This PDF file contains the front matter associated with SPIE Proceedings Volume 6935, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Thermal Protection Systems (TPS) can be subjected to impact damage during flight and/or during ground maintenance and/or repair. AFRL/RXLP is developing a reliable and robust on-board sensing/monitoring capability for next generation thermal protection systems to detect and assess impact damage. This study was focused on two classes of metallic thermal protection tiles to determine threshold for impact damage and develop sensing capability of the impacts. Sensors made of PVDF piezoelectric film were employed and tested to evaluate the detectability of impact signals and assess the onset or threshold of impact damage. Testing was performed over a range of impact energy levels, where the sensors were adhered to the back of the specimens. The PVDF signal levels were analyzed and compared to assess damage, where digital microscopy, visual inspection, and white light interferometry were used for damage verification. Based on the impact test results, an assessment of the impact damage thresholds for each type of metallic TPS system was made.

Advanced composites are being used increasingly in state-of-the-art aircraft and aerospace structures. In spite of their many advantages composite materials are highly susceptible to hidden flaws that may occur at any time during the life cycle of a structure and if undetected, may cause sudden and catastrophic failure of the entire structure. An example of such a defects critical structural component is the "honeycomb composite" in which thin composite skins are bonded with adhesives to the two faces of extremely lightweight and relatively thick metallic honeycombs. These components are often used in aircraft and aerospace structures due to their high strength to weight ratio. Unfortunately, the bond between the honeycomb and the skin may degrade with age and service loads leading to separation of the load-bearing skin from the honeycomb (called "disbonds") and compromising the safety of the structure. This paper is concerned with the noninvasive detection of disbonds using ultrasonic guided waves. Laboratory experiments are carried out on a composite honeycomb specimen containing localized disbonded regions. Ultrasonic waves are launched into the specimen using a broadband PZT transducer and are detected by a distributed array of identical transducers located on the surface of the specimen. The guided wave components of the signals are shown to be very strongly influenced by the presence of a disbond. The experimentally observed results are being used to develop an autonomous scheme to locate the disbonds and to estimate their size.

Responsive space satellites must be assembled and tested in extremely short times. Integrity of structural joints is one of the major concerns during satellite assembly and qualification processes. A structural health monitoring (SHM) approach based on nonlinear ultrasonics is suggested for rapid diagnostics of structural connectors and joints. Embedded piezoelectric sensors are utilized to enable propagation of elastic waves through bolted aluminum panels. Signal parameters indicative of the nonlinear behavior are extracted from the received waveforms and are used for assessment of structural integrity. Experimental studies reveal variation of the nonlinear response of the joint due to applied structural loads. These changes are explored as diagnostic features of the method. We discuss theoretical aspects of the nonlinear wave propagation through joints and provide experimental data showing feasibility of the embedded nonlinear ultrasonics method for monitoring of structural integrity.

A chiral honeycomb configuration is developed with embedded piezosensors and actuators for smart sandwich panel applications. The chiral honeycomb concept is made of repeating units of cylinders and plates (ligaments), featuring an in-plane negative Poisson's ratio. Rapid Prototyping vacuum-cast and FDM (Fusion Deposition Moulding) techniques are developed to embed micro fibres composites to be used for potential structural health monitoring (SHM) applications, and microwave absorption screens for electromagnetic compatibility. Finite Element models are also developed to prototype and simulate the response, sensing and actuation capability of the honeycombs for design purposes. Dynamic tests using scanning laser vibrometers and acoustic wave propagation are carried out to assess the feasibility of the concept.

For several years guided waves have been used for pipe wall defect detection. Guided waves have become popular for monitoring large structures because of the capability of these waves to propagate long distances along pipes, plates, interfaces and structural boundaries before loosing their strengths. The current technological challenges are to detect small defects in the pipe wall and estimate their dimensions using appropriate guided wave modes and to generate those modes relatively easily for field applications. Electro-Magnetic Acoustic Transducers (EMAT) can generate guided waves in pipes in the field environment. This paper shows how small defects in the pipe wall can be detected and their dimensions can be estimated by appropriate signal processing technique applied to the signals generated and received by the EMAT.

It has recently been demonstrated theoretically and experimentally that Green's functions (impulse responses) can be estimated from coherent processing of random vibrations using only passive sensors studies in various applications (ultrasonics, acoustic, seismic...). This article investigates the passive-only estimation of coherent guided waves waves (DC-500 kHz) in an aluminum plate of thickness comparable to aircraft fuselage and wing panels. Furthermore these passively reconstructed waveforms can also be used for damage detection in the plate similarly to conventional active testing. Based on this study, passive structural health monitoring techniques for aircraft panels can be developed using random vibrations.

A new guided wave based nondestructive testing (NDT) technique is developed to detect crack damage in metallic plates commonly used in aircraft without using prior baseline data or a predetermined decision boundary. In conventional guided wave based techniques, damage is often identified by comparing the "current" data obtained from a potentially damaged condition of a structure with the "past" baseline data collected at the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. In order to tackle this issue, a reference-free damage detection technique is previously developed using two pairs of collocated lead zirconate titanate transducers (PZTs) placed on both sides of a plate. In this study, this reference-free technique is further advanced so that the PZT transducers can be placed only on one side of the specimen. Crack formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the crack by extracting this mode conversion from the measured Lamb waves. This study suggests a reference-free statistical approach that enables damage classification using only the current data set. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to instantaneous crack detection.

This work aims at developing a compact and wireless structural health monitoring system (WSHM). The system samples ultrasonic wave propagation data, analyzes the collected data using a statistical damage index (SDI) approach and transmits the results to a remote location. The analysis provides an insight into the state of health of the structure under test as a function of time. The approach is designed to overcome the complexity and variability of the signals in the presence of damage as well as the geometric complexity of the structure, requiring minimal operator intervention. The approach establishes a baseline drawn from measurements done on an undamaged or partially damaged structure. This baseline is used to monitor for changes in the health of the structure. Damage indices are evaluated "instantly" by comparisons between the frequency response of the monitored structure and an unknown damage under the same ambient conditions. The approach is applied to identify several types of structural defects in steel girders and stiffened composite panels for different arrangements of the ultrasonic source and the ultrasonic receivers. The objectives are to deliver an early indication of the risk associated with the defect and to develop inspection and mitigation strategies to manage the risk using detailed, local, nondestructive evaluation of the areas identified with possible defects. The wireless data acquisition system and the automated data analysis tool developed under this work should improve the reliability of the defects detection capability and aid in the development of near real-time health monitoring systems for defects-critical structures.

