety purposes. In this paper, a piezoceramic-based innovative approach is proposed for the damage detection and health monitoring of concrete piles. A multi-functional piezoceramic-based transducer device, the smart aggregate, is developed for health monitoring purposes. An active-sensing network is formed by embedding the proposed smart aggregates at the pre-determined locations in the concrete piles before casting. In the proposed approach, one smart aggregate is used as an actuator to excite the desired waves and the other distributed smart aggregates are used as sensors to detect the wave responses. An energy distribution vector is formed based on the wavelet-packet analysis results of sensor signals. A damage index is formed by comparing the difference between the energy distribution vectors of the health concrete pile and that of the damaged concrete pile. To verify the effectiveness of the proposed approach, two concrete piles instrumented with smart aggregates are used as testing objects. One concrete pile is intact and the other has a man-made crack in the middle of the pile. Experimental results show that the there are differences between the energy distribution vectors of the damaged pile and that of the intact pile due to the existence of the crack. The proposed method has the potential to be applied to perform automated integrity inspections for new piles and for the long-term health monitoring of piles in services.

A considerable proportion of railroad infrastructure exists in regions which are comparatively remote. With regard to the cost of extending electrical infrastructure into these areas, road crossings in these areas do not have warning light systems or crossing gates and are commonly marked with reflective signage. For railroad track health monitoring purposes, distributed sensor networks can be applicable in remote areas, but the same limitation regarding electrical infrastructure is the hindrance. This motivated the development of an energy harvesting solution for remote railroad deployment. This paper describes on-track experimental testing of a mechanical device for harvesting mechanical power from passing railcar traffic, in view of supplying electrical power to warning light systems at crossings and to remote networks of sensors. The device is mounted to and spans two rail ties and transforms the vertical rail displacement into electrical energy through mechanical amplification and rectification into a PMDC generator. A prototype was tested under loaded and unloaded railcar traffic at low speeds. Stress analysis and speed scaling analysis are presented, results of the on-track tests are compared and contrasted to previous laboratory testing, discrepancies between the two are explained, and conclusions are drawn regarding suitability of the device for illuminating high-efficiency LED lights at railroad crossings and powering track-health sensor networks.

We developed a self-powered wireless autonomous Structural Health Monitoring (SHM) sensor node using a Texas Instruments MSP430 evaluation board. The sensor node employs a PZT (Lead Zirconate Titanate) based impedance method, which saves power by eliminating a digital-to-analog-converter (DAC) for generation of an excitation signal and an analog-to-digital converter (ADC) for sensing the response. The sensor node wakes up at a predetermined interval, performs an SHM operation, and reports the result to the host computer wirelessly. The sensor node consumes only 0.3 J and is powered up by the energy harvested from vibrations, often available from infrastructures. The power management circuit integrated with a piezoelectric cantilever with the size of 50 mm x 31.8 mm generate up to 2.9 mW under 0.5g (rms) base acceleration, which is sufficient to run an SHM operation on every two minutes.

Structural health monitoring technology is perceived as a revolutionary method of determining the integrity of structures involving the use of multidisciplinary fields including sensors, materials, system integration, signal processing and interpretation. The core of the technology is the development of self-sufficient systems for the continuous monitoring, inspection and damage detection of structures with minimal labor involvement. A major drawback of the existing technology for real-time structural health monitoring is the requirement for external electrical power input. For some applications, such as missiles or combat vehicles in the field, this factor can drastically limit the use of the technology. Having an on-board electrical power source that is independent of the vehicle power system can greatly enhance the SHM system and make it a completely self-contained system. In this paper, using the SMART layer technology as a basis, an Autonomous Self-powered (ASP) Structural Health Monitoring (SHM) system has been developed to solve the major challenge facing the transition of SHM systems into field applications. The architecture of the self-powered SHM system was first designed. There are four major components included in the SHM system: SMART Layer with sensor network, low power consumption diagnostic hardware, rechargeable battery with energy harvesting device, and host computer with supporting software. A prototype of the integrated self-powered active SHM system was built for performance and functionality testing. Results from the evaluation tests demonstrated that a fully charged battery system is capable of powering the SHM system for active scanning up to 10 hours.

Technological advancement in electronics has greatly reduced the power requirement Piezoelectric transduction mechanism has received great attention for being a possible candidate to harvest energy from ambient vibration. In many applications, piezoelectric transduction can be used to harvest energy from ambient vibration by applying them on a specially designed structure or innovatively coat them on the main structural components which are subjected to vibration during operation. A simple example of the host structure could be a vibrating plate. In this paper, a mathematical model is proposed for a vibrating unimorph and bimorph plate used as an energy harvester. Generally ambient vibration is random in nature and hence requires different mathematical technique to solve the problem. In this derivation Kelvin-Voigt type damping and viscous damping were considered separately in the dynamic equation. A solution mechanism is proposed for the system. Then modal analysis is performed in a short circuit condition and solution from the transcendental equation is used to calculate the modal parameters. The backward coupling term is then calculated using the modal coefficients and the explicit equation for the power output is presented.

This work presents application of SHM system based on optical fiber sensors for a power boiler monitoring. The test object was a modern fluid boiler made by RAFAKO SA. Because of the need to replace the pre-heaters it was necessary to make sure that such refurbishment would not menace the safety of the whole construction. Possible dangers could arise from the fact that additional openings in the main combustion chamber walls were made. For this purpose an SHM system based on SOFO® sensors was applied. The main task of the system was to locally measure a deformation of the construction, to give information about emerging threats as well as to start programmed alarms. The data obtained were continually published on the secured website. The arrangement of the sensors was supported by FEM analysis of the whole construction made by boiler producer. The sensors were installed on 12 strings of the combustion chamber. Additional 12 sensors were located directly on the chamber walls. Applied sensors were used to measure the deformation values in selected points. Then determined strain/stresses were compared with the design as well as with calculated values. It enabled evaluation of the inhomogeneous loads distribution and increased safety of the construction during its repair.

Since steel cables are widely used to be crucial components in cable-stayed bridges and architectural structures, stress measurement of the steel cables has been given serious attentions. Among the current stress measurement methods, magnetic method seems to be the most potential one, but its application is limited because of the complex theoretical mechanism. According to the magneto-mechanical effect, which demonstrates that magnetization in the ferromagnetic material varies with applied stress, a theoretical model of magnetic method is proposed to perfect the theoretical mechanism. Thus, an equation is derived about the relation between magnetization in steel cables and cable stress. In this model, a magnetic stress sensor is designed, with a smart steel cable as a part of it, and then a cable stress measurement system based on LabVIEW is developed. This method allows new application in non-destructive testing, such as monitoring the conditions of stayed-cable. Considering the impact of the magnetic hysteresis, positive and negative pulsed current excitation was used to demagnetize and decrease the output of heat. This method is applied to the stress measurement of prestressed steel cable in Jiangsu Fasten Nippon Steel Cable Company, the experimental results agree with theoretical assumptions, which indicates that the method is feasible and can improve the mechanical stress measurement.

The polypropylene (PP) /polyethylene terephthalate (PET) /Nanosilver (Ag) nanocomposite fibers were prepared for the achievement of permanent antibacterial activity to common synthetic textile. The fibers were melt-spun by co-extrusion of PP/PET with compatibilizer (PP-g-MA) as core and PP/Ag master-batches as sheath and vice versa then fiber formation was carried out through the spinneret. The effects of content PP-g-MA as compatibilizer were also investigated. The morphology and mechanical properties of uncompatibilized and compatibilized PP/PET fibers were comprehensively assessed utilizing scanning electron microscopy (SEM) and tensile test experiments. It was observed that the fibrillar distributed morphology achieved at 3.5 Wt% of PP-g-MA has a significant performance. The antibacterial activity of nanosilver in fibers was evaluated after certain contact time and calculated by percent reduction of two kinds of bacteria; Staphylococus aureus and Escherichia coli. The antibacterial efficacy of spun fibers was excellent when the masterbatch used as the sheath. The SEM micrograph of these fibers (PP/ PP-g-MA/PET)/(PP/Nanosilver) shows nearly good distribution of nanosilver particles with little aggregation. Mechanical and antibacterial properties data have also shown that the fiber has a significant performance when the master-batch used as the sheath.

