In order to create the scientific foundation of measurement, the national metrology institutes (NMIs) realize the units in compliance with the definition agreed on the international level and disseminate the units to the users through comparison. The PTB - as the National Metrology Institute of Germany providing scientific and technical services for Germany and other countries - has focused major activities to respond to the needs of manufacturers and users of laser vibrometers and of calibration systems applicable to laser vibrometer calibration and/or based on laser interferometry. Theoretical and experimental investigations and comparisons of different standard measuring devices (national standards of Germany) resulted in extended measurement ranges and increased accuracy. PTB has achieved, among other upgraded capabilities, primary calibration of laser vibrometer standards in the frequency range from 0.4°Hz to 20°kHz with a measurement uncertainty of 0.1°% to 0.2°% (frequency dependent, coverage factor k°=°2). This enabled one of the calibration laboratories in Germany, within the framework of the Deutscher Kalibrierdienst (DKD), to be accredited for the service of primary calibration of laser vibrometers in the frequency range of 0.4 Hz to 20 kHz with a best measurement uncertainty 0.25°% to 0.5°%. Improved methods and techniques of laser interferometry, and results of their experimental investigation will be presented. A survey will be given on proposed specifications of laser vibrometers and a first international standardization project for the calibration of laser vibrometers.

Scientists have researched the nonlinearity of laser interferometer systems in various degrees of detail over the past decades. This research has delivered numerous methods of determining the causes and explaining the sources of nonlinearity. Some mathematical formulae to determine the magnitude of the nonlinearity and methods how to minimize the nonlinearity has been reported. All of which emphatically proves that in practice, nonlinearity in interferometers exist and cannot be eliminated. The residual nonlinearity sources are investigated and their error contribution with respect to the interferometer's phase response as part of the complex (magnitude and phase) displacement measurement is reported on. These error components are used to estimate the uncertainty of measurement for phase shift measurements in homodyne laser interferometry as prescribed in the ISO "Guide to the Expression of Uncertainty in Measurement" (GUM).

In this paper, we outline a preliminary implementation of primary calibration for a laser vibrometer (LV) on the basis of newly proposed first ISO draft. The sine approximation method is applied to our calibration system. Under some different measurement conditions, primary calibration is preliminarily carried out for achieving reliable measurements. From these results, the effects of acceleration amplitude stability, mechanical distortion, position of measuring beam, and spot diameter of measuring beam have been discussed. Some conditions required for achieving the reliable calibration is indicated on the basis of the discussion. Additionally, the strict regulations of the distance between spots and such amount of mechanical distortion would be indispensable for guaranteeing a higher reliability of such calibration within an expanded uncertainty (k = 2) of less than 0.5 %.

Typical accelerometer calibrations by laser interferometer are performed by measuring displacement at three places on the shaker table. Each of these measurements, made along the perimeter of the accelerometer, requires repositioning and realigning of the interferometer. This is done to approximate the actual displacement of the accelerometer. Using a dual-coil shaker with a small moving element and two coaxially-located and rigidly-attached mounting tables allows placing the accelerometer on one table and measuring displacement directly on the center axis of the second table. This was found to work effectively at lower frequencies, up to about 5 kHz, with mounting tables of conventional materials such as stainless steel. However, for higher frequencies the use of steel results in unwanted relative motion between the two mounting tables. Mounting tables of beryllium with nickel coating have been used at NIST to overcome this difficulty. This paper shows the calibration results of single point, on-axis measurements, using fringe counting and sine-approximation methods. The results compare favorably with three point measurements made by fringe disappearance using a conventional piezo-electric shaker at frequencies up to 15 kHz.

This paper presents an automated accelerometer calibration system based on an homodyne quadrature interferometer. The vibration exciter and the interferometer are mounted on separate seismic blocks. To minimize the influence of low frequency noise due to the relative movement between the blocks, a high-pass recursive moving average filtering algorithm is implemented. The vibration and the measuring system are fully synchronized. A flexible setting of the acquisition rate is used to improve the computational efficiency and allow the calibration at any desired frequency within the frequency range from 10 Hz to 10 kHz. The theory of the method is briefly described. The experimental set-up is presented and some results are given.

A system based on digital holographic interferometry for the measurement of vibrations is presented. A high power continuous laser (10 W) and a high speed CCD camera (1 kHz) are used. Hundreds of holograms of an object that has been subjected to dynamic deformation are recorded. The acquisition speed and the time of exposure of the detector are controlled by the vibration frequency. Two methods for triggering the camera in order to acquire at a given phase of the vibration are presented. The phase of the wave front is calculated from the recorded holograms by use of a two-dimensional digital Fourier-transform method. The deformation of the object is obtained from the phase. By combination of the deformations recorded at different time it is possible to reconstruct the vibration of the object.

A rigid endoscope is used in pulsed digital holography to simultaneously evaluate the three orthogonal displacement components from hidden areas of a harmonically vibrating metallic cylinder. The cylinder is illuminated from three different illuminating directions. The optical path for each illumination direction is matched to its corresponding reference beam, but also in such a way that each object-reference beam pair optical path is mismatched such that they are incoherent and can be stored in a single CCD frame. As is typical in these types of interferometric arrangements, two digital holograms are needed in order to compare two different states of the cylinder. Each hologram is Fourier transformed and due to the incoherence introduced three separate spectra are readily identified, each belonging to a object-reference beam pair. On comparing by subtraction the phase obtained from the two pulsed digital holograms it is possible to gather quantitative 3D results from harmonic displacements.

Deterioration of wood artwork is often connected to mechanical material degradation that starts on microscopic scales. Insight into decay mechanisms can be obtained by monitoring surface microscopic deformation and displacement fields. This paper presents the application of Electronic Speckle Pattern Interferometry (ESPI) to detect invisible on the surface intrinsic defects of a wood samples. The different artificial defects were created under the pine wood surface to simulate "defected" samples. The fiber-optic ESPI set-up based on a He-Ne CW laser has been developed and used for the studying the possibility determination of locations, sizes and shapes of wood defects. For this end two digital holograms of the test object, corresponding to vibrating states of the non-heated and heated states of object, are captured at two video frames of the CCD camera, transferred in a frame-grabber and then processed in a PC. The resulted the fringe pattern has the information about the defects. Obtained fringe patterns of all defects are presented. The purpose of work was determining the sensitivity of ESPI method in application to different sizes and forms of defects.

