The use of a laser Doppler vibrometer to obtain velocity information from vibrating structures has gained wide acceptance in recent years. Although use of such an instrument can yield a spatially dense matrix of velocity information, several users have noted `noise' at certain points in the spatial field. The technique by which the SLDV system operates results in occasional velocity `drop-outs' which are unidirectional, always estimating the velocity response closer to zero than reality. These `drop-out' areas occur more predominately at points of maximum velocity response with small rotational components. Alternatively, points exhibiting minimum velocity response with large rotational components are less susceptible to the `noise'. In this paper, an experiment to visualize the speckle pattern motions received by the photodetectors during these vibration conditions is presented. Theories regarding the source(s) of the `noise' are developed.

The range of potential applications of the Laser Doppler Vibrometer is significantly influenced by the behavior of the speckle pattern that is incident on the instrument's photodetector. A speckle pattern is formed when coherent laser light is scattered from an optically rough target. This paper investigates experimentally how photodetector size and position relative to the target can lead to noise floor reduction in the instrument's output. An optimum detector position is specified for the rotating target condition considered. The experimental results are compared with theoretical results in order for the predictive of further noise reduction to be made. For reliable operation and increased reduction it is essential to minimize the speckle noise contribution to the Laser Vibrometer output.

The most simple interferometric systems of the `direct current' have relatively low maximum of permissible velocity of displacement of interferometer reflectors because of inability of providing of shift of phase of photoreceiver output signals equal to (pi) /2 for this velocity. We developed electronic block for interferometric system of `direct current', which doesn't impose significant restrictions on the velocity characteristics. When frequency f of photoreceiver output signals exceeds chosen reference frequency f_r equals 100 divided by 200 kHz, the sign of velocity is stored and is used in process of measurements for count pulses while f > f_r. This method doesn't demand the shift of signal phases to be equal to (pi) /2 for the normal performance of block. The analysis of the results of joint processing of output signals of photoreceivers shows that frequency of output and input signals of photo-receiver may be considered as signed value, which sign is determined by the displacement direction of one of interferometer reflectors.

The paper deals with development and realization of a heterodyne He-Ne laser Doppler system able to measure from distance the mechanical vibrations of a radar antenna. These vibrations, caused by wind and/or by proper system, could give false information concerning the velocity of a target. To measure the frequency and the amplitude of mechanical vibrations we used the optical heterodyne technique.

The paper presents a method for measuring of the amplitude and phase angle of a sinusoidal vibration in the nanometer range. The method is proposed for the calibration of accelerometers in the frequency range from 1 kHz to 50 kHz using heterodyne interferometer signals. The developed method is based on quadrature signals generated by digital signal processing. The vibration signal is regenerated as discrete-time phase sequence of quadrature signals using an arc tangent subroutine. The displacement amplitude and the phase angle of the vibration are obtained by applying least squares estimation to the phase sequence. The theoretical background and details of the generation of quadrature signals and of the estimation of displacement amplitude and phase angle are given. Results of an investigation into the errors due to various disturbing parameters are presented. The performance of the proposed signal processing method was examined by means of computer simulation and experimental data taken from both a test measuring system and a measuring system for the calibration of accelerometers.

This paper deals with the applications of Pressurized Water Reactor fuel assembly vibration measurements by laser vibrometry. Two laser vibrometers are compared in terms of accuracy and handiness. One of them is a high precision integrated low powered device. The comparison of signals issued from simple experiments is made. The results are analyzed by using three classical modal analysis methods (logarithmic decrement, frequency band width, PRONY's method). This study will find applications in measuring the damping factor of fuel assembly by new signal processing methods.

Precise and detailed knowledge of the dynamic characteristics of structures has become increasingly important in recent years. As a consequence, the accuracy of experimental data, which is often used to validate and to update finite element models, has become extremely important. It has been shown experimentally that small changes in ambient temperature can cause distinct variations in the natural frequencies of a lightly damped structure which, in turn, may result in significant errors in experimental and analytical results. Therefore, a good understanding of the physical driving mechanisms involved is necessary so that adequate stability control measures may be implemented. This paper presents an analytical investigation of the variations in natural frequency caused by small changes in temperature. An analytical plate dynamic model is developed accounting for the effects of temperature- dependent material properties. Changes in temperature influence Young's modulus, structural dimensions (via thermal expansion), and boundary condition effects. These change cause variations in the natural frequencies which result in marked changes in structural dynamic response at frequencies near resonance, especially when damping is low. Natural frequencies decrease linearly with increasing temperature over the limited temperature range in this study. A sensitivity analysis indicates that the temperature-dependence of Young's modulus is the dominant factor influencing the variations in natural frequency, but boundary condition effects may also be important.