Structural health monitoring (SHM) is the component of damage prognosis systems responsible for interrogating a structure to detect, locate, and identify any damage present. Guided wave (GW) testing methods are attractive for this application due to the ability of GWs to travel over long distances with little attenuation and their sensitivity to different damage types. The Composite Long-range Variable-direction Emitting Radar (CLoVER) transducer is introduced as an alternative concept for efficient damage interrogation and GW excitation in GW-based SHM systems. This transducer has an overall ring geometry, but is composed of individual wedge-shaped sectors that can be individually excited to interrogate the structure in a particular direction. Each wedge-shaped sector is made with piezoelectric fibers embedded in an epoxy matrix surrounded by an interdigitated electrode pattern. The multiple advantages over alternative transducer concepts are examined. In particular, it is shown that the geometry of each sector yields actuation amplitudes much larger than those obtained for a ring configuration under similar electric inputs. The manufacture and characterization procedures of these devices are presented, and it is shown that their free strain performance is similar to that of conventional piezocomposite transducers. Experimental studies of damage detection simulating the proposed damage interrogation approach are also presented.

Lamb wave propagation is evaluated for cross-ply laminate composites exhibiting through-the-thickness negative Poisson's ratio. The laminates are mechanically modeled using the Classical Laminate Theory, while the propagation of Lamb waves is investigated using a combination of semi analytical models and Finite Element time-stepping techniques. The auxetic laminates exhibit well spaced bending, shear and symmetric fundamental modes, while featuring normal stresses for A₀ mode 3 times lower than composite laminates with positive Poisson's ratio.

This paper presents a set of results from an experiment that is designed to evaluate a damage detection approach for through-thickness fatigue cracks emanating from a rivet hole in a high-performance aircraft bulkhead. Because fatigue cracks have been found through depot-level visual-inspections at the same location in several aircraft bulkheads, a "hot-spot" approach to monitor this area with Lamb waves generated from surface-mounted lead ziconate titanate (PZT) transducers is evaluated. Detecting these fatigue cracks is challenging because the cracks propagate through an area of restricted geometry - a small plate-like area surrounded by thick webbing - which results in the interference of reflected wave components with the direct path wave components when using a pitch-catch approach. To minimize this interference, time-of-flight windows are applied to remove the reflected signals, and to increase probability of detection, Lamb wave mode tuning is used. Finally, to make the crack easier to detect, various static loads are applied to open the crack, but new challenges are presented when attempting to detect damage under a static load.

It has been shown by many researchers that guided wave structural health monitoring is capable of detecting the presence of damage in a structure. The requirements for grid spacing and sensitivity to temperature change have been established and can be used to specify an array with a given signal to noise ratio. What is not clear at this point is how, given that damage is detectable, its location should be found. This paper discusses two different imaging algorithms and investigates the relative merits of each. This is initially done on the smallest possible array of three transducers. This is then carried forward to larger sparse arrays to show how a larger structure with a distributed sensor network can be imaged with several "units" of transducers working together. It is shown that in general using more transducers is beneficial to the quality of imaging achieved. However it is still necessary to perform imaging using smaller arrays to ensure that in the event of multiple damage sites occurring simultaneously each can be detected.

The paper presents guided elastic waves and their identification and damage interaction in a CFRP plate. After the excitation of a fiber transducer, different elastic waves emerge in a plate. By using specially developed 3D laser scanning software it was possible to specify the different wave modes. These wave modes have been described concerning their propagating velocities and different motion components. The interaction of different wave modes with introduced impact damage (7J) is shown. In some experiments, it was proven that impact locations can be derived from the detected Lamb waves. This work is continued to develop structural health monitoring systems (SHM) for selected aircraft components (e. g. stringer elements, panels).

The level of post-subtraction noise due to benign structural features limits the sensitivity that guided wave structural health monitoring systems can achieve. Subtraction of reference signals without compensation leads to unacceptably high post-subtraction noise in the presence of modest environmental changes, and in particular temperature. Hence some form of compensation is necessary. In this paper, various compensation strategies are investigated and their performance quantified. Factors such as the length of time-window considered, sensor variations and inhomogeneous temperature variations are also addressed. It is concluded that the best performance that can currently be achieved is by (a) obtaining the best matched signal from an ensemble of multiple reference signals recorded at different temperatures and (b) fine tuning this signal by numerically stretching or compressing it.

This paper presents several challenging issues on wireless structural health monitoring techniques for critical members of civil infrastructures using piezoelectric active sensors. The basic concept of the techniques is to monitor remotely the structural integrity by observing the impedance variations at the piezoelectric active sensors distributed to critical members of a host structure. An active sensing node incorporating on-board microprocessor and radio frequency telemetry is introduced in a sense of tailoring wireless sensing technology to the impedance method. A data compression algorithm using principal component analysis is embedded into the on-board chip of the active sensing node. The data compression algorithm would promote efficiency in terms of both power management and noise elimination of the active sensor node. Finally, a piezoelectric sensor self-diagnosis issue is touched introducing a new impedance model equation that incorporates the effects of sensor and bonding defects.

The paper discusses application of a Magneto-Mechanical Impedance (MMI) technique for damage diagnostics in metallic structures. A magneto-elastic active sensor consisting of a coil and a permanent magnet is utilized for generation of elastic waves via the eddy current mechanism. The generated waves travel in the host structure and reflect off boundaries producing standing (modal) spatial patterns at respective resonance frequencies. Frequency dependent response to the applied excitation is obtained by the same sensor and is presented in terms of the dynamic impedance. It is shown that the impedance measured in the MMI technique reflects structural dynamic characteristics. Experimental studies involving simple and complex structural elements are presented that explore MMI spectral features for damage diagnostics. Comparison of the impedance data reveals shift and redistribution of impedance peaks in the MMI spectra associated with the damaged samples. We conclude that MMI technique can be employed for structural diagnostics in the embedded SHM or re-configurable NDE formats.

In NDT (nondestructive testing) often a side-drilled hole (circular cavity) is used for calibration. In this paper scattering of ultrasonic waves by a circular hole is studied. The ultrasonic wave is generated by a transducer of finite dimension. A newly developed semi-analytical technique called Distributed point source method (DPSM) has been adopted to solve this problem. Even though this is an old problem the complete field of the scattered waves in presence of a hole in a half space near its boundary has not been shown in the literature yet. The scattered ultrasonic field (stress and displacement) is computed using DPSM and presented in the paper. Solution of this problem will also help us to understand the distortion of the ultrasonic field in the half-space due to the presence of a circular anomaly (cavity or inclusion) which plays an important role in structural health monitoring.

The Operationally Responsive Space (ORS) strategy hinges, in part, on realizing technologies which can facilitate the rapid deployment of satellites. Presently, preflight qualification testing and vehicle integration processes are time consumptive and pose as two significant hurdles which must be overcome to effectively enhance US space asset deployment responsiveness. There is a growing demand for innovative embedded Structural Health Monitoring (SHM) technologies which can be seamlessly incorporated onto payload hardware and function in parallel with satellite construction to mitigate lengthy preflight checkout procedures. In this effort our work is focused on the development of a joint connectivity monitoring algorithm which can detect, locate, and assess preload in bolted joint assemblies. Our technology leverages inexpensive, lightweight, flexible thin-film macro-fiber composite (MFC) sensor/actuators with a novel online, data-driven signal processing algorithm. This algorithm inherently relies upon Chaotic Guided Ultrasonic Waves (CGUW) and a novel cross-prediction error classification technique. The efficacy of the monitoring algorithm is evaluated through a series of numerical simulations and experimentally in two test configurations. We conclude with a discussion surrounding further development of this approach into a commercial product as a real-time flight readiness indicator.