The certain step in development of dynamic speckle interferometry is made. The technique of the spectral analysis of speckle dynamics is fulfilled. The technique is tested on experiments on moving the samples having a different roughness, and at a tension of objects up to fracture. The effect of expansion of spectra before destruction is found out. The new optical technique of measurement of velocity of ultrasonic Rayleigh waves is developed and tested. Advantage of a method consists that here it is not necessary to polish a surface before measurements.

Here we present our approach to apply the direct Radon transform for the analysis of interferometric images, in particular for the laser speckle velocymetry, and for the ESPI measurements. A technique for the precise velocity measurement is based on the precise calculation of the common movement of a laser speckle field. This approach allows realising a velocimeter suitable for use in extreme conditions. The latest results of our investigations are presented in this report. We also present the method of image analysis for the automatic set up of an Electronic Speckle Pattern Interferometry (ESPI). The idea of our method is to make a direct Radon-like transformation for each pixel (x₀, y₀) a 2D field of an image brightness B(x,y):, and than we calculate the rms spatial deviation by s, the maximum of which determines two values: (i) immediate max_φ(σ_s), and (ii) the corresponded angle φ((σ_s)_max). So, from 2D function B(x,y) we have two functions depended from same 2D field, but gives a clear defect location. Our investigations show a perspective of our approach. The submitted results have both methodological and applied significance for the pattern analysis.

The Organ of Corti is a complex structure with many reflecting surfaces characterized by a wide range of reflectivities. Heterodyne interferometry has been the primary technique for measuring motion of the cochlear sensory tissue for some time. We would like to know under what conditions reflections from out-of-focus surfaces affect the measured velocity of the in-focus surface. Heterodyne interferometry uses interference between two laser beams (object and reference). The velocity of the test object shifts the frequency of the object beam due to the Doppler effect. The heterodyne signal (a frequency modulated (FM) wave) is decoded using a frequency demodulator. By reviewing the theory of FM demodulation and showing tests with our Revox FM demodulator, we demonstrate that the influence of a secondary signal on a measurement depends on the modulation index (ratio of the frequency deviation (Δf=2V_o/λ) to the modulation frequency, f_m where V_o is the velocity amplitude and λ is the laser wavelength). For high-modulation-index signals, the fundamental component of the FM demodulator output is not affected by a secondary signal unless the secondary signal's power is nearly as large as that of the primary signal. However, the output waveform can be distorted. For a low-modulation-index signal, a secondary competing signal can have a relatively large effect on the fundamental component of the output signal, but the output signal waveform is not distorted. The results underscore the benefit of steep optical sectioning to reduce contamination by out-of-focus signals.

We have shown that the vibration of the stapes in human, cat and gerbil exhibits all 3-D components of translation and rotation, but also that non-piston components do not contribute to the transmission path. In most experiments access for direct measurement of stapes motion in line with the piston axis is not available and piston motion is estimated from single component interferometric measurements done under observation directions that make angles up to 50° with the piston axis. We used a heterodyne microscope/interferometer to measure the vibration velocity of the stapes in human, cat and gerbil from different observation angles and calculated the complete set of 3-D motion components for the stapes. Using micro CT scans of the experimental ears, we could express the components in an intrinsic reference system and foretell the motion component that will be obtained when a single axis interferometric measurement is done under various angles with the piston axis. For low frequencies (f<2kHz) a cosine factor provides a good correction for the axis off-set, at higher frequencies the piston component can not correctly be estimated from a single off-axis observation. We will show that this may lead to serious misinterpretations of experimental results.

In this paper we present a novel, non-invasive measurement system for optical monitoring of the cardiac rate. This measurement method, called vibrocardiography (VCG), is based on the use of a laser Doppler vibrometer for the measurement of the velocity of displacement of the skin in correspondence of the chest wall. We report the typical VCG signals measured on 4 healthy subject and in particular, we investigated the effect on the signal of the measurement position respect to the chest wall as well as the effect of the surface characteristics on the measured signal.

Cercal hairs represent in cricket a wind sensitive escape system, able to detect the airflow generated from predating species. These sensors have been studied as a biomimetic concept to allow the development of MEMS for biomedical use. In particular, the behaviour of the hairs, including airflow response, resonant frequency and damping, has been investigated up to a frequency of 20 kHz. The microscopic nature of the hairs, the complex vibrations of excited hairs and the high damping of the system suggested that the use of Laser Doppler vibrometry could possibly improve the test performance. Two types of tests were performed: in the first case the hairs were indirectly excited using the signal obtained from a vibrating aluminium plate, whilst in the second case the hairs were directly excited using a white noise chirp. The results from the first experiment indicated that the hairs move in-phase with the exciting signal up to frequencies in the order of 10 kHz, responding to the vibration modes of the plate with a signal attenuation of 12 to 20 dB. The chirp experiment revealed the presence of rotational resonant modes at 6850 and 11300 Hz. No clear effect of hair length was perceivable on the vibration response of the filiform sensors. The obtained results proved promising to support the mechanical and vibration characterisation of the hairs and suggest that scanning Laser vibrometry can be used extensively on highly dampened biological materials.

A 3D experimental arrangement for pulsed digital holography is used to measure the depth position for both a glass sphere and tumor tissue, immersed in a semi-solid gel model. A master gel, one without inhomogeneities, is set to resonate via sound waves generated with a conventional speaker placed a few centimeters away from the gel container. Later an identical prepared gel with an inhomogeneity is placed in the original set up and interrogated at the same resonant frequency. On comparison and using only an out of plane sensitive set up it is possible to measure the displacement of the gel surface, indicating the presence of an internal inhomogeneity. However the depth position cannot be measured accurately since the out of plane component has also the contribution of the in-plane surface displacements. With the information gathered from the 3D pulsed digital holography set up it is possible to obtain three sensitivity vectors that serve to independently separate the contributions from each of the three x, y and z components of the vibration displacement, for the same exciting mechanical wave. It is then possible to build individual maps of displacement along the three rectangular axes and thus measure accurately the depth position of the inhomogeneity. Results from the optical data were correlated to the measured position for different inhomogeneity types, sizes and depths and on comparison an error in the position of less than 1% was found. This optical non invasive method is able to accurately find the inhomogeneity and its position within the gel making it a promising method for the study of mammal tumors, representing and alternative to the traditional invasive methods.