An all fiber optic multi-axis laser vibrometer system has been constructed for measurements associated with structural acoustics research. This unique experimental capability was developed to allow the measurement of full 3D velocity vectors of both the interior and exterior of a structurally complex submerged cylindrical shell. The system consists of two laser vibrometers positioned by scanning robots. The design of this system as well as some preliminary measurements will be discussed.

An experimental comparison has been carried out between two laser Doppler vibrometers, different as for frequency shift generation between measuring and reference beam of the interferometer. In particular, two systems, based either on a Bragg cell or on a rotating diffraction grating for frequency shifting, have been compared, with reference to both metrological and operating behavior. Based on the analysis of experimental information, a quantitative evaluation has been carried out of the effect on either optical configuration of the most typical operative parameters to be taken into account in laser Doppler vibrometry, in order to define the best optical lay-out and configuration depending on the specific industrial application.

First application of Digital Hilbert Transform for processing of Laser Doppler Vibrometer signals is considered. The possibility of the vibration amplitude measurement with relation errors 1 divided by 5% in the amplitudes interval 0.1 (Lambda) divided by 10 (Lambda) , where (Lambda) is the fringe spacing, and the linear velocity measurement of the examined object has been proved. The analysis of the amplitude measurement errors is given. The applications of the method under review are discussed.

This paper discussed the presence of `laser noise' in velocity measurements taken with an SLDV system. In this paper, an experiment is presented to investigate the optimal operating range of velocities for the SLDV system. Additionally, an experiment investigating the effect of the use of a highly retroreflective surface treatment on `laser noise' is also presented. In order to determine the relative extent of the `laser noise' in these scans, a novel statistical value which quantifies the overall quality of the scan data is developed, presented, and exercised on experimental test data.

A new idea of measuring video flutter of VTR is proposed in this paper. Based on the Laser Doppler Anemometry, the instability of a working piece can be studied by inspecting its instantaneous speed. Experiments show that this method can realized non-contact measurement while the VTR is playing, and can be used to analyze the dynamic characteristics of other kinds of rotating machinery.

Laser methods are being applied to automotive seat vibration testing methods. The ability to perform non-contact tests is very useful when test specimens are handmade prototypes which cannot be damaged. More importantly, the low input force levels required by laser vibrometers results in more linear response from seats during modal tests; low input force levels limit the effect of freeplay in the recliner and tracks. Finally, the absence of mass loading allows exploring the dynamic interaction of the cover and frame.

The performance of a machining process using saw blades depends on the quality of the resulting cross-sectional area. This is determined by parameters like e.g. vibration and axial stiffness of the saw blade. These parameters are itself established by the respective materials, the dimensions of the saw blade and its tension. To evaluate the quality of a saw blade we propose neural networks to analyze vibration measurements.

Previous studies have demonstrated convenient techniques using a continuously-scanning Laser Doppler Vibrometer for measuring and quantifying vibration mode shapes defined along straight or circular scan lines, and for measuring angular vibration. This paper concentrates on a new conical- scanning technique which gives an easily-quantifiable measure of the magnitude and direction of the vibration of a point, even if the vibration is in-plane. Where the vibration is complex (i.e. it follows an elliptical path), derivation of the component vectors is more difficult. However, easy solutions exist for some practical special cases.

The problem of the energy transmission in vibrating structures is of paramount importance under practical and theoretical points of view. In this field the Statistical Energy Analysis is nowadays the most useful theory, even if the effects of its basic assumptions are difficult to evaluate. Based on the thermal behavior of mechanical energy among coupled vibratory systems, S.E.A. provides information on the stored and dissipated energy and on the transmitted power between them. Starting from the S.E.A. thermal assumptions, some energy models have been developed for the dynamic analysis of mechanical systems vibrating in the high frequency range. The basic principle of thermal propagation of mechanical energy has been examined under the theoretical point of view. The results seem to suggest that the analogy between thermal and mechanical energy propagation should be an acceptable approximation only for 1D systems but it is no longer valid for complex 2D and 3D structures. The present paper describes some experiments designed with the aim of validating the theoretical predictions developed. The experimental tests have been performed on one beam and one plate, excited in a relatively high frequency range. Consequently short characteristic wavelengths are generated and a very fine measurement grid is required. The laser measurement technique is in this case the most effective way to investigate the phenomena related to the wave mechanical energy propagation. The results of the comparison between theory and experiments confirm the dependence of the energy transmission law on the spatial scale range and the general failure of the vibrational conductivity principle.