Higher-order spectra (HOS) appear often in the analysis and identification of nonlinear systems. The auto-bispectrum is one example of a HOS and is frequently used in the analysis of stationary structural response data to detect the presence of structural nonlinearities. In this work we derive an expression for the auto-bispectrum of a multi-degree-of-freedom structure with quadratic nonlinearities. A nonlinearity detection strategy, based on estimates of the bispectrum, is then described. The performance of several such detectors is quantified using Receiver Operator Characteristic (ROC) curves illustrating the trade-off between Type-I error and power of detection (1-Type-II error).

Higher-order spectra have become a useful tool in spectral analysis, particularly for identifying the presence and sometimes type of nonlinearity in a system. Two such spectra that have figured prominently in signal processing are the bispectrum and trispectrum. The bispectrum is well-suited to capturing the presence of quadratic nonlinearities in system response data while the trispectrum has proved useful in detecting cubic nonlinearities. In a previous work, the authors developed an analytical solution for the auto-bispectrum for multi-degree-of-freedom systems. Here this analysis is extended to the trispectrum. Specifically, an expression is developed for the trispectral density of a multi-degree-of-freedom system subject to Gaussian excitation applied at an arbitrary location. The analytical expression is compared to those obtained via estimation using the direct method.

Techniques that analyze nonlinear transformations of high frequency vibration signals, such as harmonic distortions and frequency modulations, termed nonlinear acoustic techniques (NAT), offer unique advantages in detecting and characterizing structural damage. Linear techniques are limited in their ability to detect small incipient damage and false indications caused by environmental variability and structural features of comparable size to damage. Defects with contact surfaces, such as cracks and delaminations, lead to strong nonlinear behavior in the form of nonlinear frequency interactions. The advantage of NAT over traditional linear techniques in detecting incipient small-scale nonlinear damage is demonstrated by initiating and identifying a fatigue crack in notched beam specimens. Impact-modulation (IM) is utilized to identify frequency modulation caused by the initiation of fatigue cracks. Piezo-stack actuators and modal impact hammers are used to generate structural excitations measured using high frequency accelerometers. Practical implementation issues of NAT are discussed, such as characterizing the inherent nonlinearities of electronics, actuators and sensors for reliable defect characterization.

Variations in parameters representing natural frequency, damping and effective nonlinearities before and after damage initiation in a beam carrying a lumped mass are assessed. The identification of these parameters is performed by exploiting and modeling nonlinear behavior of the beam-mass system and matching an approximate solution of the representative model with quantities obtained from spectral analysis of measured vibrations. The representative model and identified coefficients are validated through comparison of measured and predicted responses. Percentage variations of the identified parameters before and after damage initiation are determined to establish their sensitivities to the state of damage of the beam. The results show that damping and effective nonlinearity parameters are more sensitive to damage initiation than the system's natural frequency. Moreover, the sensitivity of nonlinear parameters to damage is better established using a physically-derived parameter rather than spectral amplitudes of harmonic components.

Ultrasonic guided wave testing necessitates of quantitative, rather than qualitative, information on flaw size, shape and position. This quantitative diagnosis ability can be used to provide meaningful data to a prognosis algorithm for remaining life prediction, or simply to generate data sets for a statistical defect classification algorithm. Quantitative diagnostics needs models able to represent the interaction of guided waves with various defect scenarios. One such model is the Global-Local (GL) method, which uses a full finite element discretization of the region around a flaw to properly represent wave diffraction, and a suitable set of wave functions to simulate regions away from the flaw. Displacement and stress continuity conditions are imposed at the boundary between the global and the local regions. In this paper the GL method is expanded to take advantage of the Semi-Analytical Finite Element (SAFE) method in the global portion of the waveguide. The SAFE method is efficient because it only requires the discretization of the cross-section of the waveguide to obtain the wave dispersion solutions and it can handle complex structures such as multilayered sandwich panels. The GL method is applied to predicting quantitatively the interaction of guided waves with defects in aluminum and composites structural components.

Recent years have seen growing interest in applying wireless sensing and embedded computing technologies for structural health monitoring and control. The incorporation of these new technologies greatly reduces system cost by eliminating expensive lengthy cables, and enables highly flexible system architectures. Previous research has demonstrated the feasibility of decentralized wireless structural control through numerical simulations and preliminary laboratory experiments with a three-story structure. This paper describes latest laboratory experiments that are designed to further evaluate the performance of decentralized wireless structural control using a six-story structure. Commanded by wireless sensors and controllers, semi-active magnetorheological (MR) dampers are installed between neighboring floors for applying real-time feedback control forces. Multiple centralized/decentralized feedback control architectures have been investigated in the experiments, in combination with different sampling frequencies. The experiments offer valuable insight in applying decentralized wireless control to larger-scale civil structures.

Metal corrosion is a significant problem for the US concrete infrastructure. Accurate and continuous corrosion sensing methods would help reduce this cost and enable effective health monitoring and service life prediction. In this paper, recent efforts to apply giant magneto-resistive response (GMR) and eddy current sensors for corrosion sensing are described. The sensors are applied in passive and active sensing configurations, neither of which require excavation of the concrete, so remote sensing at a surface and internal sensing with an embedded unit are possible. The passive and active testing configurations are described. Then experimental results for aluminum corrosion are presented, with the aim of identifying existing corrosion state to date and rate of active corrosion at time of sensing.

Structural health monitoring using permanently attached, distributed sensors for guided waves offers an efficient monitoring methodology for large structures. The measurement concept has been demonstrated for plate structures and shown to be able to localize defects. For the application to real technical structures it needs to be shown that the methodology works equally well in the presence of structural features, which have been identified as safety-critical areas. Problems can occur due to environmental or secondary changes in the signal pathway. Different signal processing options to reduce these detrimental effects are compared, including the automatic identification of defect signals and truncation of secondary pulses. The influence of the signal processing parameters and transducer placement on the damage localization accuracy is discussed. Results are presented using experimental and simulated signals for large structures with features such as stiffeners and crack-like defects.

There has been a massive increase in the use of ultrasonic arrays for non-destructive evaluation (NDE) in recent years. However, much of this technology is either based on medical ultrasound imaging or is designed simply to mimic traditional NDE inspections performed with monolithic transducers. This paper addresses the issue of array system design and data processing specifically for quantitative NDE. It is shown that arrays offer huge potential for defect characterization in NDE beyond that currently exploited and possible directions are discussed. In particular, it is shown that obtaining all the time-domain signals from every transmitter receiver combination combined with post-processing is the preferable strategy for NDE. Not only can information in the full data-set provide the highest possible resolution image, but that it can also be exploited to perform sub-wavelength reflector characterization by extracting portions of the reflector scattering matrix. Experimental results on artificial defects are used to illustrate this point.