This paper presents the implementation of a chirplet-based matching pursuit technique called excitelet for imaging. High frequency bursts are injected into a structure by a piezoceramic (PZT) actuator and measurement is conducted by a compact array of PZT sensors, located remotely from the damage. The matching pursuit algorithm is implemented with a dictionary of atoms obtained from dispersed versions of the excitation, where the parameters of each atom are the propagation distance and the mode. For a selected point in the scan area and a given mode, the measured signal is correlated with a given atom value for each propagation path in the array configuration. A round-robin technique is used to add the contributions of all these correlation values for each point in the scan area for imaging. Simulations are first conducted for a 1.5 mm thick aluminium plate with signals synthesized for A₀ mode propagating over distances corresponding to the location of a reflection or diffusion point in an area in front of an array of measurement points. The simulations show that the excitelet offers better localization of the reflection point, when compared with a group velocity-based, or time-of-flight (ToF) approach. The simulation results are validated experimentally using a 1.5 mm thick aluminium plate with a notch in the periphery of a hole. Bonded PZTs are used for both actuation and sensing of 2.5 cycles bursts at 300 kHz, 500 kHz and 850 kHz. Significant improvement of imaging quality is demonstrated with respect to classical imaging techniques.

Integrity of bolted joints is critical for successful deployment and operation of space structures. Conventional structural qualification tests span weeks if not months and inhibit rapid launch of space systems. Recent developments in the embedded ultrasonic acousto-elastic method offer fast diagnosis of bolted joints and opportunities for locating the fault. However, in current acousto-elastic measurement procedures, a baseline representing the healthy condition of the joint is necessary. To mitigate a requirement of the baseline, a new methodology based on relative amplitude and phase measurements is developed. The approach has been validated on laboratory specimens, and modifications were suggested for applications in realistic structures. The paper discusses principles of the baseline-free acoustoelastic method, its practical realization, and respective advantages and disadvantages. Comparison of baseline and baseline-free approaches is presented showing the utility of the recently proposed methodology. Fundamentals of the acousto-elastic response were studied in experiments involving guided wave propagation in a thin plate under tension. The results indicate a difference between acousto-elastic responses collected using sensors oriented parallel and perpendicular to the applied stress. It is suggested that this effect may be used to infer stress orientation in the sample. Practical issues related to acousto-elastic measurements in realistic complex structures are discussed, damage diagnosis algorithms are presented, and potential extensions of the acousto-elastic technique are proposed.

Due to the complex nature of sandwich structures, damage detection in honeycomb sandwich structures inherently imposes many challenges. In this study, leaky guided wave properties generated by piezoelectric wafer actuators/sensors in honeycomb sandwich structures are first simulated by the finite element method. In the numerical model, the detailed honeycomb core geometry is considered. Differential features due to presence of debonding are determined through an appropriate damage index analysis of the signals at the normal and debonded conditions. The image of the debonding is formed by using a probability analysis of the leaky guided wave at each frequency. The final image of the structure can be fused from multi-frequency leaky guided waves. A new method for multi-debonding detection is proposed. Based on the analysis, information about the debondings in the honeycomb sandwich structures can be quantitatively characterized.

The analog-to-digital converter (ADC) of a Lamb wave system samples a response signal and converts it into a digital signal for further processing in the digital domain. A typical ADC used for a Lamb wave system consumes a large amount of power. It also increases the complexity of the signal processing for the processor, which, in turn, increases the power consumption of the processor. Elimination of the ADC can therefore significantly reduce the overall power dissipation of a Lamb wave system. In this paper, we propose a method to eliminate the ADC of a Lamb wave system, in which the ADC is replaced by two comparators. Our method quantizes the sampled signal into three levels rather than 2ⁿ levels as with an n-bit ADC. The experimental results performed with our prototype indicate that the proposed method is effective at detecting simulated damage on aluminum plates.

Military missiles are exposed to many sources of mechanical vibration that can affect system reliability, safety, and mission effectiveness. One of the most significant exposures to vibration occurs when the missile is being carried by an aviation platform, which is a condition known as captive carry. If the duration of captive carry exposure could be recorded during the missile's service life, several advantages could be realized. Missiles that have been exposed to durations outside the design envelop could be flagged or screened for maintenance or inspection; lightly exposed missiles could be selected for critical mission applications; and missile allocation to missions could be based on prior use to avoid overuse. The U. S. Army Aviation and Missile Research Development and Engineering Center (AMRDEC) has been developing health monitoring systems to assess and improve reliability of missiles during storage and field exposures. Under the direction of AMRDEC staff, engineers at the Pacific Northwest National Laboratory have developed a Captive Carry Health Monitor (CCHM) for the HELLFIRE II missile. The CCHM is an embedded usage monitoring device installed on the outer skin of the HELLFIRE II missile to record the cumulative hours the host missile has been in captive carry mode and thereby assess the overall health of the missile. This paper provides an overview of the CCHM electrical and package design, describes field testing and data analysis techniques used to identify captive carry, and discusses the potential application of missile health and usage data for real-time reliability analysis and fleet management.

On line detection techniques to monitor the health of rotating engine components are becoming increasingly attractive options to aircraft engine companies in order to increase safety of operation and lower maintenance costs. Health monitoring remains a challenging feature to easily implement, especially, in the presence of scattered loading conditions, crack size, component geometry and materials properties. The current trend, however, is to utilize noninvasive types of health monitoring or nondestructive techniques to detect hidden flaws and mini cracks before any catastrophic event occurs. These techniques go further to evaluate materials' discontinuities and other anomalies that have grown to the level of critical defects which can lead to failure. Generally, health monitoring is highly dependent on sensor systems that are capable of performing in various engine environmental conditions and able to transmit a signal upon a predetermined crack length, while acting in a neutral form upon the overall performance of the engine system. Efforts are under way at NASA Glenn Research Center through support of the Intelligent Vehicle Health Management Project (IVHM) to develop and implement such sensor technology for a wide variety of applications. These efforts are focused on developing high temperature, wireless, low cost and durable products. Therefore, in an effort to address the technical issues concerning health monitoring of a rotor disk, this paper considers data collected from an experimental study using high frequency capacitive sensor technology to capture blade tip clearance and tip timing measurements in a rotating engine-like-disk-to predict the disk faults and assess its structural integrity. The experimental results collected at a range of rotational speeds from tests conducted at the NASA Glenn Research Center's Rotordynamics Laboratory will be evaluated using multiple data-driven anomaly detection techniques to identify anomalies in the disk. This study is expected to present a select evaluation of online health monitoring of a rotating disk using these high caliber sensors and test the capability of the in-house spin system.

This paper describes work conducted into mobile, wireless, semi-autonomous NDE inspection robots developed at The University of Strathclyde as part of the UK Research Centre for Non Destructive Evaluation (RCNDE). The inspection vehicles can incorporate a number of different NDE payloads including ultrasonic, eddy current, visual and magnetic based payloads, and have been developed to try and improve NDE inspection techniques in challenging inspection areas (for example oil, gas, and nuclear structures). A significant research challenge remains in the accurate positioning and guidance of such vehicles for real inspection tasks. Employing both relative and absolute position measurements, we discuss a number of approaches to position estimation including Kalman and particle filtering. Using probabilistic approaches enables a common mathematical framework to be employed for both positioning and data fusion from different NDE sensors. In this fashion the uncertainties in both position and defect identification and classification can be dealt with using a consistent approach. A number of practical constraints and considerations to different precision positioning techniques are discussed, along with NDE applications and the potential for improved inspection capabilities by utilising the inherent reconfigurable capabilities of the inspection vehicles.

Next generation technology of integrated health management systems for air-transportation structures will utilize SHM methods in combination with simulation techniques for the prediction of structural degradation induced by adverse events such as impacts. The contribution focuses on the development of an advanced real-time monitoring system for impact loads using passive sensing networks. Starting from the fundamental approach of real-time monitoring based on system identification models, problems of model order, signal conditioning and efficient model training will be addressed. Finally, the load monitoring system is interactively linked to a damage prediction module based on numerical failure analysis employing composite failure criteria. The utilization of appropriate database techniques allows a real-time prediction of impact induced damage after detection of any adverse impact event making information available on developing degradation at the earliest possible state.

The scattering of waves by defects is central to ultrasonic NDE and SHM. In general, scattering problems must be modeled using direct numerical methods such as finite elements (FE), which is very computationally demanding. The most efficient way is to only model the scatterer itself and a minimal region of the surrounding host medium, and this was previously demonstrated for 2-dimensional (2D) bulk wave scattering problems in isotropic media. An encircling array of monopole and dipole sources is used to inject an arbitrary wavefront onto the scatterer and the scattered field is monitored by a second encircling array of monitoring points. From this data, the scattered field can be projected out to any point in space. If the incident wave is chosen to be a plane wave incident from a given angle and the scattered field is projected to distant points in the far-field of the scatterer, the far-field scattering or S-matrix may be obtained, which encodes all the available scattering information. In this paper, the technique is generalized to any elastic wave geometry in both 2D and 3D, where the latter can include guided wave scattering problems. A further refinement enables the technique to be employed with free FE meshes of triangular or tetrahedral elements.