Structural power flow is an alternative way of analyzing vibrations, where, differently from traditional techniques, the emphasis is put on the active part of the vibration energy instead of the total. The active vibration energy is directly related to the injection and dissipation of energy in the structure and can, therefore, be a valuable tool for solving vibroacoustical problems. However, measuring the active part of the vibration energy in the presence of a highly reverberant field is often impractical. This paper presents an experimental method especially adapted for the computation of structural power flow using spatially dense vibration data measured with scanning laser Doppler vibrometers. In the proposed method, an operational deflection shape measured over the surface of the structure is curve-fitted using a 2D discrete Fourier series approximation. This approximation minimizes the effects of spatial leakage. From the wavenumber-frequency domain data thus obtained, it is straightforward to compute the spatial derivatives that are necessary to determine the structural power flow. An example consisting of a rectangular aluminum plate supported by four rubber mounts and excited by an electrodynamic shakes is used to appraise the proposed method. Both numerically simulated data and experimental data are used.

A subtraction technique, continuous phase shift subtraction, is presented and compared both theoretically and experimentally to some Digital Speckle Pattern Interferometry (DSPI) techniques for vibration measurements. The method is found to be an improvement to other techniques in rough environments due to low sensitivity to disturbances. Continuous phase shift subtraction is a technique for finding resonance frequencies and corresponding modal shapes which is cost effective, robust, stable and easy to handle, i.e. a technique suitable for industrial use. The comparison assumes a DSPI system for out-of-plane measurements and the described methods are all based on the time-averaged technique with additional digital image processing.

Various signal processing methods have been developed for application with specifically modified Michelson interferometers and the novel diffraction grating interferometers for the accurate measurement of translational and rotational motion quantities at sinusoidal and shock-shaped time-dependencies. After a survey of these methods and their particular ranges of applicability, the methods based on the determination of the time-intervals between the zero crossings of the interferometer signals are presented. Different versions of time interval determination are described, which are adapted to either homodyne or heterodyne interferometers. It is shown that time interval analysis can be applied in two different ways--either to identify the phase-modulation of the interferometer signal as a measure of the displacement or rotational angle, or to identify the frequency-modulation of the interferometer signal as a measure of the velocity or angular velocity. Results of the theoretical and experimental investigations and of the application of the time interval analysis for the calibration of accelerometers and angular accelerometers are presented.

The notion of vibratory energy flow has developed at the end of the 70s. The utilization of finite difference techniques between a set of sensors (accelerometer, strain gauges or laser vibrometers) has allowed to develop usable formulations in beams and in plates. Other methods, other types of structures have been considered thereafter. The interest of the vibratory intensity concept is double: it uses first of all energy magnitudes that have the advantage to be common to waves of different nature and to different propagation media, finally, it possesses a vectorial nature that is able to provide an imagery of transfer phenomena in complex structures. However this last point is less evident than for the acoustic intensity: the confinement of mechanical structures and the multiplicity of sources of excitation is often going to reduce the practical utilization of the vectorial characteristic. For example, several independent or partially correlated sources are going to produce at a point components of different orientation whose resulting vector will not be able to show transfers of energy. In the extreme case, results are going to compensate, until to cancel the vector.

A powerful technique for monitoring and analyzing mechanical systems is the application of laser Doppler vibration measurements. When the object to be analyzed rotates, the measurement becomes difficult. That is, when a steady laser beam is used, the presence of a tangential motion of surface determines a noisy disturbance. The speckle pattern produced by the roughness of the analyzed surface is moving with the surface itself, and this phenomenon is observed as a signal with a frequency depending on the rotational speed. For these reasons, the aim of the present work is to show the possibility of Eulerian approach to the vibration measurement of rotating objects. A Laser Scanning Vibrometer has been used for the tracking of the same point in the complete circular motion. The capabilities of this system are tested on the measurement of vibration map of blades of a model of naval propeller working in water: a comparison has been found with the static analysis, in water and air, of the same propeller. Some results are shown.

In holographic methods of vibration registration a key role belongs to dynamic photorefractive materials. Polymer films with fragments of purple membranes containing biological photoreceptor bacteriorhodopsin (BR) have attracted a lot of attention as a dynamic photorefractive material in recent years. In this work, we propose the application of holographic gratings recording resulting from superfast photorefractive mechanism in BR-films for efficient vibrations registration in Raman-Nath self-diffraction conditions. It is shown that this holographic method enables the registration of start and final of vibration with very high precision. The selection of forward and reverse motions is performed by means of this holographic method.

We report the operation and performance of a time-averaged holographic interferometry setup for the measurement of vibrational mode patterns in a surface, using the He-Ne laser 632.8 nm wavelength line and a photorefractive Bi₁₂TiO₂₀ crystal as the recording medium. The photorefractive crystal allows the real-time reversible recording and display of the hologram without any (chemical or thermal) development processing. The particular light polarization features of this sillenite family crystal allow the display of vibrational mode patterns and at the same time enable to actively stabilize the holographic setup. Good quality images are obtained even using low power laser beams requiring a long exposure time in comparatively perturbated environment.