Ultrasonic methods have been implemented for in situ sizing of fatigue cracks near fastener holes. These techniques, however, only provide an estimate at the time of the measurement and cannot predict the remaining life of the structure. In contrast, statistical crack propagation approaches model the expected fatigue life based on worst-case fatigue process assumptions. The authors have recently developed a Kalman filter approach for combining ultrasonic observations with crack growth laws. An ultrasonic angle-beam technique, combined with an energy-based wave propagation model, serves as the measurement model. Paris's crack growth equation acts as the system model for crack propagation. For simulated data, this approach provided more accurate crack size estimates than either the ultrasonic measurements or crack growth approach alone. Presented here are experimental results to assess the ability of the Kalman filter to provide reasonable crack size estimates.

This paper presents an algorithm for autofocusing imagery obtained from a flexible ultrasonic array with unknown geometry. The relative positions of the array elements are parameterised using a polynomial function. The polynomial coefficients are estimated by iterative maximisation of the SAFT image contrast via simulated annealing. The estimate can be refined in the final stages of iteration using the full 3-D matrix of echo data via the total focusing method. The resultant polynomial gives an estimate of the array geometry and the profile of the surface that it has conformed to, providing a well-focused, high quality image. The algorithm is demonstrated on experimental data obtained using a flexible array prototype.

Sparse ultrasonic arrays spatially distributed over a large area of a structure have been proposed and tested in the laboratory for in situ detection and localization of damage. Detection algorithms are typically based upon comparison to a baseline, where differences not explained by benign environmental effects are interpreted as damage. Most localization methods are either based upon an arrival time analysis of differenced signals or spatial distribution of a damage index. Triangulation and delay-and-sum type methods fall into the first category and, under ideal conditions, can accurately locate discrete damage such as a single crack. Methods in the second category do not rely on precise timing of scattered signals, but are limited in their ability to precisely locate discrete damage using a small number of sensors. This paper evaluates the effectiveness of both types of methods for locating a single site of discrete damage, and considers the degradation in performance resulting from errors in both wave speed and transducer locations.

A crack detection technique based on nonlinear acoustics is developed in this study. Acoustic waves at a chosen frequency are generated using an actuating lead zirconate titanate (PZT) transducer, and they travel through the target structure before being received by a sensing PZT wafer. Unlike an undamaged medium, a cracked medium exhibits high acoustic nonlinearity which is manifested as harmonics in the power spectrum of the received signal. Experimental results also indicate that the harmonic components increase non-linearly in magnitude with increasing amplitude of the input signal. The proposed technique identifies the presence of cracks by looking at the two aforementioned features: harmonics and their nonlinear relationship to the input amplitude. The effectiveness of the technique has been tested on aluminum and steel specimens. The behavior of these nonlinear features as crack propagates in the steel beam has also been studied.

This paper continues the development of a heuristic initialization methodology for designing multilayer feedforward neural networks aimed at modeling nonlinear functions for engineering mechanics applications as presented previously at SPIE 2003, and 2005 to 2007. Seeking a transparent and domain knowledge-based approach for neural network initialization and result interpretation, the authors examine the efficiency of linear sums of sigmoidal functions while offering constructive methods to approximate functions in engineering mechanics applications. This study provides details and results of mapping the four arithmetic operations (summation, subtraction, multiplication, division) as well as other functions including reciprocal, Gaussian and Mexican hat functions into multilayer feedforward neural networks with one hidden layer. The approximation and training examples demonstrate the efficiency and accuracy of the proposed mapping techniques and details. Future work is also identified. This effort directly contributes to the further extension of the proposed initialization procedure in that it opens the door for the approximation of a wider range of nonlinear functions.

The Air Force Research Laboratory/Space Vehicles Directorate (AFRL/RV) is developing Structural Health Monitoring (SHM) technologies in support of the Department of Defense's Operationally Responsive Space (ORS) initiative. Such technologies will significantly reduce the amount of time and effort required to assess a satellite's structural surety. Although SHM development efforts abound, ORS drives unique requirements on the development of these SHM systems. This paper describes several technology development efforts, aimed at solving those technical issues unique to an ORS-focused SHM system, as well as how the SHM system could be implemented within the structural verification process of a Responsive satellite.

The development of high sensitivity sensors capable of accurately reproducing propagating Lamb waves is crucial for the success of AE based structural health monitoring applications. Plate like members are the most common elements encountered in structural health monitoring. The stress waves propagate as guided waves or Lamb waves in these members. While the traditional acoustic emission sensors are sensitive to displacements normal to the surface of the structural member, the bonded sensors are sensitive to the surface strains. A calibration procedure specifically for the Lamb wave modes is devised using a Laser Vibrometer. The calibration was performed by observing the stress waves propagating in aluminum plates. Based on this calibration, it is established that the bonded PZT sensors reproduce the stress waveforms in these structures reasonably well. This ability was probably responsible for the success of these sensors in distinguishing different source mechanisms and correlation with crack growth rates seen in past studies. In addition to this calibration, the two simulated AE sources were also modeled using finite element technique. The results of the numerical simulation were found to correlate well with the experimental results.

Double wall structures are three-layered systems in which the second or intermediate layer is frequently a liquid. The liquid aids in the cooling process when the interior is at high temperature. Examples are double wall steam pipes, pressure vessels and heat exchanger plates. Structural health monitoring and nondestructive testing from the outside, through three layers to the inside wall is difficult. This paper presents a viable solution by proposing the use of ultrasonics to generate a slow guided wave in the structure enabling inspection of the inner wall for flaws. The results of calculations, simulations and experiments are presented and compared. In particular, a two-dimensional model of the setup is introduced and a procedure for obtaining group velocity dispersion diagrams. The model is validated using theoretical and experimental results. Sample dispersion diagrams are presented and compared with those obtained with matrix methods. Finally, the FEM simulation results depict the displacement profiles across the waveguide. The results of both modeling techniques are in good agreement and they provide interesting insights into the wave mechanics of the three-layered waveguide.

Several investigators have modeled ultrasonic fields in front of finite sized transducers. Most of these models are based on Huygens principle. Following Huygens-Fresnel superposition principle one can assume that the total field of a finite size transducer is obtained by simply superimposing the contributions of a number of point sources uniformly distributed on the transducer face. If the point source solution, also known as the Green's function, is known then integrating that point source solution over the transducer face one can obtain the total ultrasonic field generated by a finite transducer. This integral is known as Rayleigh-Sommerfield integral. It is investigated here how the ultrasonic field in front of the transducer varies for different interface conditions at the transducer face-fluid interface such as 1) when only the normal component of the transducer velocity is assumed to be uniform on the transducer face and continuous across the fluid-solid interface, or 2) when all three components of velocity are assumed to be uniform on the transducer face and continuous across the interface, 3) when the pressure instead of velocity is assumed to be uniform on the transducer face and continuous across the interface. All these different boundary and interface conditions can be modeled by the newly developed Distributed Point Source Method (DPSM). These results are compared with the Rayleigh-Sommerfield integral representation that gives the fluid pressure in front of the transducer when the transducer-fluid interface is subjected to uniform normal velocity.