Optical techniques are widely used to measure the vibration response patterns (ODSs) of structures over a scanned area, excited at resonance frequencies. The ODSs may be similar to natural mode shapes, but not if there are close modes coupled together by the structural damping. Natural mode shapes are usually extracted by analysis of frequency responses measured at every response point, but this is impracticable with area-scan measurements. The vibration responses at resonance frequencies can be regarded as being a linear combination of just a few natural mode shapes, and these can therefore be separated by combining an equivalent number of area-scan ODSs. For m component modes, measurements of real and imaginary ODS components at m/2 test frequencies and frequency responses at m points on the structure are required. Vibration responses can equally be regarded as being a combination of undamped natural mode shapes and these can be extracted in a similar way, if their amplitudes are known a priori at m points on the structure. Continuous-scan LDV measurements of the ODSs of a damped rectangular plate are used to demonstrate the techniques, and some suggestions are made on the inclusion of split modes and of extraneous resonances.

The application of both scanning laser vibrometry and thermoelasticity for measurement of stress and strain fields on mechanical components is proposed. A theoretical approach on both the measurement principles is illustrated and an application to a practical case, as an automotive fan blade, is described. The problem of the fan blade failure is tightly due to the force amplitude and frequency, that are applied in working condition; it is, therefore, important, to know the blade resonance frequencies and the mode shapes. For this reason, the measurement techniques, based on scanning laser Doppler vibrometer, give the chance to quickly perform an experimental modal analysis with high accuracy and spatial resolution and to obtain the structure's mode shapes. In the same time, it is important to assess the stress distribution level on the blade associated to every mode shape. Measurement techniques, that apply thermoelastic principle, allow to quickly determine the blade stress pattern at each load frequency. It is, therefore, possible to establish the stress pattern corresponding to the mode shape and predict the fatigue life of the component.

A problem of diagnostics of rotors systems do not destroying quality of work is analyzed in this paper. It is setting forth the main principals of work of rotors systems with bearings of sliding. The main problems of diagnostics of rotors systems and of monitoring are described in this work too. It is describing laser transducers using for measurements and it is giving its main characteristics. Possible variants of setout of lasers in moment of measurement and principal scheme of research stand are described schematic. The single view of research system is giving in the photos. It is giving methodology of experimental measurements and methodology of analyses of measurement signals that are getting experimentally. Getting results of measurement and analyses are giving in diagram form.

Composite booms are an emerging low weight structural alternative for on-orbit satellites. With any satellite, vibrational control of the structure is a concern. Using traditional measurement techniques, possible inaccuracies may result due to the lightweight natures of the composite boom. Laser vibrometry techniques are investigated in this paper as an alternative to standard accelerometer measurements. The advantages of non contact measurement are presented in two different experimental setups. Using the dynamic measurements obtained from these experiments, a positive feedback controller is developed to attenuate the vibration of the strut.

In the last decade the laser Doppler vibrometer (LDV) has become a widely spread instrument for measuring vibrations. It often offers accurate measurements with a high spatial resolution. However, the measurement time of the LDV and especially for the scanning LDV is long. Therefore reducing the measurement time is an attractive objective. A way to achieve this is to use a single sine excitation (on a resonance frequency). However this technique has two major drawbacks: the inability to provide accurate information on the damping and an operational deflection shape that can differ from the true mode shape. In this article a method will be introduced to reduce measurement time for scanning LDV measurements without these defaults. This is done by using a narrow band multisine excitation signal. Now for uncoupled normal modes the obtained time domain sequences for each scan point are in direct linear relation with each other. Therefore it is possible to estimate the full time domain sequence from the current scan point by using the previous scan point and a limited number of time samples from the current scan point, hence reducing the measurement time. This method is a key benefit for in-line quality control, which can have upwards of 1000 spatial measurement locations. The proposed technique will be validated on both simulations and experiments of varying complexity.

A method of measuring vibration response on rotating components using an LDV and its application on bladed disks are presented. Understanding and controlling of vibration amplitudes of bladed disks has been a primary concern for aero-engine manufacturers for many years. The vibration amplitudes of these components are known to be significantly affected by break down of symmetry due to variations in dimensional or material properties. A bladed disk exhibiting these variations is said to be mistuned and considerable research effort is put into acquisition of prediction tools to calculate the effects of these variations. However, the validation of these tools against real measurements is often ignored because of the difficulties involved in application of appropriate excitation and measurement techniques in rotating conditions. In this paper we present successful use of non-intrusive measurement and excitation techniques towards achievement of this goal. These techniques are independent of rotational speed. The so-called self-tracking LDV measurement method used in this paper was introduced in a previous paper by the authors. Here the use of method for acquisition of high quality reference response data for validation of mistuned bladed disks and those fitted with under-platform friction dampers are given.

In this paper we present an optical derotator for scanning vibrometer measurements on rotating objects. The main part of an optical derotator is a rotating prism. Several concepts are known from literature. We have chosen a Dove prism because it can derotate the rotation of the specimen by simply watching through the prism, which rotates with half the speed. The design of our derotator is presented in this paper as well as a discussion of the system performance. In addition we show experimental measurement results on a fan rotating with 3000 rpm.

The Laser Rotational Vibrometer is well suited to non-contact measurement of angular vibration on rotating targets, particularly by virtue of inherent insensitivity to target shape and translational motion. A differential measurement is proposed using two Vibrometers to allow a calculation of dynamic backlash between spur gears from relative tangential displacements. It is known that target motions, such as rotation, produce changes in the speckle pattern on the photodetector which add noise to the Vibrometer output. The significance of noise is always increased when differential measurements are required. The noise produced by the speckle pattern is apparent but the data reveals that it is possible to make the dynamic backlash measurement in this way. The dynamic backlash measurement is verified against equivalent high speed video footage, confirming the suitability of Laser Vibrometry in this application.