Two robust systems for vibration measurements are presented. Both systems are based on low-cost laser diodes. The stability of the optical systems is achieved by implementing the optical system in a holographic optical element while using a common-path interferometer concept for the measurement scheme. The former system facilitates real-time simultaneous tracking of vibrations about two axes perpendicular to the optical axis. The latter system is an electronic speckle pattern interferometer working in a differential mode providing whole-field information on the angular deformation about one axis between two states of the object. It will be argued that these concepts will provide compact, self-aligning systems for industrial use due to the inherent possibility for mass fabrication.

The original two coordinate step wave motors of synchronous type are analyzed. In them the output member is pushed by the standing waves excited in the input member. The input link may be a rectangular plate or a cylinder or similar. The output member is pressed to the working surface of the input member by the elastic-dissipative elements. The positions of the nodal and peak points of the input member may be changed in various ways. The created model and the performed research of the dynamics determine the characteristics of those motors. The experimental research is complicated because in the input member for example in case of a rectangular plate besides of the orthogonal standing waves the waves of various frequencies travelling and non orthogonal and of damped type arise. That is why for the solution of those problems the method is created based on the method of laser holography and the research is performed. The results of research are effective in the creation of advanced constructions of step motors of the types analyzed.

Ductile cast iron containers for transportation and deposition of radioactive waste have to be designed carefully in order to avoid unacceptable damages and leakages in case of an accident. Therefore various calculation and experimental methods are used during development and licensing of the containers. Besides others the container has to suffer severe impacts (e.g. falling from a height of several meters onto a concrete base). The level of strains must not exceed a value which would adversely affect the package in such a way that it would fail to meet the applicable requirements. In practice complex events such as drop tests are very difficult to calculate. Both the position of Maximum stress and the time of its occurrence are not easy to be predicted with the method of FEM. The uncertainty of the material modelling for plastic deformations by dynamic loading rates is the limiting factor. Therefore holography as an integral measuring technique in combination with strain gauge techniques were used to fit the FEM. By using the FEM calculations in the case of licensing, the FE and the material model have to be verified. The verification of the FE model has to be done by comparison of the local maxima measured by strain gauges and by comparison of the vibration modes. These vibration modes we take from holographic measurements. In this paper we explain container vibrations after impact analyzed with holographic measurements, FEM calculations and the comparison of the results. The comparison of the local maxima (strain gauges/FEM) is reported earlier.

This research is related to optical signal processing. We discuss the operating principle of traveling wave type-like optical modulator in the scheme of optical holographic correlator. The theoretical expressions are shown. The working modes of experimental setup and experimental results are presented.

In this paper the laser-Doppler-velocimeter is used to measure the responsive velocity of car body and cylinder of engine. It is made of the cylindrical beam as emissive light, avalan-che pipe as receiver and wide-band monitor as signal processor. The frequency response function can be easily obtained from the output signal of laser-Doppler- velocimeter after A/D converting and FFT transforming. The modal parameters data of modal shape may be gotten with test modal software.

Laser vibrometry became a well-established method for vibration detection of solids. By the means of laser Doppler interferometry it is possible to obtain information about displacement and velocity of the system under test. This approach allows the non-contact measurement of small vibrations, and is therefore capable of investigating vibration response of the middle ear ossicles or tympanic membrane due to sound simulation. There have been investigated 20 fresh human temporal bone specimens. Various components related to the sound transmission due to acoustic or mechanic stimulation have been measured by a commercial laser vibrometer (OFV3000 + OFV302/Polytec). Data acquisition, signal processing and test signal generation have been provided by a signal analyzer B&K3550/Bruel&Kjaer or integrated into a Notebook PC. The samples became prepared to allow laser beam access to the regions of interest. Generally our experiments show the capability of laser vibration measurements of the temporal bone specimen for middle ear sound transmission investigations. But the complexity is limiting that method unfortunately. 1D detection could represent insufficient information about the acoustic transmission characteristics only. The request of possibly 3D scanning is limited by anatomic conditions, e.g., according to the narrowness of the tympanic cavity. Nevertheless, for specific problems, e.g., investigation of spatially resolved tympanic membrane vibration characteristics, laser vibrometry performs a unique and high-sensitive approach. After removing the external ear canal different, well-defined points of the tympanic membrane surface have been manually scanned by the open laser beam. Particular care has been taken of the problem of perpendicular beam incidence, in order to detect identical vector components of the vibration amplitude. Laser vibrometry becomes suitable for functional investigation of the vibrating system `ear' influenced by boundary condition changes too. Vibration measurements of the umbo corresponding to manipulations of the ossicular chain allow conclusions regarding its sound transmission characteristics.