Two points source method was proposed for damage detection in concrete structures. To validate the proposed method, finite element simulations were carried out. In 3-D models, non-reflecting boundary conditions were considered to model an infinite medium so that the models prevented artificial dilatational stress wave reflections generated at the boundaries from reentering the model and contaminating the results. Then, two different types of damages (crack and deterioration) were introduced to investigate if the proposed method could detect the damages. From the finite element simulations, it is shown those damages are detectable and their severities can also be identifiable. Besides, the proposed method has shown that two points source method does not require any baseline signal for the damage detection; hence, its efficiency is verified.

For applications involving the determination of variations of the time-of-flight in pulsed echo or transit experiments a method has been developed based on Fourier transformation with forced optimized compression of the reference signal to an only bandwidth limited approximation of a Dirac-function. The respective transformation of time shifted response signals allows the effective separation of otherwise overlapping signals and the detection of differences in the time-of-flight for the individual components with high resolution. The developed processing scheme corrects for dispersion and attenuation in the electronics, the transmission lines, and the transducers. The method is presented and applications are demonstrated.

Simultaneous recording of shear and pressure is an important requirement for study the causes of foot ulceration. In order to obtain a more robust and meaningful picture of what is occurring on the plantar surface of the foot, we have developed a multi-layered optical bend loss sensor that can be accommodated for shear and pressure measurement of an extended area. The sensor is made of two layers of crisscross fiberoptic sensor array separated by an elastomeric layer. Each sensing layer has multiple fibers molded into a thin polydimethylsiloxane (PDMS) substrate to form a mesh array. The top layer uses 6 fibers to create a 3 by 3 mesh with 9 intersection points and the bottom layer uses 8 fibers to create a 4 by 4 mesh with 16 intersection points. The space between the adjacent fibers is 0.5cm. Measuring changes of light intensity transmitted through the fiber provides information about the force induced changes of the fiber's radius of curvature. Pressure is measured based on the force induced light loss from the two affected crossing fibers divided by each sensing area. Shear was measured based on the relative position changes on these pressure points between the two fiber mesh layers. The design is an offset layout because the intersection points of the top and bottom layer are offset by 0.25 cm which can increase the shear sensing sensitivity. For testing the sensor with various loading condition, a neural network algorithm is induced to identify the loading pattern and the shear direction. Three loading patterns with 5 different loading directions were tested and a >90% accuracy was obtained using an algorithm using 2 neural networks.

The determination of the velocity of sound for small objects suffers from limited resolution concerning as well the determination of the extension along the path of the sound waves as the determination of the time of flight. Imaging of planar objects with a wedge shaped boarder allows imaging in transmission with no object and the full object in the path of the acoustic waves in a continuous manner. Such phase tracking available by PSAM can be used to determine the variation of the time-of-flight with ultimate resolution. Furthermore, for a coupling fluid with a speed equal to the speed of the object under study, the extension of the object does not contribute to the result. Similarly for coupling fluids with sound velocities close to the one of the object under study the error concerning the extension which can be substantial for microscopic objects is reduced and can be minimized by selection of suitable fluids. The method is demonstrated and application involving different objects and fluids are demonstrated.

The use of flat panels based on amorphous silicon technology for digital radiography has been accepted in the medical community due to their advantages over film for several applications. For industrial applications similar advantages for panels exist. Digital radiography gives the user improved sensitivity, better contrast resolution and enables sequential image acquisition. A mixture of radiographic and computed tomographic images are presented that covers the energy range from 125 kVp to 9 MeV.

A fluid viscosity sensor using bend loss theory is presented. The sensing principle makes use of the damping characteristic of a vibrating optical fiber probe with fix-free end configuration. By measuring the frequency response of the fiber probe, the viscosity can be determined from the displacement of the fiber. Experimental results are presented for sucrose solutions of different concentrations with a viscosity varying from 1 to 15 cP.

The goal of this study is to present unconventional detection and imaging principles which may lead to novel detection and characterization methodologies for standoff detection of radiation. While there currently are a number of effective technologies and methodologies for nuclear detection based on direct and indirect-ionization detector architectures operating on radiation counting techniques, the problem of detecting nuclear radiation at significant standoff distances remains one of the most difficult and most important challenges. The phenomenology of alternative signatures, a physical algorithm aimed to assess remotely biological hazards of nuclear radiation, and the design of efficient standoff detection architectures are presented.

Debonding of externally bonded carbon fiber reinforced polymer (CFRP) materials used for repair of reinforced elements is commonly observed and is often the critical limit state for such systems. This paper presents an acoustic emission (AE) study performed during laboratory tests of concrete slab specimens strengthened with CFRP strips. Several specimens having different b_f/s ratio (ratio of CFRP width-to-CFRP spacing) were monitored. An AE paradigm to monitor damage initiation, progression, and location in the test specimens is demonstrated. An algorithm to classify the cracks in concrete, the disbond of the CFRP strips from the soffit of the slab, and the eventual failure (debonding or concrete shear) is also presented. The proposed general approach can be applied to large scale CFRP-concrete systems. The results presented here are part of a broader study, conducted at the University of Pittsburgh, aiming at characterizing the structural response and the debonding behavior of reinforced concrete strengthened with CFRP.

Structural Integrity of predetermined critical zones in a structure is of growing interest in the non-destructive testing (NDT) and structural health monitoring (SHM) communities. Quite often the presence of defects does not imply the end of life of the underlying structure and it could be economical to continue using the structure until the damage severity reaches a point where it can no longer be used. For structures like pipelines and aircraft in which a failure can be catastrophic, it is extremely important to monitor continuously any defects on the structure. Leave in place sensors provide a convenient way to embed the sensors permanently on the structure to monitor periodically and to establish its integrity. Wireless sensing units provide a robust means to regularly monitor a structure and return the data to a central data collection infrastructure. In this study we explore the design of a wireless tomographic imaging system that uses Lamb wave propagation characteristics on a structure to map accurately the material loss zones due to corrosion in the area enclosed by the sensors. The wireless unit has an actuator to excite the piezoceramic sensors and the computational capability to interrogate the signals in real time and to communicate the information. The capability of the system is illustrated by testing it on an aluminum plate with simulated corrosion damage and the results are presented.

In this paper, a hybrid vibration-impedance approaches is newly proposed to detect the occurrence of damage, the location of damage, and extent of damage in steel plate-girder bridges. Firstly, theoretical backgrounds of the hybrid structural health monitoring are described. The hybrid scheme mainly consists of three sequential phases: 1) to alarm the occurrence of damage in global manner, 2) to classify the alarmed damage into subsystems of the structure, and 3) to estimate the classified damage in detail using methods suitable for the subsystems. Damage types of interest include flexural stiffness-loss in girder and perturbation in supports. In the first phase, the global occurrence of damage is alarmed by monitoring changes in acceleration features. In the second phase, the alarmed damage is classified into subsystems by recognizing patterns of impedance features. In the final phase, the location and the extent of damage are estimated by using modal strain energy-based damage index methods. The feasibility of the proposed system is evaluated on a laboratory-scaled steel plate-girder bridge model for which hybrid vibration-impedance signatures were measured for several damage scenarios.