In recent years, the CSLDV (Continuing Scanning LDV) technique has been developed to obtain the ODS (Operational Deflection Shape) of a structure within a very short period of time. The ability to predict and to measure the ODS of a vibrating structure suggests its use to increase the potential for structural damage detection, localization and severity assessment. Previous research based on simulation of some simple test cases showed the effect of excitation locations on structural damage detection. Four steel plates were acquired and a FEM model of that structure was produced. Modal analysis, theoretical and experimental, was performed on the plate to obtain eigenvalues and eigenvectors and to update the FEM model. This time, the damage was simulated either using two permanent magnets which could be attached and de-attached easily without compromise the integrity of the structure or reducing the thickness of some elements. Hence, 4 damaged plates were modelled in FE software upon the position of the damage. The simulation and testing of the ODSs and the MSE (Mean Square Error) of the 4 plate structures in the damaged and the undamaged cases were performed based on CSLDV measurement method and compared respectively. Results show effect of vibration excitation location in the damage detection.

One major problem facing finite element model updating is the spatial incompatibility between the measurement of mode shapes through a limited set of physical sensors and the corresponding analytical predictions at a large number of finite element DOFs. Expansion of the measured mode shape data or reduction of the size of the initial FE model to the measured degrees of freedom is normally used to match the requirement. However, both techniques bring some erroneous information into the process. With the Continuous Scanning Laser Doppler Vibrometry (CSLDV) technique, a large number of degrees of freedom (DOFs) can be measured and accurate mode shapes can be achieved in a relatively short testing time. Such features provide great potential for dealing with the problem of the spatial incompatibility in FE model updating. In this paper, an application of finite element model updating using the continuous scanning laser Doppler vibrometry measurement is discussed. A real test piece of a square steel plate and its FE model were built. The first 20 natural frequencies and the corresponding mode shapes expressed by a large number of DOFs were measured using the CSLDV technique and further used for FE model updating. The initial FE model was assumed that random errors up to 20% of the theoretical values of Young's modulus were distributed among 25 areas of the plate due to uncertainties on the physical parameters. Model updating was undertaken to minimise the discrepancy between the FE model predicted and the experiment measured modal parameters and satisfactory results were obtained.

The aim of this paper is to present an overview of the CAISER MYMESIS software platform that has been developed to simulate and to perform the vibration measurement procedures using Tracking/Continuous Scanning LDV (T/CSLDV) methods, such as area scan on structures under both stationary and rotating conditions. Mathematical models to simulate the LDV output for all CSLDV methods are also included in the software platform as well as the traditional Step-Scanning approach. The software platform can be used in one of two modes: (i) first, to conduct a 'virtual test' to explore various proposed test configurations in order to define an optimum test specification, and (ii) second, to carry out an actual measurement, including driving the scanning mirrors, acquiring data and quickly post-processing data for an immediate inspection of the ODS of the vibrating structures.

In this work laser Doppler vibrometry has been used for damage detection in frescoes. Results were compared with the ones obtained through infrared thermography, and, for both techniques, mathematical models were implemented to simulate the physical domains and conditions of the employed test sample. The limitations of each methodology are also discussed. The numerical model of the vibrometric investigations has been constructed using Finite Elements Method modeling. A new procedure based on the observation of Rayleigh waves propagation velocities allowed to acquire sample mechanical parameters. Comparison of experimental and simulated data and independent defect diameter measurement by echographic equipment, allowed to establish the confidence level and the discrepancies in the developed model. Also operational limits of the vibrometric technique have been studied by acquisition of Signal-to-Noise ratio on different areas of a sample. The Fourier equation has been used for the mathematical model employed for the numerical simulation of the thermographic investigations. Numerical technique with formularization in finite volumes has been employed and a FORTRAN code has been developed to solve the thermal problem.

The distance changes between structural elements inside a building (e.g. walls, pillars, stairs, etc.) ought to be monitored, especially in seismic-prone areas, in order to assess its stability. Fibre Bragg grating (FBG) sensors are now the most interesting choice for this purpose, since several gratings can be included in the fibre, resulting in a quasi-distributed sensor, which can be illuminated using a single light source and interrogated simply by a single optical spectrum analyzer (OSA), using wavelength multiplexing. The paper deals with such a sensor, which was installed for monitoring the distance changes in a construction joint between two building blocks inside the University "Politehnica" of Bucharest. Since this city is placed in a seismic-prone area, we use a fast scanning OSA, so that the dynamic behavior of the monitored construction joint is expected to be captured during future earthquakes. Slow drifts of the construction joint width will be also monitored. The paper describes the sensor structure and working principle, the experimental tests and main parameters evaluation. The reported sensor is temperature compensated. It has an estimated distance resolution better or equal to 10 μm, and a linearity of +0.2%...-0.35% for displacements up to 0.55 mm. Simulated dynamic tests are also reported.

Near acoustic frequencies from seismic activities can be observed by sensors with band pass higher than the 5-second period peak noise. By using a single mode fibre optic specially adjusted, a planar vibration travelling on surface can modify the optogeometrical properties of its material and enhanced a birefringence effect. This type of sensor already effective in acoustic frequencies is now adapted to seismic vibration. The high noise background at these frequencies disturbs greatly the measure and isolation by adjustment of spring and plates dimensions leads to interesting questions in regard of dynamic behaviour in this window. Currently, the sensor can detect small and local vibrations but cannot measure with good precision its velocity and acceleration value. In the first part of this paper, the basics of seismic vibration will be briefly exposes in coordination with the way the sensor works; a brief walkthrough of the fibre optic sensing behaviour will be exposed. The next part will display the different elements of the sensor and the choices that were made at this stage. Eventually, the behaviour of the sensor will be displayed along with the calibration method and the different errors that need to be corrected.

A complex portable optoelectronic setup for on site interventions introduces an accessible concept that incorporates latest technologies and techniques. Its components are highly technical, extremely versatile, addressing a wide range of materials: Systems for laser cleaning in microscopic field that assures a high cleaning precision, and also, coupled with other monitoring systems can provide photo-video recordings, thermovision analysis, UV-VIS-NIR multispectral analysis; results of the latest researches: qualitative evaluation techniques using LIF, LIBS and 3D laser scanning of large objects - up to some historical buildings; UV-VIS Spectroscopy concerning transmission and reflection spectra measurements, as well as Colorimetry can provide helpful information for artworks composite materials and degradations characterization; microclimate conditions and environmental pollutant agents monitoring; large surfaces laser cleaning system is also integrated to the other operations and systems presented. Optimization of the functional structure, as well as the operating precision of the techniques are established in direct corroboration with important case studies such as thermal emissivity control for non-contact crust layer cleaning evaluation and integration of optoelectronical techniques in conservation of Stavropoleos Church from Bucharest.