Sound radiation from vibrating thin walled tubes and from organ flue pipes is investigated. Measurements with a laser scanning vibrometer on this object show some new interesting results, e.g. the basic azimuthal vibration mode of thin walled tubes and organ pipes is of a stable quadrupole type. Typical vibrometer scans of thin walled tubes, metallic and wooden organ pipes are presented and interpreted with respect to sound emission and design of organ pipes. The application of the results to the domains of organ building and noise reduction seems to be useful.

When using conventional or laser Doppler vibrometer methodologies, the resonance-dwell technique is used to characterize the response shapes of structures vibrating near resonance. If the structure is large (and/or complex) and if high spatial density data is required, data acquisition could take a significant amount of time. During that time, changes in structural characteristics can occur with cause very large variations in the vibration response amplitudes at the same structural point. An understanding is needed of why such changes occur and of how a structure can be stabilized during prolonged dynamic testing. The goal is to make the measured response data as accurate as possible. This paper presents an experimental investigation of the variations in natural frequency caused by short- or long- term temperature changes. The rectangular steel plate natural frequencies were determined at temperatures slightly above and below standard room temperature. Two boundary condition configurations were studied: a clamped (pseudo- cantilever, C-F-F-F) configuration, and a free (F-F-F-F) configuration. The results indicate that natural frequencies decrease with increasing temperature, resulting in large variations in the response near resonances. Furthermore, larger natural frequency variations are observed in the clamped configuration than in the free configuration, indicating that temperature-induced boundary condition effects are important.

The load acting on the wall of a pipe by a throughgoing detonation is not yet well characterized. Reasons are the limited amount of data on sufficiently accurate pressure/time traces of the detonation peak and the requirement of considering the dynamics of the system instead of just doing a static approach. To determine the dynamic response of the pipe wall on a detonation we performed laser velocimetric measurements and compared the results to theoretical calculations. There is good agreement between measured and predicted values of vibration frequencies, amplitudes and vibration velocities. Furthermore it was found that various radial vibration modes other than the fundamental one ((phi) -symmetry) are excited. This must be attributed to the complex structure of the detonation front which is not just a plane of high pressure oriented vertical to the axis of the pipe.

The dynamic behavior of a 3D impeller (1100 mm diameter) has been modelled by means of a standard FEM code (ANSYS) and experimentally validated using a laser scanning vibrometer based measurement technique. The theoretical finite element model has been previously developed. Attempts made by using classical measuring techniques has not allowed to obtain the low frequency cyclic modes calculated. Those modes have been obtained using a laser scanning vibrometer. Sine sweep to detect frequencies and sine excitation at resonance frequencies, in order to improve the accuracy of the modal shape, have been used. The keys of success was the ability of the laser vibrometer to detect very low vibration amplitudes (of the order of nanometers) with a high spatial resolution, inside an industrial environment, in very low testing time, all fundamentals for this application. The experimental and numerical activity presented in this work has been carried out from Nuovo Pignone together with the University of Ancona with the final purpose of establishing a new fast procedure to identify, in production industrial environment, the dynamic behavior of large dimensions impellers for centrifugal compressors.

As illustrated in previous works a laser scanning vibrometer can be used to detect vibration transmitted to human body, in particularly vibration velocity on hand skin. The problem still open to investigation of hand mechanical impedance, i.e. the ratio between force and velocity. This parameter, and its distribution on the hand, is of paramount importance for example to build multi input - multi output models or develop and test insulating devices. Another well known fact is that vibration transmission to human hands depends on the overall grip force applied by the subject. In this work film sensors to detect local contact pressure has been analyzed and tested in different situations. The signals of those sensors are then used to calculate mechanical impedance maps of human hands using also results obtained by a scanning laser Doppler vibrometer.

The daily practice of vibration experiments in automotive engineering is characterized by non-harmonic motion, non- constant frequencies, many-body interactions and parts of construction with internal damping. Examples of all these features are given. They are discussed and the conclusions are listed.

The micro- and nano-science and technology has been developing in recent years. Employing the state-of-the-art manufacturing technology the sizes of microstructures are generally in micrometer scale or even in nanometer scale. This paper describes several vibration measurements in microstructure investigations with a laser vibrometer. The microstructures are Si lever, cantilever and cantilever probe in the AFM. Dynamic characteristics of optical fiber building the distance regulation in the NSOM and of Si membrane excited with laser beam in single direction and double opposite direction in thermal sensors were investigated. The vibration curves and experimental results are given. Further possible vibration measurements in micromachine and nano-science and technology is discussed.