One important application of guided wave ultrasound is that of rail condition monitoring where long lengths of rail can be monitored from permanently attached transducer locations. During the development of transducers for such a system it is advantageous to be able to measure the amplitude of the individual modes of propagation on a short length of rail in the laboratory. This paper describes a method of extracting modal amplitudes from measured time domain signals performed at a limited set of points on the waveguide. The method uses the wave propagation characteristics of the waveguide, predicted by a semi-analytical finite element model, to extract the modal amplitudes from experimental measurements. The frequency response at a set of measurement locations is described by a superposition (with unknown amplitude coefficients) of the frequency response of the modes that propagate in the frequency range of interest. Experimental time domain responses are measured and transformed to frequency responses. The amplitude of each mode is estimated using the pseudo-inverse to provide a minimum norm least-squares estimate. The technique is demonstrated on a rail excited by a piezoelectric patch transducer. A laser vibrometer was used to measure displacements at five points around the rail circumference at three distances giving a total of 15 measurements. Eight propagating modes were extracted from these measurements. The extracted modes were then used to predict the response at points further along the waveguide and these predictions were verified by further measurements indicating that the modes of propagation were accurately estimated. The technique requires that the distance between the measurement points be known but does not require that the distance from the transducer be known. This feature and the fact that only a few measurements are required make the method suitable for measuring the propagation of individual modes over long distances in the field.

Traditionally ultrasonic testing is used to estimate the extent of damage in a concrete structure. However Pulse-velocity and amplitude attenuation methods are not very reliable, and are difficult to reveal early damage of concrete. In a previous study, a new active modulation approach, Nonlinear Active Wave Modulation Spectroscopy, was developed and found promising for early detection of damage in concrete. In this procedure, a probe wave is passed through the system in a fashion similar to regular acoustic methods for inspection. Simultaneously, a second, low-frequency modulating wave is applied to the system to effectively change the size and stiffness of flaws microscopically and cyclically, thereby causing the frequency modulation to change cyclically as well. It has been also shown that it is advantageous to apply the Hilbert-Huang transform to decompose nonlinear non-stationary time-domain responses of plain concrete. Such procedure leads to improving the damage detection sensitivity of this modulation method in concrete. In this paper, further investigation on mortar and fiber reinforced concrete will be presented and discussed.

Though the brief introduction of the completed structural health and safety monitoring warning systems for Shenzhen-Hongkong western corridor Shenzhen bay highway bridge (SZBHMS), the self-developed system frame, hardware and software scheme of this practical research project are systematically discussed in this paper. The data acquisition and transmission hardware and the basic software based on the NI (National Instruments) Company virtual instruments technology were selected in this system, which adopted GPS time service receiver technology and so on. The objectives are to establish the structural safety monitoring and status evaluation system to monitor the structural responses and working conditions in real time and to analyze the structural working statue using information obtained from the measured data. It will be also provided the scientific decision-making bases for the bridge management and maintenance. Potential technical approaches to the structural safety warning systems, status identification and evaluation method are presented. The result indicated that the performance of the system has achieved the desired objectives, ensure the longterm high reliability, real time concurrence and advanced technology of SZBHMS. The innovate achievement which is the first time to implement in domestic, provide the reference for long-span bridge structural health and safety monitoring warning systems design.

In this paper, one large Fiber Bragg Grating (FBG) sensor sensing network for bridge local health monitoring was studied, designed and implemented to Harbin Sifangtai Bridge, China. According to the hot point principle and finite element analysis results, FBG sensors installation scheme was made to monitor the local strain of key elements, respectively. 60 FBG sensors had been installed in monitoring points along the height of I-shape girders distributed in three main monitoring sections along the bridge. Monitoring results in load testing period was obtained, the static and dynamic results show that FBG sensors can monitoring the local strain precisely, and the local strain response is in the safe range under test vehicle load. Monitoring results in service period was obtained, 9 months after load test. Results show that maximum local strain responses in three main monitoring sections are in the safe range, under the dynamic vehicle load. Comparison of the monitoring results from FBG sensor sensing network are used to unveil the local health condition of Sifangtai Bridge reflected by local strain response.

Recent research has shown that chaotic structural excitation and state space reconstruction may be used beneficially in structural health monitoring (SHM) processes. This relationship has been exploited for use in detection of bolt preload reduction by using a chaotic waveform with ultrasonic frequency content with a damage detection algorithm based on auto-regressive (AR) modeling. The signal is actively applied to a structure using a bonded macro fiber composite (MFC) patch. The response generated by the mechanical interaction of the MFC patch with the structure is then measured by other affixed MFC patches. In this study the suitability of particular chaotic waveforms will be investigated through the use of evolutionary algorithms. These algorithms are able to find an optimum excitation for maximum damage state discernability whose fitness is two orders of magnitude greater than choosing random parameters for signal creation.

A neural networks-based structural identification method using absolute acceleration without mode shapes and frequency extraction is proposed and validated with vibration absolute acceleration measurements from shaking table test of a two-storey frame structure. An acceleration-based neural network modeling for acceleration forecasting and a parametric evaluation neural network for parametric identification are constructed to facilitate the whole identification process. Based on the two neural networks and by the direct use of absolute acceleration measurement time histories of the object frame structure under base excitation, the inter-storey stiffness and damping coefficients of the frame structure are identified. The identified results by the proposed methodology are compared with them by solving eigenvalues equation. Results show that the structural stiffness and damping coefficients identification accuracy is acceptable and the proposed strategy can be a practical tool for model updating and damage detection of engineering structures.

This study presents a damage detection algorithm based on the proper orthogonal decomposition technique for health monitoring of composite structures. A finite element model of a carbon/epoxy composite plate is used to generate vibration data for healthy and damaged structures. Varying levels of stiffness reduction for the elements in the damaged zone of the structure simulate impact damage. Different random excitation inputs are used for each of the three damage locations investigated in order to introduce variation in the loading conditions of the model. An experimental investigation is also performed using a carbon/epoxy plate similar to the numerical model. The composite plate is mounted as a cantilever and the fixed end of the plate is excited with an electro-magnetic shaker. Impact damage is introduced into the plate dropping a steel ball in one area of the plate from different heights. The results of the damage detection method indicate that damages can be detected and localized using this algorithm.

Carbon-fiber composites will increasingly be used in next generation air transportation vehicles. Therefore, it is critical to develop state awareness models that can accurately capture the damage states and predict remaining useful life based on current and future loading conditions. In the current research, a structural health monitoring (SHM) and prognosis framework is being developed for heterogeneous material systems. The objective of this paper is to present some of the experimental components of this work. In the experiments preformed, the use of a pitch catch method using piezoelectric transducers for both the actuator and sensor were employed for collecting information on the damage status. The focus of this work is to quantify damage within the sample by relating parameters in the sensor signal to damage intensity. Good correlation has been observed in several tests between damage level and wave attenuation. These results are confirmed using off-the-shelf NDE techniques.