The determination of the state of conservation of historical masonries by non-destructive and non-invasive techniques must still gain its due widespread use, and this is clearly reflected in national norms that often refuse them as not being reliable enough to be used without the support of destructive ones (see for example the Italian OPCM 3274/2003 and subsequent modifications). Anyhow, the clear advantages of such techniques, and especially laser based ones like the Scanning Laser Doppler Vibrometry - SLDV here employed, drive the research towards this direction. In this work we will illustrate a case study done in the south of the Marche region, namely the investigations conducted inside and outside the Lanciano castle, near Castelraimondo (MC). A series of SLDV measurements have been made that have lead to the discovery of many hidden structural defects, such as delaminations of superficial layers, minor and also important cracks. To validate our findings a well reputed and consolidated technique has been employed, a Ground Penetrating Radar - GPR, along with manual beating of suspected areas. Also a brief session using an infrared camera has been conducted to check the results relative to superficial delaminations, where the GPR could fail due to insufficient spatial resolution.

The methods of direct measurement and analysis of the dynamic response of a building structure through real-time recording of the amplitude of low-frequency vibration (tilt) have been presented. Subject to analyses was the reaction induced either by kinematic excitation (road traffic and mining-induced vibration) or controlled action of solid-fuel rocket micro-engines installed on the building. The forces were analysed by means of a set of transducers installed both in the ground and on the structure. After the action of excitation forces has been stopped, the system (structure) makes damped vibration around the static equilibrium position. It has been shown that the type of excitation affects the accuracy of evaluation of principal dynamic parameters of the structure. In the authors opinion these are the decrement of damping and natural vibration frequency. Positive results of tests with the use of excitation by means of short-action (0.6 second) rocket micro-engines give a chance to develop a reliable method for periodical assessment of acceptable loss of usability characteristics of building structures heavily influenced by environmental effects.

A non-destructive testing (NDT) technique should be able to calculate the position and the size of any defects, in order to measure quality and safety of materials. Complexity is an issue for most NDT tests, requiring specialist knowledge of the technique. This generally means using qualified staff, and omits the possibility of any kind of automation. In this article an experimental methodology for crack detection using Surface Acoustic Waves (SAWs) and optical laser vibrometer measurements will be introduced. The materials under test are a damaged slat track of an Airbus A320 and a steel beam (because in the zone where critical crack propagation occurs the slat track has a beam-like shape) with slots of known depth (0.2, 0.4, 0.6, 0.8 mm). The goal of this article is to compare these ultrasonic-laser measurements in order to understand how much they are suitable to detect damages and imperfections present on the material itself. For future applications, this methodology can be used to monitor the slat track during a fatigue test, to detect damages in an early stage, before a rapid crack growth.

Mechanical fault diagnostics for quality control of manufacturing appliances is often based on the analysis of machine vibrations. In the presence of mechanical faults, vibration signals comprise periodic impulses with a characteristic frequency corresponding to a particular defect. Vibrometers based on LDV (Laser Doppler Vibrometry) are an alternative to the traditional use of piezo-electric accelerometers, devices that are the most common and popular vibration transducers. Laser vibrometry is now an established technique for vibration measurements in industrial applications where non-contact operations are essential. Despite the advantages of LDV, speckle noise occurs when rough surfaces are measured and the object is moving. Therefore, removal of speckle noise is a crucial point of a reliable system for diagnostics of mechanical faults. This paper deals with the analysis of vibration signals measured by a Laser Doppler Vibrometer from different electromechanical components such as compressors and electrical motors. The goal is to suppress the speckle-noise effect, coming both from the surface of the electro-mechanical components and its movement, in order to perform an automatic test for mechanical fault detection in the production line. First, data acquisition and its problems are introduced. Then, the chosen solution is presented. In particular, a statistical approach based on kurtosis is used for detection of speckle noise and selection of an undistorted region within the signal. The algorithm is composed of band-pass filtering, segmentation of the signal and computation of a scalar indicator KR (Kurtosis Ratio) for each signal segment, in order to detect outlying samples caused by speckle noise. Finally, real examples are shown to test the proposed method, and a tool for validation of signal databases is briefly presented.

In the piping systems carrying fluids the phenomenon of cavitation may occur in a number of places. It is generated where the local pressure drops below the saturated vapour pressure. In various piping systems cavitation takes place in pumps, in cut-off fittings, regulator fittings, etc. In most cases it is detrimental. Cavitation affects the environment through noise- and vibration-related effects apart from causing physical damage of the boundary surfaces of the flow. In today's light construction buildings the vibrations may easily diffuse and this may also damage the machines and the equipment inside. Harmful vibrations arising due to cavitation may severely damage the machines, and influence their operation in a negative way. In hydraulic systems pumps are critical elements from cavitation point of view, since damage may appear in the pump on its inlet side.

Shearography is an optical and nondestructive technique that has been largely used for damage detection in layered composite materials where delaminations and debondings are the most common flaws. In Shearography the sample under test is illuminated using a laser and imaged on a CCD camera. A special optical shearing element allows a coherent superposition of two laterally displaced images of the surface of the sample on the CCD plane. The images are recorded for different loading conditions of the sample. The loading should induce some deformation or alter the deformation state of the surface of the sample. In this work a thermal loading has been used. The absolute difference of two phase maps recorded at different loading situations of the sample results in an interference fringe pattern which is directly correlated to the difference in deformation state. The phase maps usually have strong noise and low contrast. For this reason, a further improvement in image quality should be obtained. Two methods, known as "difference of phases" and "phase of differences", are used with a spatial and temporal phase unwrapping algorithms, respectively, in an experiment using a steel pipe wrapped in a composite sleeve. A qualitative comparison of the methods is done and the results, advantages and difficulties are discussed.