A study of the metrologic problems connected to performing laser vibrometer measurements through combusting flows has been presented in this paper, in order to test the real applicability of laser vibrometer techniques to carry out measurements on full-scale burners. A model of the instrument is developed to describe main effects on the measurement system due to time varying refractive index within the flame; measurement uncertainty sources are discussed. Variations in the optical path length of the measuring arm of the interferometer due to changes in the laser beam wavelength and propagation direction caused by refractive index gradients seem to be the most influent effects and they are modulated at the natural flickering frequency of the flame. Experimental results from measurements performed by a single-point laser vibrometer through an unconfined CH₄ flame from a Bunsen burner are in agreement with the model and provide an explanation of the phenomena which affect uncertainty in these particular measurements.

The Laser Doppler Displacement Meter (LDDM), has been applied for the measurement of structure dynamics, such as resonance frequency, Bode plot, settling time, etc. in machine tools, rotary machinery, XY-stages, and servo controls. Other applications are in micromachining and in hard disk drive, such as flight height, head gimbal resonance, runout, etc. The basic principle of the LDDM, its comparison to laser interferometer and also vibrometer, major features and application are described.

Electronic speckle pattern interferometry (ESPI) and holographic interferometry are powerful tools for vibration analysis. They allow to measure the spatial distribution of a vibration amplitude in the micrometer or submicrometer range for the purpose of modal analysis for nondestructive testing. As for ESPI, this method principally is very suited for large-scale industrial optical inspections because the interferograms are recorded with a video camera and evaluated in quasi real time with a computer and no media costs for the measurements arise. However current speckle pattern interferometers have rather complicated and expensive optical setups whose elements are aligned with difficulty. On the other hand, holographic interferometry which can provide interferograms with less noise and higher resolution requires an optical setup of at least similar complexity, and in addition a holographic recording medium such as silver halide material or photothermoplastic film. The negative influence of all these drawbacks are drastically reduced in a method which combines positive features of ESPI and holography. This method has already proved its validity for different objects loaded in statics. It can be successfully applied to vibrating objects.

Pointwise modal analysis techniques suffer from the compromises required to infer wholefield vibration behavior from a predetermined number of measurement data points. The measurement grid is normally chosen before the most sensitive area of the test piece have been identified and this can lead to a requirement for further grid refinement, with the consequent spatial and temporal disadvantages. This paper presents a technique for obtaining wholefield modal data using electronic speckle pattern interferometry (ESPI), and focuses on the manipulation of optical information to provide a grid of data points which is transferred to a modal analysis software package for comparison with traditional pointwise modal data sets. The advantages of obtaining the initial wholefield vibration picture in real time and subsequently overlaying a chosen measurement data grid, are demonstrated. Modal analysis of a steel plate is presented. By taking advantage of wholefield data, grabbed at the same instant in time and then transferred into modal analysis software, ESPI mode shape information is directly compared with measurements using other pointwise techniques and finite element analysis (FEA), through a modal assurance criterion calculation. Results showing successful mode identification by ESPI are illustrated, by comparison of results for the fourth resonant mode of the plate with those from laser Doppler vibrometry, accelerometer measurements and FEA.

Classical Modal Testing techniques, using accelerometers, are faced with problems of mass loading and spatial resolution if lightweight structures and/or high frequency modes have to be measured. Until today, holographic techniques, such as Electronic Speckle Pattern Interferometry (ESPI) are mainly used as a qualitative rather than quantitative measurement technique and usually lack the capability to measure phases of the vibration. An approach, using ESPI, has been developed which allows to measure the response displacement of the complete structure in amplitude and phase format. If referenced to the measurement of input force, it allows to obtain the complete frequency response functions, which can then be processed by classical modal parameter identification techniques in order to extract the frequency and mode shape information. The approach has the advantage to give very high density spatial information (several thousands points measured simultaneously without mass-loading) in a numerical format directly usable for further numeric analysis. This paper explain the approach and shows how it has been used to perform a modal analysis of a brake drum, in view of a correlation analysis with the FE model of this drum. It will discuss practical aspects involved in the measurements, present obtained results and highlight possible further development and automation.

Laser-diode (LD) interferometry based on phase-shifting techniques has been applied to holographic interferometry for measuring the vibration amplitude and phase. First the developments including a phase-shifting interferometer with a frequency-modulated LD are reviewed. Second, stroboscopic holographic interferometry by a pulse-driven laser diode gives the measurement of the vibrating amplitude at any epoch. The frequency chirp of the laser-diode pulse used for real-time stroboscopic illumination cancels the Doppler frequency shift due to the motion of a sinusoidal vibrating object.