Efficient numerical models are essential for the simulation of the interaction of propagating waves with localized defects. Classical finite elements may be computationally time consuming, especially when detailed discretizations are needed around damage regions. A multi-scale approach is here propose to bridge a fine-scale mesh defined on a limited region around the defect and a coarse-scale discretization of the entire domain. This "bridging" method is formulated in the frequency domain in order to further reduce the computational cost and provide a general framework valid for different types of structures. Numerical results presented for propagating elastic waves in 1D and 2D damaged waveguides illustrate the proposed technique and its advantages.

Transient ultrasonic waves in an elastic half-space generated by an ultrasonic transducer of finite size are modeled by the Distributed Point Source Method (DPSM). DPSM which is a Green's function based semi-analytical mesh-free technique is modified to incorporate the transient loading from a finite size acoustic transducer. Fast Fourier transform (FFT) of the transient loading is computed and then DPSM is used to compute the ultrasonic field at different frequencies and then inverse fast Fourier transform (IFFT) is taken to get the transient response of an elastic half-space excited by a bounded acoustic beam. Numerical results are generated for elastic half-space excited with normal incidence of acoustic beam. Then the transient Rayleigh wave in the solid half-space is generated. The modeling is then extended to the transient response of an elastic half-space containing a crack, struck by a bounded acoustic beam. It is discussed in the paper what type of useful information that is hidden in the steady state solution can be obtained from the transient results.

The paper describes a numerical approach for the analysis of Lamb wave generation in plate structures. Focus is placed on the investigation of macro fiber composite (MFC) actuators and their directivity properties when actuated individually. A local Finite Element model of the electro-mechanical behavior of the actuator/substrate system estimates the distribution of the interface stresses between the actuator and the substrate, which are subsequently provided as inputs to the analytical procedure that estimates the far-field response of the plate. The proposed approach allows handling of complex actuation configurations, as well as the presence of a bonding layer. As an example, the technique is applied to estimate the directional Lamb wave generation of two types of macro fiber composite transducers. The numerical results are validated experimentally by using a Polytec PSV400 MS scanning laser doppler vibrometer. The results suggest the potentials of the approach as a tool for the prediction of the excitation provided by actuators of complex shapes.

The propagation of ultrasonic guided waves and their interaction with a defect is of interest to the nondestructive testing community. There is no general solution to the scattering problem and it is still an ongoing research topic. Due to the complexity of guided wave scattering problems, most existing models are related to the 2D case. However, thanks to the increase in computer calculation power, specific 3D problems can also be studied, with the help of numerical or semi-analytical methods. This paper describes two efficient methods aimed at modeling 3D scattering problems. The first method is the use of the Huygens' principle to reduce the size of finite element models. This principle allows the area of interest to be restricted to the very near field of the defect, for both the generation of the incident field and the modal decomposition of the scattered field. The second method consists of separating the 3D problem into two 2D problems for which the solutions are calculated and used to approximate the 3D solution. This can be used at low frequency-thickness products, where Lamb waves have a similar behavior to bulk waves. These two methods are presented briefly and compared on simple scattering cases.

Dynamic measurements are widely used for structural condition assessment and damage detection. A wide range of studies are available on vibration-based detection and identification of fatigue cracks in simple and complex structures. This research explores the application of the electromechanical impedance method and nonlinear resonance measurements to high frequency detection of incipient fatigue damage in aluminum alloy specimens. The electromechanical impedance method relies on the coupling between the mechanical properties of a structure and the electrical properties of attached piezoelectric wafer active sensors (PWAS). This coupling allows structural properties to be inferred from the electrical impedance signature of the sensor. In this study, the electromechanical impedance method is utilized for assessment of material deterioration under cyclic fatigue loads. Aluminum specimens were subjected to increasing fatigue cycles at stress amplitudes below the yield point, and electromechanical impedance signatures were taken at discrete levels of fatigue damage. Linear and nonlinear features of the impedance signatures were compared for different damage conditions. The results show a downward frequency shift of impedance peaks with increasing fatigue load. This frequency shift is observed before visible crack development and fracture. Nonlinear resonance tests were applied to fatigued aluminum samples. PWAS were utilized for transmission and reception of elastic waves at increasing amplitude levels. Variations in structural dynamic characteristics were considered for different excitation conditions and increasing damage severity. This paper discusses damage detection capabilities of each method and provides perspectives for utilizing information on incipient damage for predicting structural performance under known operational loads.

Magneto-elastic active sensors (MEAS) offer an alternative to piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM) applications. In essence, a MEAS consists of a coil of wire carrying a timevarying electrical current in the presence of a static magnetic field. The Lorentz-force mechanism facilitates transduction without a mechanical bond between the sensor and the host structure, thereby circumventing some of the shortcomings of PWAS. In this paper, the development of MEAS is briefly recounted and applications of MEAS to SHM are presented. The miniaturization of MEAS for improved embeddability is also discussed. The ability of MEAS to detect loose bolts by the pitch-catch method is presented. MEAS application for near-field and far-field crack detection is also explored. Finally, the utilization of MEAS in Magneto-Mechanical Impedance (MMI) method is discussed. The MMI technique provides a means of assessing the integrity of metallic structures through measurement of structural dynamic response. Since structural damage affects mechanical properties, it modifies structural dynamic characteristics reflected in MMI signature. The use of MMI to monitor fatigue damage in aluminum alloys is presented. Aluminum samples were subjected to cyclic loading in increments of 10,000 cycles until cracks appeared. The MMI responses show downward frequency shift of impedance peaks as samples deteriorate under fatigue loading, confirming the capability of MMI techniques to detect incipient fatigue damage. Thus, the applicability of MEAS to various SHM techniques is demonstrated, and the advantages and disadvantages of MEAS are explored.

Localized and distributed guided ultrasonic waves array systems offer an efficient way for the long-term monitoring of the structural integrity for large structures. The use of permanently attached sensor arrays has been shown to be applicable to detect simulated corrosion damage. However, the detection sensitivity for fatigue cracks depends on the location and orientation of the crack relative to the transducer elements, and for some transducer locations no change in the signal even for a significant defect will be detected. Crack-like defects have a directionality pattern of the scattered field depending on the angle of the incident wave relative to the defect, the defect depth, and the ratio of the characteristic defect size to wavelength. The directionality pattern of the scattered field for the A0 Lamb wave mode is predicted from 3D Finite Element simulations and verified from experimental measurements at machined part-through and through-thickness notches using a laser interferometer. Good agreement is found and the directionality pattern can be predicted accurately. These results provide the basis for the quantification of the detection sensitivity for defects in plate structures using guided wave sensors.

Fatigue crack detection and quantification is by far the most challenging task in Structural Health Monitoring (SHM). In the past decade numerous techniques were developed to detect and quantify fatigue damages. Fatigue loading leads to fatigue crack development in metals and delamination growth in composites. It has been found that different techniques are suitable for different damage development. Hence, the selection of the appropriate analysis methodologies pertaining to different problems is crucial. At the same time there has been an effort to reduce the power requirement for data analysis. This in turn triggered the idea of developing low power damage detection algorithms. In this paper a comparison between different damage detection techniques are presented and problems with different materials and structural geometries are considered. Three damage detection techniques were selected and evaluated.

In the literature, there are several examples where wires of magnetostrictive material are used for both sensing and nondestructive inspection applications. However, the magnetostrictive material may not be suitable for certain environments (such as corrosive environments). Therefore, designs where the magnetostrictive material is coupled to a more robust waveguide material are of interest. The work presented in this paper examines a design based on a cylindrical sleeve of magnetostrictive material. Experiments were conducted to compare the new sleeve design to the old approach of using a brass coupling. In addition to simplifying the manufacturing process, the sleeve design was found to eliminate signal artifacts encountered in previous results.

The purpose this paper is the development a novel polymeric fiber-optic magnetostrictive metal detector, using a fiber- optic Mach-Zehnder interferometer and polymeric magnetostrictive material. Metal detection is based on the straininduced optical path length change steming from the ferromagnetic material introduced in the magnetic field. Varied optical phase shifts resulted largely from different metal objects. In this paper, the preliminary results on the different metal material detection will be discussed.