The initiation and propagation of damage in composite laminates generate Acoustic Emission. The use of real time AE monitoring has been quite extensive for in-service composite structures. In the present work, experimental and numerical studies were performed to characterize the acoustic wave propagation in thin glass/epoxy composite plates. Experimentally obtained and simulated emission signals were used to identify and locate the source of the acoustic wave. Signal processing algorithms and a passive damage diagnosis system based on AE techniques were proposed for continuously monitoring and assessing the structural health of composite laminates. The local sensing and distributed processing features of the sensor system result in a decreased demand for bandwidth and lower computational power needed at each node.

Presented here is an amplitude and frequency modulation method (AFMM) for extracting damage-induced nonlinear characteristics and intermittent transient responses by processing steady-state/transient responses using the empirical mode decomposition, Hilbert-Huang transform (HHT), and nonlinear dynamic characteristics derived from perturbation analysis. A sliding-window fitting (SWF) method is derived to show the physical implication of the proposed method and other methods for time-frequency signal decomposition. Similar to the short-time Fourier transform and wavelet transform the SWF uses windowed regular harmonics and function orthogonality to extract time-localized regular and/or distorted harmonics. On the other hand the HHT uses the apparent time scales revealed by the signal's local maxima and minima to sequentially sift components of different time scales, starting from high-frequency to low-frequency ones. Because HHT does not use predetermined basis functions and function orthogonality for component extraction, it provides more accurate instant amplitudes and frequencies of extracted components for accurate estimation of system characteristics and nonlinearities. Moreover, because the first component extracted from HHT contains all original discontinuities, its time-varying amplitude and frequency are excellent indicators for pinpointing times and locations of impulsive external loads and damages that cause intermittent responses. However, the discontinuity-induced Gibbs' effect makes HHT analysis inaccurate around the two data ends. On the other hand, the SWF analysis is not affected by Gibbs' effect, but it cannot extract accurate time-varying frequencies and amplitudes. Numerical results show that the proposed AFMM can provide accurate estimations of softening and hardening effects, different orders of nonlinearity, linear and nonlinear system parameters, and time instants of intermittent transient responses for damage detection and estimation.

In this paper, a Dempster-Shafer evidence theory based approach for structural health monitoring is presented. Firstly, Bayesian method is employed to calculate the damage probabilities of substructures using each data set measured from the monitored structure, and the damage probabilities of substructures are transformed to damage basic probability assessments which used in evidence theory. Then the Dempster-Shafer evidence theory is employed to combine the individual damage basic probability assessments for getting the last damage detection results. With considering multi-sensors data including acceleration and strain, and measurement noise the numerical studies on a 14-bay planar rigid frame structure are carried out. The results indicate that the damage detection results obtained by combining the damage basic probability assessments from each test data are improved compared with the individual results obtained just by each test data separately.

Conducting micro-spheres approximating point probes have been employed to piezoelectrically excite and detect ultrasonic wave packages in anisotropic single crystals. Imaging based on the detection of magnitude and phase is performed in transmission. The experimental data can be used for the determination of the elastic constants of the material. Here we compare this approach with imaging using conventional ultrasonic lenses and water as a coupling fluid. The large bandwidth and the absence of internal lens echoes in the Coulomb excitation and detection scheme permit unperturbed monitoring of multiple echoes in plane-parallel samples and the detailed investigation of mode conversion processes of longitudinal and transverse waves at the surfaces of the crystal. Due to differences in the coupling between the probes and the ultrasound in the sample, excitation of ultrasound by an acoustic lens or an electrical point contact, respectively, result in noticeably different phonon focusing patterns. This is illustrated for lithium niobate single crystals.

A polymeric magnetostrictive fiber-optic sensor is presented. The sensor uses a newly developed ferromagnetic polymer (WCS-NG1) as the magnetostrictive coating for magnetic field detection. A simple fiber-optic Mach-Zehnder interferometer is deployed; where magnetic field induced magnetostriction effect is detected based on the phase modulation measurement. The magnetostrictive effect has a number of advantages of sensor. It is relatively simple to fabricate on the optical fiber. Optical technique also provides high sensitivity in its measurant. Therefore, magnetostrictive effect is used for the fiber optics magnetometer. Comparison with Tefonol or other conventional magentistrcition sensors, this novel polymeric magnetostrictive fiber-optic sensor is much less complex relatively smaller in size, and optical technique also prevents RF interference that is common in typical electromagnetic type sensors. In this paper, characterization of the material and magnetic properties of the embedded polymer will be discussed. Preliminary results on the magnetic field and current sensing will be presented.

Vibration energy harvesting is an attractive technique for potential powering of wireless sensors and other low power micro devices. In order for the device to have maximum power output, it is necessary to match electrical and mechanical damping. In this work a coupled piezoelectric and electromagnetic energy harvesting device is evaluated for its efficiency and compared with optimized standalone piezoelectric and electromagnetic techniques. A piezoelectric cantilever beam with a cylindrical magnet as its tip mass and a resonance frequency of 19 Hz is used, with a coil winding vertically aligned with the magnet such that the magnetic tip would pass through the coil. The total power output from the coupled energy harvesting technique is monitored which produced a power output of ~340 μW compared to 301 μW from an optimized standalone piezoelectric energy harvesting and 120 μW from an standalone electromagnetic energy harvesting device. The total damping in the system is determined to be 0.054 compared to 0.046 and 0.04 for piezoelectric and electromagnetic techniques.

Thin films of polystyrene (PS)/polymethylmethacrylate (PMMA) blends were made by casting from solutions with solvents of varying vapor pressure. Solvents used were chloroform, toluene and dichloromethane. Spin coating was carried out at varying speeds yielding films of different thickness. Atomic force microscopy and phase-sensitive acoustic microscopy were used to investigate the effects of spin speed and solvent vapor pressure on morphology. The domains formed due to lateral phase separation proved to be strongly influenced by vapor pressure with completely different surface structures for the three solvents. The films cast from high vapor pressure solutions displayed an increased surface roughness. Surface morphology is explained by the relative solubility in the different solvents, surface affinity, spin speed and viscosity.

A 13 cm × 13 cm size mercuric iodide (HgI₂) imager was tested for high (MeV) energy X-ray imaging with a 6 MeV Betatron and a 4 MeV Linac x-ray source, and the data were compared to those measured at diagnostic (keV) energies. The 127 μm pixel size imager gave excellent resolution, with a MTF (modulation transfer function) of 45% at the Nyquist frequency, similar to that of measured at diagnostic (keV) energies. The sensitivity of the imager was measured using a 1 mm thick Cu and a 0.5 mm thick Ta buildup plate, placed on the top electrode of the HgI₂ layer and also without any buildup plate. The highest signal levels were obtained without a buildup plate. The imager can also capture fluoroscopic images at up to 15 fr/sec in the full resolution mode, and at up to 30 fr/sec with 2 × 2 pixel binning. . With this imager, small steel objects were clearly visible behind a 1/8" thick steel plate. These experiments with high energy x-rays, demonstrate that HgI₂ imagers can be used, not only for the diagnostic energy range, but also for the MeV energy range. Moreover the same imager can be used for dual energy (keV and MeV) imaging for medical, NDE (non destructive evaluation) and homeland security applications.