Modal analysis of a metallic specimen has been performed by use of Double Pulsed Holographic Interferometry. The specimen was excited by an electromagnetic shaking platform operating in an industrial-like environment, in day light and with severe floor vibration. A piezoelectric accelerometer was used to detect the specimen natural frequencies, Double Pulsed Holographic Interferometry was used to detect vibration modes. For each identified natural frequency, various double pulsed interferograms were made in order to obtain a sequence of fringe patterns showing a `stroboscopic' video-recording of the specimen displacement. Numerical modal analysis of the specimen was performed by use of Finite Elements Model analysis (ABAQUS s/w). Comparison between numerical and experimental results showed that the numerical model originally assumed with `no degree of freedom' at the edge fixed on the shaking platform, had to be corrected to improve the description of the real constrain. After the correction was made, very good agreement between numerical and experimental modal shapes was obtained, thus demonstrating that effective validation of numerical model can be obtained by holographic experimental measurements. The highly reliable validation obtained by use of Holographic Interferometry, is compared to the validation obtainable by classic methods based on comparison between numerical and experimental natural frequencies.

This work presents an analysis method of vibratory blades of a turbine by holography. This method consists in use the holography in real time during the turbine running illuminated by a laser to continuous emission or a stroboscopic laser of maximal frequency 10 KHZ.

The automotive industry has particular interest in obtaining modal models of panel-like structures in the higher frequency range where the accuracy of FE-models normally is not longer sufficient to predict the dynamic response of a car body structure to a given operational excitation. Experimental modal analysis can fill this gap. However, the sensors which are currently used for the acquisition of vibrational data (accelerometers, laser vibrometer) are limited in spatial resolution and therefore higher-order panel modes are hard to be investigated. Holographic interferometry is widely used for qualitative and quantitative measurements of the mode shapes of dynamic systems, where its high spatial resolution outperforms any other kind of vibrational dynamic sensor. The limitations of holography with respect to the sampling rate can be overcome in the context of modal analysis by using stepped sine testing. A large number of holograms is then automatically recorded and evaluated. First results on a test structure which exhibits narrow-spaced eigenmodes are shown using this kind of measurement setup with a high frequency resolution. The dense vibration data enables the modal analysis software to separate the eigenmodes.

Laser holographic interferometry has been applied to experimentally investigate the effect of flexure-torsion coupling stiffnesses on the vibrational characteristics. Test specimens are two special types of angle-ply laminates, which enables us to examine the influence by a flexure- torsion coupling term alone. The theoretical analysis by a finite element method is also conducted to support the experimental results. It is found that the effect of coupling stiffnesses on the natural frequencies is comparatively small. On the other hand, the mode shapes are strongly affected by the coupling terms depending both on the fiber orientation and on the aspect ratio of a cantilevered laminate.

This paper describes the recent developments of the digital shearography for vibration analysis, i.e. real time observation of the time-average digital shearogram with refreshed reference frame and stroboscopic illumination in conjunction with the phase shifting technique for quantitative evaluation of the digital shearogram. Time- average method is by far the most usual technique for qualitative vibration analysis. In the conventional technique for real time observation of the time-average interferogram, the fringe contrast is poor because the fringe pattern is modulated by 1-J₀ ((Omega) ). In addition, the fringe is very sensitive against ambient noises such as thermal air waves or lower frequency vibrations. With the introduction of the refreshing reference frame technique, the fringe pattern is modulated by J²₀ ((Omega) ) and the fringe contrast becomes much better. Furthermore, the low frequency ambient noises are greatly suppressed by the technique. It is suited well for qualitative vibration analysis such as NDT and qualitative modal analysis. For quantitative vibration analysis, the stroboscopic technique in conjunction with the phase shifting method is applied, the accurate phase map of digital shearogram for a vibrating object can be obtained. Therefore, the dynamic deformation and strain fields of the vibrating object can be determined.

In the last years, diffraction grating interferometry has been made use of to accurately measure rotational quantities. A new diffraction grating interferometer developed for this purpose was presented in a paper given at the First International Conference on Vibration Measurements by Laser Techniques. Since then, various investigations have been carried out into the behavior of different versions of diffraction grating interferometers based on homodyne and heterodyne techniques. The paper describes these investigations, their results and the uncertainties achieved in measurements of the physical quantities of angular acceleration, angular velocity and rotation angle.

Laser speckle produced from a diffuse object may be used in determining the angular position of a rotating object. When the object rotates the backscattered speckle patterns are sampled by a suitably positioned photodetector. The photodetector output signal is periodic and one period is stored in memory as a reference. Shaft position is then determined by cross-correlating this stored reference signal with the current photodetector output signal. When the shift is axially displaced the back scattered speckle patterns change and the cross-correlation between the reference signal and the current signal is reduced. The Laser Torquemeter is an instrument designed to measure the time- resolved torque transmitted in a rotating shaft and uses two probe laser beams, axially separated on a shaft of known mechanical properties. In order to design a robust Laser Torquemeter it is necessary to determine the cross- correlation of the current photodetector output signal and the stored reference signal as a function of axial shift position because the reduced cross-correlation due to axial motion results in a loss of tracking which is determined to the performance of the Torquemeter. Experiments conducted to measure the photodetector output cross-correlation show that the ratio of decorrelation displacement to beam diameter can achieve a maximum value of 0.7. For a typical axial shaft vibration of 0.6 mm peak to peak, a minimum beam diameter of 1 mm is recommended and further details of the optical configuration necessary to achieve this optimum resistance to decorrelation are suggested.