The array of axially aligned air channels and the robust waveguide characteristics of index-guiding photonic crystal fibers (IG-PCFs) integrated with long-period gratings (LPGs) make them a powerful platform for chemical sensing and detection. Compared to their conventional all-solid fiber counterpart, the IG-PCFs are a particularly attractive sensing device as they are both a waveguide and a vapor/aqueous transmission cell, permitting light intensity-analyte interaction over long path length without the removal of fiber cladding. While the fundamental core-mode in the IG-PCF has been utilized for evanescent field based sensing, there exist two inherent limitations: (1) only short distance extended by evanescent waves from the guiding core to the surrounding PCF cladding air channels to restrict the probing of an analyte only in the inner most ring of the air channels in cladding, and (2) less than 1% power of the core-mode overlap with the surrounding air channels leading to weak light intensity-analyte interactions due to the localization of the coremode in the fiber core area. Should a cladding-mode with maximum overlap in air channels be excited by an LPG, it would fundamentally increase the evanescent field sensitivity. In this work, we present the simulation for the mode properties of selected IG-PCF for optimization of mode field distribution and light power overlap with air channels in fiber cladding. The numerical calculation reveals that if the optimized cladding-mode is selectively coupled, the evanescent wave overlap (at wavelength of 1550 nm) with cladding air channels of the round and hexagonal structures can be increased from 0.11% and 0.13% up to 4.01% and 6.54%, respectively.

The structure health monitoring becomes more and more important to increase the reliability of important assemblies and structures. Therefore, a silicon test chip was developed to analyse acting mechanical loads at critical structure locations. Standard MEMS technologies are used for manufacturing an array structure of stress sensitive elements. Up to 16 sections with each 6 stress sensitive resistors can be measured continuously by one measurement hardware unit. Interpretation and correction of the measured raw data is performed in proper computer software. The whole system can be utilized as a self-sufficient measurement chain for structure health monitoring.

In this paper, we present a novel polymeric 3-D tactile sensor. The tactile sensor comprises of a flexible quad capacitor array where three axial forces can be measured from the sensors' relative areas and gap distances changes using a simple differential equation. To improve the overall performance of the sensor, several high dielectric polymers were developed so that a smaller sensor area (< 1×1cm²) can be achieved. A specially designed LC circuit was also developed to improve the capacitance detection. With the current configuration, the sensor is capable of detecting forces in any arbitrary direction with a sensitivity of 0.1N and a force range up to 45N.

Excitation and detection of acoustic waves in piezoelectric materials relies on a gradient in the piezoelectric properties respectively a gradient in the electric field. The relatively weak coupling is usually enhanced for established practical applications by mechanical, geometrical and electrical resonances. The geometrical resonances, as present for the commonly used inter digital transducer (IDT), lead to limitations concerning the spatial and temporal resolution that can be achieved with such devices. Concentration of the electric field by geometrical means and point like conversion at the surface of piezoelectric materials is the basis for the novel scheme presented here. The principles of the developed method together with instrumental details are discussed. Applications involving two dimensional imaging with time resolved recording for each pixel of the image for phase and magnitude of the transfer and echo signals are presented.

During operation of vehicles and structures, excessive transient loading can lead to reduced fatigue life and even mechanical failure. It has been shown that when a structure undergoes a damaging sequence of events, such as those occurring during a helicopter hard landing, the structural health of a specimen can be severely affected. In order to effectively quantify damage and monitor the structural health of the specimen, experimental data is required across a wide area of the helicopter. Within this paper the use of three-dimensional (3D) digital image correlation (DIC) and dynamic photogrammetry (DP) is examined as a possible method to acquire the necessary data to perform structural health monitoring in a non-obtrusive manner. DIC and DP are a non-contacting measurement techniques that utilizes a stereo pair of digital cameras to track prescribed surface pattern or optical targets placed on the structure. The approaches can provide global information about changes to the structure over the entire field of view. A scale laboratory test is performed on a helicopter to simulate several loading scenarios. The changes in the structural shape and strain field of the model helicopter fuselage as a direct result of the loadings are identified. The tests demonstrate that this technique is a valid way to determine the damage inflicted on the structure due to an excessive applied loading or dynamic maneuver. Practical applications and common limitations of the technique are discussed.

In this work, the Foucault knife-edge test, which has traditionally been known as the classic test for optical imaging devices, is used to characterize an acoustic lens for operation at 1.2 GHz. A confocal laser scanning microscope (CLSM) was used as the illumination and detection device utilizing its pinhole instead of the classical knife edge that is normally employed in the Foucault test. Information about the geometrical characteristics, such as the half opening angle of the acoustic lens, were determined as well as the quality of the calotte of the lens used for focusing. The smallest focal spot size that could be achieved with the examined lens employed as a spherical reflector was found to be about 1 μm. By comparison to the idealized resolution a degradation of about a factor of 2 can be deduced. This limits the actual quality of the acoustic focus.

The displacement measurement in structural health monitoring (SHM) was not popular due to inaccessibility and the huge size of the civil infrastructures. The frequently employed approaches such as accelerometer, strain gauge, PZT, GPS, LVDT(Linear Variable Differential Transformer) require high cost and are difficult to install and maintain. To develop an SHM system that directly measures the displacement of the structure using lowcost sensor, we proposed a multiple paired structured light (SL) system. The proposed paired SL module which uses two lasers and a camera in pair is inexpensive to implement and can directly measure the accurate relative displacement between any two locations on the structure. The steepest descent and extended Kalman filter-based displacement estimation methods was proposed by deriving a kinematic equation and its constraints. In this paper, we theoretically justify the minimal configuration of the proposed paired structured light system. To do so, another configurations are further investigated. The calibration method was proposed for this specific configuration. After building a prototype of the paired SL module, some real experiments are performed to test the feasibility of the system for a structural displacement monitoring.

A number of Extrinsic Fabry-Perot Interferometer processing techniques have been demonstrated for use to extract gaugelength measurements from optical detector output signals. These include: (1) an artificial Neural Network method, (2) a direct phase synthesid method, and (3) an iterative search method. For applications where the processing is to be performed with low-power hardware, co-located with the sensor, the hardware implementation architecture and complexity become critical for a practical solution. In this paper, implementation complexity tradeoffs and comparisons are given for various implementation architectures for each method with respect to each gauge-length estimate. Our research considers complexity as measured in terms of the number of hardware-resident arithmetic operators, the total number of arithmetic operations performed, and the data memory size. It is shown that accurate gauge-length estimates are achievable with implementation architectures suitable for applications including low-power implementations and scalable implementations.

This paper describes the design and fabrication of feedback control system for a three phase motor with a diamagnetically levitating rotor. The planar rotor described in this paper uses a triangular configuration of magnets that rotates due to nine electric coils evenly spaced around the rotor. An optical mechanical feedback system controls the frequency at which the rotor spins. The current input to the coil is controlled by a mechanical relay circuit which latches based on a DC pulse signal generated by a PID control algorithm. The mechanical relay circuit allows current to flow to each coils (the actuators of this system), which then produces a magnetic field strong enough to spin the rotor.

Foam bonded on metal is a common design in space applications. Despite the fact that high efficacy bonding processes exist, there is no a priori insurance in the bonding quality. So, careful bonding inspection is needed as adhesion loss can be critical during chronology. for small structures there is no real problem, as good NDT methods are available. But, at large scale, not only the quality of the control but also the productivity of the tesing process must be relevant. Such constraints have been taken into account, at Onera, in developing a tool which can be used in industrial environment. Techniques used are not very original and their association has been broadly developed and used in the past. But, the need arose for such a method in inidustrial environments with qualities like fast response, full-field and robust interpretation. This paper describes the ways used to cope with these constraints in designing a tool which seems to be compatible with the targeted application.

This paper presents numerical results on the dynamic behavior of continuously welded rails (CWR) subjected to a static axial stress. The results quantify the sensitivity of guided waves to stress variations and could be potentially used to estimate the stress level in CWR or alternatively the rail Neutral Temperature (stress free rail temperature). This work represents the initial concept phase of a research and development study funded by the Federal Railroad Administration. The ultimate objective of this study is to develop and test a prototype system that uses non-contact dynamic sensing to measure in-situ rail stress in motion, to determine rail Neutral Temperatures (NT) and the related Incipient Buckling Risks in CWR.