Microscopic objects including living cells on a planar substrate are investigated in bio-medical applications of scanning acoustic microscopy. Beside of the observation of lateral structures, the determination of sample properties such as density, sound velocity, and attenuation is desired, from which elastic properties can be derived. This can be achieved with the aid of the acoustic phase and magnitude contrast represented in a polar plot. For homogeneous and sufficiently planar objects the contrast in magnitude and phase is a function of the properties of the substrate and the coupling fluid, which both can easily be determined, and of the mechanical properties of the sample under observation. For observation in reflection and variable thickness of the sample the signal will depend on the actual thickness. This signature of the object can be fitted based on a conventional ray model for the sound propagating in the coupling medium and the sample. The model includes also the refraction and reflection at all interfaces between transducer, lens material, coupling fluid, object, and substrate. The method is demonstrated for a chitosan film deposited on a glass substrate. The scheme presented here is capable to reach a resolution of about and even below 1% for relevant quantities in applications involving imaging at 1.2 GHz in aqueous coupling fluids.

Colonoscopy is the gold standard for screening for inflammatory bowel disease and colorectal cancer. Flexible endoscopes are difficult to manipulate, especially in the distensible and tortuous colon, sometimes leading to disorientation during the procedure and missed diagnosis of lesions. Our goal is to design a navigational aid to guide colonoscopies, presenting a three dimensional representation of the endoscope in real-time. Therefore, a flexible sensor that can track the position and shape of the entire length of the endoscope is needed. We describe a novel shape-tracking technology utilizing a single modified optical fiber. By embedding fluorophores in the buffer of the fiber, we demonstrated a relationship between fluorescence intensity and fiber curvature. As much as a 40% increase in fluorescence intensity was achieved when the fiber's local bend radius decreased from 58 mm to 11 mm. This approach allows for the construction of a three-dimensional shape tracker that is small enough to be easily inserted into the biopsy channel of current endoscopes.

Ultrasonic monitoring allowing the evaluation of the performance of muscles under training has been developed. The monitoring scheme is suitable to determine muscle movement and is based on the measurement of the transit time of longitudinally polarized ultrasound propagating across the observed muscle. Variations of the length of the muscle lead to variations of the lateral extension since the volume of the muscle is conserved. The corresponding variations of the observed time-of-flight result dominantly from the variation of the path length. This allows the time-resolved detection of the movement of the muscles in the path of the ultrasonic beam. In this way not only the degree of contraction or relaxation, but also the speed of these processes can be quantitatively monitored. The muscle thickness has been determined with a resolution of ± 0.02 mm corresponding to about ± 0.2 % of the thickness of the relaxed muscle. This resolution is already in the range of unavoidable uncertainties caused by the surface structure of the individual muscles. Similarly, the already obtained resolution in time corresponds to a fraction 1/750 of the time of the fastest known human muscle movement of 7.5 ms, observed for the full contraction of the eye lid muscle. The time of flight is measured along a line between two electro-acoustic transducers positioned on the skin on opposite sides of the monitored muscle. The transducers can be placed at any desired position but should be positioned such, that no bones or intestines are obstructing the path between them. The time-of-flight from which all other data is derived is observed with the aid of a computer-controlled arbitrary function generator and a synchronized transient recorder. Even in the demonstrated developmental state the equipment is already rather compact (lap-top size) and can be battery operated.

This paper presents experimental data and theoretical grounds of the forced vibration of a partially immersed fiber in liquid. An optical method utilizing a forward light scattering pattern has been used to detect small (< 1.0 μm) vibrational amplitude of the fiber. The physical and mathematical model of the partially immersed fiber vibration has been put forward. Based on an analytical solution of the model without damping, natural frequencies of this system have been found; they are roots of the transcendental equation. An "effective" velocity of the wave propagation over the fiber has been introduced; it allows one to find out the physical meaning of normal modes. Numerical method for solution of the problem has been proposed. Numerical computations carried out in the wide ranges of the different liquids and depths agree well with experiment data. Based on numerical results it was shown that variations of the maximum vibrational amplitude and the bandwidth can be presented by the linear functions of the coordinate (ρ_sμ_s)^1/2. It allows one to suggest a simple way for viscosity extraction from both the vibrational amplitude and bandwidth variation, and derive an explicit formula for the achievable accuracy of the viscosity sensing.

This paper presents the development of a Bragg grating interrogation technique for measurements of strain, stress, temperature, and ultrasonic waves. The sensor design and instrumentation technique offer a number of advantages including sensor compactness, lightweight, low-cost, and multiplexing capability for damage detection and corrosion monitoring of advanced structures and components. Using a robust lock-in laser-based demodulation technique, simultaneous measurements of strain, temperature, and damage induced acoustic fields can be performed with high precision, high resolution, and high sensitivity. The interrogated sensor device containing an array of optical Bragg grating fibers and waveguides can be surface mounted on monitoring structures for non-destructive testing applications including highresolution strain measurement and high sensitivity damage and corrosion monitoring.

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.

Phased array with all-azimuth angle coverage would be extremely useful in structural health monitoring (SHM) of planar structures. One method to achieve the 360° coverage is to use uniform circular arrays (UCAs). In this paper we present the concept of UCA adapted for SHM applications. We start from a brief presentation of UCA beamformers based on the principle of phase mode excitation. UCA performance is illustrated by the results of beamformer simulations performed for the narrowband and wideband ultrasonic signals. Preliminary experimental results obtained with UCA used for the reception of ultrasonic signals propagating in an aluminum plate are also presented.

We present several techniques utilizing radio-frequency identification (RFID) technology for personal health monitoring. One technique involves using RFID sensors external to the human body, while another technique uses both internal and external RFID sensors. Simultaneous monitoring of many patients in a hospital setting can also be done using networks of RFID sensors. All the monitoring are done wirelessly, either continuously or periodically in any interval, in which the sensors collect information on human parts such as the lungs or heart and transmit this information to a router, PC or PDA device connected to the internet, from which patient's condition can be diagnosed and viewed by authorized medical professionals in remote locations. Instantaneous information allows medical professionals to intervene properly and timely to prevent possible catastrophic effects to patients. The continuously monitored information provides medical professionals more complete and long-term studies of patients. All of these result in not only enhancement of the health treatment quality but also significant reduction of medical expenditure. These techniques demonstrate that health monitoring of patients can be done wirelessly at any time and any place without interfering with the patients' normal activities. Implementing the RFID technology would not only help reduce the enormous and significantly growing medical costs in the U.S.A., but also help improve the health treatment capability as well as enhance the understanding of long-term personal health and illness.