The construction of digital images of isolines of directional derivatives of the deflection of the plate of microstructures builds the ground for hybrid numerical-experimental procedures and enables to analyse the experimental results with greater precision. The procedure for the generation of digital images of isolines of directional derivatives of the deflection of the eigenmodes of bending vibrations of the circular micro plate is developed. The displacement based FEM formulation is developed on the deflection derivatives digital image of isolines, while the smoothing procedure enables the generation of digital images on rather coarse conventional finite element meshes. The introduction of directional smoothing (radial or angular) enables to obtain digital images of isolines with higher precision, as one of the digital images requires only radial while the other only angular smoothing. Thus the smoothing in the unnecessary direction is avoided and does not influence the image. The plotting procedure for the isolines of the directional derivatives of the circular plate is developed in order to obtain more precise images for the characterization dynamics of the microstructures.

The use of a digital speckle pattern interferometer (SPI) based on a complementary metal-oxide semiconductor (CMOS) camera for vibration measurement is described. The flexibility of the CMOS detector enables regions of interest (ROIs) to be identified with full-field time-averaged measurements, and then to interrogate those regions with time-resolved measurements sampled at up to 70 kHz. The system effectively acts as a non-contact optical vibrometer that can measure surface velocity at several points simultaneously. The CMOS detector allows measurement of the vibration frequency, amplitude and relative phase between ROIs with high spatial and temporal resolution. The multi-point vibrometer was used to collect velocity information of a centre clamped circular plate that is subjected to transient excitation. The information is processed to determine the natural frequency mode shapes from velocity data for the first time.

Digital speckle correlation techniques have already been successfully proven for accurate displacement analysis. With the use of two cameras, three dimensional measurements of contours and displacements can be carried out. The principle of this technique is pretty easy to understood and realized, opening a nearly unlimited range of applications. Rapid new developments in the field of digital imaging and computer technology, especially for very much dynamic applications, opens further applications for these measurement method up to high speed deformation and strain analysis, e.g. in the fields of, material testing, fracture mechanics, high speed testing, advanced materials and component testing. The dynamic range is combined with the capability to measure very large strains (up to more than 100%). The resolution of the deformation in space and time opens a wide range of applications for vibration analysis of objects. Since the system determines the absolute position and displacements of the object in space it is capable of measuring high amplitudes and even objects with rigid body movements, which is a big advantage against full field ESPI systems. The absolute resolution depends on the field of view and is scalable. Calibration of the optical setup is a crucial point which will be discussed in detail. Examples of the analysis of high speed harmonic vibration and transient events out of material research and industrial applications are presented. Results of measurement performed on a vibrating membrane and a tensile test sample are show typical features of the system.

Development of hybrid numerical-experimental techniques is an important method of analysis used for interpretation and validation of experimental results. Laser holography is a powerful experimental technique for analysis of high frequency vibrations of the fluid, especially when the amplitudes of those vibrations are relatively small. It is assumed that the angular frequency of excitation coincides with the eigenfrequency of the appropriate eigenmode and thus the eigenproblem is solved. The problem of fluid eigen-vibrations in axi-symmetric geometry according to the first harmonic in the circumferential direction is analyzed. This problem has a practical application in the analysis of transverse vibrations of the fluid in an axi-symmetric pipe. The numerical model is developed on the basis of the finite element model of the fluid and the method of analysis of the problems with axi-symmetric geometry. The irrotational motions of the ideal compressible fluid are analyzed. The numerical model of the system is based on the approximation of nodal displacements via the shape functions. Thus the field of the amplitudes of the circumferential variation of the volumetric strain is calculated using the procedure of conjugate approximation. By using the procedure of conjugate approximation the amplitudes of circumferential variation of nodal volumetric strains for the eigenmodes are determined. The obtained field of volumetric strain is used in the numerical procedure for the construction of the digital holographic image. Thus the calculation of the amplitudes of circumferential variation of nodal volumetric strains consists of two stages: 1) calculations using the displacement formulation for the first harmonic in the circumferential direction by the method of finite elements; 2) determination of the field of the amplitudes of the circumferential variation of the volumetric strain by using the procedure of conjugate approximation. The obtained nodal values of the amplitudes of the circumferential variation of the volumetric strain are used in the construction of the digital holographic images. For this purpose the Abel transform which is usually used in axi-symmetric problems is generalized for the problems with axi-symmetric geometry with the variation of displacements according to the first harmonic in the circumferential direction. On the basis of the generalized Abel transform the digital holographic images are constructed. The obtained digital holographic images are used in the hybrid experimental-numerical procedure for the determination of the correlation with the experimental holographic images.

We have adapted a Mach-Zender type laser velocimeter for making simultaneous measurements at several, arbitrarily chosen points. The optical design is based on a single laser source and two acousto-optic modulators, which generate a common heterodyne carrier frequency in all measurement channels. By using two modulators, one to increase the frequency of the reference beam with 80 MHz, and a second one which decreases the frequency with a bit more than 80 MHz, we can adjust the heterodyne beat signal to any frequency of choice, thus adapting it to the input of commercially available FM demodulation chips or avoiding noisy parts of the laser noise spectrum. The apparatus is intended for simultaneous vibration measurements at several points of instable objects, such as biological specimens or MEMS, so that instantaneous phase relationships and amplitude ratios can be determined. So far, instrument performance has been tested with measurements on two points of interest. In a multipoint system, especially when it uses a single laser source and a common heterodyne frequency, channel cross talk is a major point of concern. The optical design ensures very good channel separation and allows expansion to at least four channels. We present channel separation measurements obtained with one channel focused on a vibrating membrane or a vibrating plate and the other focused on an adjacent solid object. Even with these object points less than 0.4 mm apart, channel separation was found to be better than 78 dB at all frequencies. The velocity calibration of the system is determined by the laser wavelength and the sensitivity of the FM detection circuitry only. With a maximal velocity amplitude of 52 mm/s, the velocity resolution and the detection limit of our system were determined to be 2.6 square root(bandwidth) μm^.s^-1Hz^-1/2 in both channels.

An adaptive fiber-optical measuring system for vibrations monitoring, which is based on dynamic reflection hologram recorded in the photorefractive crystal of cubic symmetry without applying any electrical field is developed. Adaptive properties of dynamic hologram enable the solution of a interferometer's working point uncontrollable drift problem caused by external factors. Use of semiconductor crystal CdTe with fast recording time of a dynamic hologram makes it possible to achieve high cutoff frequencies at reasonably low light intensities. As a result the measuring system is characterized by low energy consumption and ability of stable operation of long duration in real environment. Theoretical analysis has allowed us to find the optimal set of parameters for both interacting waves and crystal to reach the maximal sensitivity of the measuring system.