Guided wave propagation has been proposed as a means to monitor the axial loads in continuously welded railway rails although no practical system has been developed. In this paper, the influence of axial load on the guided wave propagation characteristics was analyzed using the semi-analytical finite element method, extended to include axial loads. Forty modes of propagation were analyzed up to a maximum frequency of 100 kHz. The sensitivity of the modes to axial load or changes in elastic modulus was formulated analytically and computed. In practice, by using separation of signals in time it would only be possible to separate the mode with the greatest group velocity over a reasonable distance. It was found that the influence of axial load on the wavelength of such a mode should be measureable. However, the influence of changes in the elastic modulus due to temperature is expected to be an order of magnitude larger. In order to develop a practical measurement technique it would be necessary to eliminate or compensate for this and other influences.

This paper presents a generic passive non-contact based approach using ultrasonic acoustic emissions (UAE) to facilitate the neural network classification of bearing health, and more specifically the bearing operating condition. The acoustic emission signals used in this study are in the ultrasonic range (20-120 kHz). A direct benefit of microphones capable of measurements in this frequency range is their inherent directionality. Using selected bands from the UAE power spectrum signature, it is possible to pose the health monitoring problem as a multi-class classification problem, and make use of a single neural network to classify the ultrasonic acoustic emission signatures. Artificial training data, based on statistical properties of a significantly smaller experimental data set is used to train the neural network. This specific approach is generic enough to suggest that it is applicable to a variety of systems and components where periodic acoustic emissions exist.

The measurement of arch bridge suspender tension using vibration method is mostly considered that the suspender is idealized as taut strings. This idealization simplifies the analysis but may introduce unacceptable errors in many applications by ignoring the boundary condition and bending stiffness effects. The neural network intelligent methodology is proposed to compute suspenders tension, and design steps and optimization methods of neural network are given. In order to get correct neural network predictive model, 200 data of 20 bridges is used to train the neural network. The applicability of the proposed intelligent methodology is verified by comparison with the others method through a case. The result shows that the error isn't beyond percent of 6.

With the aid of phase contrast acoustic microscopy, the material properties related to mechanics including the speed of ultrasonic waves can be determined. For this purpose the observed variation of the magnitude and phase with the variations in the thickness of the sample in transmission is complemented by modeling in reflection. The later relates to the observation of interference. In the application presented here involving acoustical waves, also time resolved generation and detection is employed to suppress interferences for sufficiently extended objects. This allows the determination of the desired mechanical properties by first arrival techniques. Both methods, interference and first arrival, are presented and discussed. Applications involve also observations on microscopic scales with a lateral resolution of 1 μm. Some of the principles involved for modeling at the resolution limits are exemplified here also on larger scales to demonstrate the reliability of the developed schemes.

We consider the effects of acoustic pressure on the curing of a two-part epoxy, which can be considered analogous to the polymer healing process. An epoxy sample is loaded into a tube and monitored throughout the early stages of curing by measuring its vibrational response upon periodic impulses. By tracing the natural frequencies of the epoxy-tube system and cross-checking the temperature of the epoxy, the progress of the curing can be quantified. Acoustic stimulation at three different frequencies is investigated and compared to the unstimulated case. We find that external acoustic pressure does seem to affect the curing, though much work remains to be completed.

The biomaterial chitosan is used in the paper manufacturing industry, as a wound healing agent and in filtration amongst others. In this paper the longitudinal sound velocity and acoustic impedance of thin films of chitosan of varying thicknesses are determined by vector-contrast acoustic microscopy. The exploitation of the relative reflectivity information from the maximum amplitude images and a comparison of the experimentally obtained V(z) curves with simulations using appropriate models are applied for the evaluation of the sound velocity. These results were compared to those previously obtained results with the same instrument.

Structural integrity management is key to the safe and economic operation of offshore structures. Presently, regular manual inspections are conducted. This is expensive, time consuming, and prone to human error. This paper investigates the possibility of using the bicoherence function of the measured structural acceleration to provide automatic early detection of damage in an offshore structure. The method is shown to be insensitive to typical operating parameter variations and to variations in wave excitation force, and demonstrates that very small changes in stiffness of individual structural members are detectable from measurements of global structural motion.

The goal of this paper is to detect structural damage in the presence of operational and environmental variations using vibration-based damage identification procedures. For this purpose, four machine learning algorithms are applied based on auto-associative neural networks, factor analysis, Mahalanobis distance, and singular value decomposition. A baseexcited three-story frame structure was tested in laboratory environment to obtain time series data from an array of sensors under several structural state conditions. Tests were performed with varying stiffness and mass conditions with the assumption that these sources of variability are representative of changing operational and environmental conditions. Damage was simulated through nonlinear effects introduced by a bumper mechanism that induces a repetitive, impacttype nonlinearity. This mechanism intends to simulate the cracks that open and close under dynamic loads or loose connections that rattle. The unique contribution of this study is a direct comparison of the four proposed machine learning algorithms that have been reported as reliable approaches to separate structural conditions with changes resulting from damage from changes caused by operational and environmental variations.

Due to the dependence on a limited amount of parameters, the dispersion relations of Lamb waves can be presented in a generalized way. This is exemplified for the different established typical representations. Special attention is given to the representation of the momentum on energy, which is well suited to discuss basic features since energy as well as momentum is the properties which are strictly conserved in loss free homogeneous materials. Representations involving the phase and group velocity are discussed. Features related to level crossing of interacting modes and relations to basic mechanical properties especially relevant to Lamb waves are included in the presentation and discussion.

A 2D model based on Legendre spectral element method (SEM) of a piezoceramic (PZT) patch coupled with an isotropic plate is developed in details, based on coupled linear piezoelectricity and elastodynamic equations. The simulation results are validated experimentally using a notched aluminum plate with surface bonded PZTs, for both actuation and sensing. Good agreement between simulation and experimental results is demonstrated for the fundamental Lamb modes A₀ and S₀, for a frequency band up to 0.75 MHz.mm on a 1.54 mm thick plate.

The increasing use of composite materials in multiple engineering applications has emphasized the need for structural health monitoring (SHM) technologies capable of detecting, locating, and classifying structural defects in these materials. Guided wave (GW) methods offer an attractive solution for SHM due to their tunable sensitivity to different defects and their ability to interrogate large structural surfaces. The complications associated with the material anisotropy and directionality in composites result in an increased need for accurate and efficient simulation tools to characterize GW excitation and propagation in these materials. This paper presents a theoretical model based on three-dimensional elasticity to characterize GW excitation by finite-dimensional transducers in composite laminates. The theory uses an eigenbasis expansion for a bulk transversely isotropic material combined with Fourier transforms, the global matrix approach, and residue theory to find the displacement field excited by an arbitrarily shaped finite-dimensional transducer. Experimental results obtained in a cross-ply composite laminate are used to assess the accuracy of the theoretical solution.

Piezoelectric wafer actuators (piezo-actuators) have been extensively used in integrated structural health monitoring systems to generate ultrasonic guided waves (GWs) for structural damage interrogation. The big issue surrounding precise characterization of piezoelectrically excited GWs is addressing the dynamic interfacial stress between the piezo-actuator and the host structure. In this paper, an analytical actuator model is developed to quantitatively describe the dynamic load transfer between a bonded thin piezo-actuator and an isotropic plate under in-plane mechanical and electrical loading. The piezoelectrically induced GW responses are studied by coupling the actuator dynamics with the Rayleigh-Lamb equations and solving the resulting integral equations in terms of the interfacial shear stress. Typical examples are provided to show the capability of the current actuator model to capture the effects of the geometry and the loading frequency upon the load transfer. The analytical prediction of transient GW mode signals from the proposed model is compared with finite element simulation results for various excitation frequencies, and excellent agreement can be observed especially for high-frequency cases, which is a useful extension to the ultrasonic frequencies of most of existing analytical solutions for low frequency approximations.

The recent engineering implementation of health monitoring system for long span bridges show difficulties for precisely assessing structural physical condition as well as for accurately alarming on structural damages, although hundreds of sensors were installed on a structure and a great amount of data were collected from the monitoring system. The allocation of sensors and the alarming algorithm are still two of the most important tasks to be considered when designing the structural health monitoring system. Vulnerability, in its original meaning, is the system susceptibility to local damage. For a structural system, the vulnerability can thus be regarded as structural performance susceptibility to local damage of structure. The purpose of this study is to propose concepts and methods of structural vulnerability for determining monitoring components which are more vulnerable than others and the corresponding warning threshold once the damages occur. The structural vulnerability performances to various damage scenarios depend upon structural geometrical topology, loading pattern on the structure and the degradation of component performance. A two-parameters structural vulnerability evaluation method is proposed in this paper. The parameters are the damage consequence and the relative magnitude of the damage scenarios to the structural system, respectively. Structural vulnerability to various damage scenarios can be regarded as the tradeoff between the two parameters. Based on the results of structural vulnerability analysis, the limited structural information from health monitoring can be utilized efficiently. The approach of the design of bridge health monitoring system is illustrated for a cable-stayed bridge.

Based on one year monitoring data of a cable-stayed bridge, it was found that the environmental temperature was one of principal environmental factors effecting structural modal parameters in long-term. The possible mechanism is due to the influences of environmental temperature on structurel material properties, such as modulus of elasticity, and structural geometry properties, such as boundary conditions. In this paper, the distribution of environmental temperature was analyzed based on the long-term monitoring data of a cable-stayed bridge. It was found that the distribution of structural temperature was consistent in longitudinal direction of the bridge and the structural temperature gradients in bridge box girder section obeyed non-Gaussian distribution. The influencing mechanism of environmental temperature on dynamic properties was theoretically analyszied and was validated based on the monitoring data. The results demonstrated that the theoretical analysis was consistent with the monitoring data. And then the effect of temperature on modal parameters was analyzed by Auto-Regressive model with eXogenous inputs (ARX) model based on the monitoring data. It was found that there was obvious time lags in the environmental temperature effects on the modal parameters and the time lag could be equivalently evaluated by multi-point temperature data. Finally, the effects of environmental temperature on modal parameters were validated by a model experiment, and the results were consistent well with that of the monitoring data.

This paper compares two different approaches to identify damage locations in structural members subjected to ambient vibrations. The concept is demonstrated using a simply supported two span steel beam. An electro-hydraulic actuator was used to simulate ambient loading by applying random loads. The vibration time histories were collected for the undamaged and damaged conditions. The structural damages were introduced by cutting notches of different sizes in the flange at different locations. The two different approaches used time-series models in the context of statistical pattern recognition to extract sensitive damage features. In the first method, the damage features were extracted using the errors from fitting autoregressive models with exogenous inputs (ARX) to the collected time histories. The fitted ARX models had been developed based on the undamaged beam. The calculated damage probability from this method could not clearly discriminate the physical damage locations although the change in the condition of the beam was identified. In the second method, variations in the coefficients of multivariate autoregressive models which had been fitted to the acceleration time histories were investigated, and the damage features were extracted by measuring the magnitude of these variations. The findings showed the sensors close to the physical damage locations are related to the larger damage features.

In this paper, a novel non-parametric Sequential Probability Ratio Test (SPRT) method based on Mann-Whitney rank sum test was proposed for structural condition assessment by utilizing long-term structural health monitoring data. Compared with the fixed sample size test, the sequential probability ratio test has many advantages and is widely used in hypothesis testing. When using the SPRT method in a process of hypothesis testing, a probability distribution function of the samples is need to be assumed, for examples, as normal or exponential probability distribution function. However, the actual probability distribution function of the samples was unknown or could not be expressed as a simple distribution function on occasion. Assuming that the samples of the normal condition were known, the log-likelihood ratio based on Mann-Whitney rank sum of the samples of undetermined condition was calculated accurately and the decision was made by comparing with the thresholds. This method did not require knowing the probability distribution function of the samples, so it could be applied to the conditions with different probability distribution functions. The method was validated by a numerical example. The results showed that this proposed method was effective to distinguish different conditions and was better than other non-parametric sequential probability ratio test method.

In this paper, the influence of disbonds on Lamb wave propagation in GLARE composites is described. Guided Lamb waves were launched and detected with Polyvinylidene Fluoride (PVDF) comb transducers. Disbond defects were introduced with ball drop test to study their influence on the Lamb wave signals. The amplitudes of the detected Lamb wave signals show distinct differences with and without disbonds, which can be used to monitor the disbond growth. In addition, a thermal imaging technique was applied to inspect the disbond region so as to cross-correlate the disbond size with its influence on the Lamb wave signals measured by the PVDF sensors. It is demonstrated that the amplitudes of the A_o mode Lamb wave decrease exponentially with increasing disbond size.

A new concept of a reference-free impedance method, which does not require direct comparison with a baseline impedance signal, is proposed for damage detection in a plate-like structure. A single pair of piezoelectric (PZT) wafers collocated on both surfaces of a plate are utilized for extracting electro-mechanical signatures (EMS) associated with mode conversion due to damage. A numerical simulation is conducted to investigate the EMS of collocated PZT wafers in the frequency domain at the presence of damage through spectral element analysis. Then, the EMS due to mode conversion induced by damage are extracted using the signal decomposition technique based on the polarization characteristics of the collocated PZT wafers. The effects of the size and the location of damage on the decomposed EMS are investigated as well. Finally, the applicability of the decomposed EMS to the reference-free damage diagnosis is discussed.

We propose a sequential Monte Carlo (SMC) based progressive structural damage diagnosis framework that tracks damage by integrating information from physics-based damage evolution models and using stochastic relationships between the measurements and the damage. The approach described in this paper adaptively configures the sensors used to collect the measurements using the minimum predicted mean squared error (MSE) as the performance metric. Optimization is performed globally over the entire search space of all available sensors. Results are presented for the diagnosis of fatigue damage in a notched laminate, demonstrating the effectiveness of the proposed method.

Micro features were created in thin film nitinol using a novel lift-off process to create an endovascular biomedical device. This manuscript describes fabrication problems with wet etching and introduces an effective way, named "Lift-off" process to solve undercut and non-uniform pattern issues. Two lift-off processes (i.e., lift-off I and II) are discussed. Lift-off I process has fracture issues and the film peels off the substrate due to high aspect ratio post structures. Lift-off II process use the film on the top of the Si substrate to fabricate various shape patterns (i.e., ellipse, diamond, circle, square, etc.) in the range of 5~60μm. The lift-off II process shows smooth and well aligned micro patterns in thin film nitinol. In-vivo tests in swine were performed to evaluate the endothelial tissue growth through fabricated micro patterns. Angiography and SEM images show patency of the artery and a uniform endothelial layer covering the device without thromobosis.

The present study is to investigate the feasibility of applying in-vivo acoustic microscopy to the analysis of cancerous tissue. The study was implemented with mechanical scanning reflection acoustic microscope (SAM) by the following procedures. First, we ultrasonically visualized thick sections of normal and tumor tissues to determine the lowest transducer frequency required for cellular imaging. We used skin for normal tissue and the tumor was a malignant melanoma. Thin sections of the tissue were also studied with the optical and high-frequency-ultrasonic imaging for pathological evaluation. Secondly, we ultrasonically visualized subsurface cellular details of thin tissue specimens with different modes (i.e., pulse and tone-burst wave modes) to obtain the highest quality ultrasonic images. The objective is to select the best mode for the future design of a future SAM for in-vivo examination. Thirdly, we developed a mathematical modeling technique based on an angular spectrum approach for improving image processing and comparing numerical to experimental results.

Skeletal muscle is a classic example of a biological soft matter . At both macro and microscopic levels, skeletal muscle is exquisitely oriented for force generation and movement. In addition to the dynamics of contracting and relaxing muscle which can be monitored with ultrasound, variations in the muscle force are also expected to be monitored. To observe such force and sideways expansion variations synchronously for the skeletal muscle a novel detection scheme has been developed. As already introduced for the detection of sideways expansion variations of the muscle, ultrasonic transducers are mounted sideways on opposing positions of the monitored muscle. To detect variations of the muscle force, angle of pull of the monitored muscle has been restricted by the mechanical pull of the sonic force sensor. Under this condition, any variation in the time-of-flight (TOF) of the transmitted ultrasonic signals can be introduced by the variation of the path length between the transducers. The observed variations of the TOF are compared to the signals obtained by ultrasound monitoring for the muscle dynamics. The general behavior of the muscle dynamics and muscle force shows almost an identical concept. Since muscle force also relates the psychological boosting-up effects, the influence of boosting-up on muscle force and muscle dynamics can also be quantified form this study. Length-tension or force-length and force-velocity relationship can also be derived quantitatively with such monitoring.

Long bones can be seen as irregular hollow tubes, in which, for a given excitation frequency, many ultrasonic Guided Waves (GWs) can propagate. The analysis of GWs is potential to reflect more information on both geometry and material properties of the bone than any other method (such as dual-energy X-ray absorptiometry, or quantitative computed tomography), and can be used in the assessment of osteoporosis and in the evaluation of fracture healing. In this study, time frequency representations (TFRs) were used to gain insights into the expected behavior of GWs in bones. To this aim, we implemented a dedicated Warped Frequency Transform (WFT) which decomposes the spectrotemporal components of the different propagating modes by selecting an appropriate warping map to reshape the frequency axis. The map can be designed once the GWs group velocity dispersion curves can be predicted. To this purpose, the bone is considered as a hollow cylinder with inner and outer diameter of 16.6 and 24.7 mm, respectively, and linear poroelastic material properties in agreement with the low level of stresses induced by the waves. Timetransient events obtained experimentally, via a piezoelectric ultrasonic set-up applied to bovine tibiae, are analyzed. The results show that WFT limits interference patterns which appear with others TFRs (such as scalograms or warpograms) and produces a sparse representation suitable for characterization purposes. In particular, the mode-frequency combinations propagating with minimal losses are identified.