In this article we will present a method to estimate sound absorption coefficients from measurements of the incident and reflected sound fields near the material under test. The sound fields are visualized using a scanning laser Doppler vibrometer (SLDV). By aiming the SLDV at a rigid (non-vibrating) object and letting the beam pass through a sound field the spatial pressure distribution can be made visible. By visualizing both incident and reflected sound field with respect to a material sample in this manner, the acoustic absorption coefficients can be determined (this is the ratio of the absorbed energy and incident energy). Two alternative set-ups are proposed in this article: a one-dimensional set-up where the sound field (i.e. the standing waves) inside a thin glass tube is measured, and a two-dimensional set-up where the propagating and reflecting sound field between two parallel glass plates is visualized. While the former can only be used to obtain normal incidence absorption coefficients the latter can also be used to estimate oblique incidence absorption values. It is shown that the method is accurate at high frequencies where traditional standardized acoustic material characterization techniques mostly fail.

Several experiments have been carried out to investigate the mechanical vibrations generated by an organ pipe. Measurements were made by using Laser Doppler Vibrometry. It is a not-invasive optical measurement technique which allows to detect pipe-wall vibrations. The mechanical vibration field is compared with the acoustic field. Namely, we study the behaviour of these fields when they are excited by different levels of pressure. Strong analogies have been evidenced by using techniques in time e frequency domain supporting the assumption that the pipe is not a passive resonator. The challenge is to understand the complex mechanism of coupling between modes of air and eigen-modes of pipe that produces the sound. Here, we present, in first approximation, a low dimensional dynamical system which describes the main characteristics of pipe-wall vibrations. What is interesting is that the same low dimensional dynamical system is able to reproduce also the recorded acoustic field, implying that wall vibrations and acoustic pressure field are strictly related one to each other.

The kantele is a musical instrument excited by plucking. It is an ancient instrument, which is still used in traditional folk music in Finland, Northwest Russia, and the Baltic countries. This paper discusses analysis and measurement results of a modified kantele, designed to have an increased loudness. The design rules to make the modified kantele louder are also proposed. The conducted measurements confirm and support the proposed design rules. The main features of the traditional design of the kantele are described, so that the presentation of the design rules and analysis results could be understood. The design rules to make a plucked string instrument louder are (1) increase the tension of the string, (2) increase the radiation surface, and (3) isolate the top plate from the sound-box with an air gap. To some extent rules (1) and (2) are straightforward and familiar for most musical acousticians. In contrast, rule (3) is more evolved and unique, since it enables a freely vibrating top plate. To confirm the design rules, the traditional design is compared with the new one, through several methodological aspects. Results from the analysis are drawn from both analytical treatments and acoustical measurements. A listening test was also conducted and the results of this test support the assumption of an increase in loudness for the new kantele design. More specifically, on the average loud plucks of the modified design are perceived as 3 dB louder than in the traditional design. Furthermore, on certain strings the loud plucks are perceived as 6 dB louder. The proposed design ideas can also be applied to other string instruments.

In this paper the mechanical characterization of a silicon based micro paddle oscillator by using a coupled experimental-numerical analysis is demonstrated. A Finite Element Model has been developed in order to study the mechanical behaviour of the system. The numerical model validation is performed by using the laser Doppler vibrometry technique that allows to dynamically characterize the systems: to find resonance frequencies, distinguish mode shapes, revealing the existence of all the vibrational modes, nonlinear behaviour and also to investigate the mechanism of mechanical energy dissipation that play a fundamental role in the performance of the devices (Quality factor assessment). This paper shows how a coupled experimental-numerical analysis produces a validate model that can be employed in order to detect the critical parameters (geometry, material and residual stress) that directly influence the performances of the oscillator and, in this way, to optimize the system design.

In this paper we investigate the transient thermoelastic dynamics of a microcantilever subject to laser irradiation. We formulate an initial boundary-value problem (IBVP) describing the transient vibration of a microcantilever caused by laser thermal effects in a vacuum environment. This IBVP includes two PDEs describing the coupled elastic and thermal fields where the elastic beam equation is augmented by viscoelastic damping. We study three laser power distributions having the same total power to analyze the steady state temperature distribution in the microcantilever: (i) sinusoidal sin(πx/2L), (ii) uniform and (iii) localized δ(x-a). Analytical solutions for a SiN microcantilever with these boundary conditions are determined. We reduce the IBVP to a modal dynamical system and consider its first mode response and obtain its transient decay to a stable equilibrium position. We note that the results of the above analysis are consistent with documented experimental results.

This study compares theoretical predictions to experimental measurements of squeeze film damping of MEMS cantilevers in a fluid environment. A series of MEMS cantilevers were fabricated on a silicon wafer. Each of the silicon beams was 2 μm thick and 18 μm wide. The lengths range from 100 to 800 μm and the air-filled gap between the cantilever and the substrate was 6 μm. An analytic model for squeeze film damping was used to predict the corresponding quality factor Q_{squeeze film} (the ratio of the mechanical energy stored in the oscillator to the energy dissipated per cycle) for these cantilevers. The results from the modeling are compared to experimental results obtained using a Polytec MSA-400 Micro System Analyzer.

The knife-edge technique in reflection mode is an alternative method for the characterization of in-plane motion and vibrations of microdevices. In this paper, we investigate this technique for sinusoidal vibration measurements of microresonators. First, we examine theoretically the effect of light reflection on the non moving substrate. It is shown that it has a significant effect on the sensitivity of the knife-edge technique to in-plane vibrations and that it introduces a slight sensitivity to out-of-plane vibrations. Then we demonstrate in-plane resonance measurements with a resolution in the nanometer range in the unfavourable case of a polysilicon resonator on a polysilicon coated substrate. Finally advantages, limitations and calibration issues of this technique are discussed.

The laser-scanning confocal vibrometer microscope (CVM) for vibration measurements in microscopic structures can map out-of-plane vibrations with picometer amplitude resolution while the locus transverse and depth resolutions are in the sub-micrometer regime. This performance has been achieved by using the measurement beam of a heterodyne laser-Doppler vibrometer (LDV) as the scanned laser beam of a confocal microscope. The power of the heterodyne carrier is a measurement of the detected light intensity. Therefore, the CVM can also be used as common confocal microscope to image and measure geometries of three-dimensional structures. In this paper the general lateral resolution limits of this new microscope type are discussed and the lateral-resolution performance of a realized system is demonstrated. This system is optimized to measure out-of-plane vibrations in microelectromechanical systems (MEMS).

All users of primary calibration systems - excepting the national metrological institutes - are under obligation to trace back their reference standards - their Laser vibrometer standards - to their respective national standard if they intend to apply for (or maintain) accreditation or to strive for a very low measuring uncertainty for other reasons. A calibration method will be described in this paper that has been used by the accredited laboratory of SPEKTRA for calibrating a greater number of Laser vibrometer standards. All these calibrations proved the reliability and the very low measuring uncertainty of this method.

This paper describes a new application of the standard ISO 16063-11 which specifies the instrumentation and procedures to be used for primary calibration of a steady state sinusoidal vibration using laser interferometry. The third method described in this standard is the one, which promises the wide frequency range application as well as less influence on the disturbance variables such as noise or harmonic distortion. In combination with a powerful digital processing technique and Successive Phase Unwrapping (SPU) function this method is tested for the middle frequency range (40-5000 Hz) as presented in this paper. The same method is intended to be used for the low and the high frequency range, the success of which depends mostly on the suitable instrumentation and in particular on the vibration source.

The changes in the spectrum of photocurrent in two-beam Doppler velocimeter caused by different types of vibration are analyzed. It is shown that, under certain conditions, periodical laser beam scan and surface vibration are producing identical changes in the spectrum of photocurrent. The changes might be quite considerable even with relatively small amplitude of laser beam scan of several arc seconds while monitoring slowly moving surface. The vibrational structure of Doppler and "pedestal" component in photocurrent are studied; it is shown that with vibrational velocity exceeding half of translational velocity the vibrational bands correspondent to "pedestal" and Doppler component are overlapping. The use of short acquisition time, which allows avoiding formation of broadband line structure in the spectrum, is also studied. The impact of bending vibration of translationally moving surface is also considered; due to averaging action of detector receiving aperture the impact of bending vibration is much less pronounced than that of laser beam scan or surface vibration.

In this work is presented a relative based interferometry technique with homodyne and heterodyne detection for accelerometers absolute calibration in the range between 10 Hz and 10 kHz with accelerations of 0.5 to 400 ms^-2. The experimental systems implemented and the acquisition and the developed data processing modules are described. The results obtained as the uncertainty budget for all the measuring range is evaluated, describing the mathematical models and identifying the corresponding uncertainty sources.

Coherent interferometric optical interferometry is one of the most interesting techniques for the primary calibration of standard accelerometers. By measuring the displacement caused by a sinusoidal excitation applied to the accelerometer, it is possible to determine the value of the acceleration. An experimental system was developed and implemented, based in relative interferometry with heterodyne interferometry, for the calibration of standard accelerometers in high frequency regime, up to 10 kHz. Heterodyne detection is needed to overcome a limitation of homodyne based systems in terms of measuring range, both in acceleration and frequency. In terms of performances, the system was capable of calibrations for frequencies from 100 Hz to 10 kHz and accelerations from 0.5 ms^-2 to 400 ms^-2. In this paper, we present a detailed description of the selected method, the implemented experimental systems and data processing algorithms, and the test results obtained in the calibration of a standard accelerometer, evaluating systems performances in terms of working range.

Realization and dissemination of the unit of sound pressure in water are carried out through calibration of hydrophones and underwater acoustic transducers. Different calibration methods applicable for different frequency ranges are available for this purpose. For calibration of reference hydrophones at low frequencies air-water pistonphone has been constructed at Turkish National Metrology Institute (UME). One of the main parts of the calibration system is optical interferometer. Two different interferometer types were used for the precise displacement measurements. The hydrophone calibrations performed by using air-water pistonphone both with homodyne Michelson interferometer and diode laser based self-mixing interferometer, ECDL.

Primary angular acceleration calibration standard is developed by CIMM to generate standard rotational angle, angular velocity and angular acceleration, which are traceable to the International System of Units (SI). It can be used to calibrate angular transducers, i.e. angular accelerometer, angular velocity transducer, and rotational angle transducer to obtain amplitude sensitivity and phase shift by sinusoidal vibration. The measurement systems based on grating and laser interferometers are introduced in this paper. The measurement system based on PXI bus instrument is used to control the angular exciter, measure the output signal of the laser interferometers and the transducer to be calibrated synchronously. The methods for calculating the amplitude and phase of sinusoidal angular movement are investigated and high performance has been achieved. It shows the standard can be used in angular movement calibration in the frequency range from 0.1Hz to 200Hz.

A white light interferometric system for remote monitoring of the expansion of a pressured foil membrane is described. The membrane will serve as a transmission "window" in liquid and gaseous target chambers for the production of radio-isotopes in an accelerator. Alternative commercial solutions are unsuitable in this environment. We describe some feasibility experiments which have been performed on a model cell pressurized to expand the foil. Pressures of up to 25 bar induce expansions of up to 1.5 mm in the center of the foil, which the optical probe, positioned 100 mm away, detects with a precision of 20 μm. The results fit well to an accepted model, yielding also the Young's modulus of the foil and its transition from elastic to plastic behavior.

In the paper it proposes the achievement of a simple device based on laser which realizes the non-contact measurements of vibrations for the small inertia mass mechanical systems. From financial point of view we suppose that this experimentally device will be accessible to laboratories from educational system. The device contents one laser micro source, one small mirror fixed on the studied body and one reception system of the reflected wave. The reception wave is modulated by the mechanically system vibration.

Oscillations of the comparator, which is used for the dynamic calibration of long optical line scales, are analyzed in the paper. The accuracy of determination of the position of optical lines on the scale depends on the velocity of the carriage, which transports the microscope with a CCD camera in relation to the line scale. Oscillations influence the velocity equability, its value, and at the same time the error compo measuring. The base part of the comparator is acted upon by external excitations which come through the foundation and supports, also due to natural frequencies of the comparator set. It is shown in the work that vibration surroundings acting on the comparator have a random character and correspond to the criteria of the normal (Gauss) distribution. It is proved experimentally that preaching amplitudes of measured components of vertical and horizontal oscillations influence the stability of the carriage movement which causes the error of measuring.