We present the theory of the optimum running approximation of input signals using sample values of the corresponding output signals of multi-path analysis filters. The presented method uses time-limited running interpolation functions. As an application, we discuss design of in-silico smart adjusting-systems to support a doctor about the plan of administering medicine that is useful in personalized medical care. In this paper, firstly, we define a set of a finite number of signals in the initial set of signals and we present a one to one correspondence between each signal contained in the set of signals and the corresponding error of approximation of a certain finite time-interval. Secondly, based on this one-to-one correspondence, we prove that the presented running approximation minimizes various continuous worst-case measures of error at the same time. Certain reciprocal properties of the approximation are presented. Thirdly, extension to signal-estimation using multiple-input one-output system is presented. Finally, an application to the above in-silico adjusting method is discussed.

The paper demonstrates application of nonlinear acoustics for crack detection in a glass plate. FE analysis is performed to establish structural resonances of the glass plate. Simulation analysis and experimental tests are used to select ultrasonic frequencies. Finally, nonlinear acoustic tests are performed to detect cracks. A high-frequency ultrasonic signal is introduced to the glass plate. At the same time the plate is modally excited using selected resonance frequencies. Surface-bonded, low-profile piezoceramic transducers are used for low- and high-frequency excitation. The experiments lead to vibro-acoustic wave modulations. The presence of modulation indicates damage and the intensity of modulation describes its severity.

Nonlinear Acoustics uses different types of nonlinear phenomena to detect structural damage. One of the major difficulties associated with this technique is the fact that nonlinearities can be produced not only by damage but also by various intrinsic effects such as material behaviour and/or structural boundary conditions. The paper investigates the effect of boundary conditions on Nonlinear Acoustics used for damage detection. A simple composite plate with impact damage is investigated. The plate is clamped using various force levels. The experimental study focuses on the effect of clamping force on vibro-acoustic interaction. The results demonstrate the importance of the effect of boundary conditions when nonlinear acoustics is used for impact damage detection.

The Nonlinear System Identification methodology uses nonlinear signal content generated by a structure with a breathing crack in order to locate the damage. A subharmonic response is one type of signal that is useful in the methodology, but subharmonic responses may not always occur and are dependent upon the input excitations. The goal herein is to find a condition on the excitation to the structure which will produce subharmonics. In this study, through analysis of a single degree of freedom oscillator, which shares similar physics with a cracked structure, such a condition is found to determine the forcing frequency needed to produce subharmonics. This condition is then verified using a finite element model of a cracked rod.

In this paper, a nondestructive, in-service structural integrity monitoring methodology that can detect and characterize local structural damages of contact-type, i.e. damages and failures which come along with generation, growth and/or changes of contacting surfaces, such as cracks, debonding, preload-loss in bolted joints, etc., is presented. The presented monitoring system consists of piezoelectric elements bonded on the structural surface, a high-frequency harmonic voltage source, and a current detector. When the structure is subjected to a vibrational load such as operational load at low-frequencies, the scattering conditions for the high-frequency elastic waves in the vicinity of the contact-type damages will change in synchronization with the structural vibration because of the fluctuation of the contact conditions. This nonlinear effects of vibro-acoustic interaction between the low-frequency vibration and the high-frequency wave field causes the change in the driving-point impedance of the structure at the high frequency range, which leads to the significant modulation of the coupled electro-mechanical impedance (or admittance) of the piezoelectric elements. Therefore, if the piezoelectric elements are driven by a fixed amplitude high-frequency harmonic voltage source, the nonlinear fluctuation of the coupled admittance can be observed as the amplitude and phase modulation of the current flowing through the piezoelectric element. A modeling and analytical study of the nonlinear piezoelectric impedance modulation is presented for a beam structure including a crack, utilizing a linear time-varying system theory. A damage evaluation measure is presented based on the dimensionless modal stiffness fluctuation estimated from the instantaneous admittance reconstructed from the demodulated current responses. Furthermore, fundamental strategies and future directions for damage localization based on the nonlinear piezoelectric impedance modulation are briefly discussed.

Membrane dynamics is often nonlinear and nonstationary because of geometric nonlinearity induced by high local flexibility, non-uniform pre-tension, light weight, dynamic coupling with surrounding air, wave propagation, supportinduced nonlinearity, and others. Hence, dynamics characterization and health monitoring of membrane structures require advanced time-frequency analysis, and the focus is on how to obtain accurate time-varying frequency and amplitude of a nonlinear nonstationary signal. Here we propose the use of a conjugate-pair decomposition (CPD) method with the empirical mode decomposition (EMD) for characterization of membrane dynamics. First, EMD with signal conditioning techniques is used to separate a compound membrane response into well-behaved intrinsic mode functions (IMFs) without assuming the signal to be harmonic. Then, a pair of sliding conjugate functions is used to accurately extract the time-varying frequency and amplitude of each IMF by using only three neighboring data points for each time instant. Because the variations of frequencies and amplitudes of IMFs contain system characteristics, they can be used for system identification and damage detection. Experimental nonlinear responses of a horizontally tensioned Kapton membrane subjected to a transverse harmonic excitation provided by a shaker at one end are used to validate the proposed methodology. Results show that the clamped-clamped supports and pre-tension cause the first-mode vibration to have a hardening cubic nonlinearity, and several other nonlinear phenomena are identified.

If sparse arrays are attached to structures for the purposes of structural health monitoring it is likely that there will be variation in the placement of the sensors, resulting in deviation from the assumed locations. In addition, poor knowledge of the material through which the signals are propagating can result in the use of incorrect velocities, or failing to take account of delays inherent in the equipment. These deviations will result in reduced performance in terms of defect detectability and characterisation. This paper outlines an autofocus approach whereby the transducer locations and material properties can be estimated from the experimental data to ensure the highest levels of defect detectability. The approach is validated using both models and a more complex real world structure. The performance of the approach is considered across a range of potential operating conditions to demonstrate its robustness. Finally limitations and potential solutions to these are addressed.

Over the past few years, ultrasonic phased arrays have shown good potential for non-destructive testing (NDT), thanks to high resolution imaging algorithms that allow the characterization of defects in a structure. Many algorithms are based on the full matrix capture, obtained by firing each element of an ultrasonic array independently, while collecting the data with all elements. Because of the finite sound velocity in the specimen, two consecutive firings must be separated by a minimum time interval. Therefore, more elements in the array require longer data acquisition times. Moreover, if the array has N elements, then the full matrix contains N² temporal signals to be processed. Because of the limited calculation speed of current computers, a large matrix of data can result in rather long post-processing times. In an industrial context where real-time imaging is desirable, it is crucial to reduce acquisition and/or post-processing times. This paper investigates methods designed to reduce acquisition and post-processing times for the TFM and wavenumber algorithms. To reduce data capture and post-processing, limited transmission cycles are used. Post-processing times is also further reduced by demodulating the data to baseband, which allows reducing the sampling rate of signals. Results are presented so that a compromise can be made between acquisition time, post-processing time and image quality. Possible improvement of images quality, using the effective aperture theory, is discussed. This has been implemented for the TFM but it still has to be developed for the wavenumber algorithm.

Recent advances in Structural Health Monitoring have provided the means of eliminating the prerecorded baseline measurement by producing an instantaneous baseline. The damage detection method presented is near-real time damage detection instantaneous baseline method by using ambient excitation and passive sensing. The method uses an array of sensors and compares the features in the data of the different wave-propagation paths to determine an undamaged baseline. The wave-propagation paths that greatly differ from the instantaneous baseline indicate the location of damage along those paths. The details of the signal processing algorithm and evaluation of the method for detecting damage are included. The damage detection method presented is able to detect damage in a wave path using an instantaneous base line.

In this paper algorithm for discontinuities localisation in thin panels made of aluminium alloy is presented. Mentioned algorithm uses Lamb wave propagation methods for discontinuities localisation. Elastic waves were generated and received using piezoelectric transducers. They were arranged in concentrated arrays distributed on the specimen surface. In this way almost whole specimen could be monitored using this combined distributed-concentrated transducer network. Excited elastic waves propagate and reflect from panel boundaries and discontinuities existing in the panel. Wave reflection were registered through the piezoelectric transducers and used in signal processing algorithm. Proposed processing algorithm consists of two parts: signal filtering and extraction of obstacles location. The first part was used in order to enhance signals by removing noise from them. Second part allowed to extract features connected with wave reflections from discontinuities. Extracted features damage influence maps were a basis to create damage influence maps. Damage maps indicated intensity of elastic wave reflections which corresponds to obstacles coordinates. Described signal processing algorithms were implemented in the MATLAB environment. It should be underlined that in this work results based only on experimental signals were presented.

During an MR procedure, the patient absorbs a portion of the transmitted RF energy, which may result in tissue heating and other adverse effects, such as alterations in visual, auditory and neural functions. The Specific Absorption Rate (SAR), in W/kg, is the RF power absorbed per unit mass of tissue and is one of the most important parameters related with thermal effects and acts as a guideline for MRI safety. Strict limits to the SAR levels are imposed by patient safety international regulations (CEI - EN 60601 - 2 - 33) and SAR measurements are required in order to verify its respect. The recommended methods for mean SAR measurement are quite problematic and often require a maintenance man intervention and long stop machine. For example, in the CEI recommended pulse energy method, the presence of a maintenance man is required in order to correctly connect the required instrumentation; furthermore, the procedure is complex and requires remarkable processing and calculus. Simpler are the calorimetric methods, also if in this case long acquisition times are required in order to have significant temperature variations and accurate heat capacity knowledge (CEI - EN 60601 - 2 - 33). The phase transition method is a new method to measure SAR in MRI which has the advantages to be very simple and to overcome all the typical calorimetric method problems. It does not require in gantry temperature measurements, any specific heat or heat capacity knowledge, but only mass and time measurement. On the other hand, it is necessary to establish if all deposited power SAR can be considered acquired and measured. In this paper, that will be shown.

MatCAKE (www.cake.unisa.it) is a toolbox for integrating 2D NMR spectra by the CAKE (Monte CArlo peaK volume Estimation) algorithm within the Matlab environment (www.mathworks.com). Quantitative information from multidimensional NMR experiments can be obtained by peak volume integration. The standard procedure (selection of a region around the chosen peak and addition of all values) is often biased by poor peak definition because of peak overlap. CAKE is a simple algorithm designed for volume integration of (partially) overlapping peaks. Assuming the axial symmetry of two-dimensional NMR peaks, as it occurs in NOESY and TOCSY when Lorentz-Gauss transformation of the signals is carried out, CAKE estimates the peak volume by multiplying a volume fraction by a factor R. It represents a proportionality ratio between the total and the fractional volume, which is identified as a slice in an exposed region of the overlapping peaks. The volume fraction is obtained via Monte Carlo Hit-or-Miss technique, which proved to be the most efficient because of the small region and the limited number of points within the selected area. Due to the large number of software packages available for processing nuclear magnetic resonance data, MatCAKE is designed just for implementing the new CAKE algorithm. In MatCAKe, in fact, only already processed bidimensional spectra are imported and, at the moment, the only volume integration (by CAKE and by the most simple standard procedure) are allowed. MatCAKE is a free software available to the scientific community, that can be obtained on line at the web address cake.unisa.it.

We discuss biomedical imaging using radio waves operating in the terahertz (THz) range between 300 GHz to 3 THz. Particularly, we present the concept for two THz imaging systems. One system employs single antenna, transmitter and receiver operating over multi-THz-frequency simultaneously for sensing and imaging small areas of the human body or biological samples. Another system consists of multiple antennas, a transmitter, and multiple receivers operating over multi-THz-frequency capable of sensing and imaging simultaneously the whole body or large biological samples. Using THz waves for biomedical imaging promises unique and substantial medical benefits including extremely small medical devices, extraordinarily fine spatial resolution, and excellent contrast between images of diseased and healthy tissues. THz imaging is extremely attractive for detection of cancer in the early stages, sensing and imaging of tissues near the skin, and study of disease and its growth versus time.

We investigate possible use of terahertz (THz) waves for medical ultrasound technique that can produce enhanced contrast and resolution for achieving high quality and accuracy of biological tissues and human organs imaging for medical applications. The use of THz is particularly suited for this application since THz waves radiate in tiny beams that can focus high energy into micro tissues to produce large thermal-induced acoustic waves needed for enhanced ultrasound imaging. The ability of confining radiation into tiny spots also makes THz well suited for certain technologies such as endoscopic ultrasound to improve minimally invasive diagnostic medical procedures. We present two possible systems for imaging biological samples and human body using a single source (or transmitter) that can generate THz waves at different frequencies concurrently along with multiple acoustic transducers and multiple antennas.

Korea has constructed the safety management network monitoring test systems for the civil infrastructure since 2006 which includes airport structure, irrigation structure, railroad structure, road structure, and underground structure. Bridges among the road structure include the various superstructure types which are Steel box girder bridge, suspension bridge, PSC-box-girder bridge, and arch bridge. This paper shows the process of constructing the real-time monitoring system for the arch bridge and the measured result by the system. The arch type among various superstructure types has not only the structural efficiency but the visual beauty, because the arch type superstructure makes full use of the feature of curve. The main measuring points of arch bridges composited by curved members make a difference to compare with the system of girder bridges composited by straight members. This paper also shows the method to construct the monitoring system that considers the characteristic of the arch bridge. The system now includes strain gauges and thermometers, and it will include various sensor types such as CCTV, accelerometers and so on additionally. For the long term and accuracy monitoring, the latest optical sensors and equipments are applied to the system.

This paper presents a novel approach to detect structural damage combining non-negative matrix factorization (NMF) and relevance vector machine (RVM). Firstly, the time history of acceleration signal are decomposed using the wavelet packet transform to extract wavelet packet node energy as the damage feature, and construct a non-negative matrix using the wavelet packet node energy index of all time history of acceleration data measured by multiple accelerometers installed on the different locations of structure. Secondly, for increasing the damage detection accuracy, the dimension of the feature non-negative matrix is reduced by NMF techniques and new representation of this matrix is obtained. Lastly, RVM, a powerful tool for classification and regression, is used to detect the location of potential damage from the reduced damage feature matrix. Numerical study on the Binzhou Yellow River Highway Bridge is carried out to illustrate the ability of the proposed method in damage detection.

The presence of noise greatly affects the effectiveness and robustness of structural damage detection methods. In this study, a new damage detection method for beam structures is presented, utilizing time, frequency and space domain information effectively. Local free vibrations of both undamaged and damaged signals are firstly extracted utilizing the Natural Excitation Technique (NExT). Then the signals are decomposed into the low frequency region and high frequency region by the wavelet packet transform (WPT). The Higuchi's fractal dimension (HFD) is applied to measure the complexity of new local signals, which combine the low frequency component of undamaged signals and high frequency component of damaged signals. Damage can be localized by the peak value of Katz's fractal dimension (KFD) analyzing the spatial curve of the calculated HFD values along the structure. For validation, the numerical studies of a simple supported beam were conducted. The results demonstrate that the method is capable of localizing single and multiple damage of various severity accurately. Furthermore, it is found that the proposed damage index is directly connected to damage severity. And the results of tests under heavy noise reveal strong robustness of the proposed method.

The age-related changes in the visco-elastic properties of the human lens are discussed with respect to presbyopia for a long time. All known measurement techniques are based on extracted lenses or are damaging the tissue. Hence, in vivo studies of lens hardness are not possible at the moment. To close this gap in lens diagnostics this project deals with an approach for a non-contact laser-acoustic characterization technique. Laser-generated wave fronts are reflected by the tissue interfaces and are also affected by the visco-elastic properties of the lens tissue. After propagating through the eye, these waves are recorded as corneal vibrations by laser vibrometry. A systematic analysis of amplitude and phase of these signals and the wave generation process shall give information about the interface locations and the tissues viscoelastic properties. Our recent studies on extracted porcine eyes proved that laser-acoustic sources can be systematically used for non-contacting generation and recording of ultrasound inside the human eye. Furthermore, a specific numerical model provides important contributions to the understanding of the complex wave propagation process. Measurements of the acoustic sources support this approach. Future investigations are scheduled to answer the question, whether this novel technique can be directly used during a laser surgery for monitoring purposes and if a purely diagnostic approach, e.g. by excitation in the aqueous humor, is also possible. In both cases, this technique offers a promising approach for non-contact ultrasound based eye diagnostics.