This paper proposes a flexible 3D coordinate system based on a theodolite pair. The maths model of the system is based on the least square method. A transition coordinate system is established to meet the requirement to move the theodolite pair in many on-site situations. This paper gives an example that the flexible 3D coordinate system is employed to complete the global calibration of a vision-based inspection system for the body-in white of car.

Bulk and surface sound waves in thermal equilibrium in solids scatter light inelastically (Brillouin scattering). From the frequency shift of the scattered light it is possible to measure the sound velocities of bulk and surface waves propagating along selected propagation directions. Then the elastic moduli can be extracted from the sound velocities. The scattered light is frequency analyzed using a Fabry-Perot interferometer, with typical frequency shifts in the range 5 - 100 GHz. The technique is non-destructive and is particularly useful for the elastic characterization of supported films and composite materials, like multilayers. Applications are shown for metallic multilayer films, polymeric films, silicon on insulator bilayers.

An application of distributed control system in Autocar-body Visual Inspection Station is presented in the paper, a distributed control system using PC as the host processor and single-chip microcomputer as the slave controller is proposed. In this paper, the physical interface of the control network and the relevant hardware are introduced. Meanwhile, a minute research on data communication is performed, relevant protocols on data framing, instruction codes and channel access methods have been laid down and part of related software is presented.

A novel full-dynamic phase-demodulator for heterodyne interferometric vibration measurements is described. Contrary to a conventional phase-demodulator, which has a limited dynamic range of +/- 90 degree(s), the proposed phase- demodulator has an unlimited dynamic range. This allows to recover phase information for displacements of the surface under test which are much greater than the wavelength of light. Noise measurements of the demodulator show that, for a carrier-to-noise ratio of 70 dB within 3 kHz bandwidth, a phase noise of less than 3 (mu) rad/(root)Hz can be expected. Finally, a digital version of the full-dynamic phase- demodulator with an extended frequency response has been developed. The comparison between the analog and digital phase-demodulator versions is discussed and examples of phase recovery are presented.

The basic structure and operation principle of a laser-based instrument for continuous measurement of tilting and vibration of structures located in mining-influenced areas have been presented in the paper. Two versions of the instrument are discussed. Examples of field operation of the instrument at some locations of the Upper Silesian coal basin have been given.

A new fiber optic accelerometer system for stator winding simultaneous multi-point vibration monitoring of hydroelectric generating sets is presented. It is composed of as many sensor heads as points to be monitored, an optical channel and a processing unit distant from the sensing area, which is exposed to strong electromagnetic interference. The evaluation scheme is based on an intensity modulation and differential detection technique so that the measure is not influenced by external perturbations. The system is able to measure accelerations ranging from 30 to 450 Hz, with a maximum amplitude of 200 m/s² RMS. Experimental results for the previous prototypes developed are showed. This sensor is intended to be integrated in a new complex system aimed to reach the goals of instantaneous protection, real time detection and evaluation of defects, failures and malfunctions in the above mentioned machines.

A new non contacting, full field, variable sensitivity optical method is proposed for an experimental analysis of the local amplitude vibration of a diffuse surface. It is based on sinusoidal fringe projection interferometer just developed for contour map. Linear sinusoidal fringes, which are formed by the interference of two wave fronts emitted from the output of a fiber coupler, are projected on the object surface. The visibility of these fringes is modulated by a function of local amplitude of vibration; thus loci of constant vibrational amplitude can be directly observed as regions of high or low fringe visibility in the image of the surface. A brief analysis of the technique and some preliminary experimental tests are presented.

The new method to measure rough body vibration is proposed. The method is based on spectrum analysis of coherent radiation scattered from rough surface and transmitted through the grating.

This paper details the design of a non-contact fiber optic sensor for the detection of acoustic emission for structural integrity monitoring in high temperature power plant applications. The sensor is based on a Sagnac interferometer and produces an output proportional to target velocity, without the need for active phase stabilization. It is inherently insensitive to low frequency perturbations of the instrument or the target and incorporates an environmentally insensitive downlead which may be of arbitrary length. It is shown that the sensor is capable of meeting the specifications for structural integrity monitoring of high temperature power plant components based on acoustic emission detection and has a velocity resolution of 50 nms^-1Hz^-1/2.

This paper describes a non contact measurement technique for the transverse vibration of small cables and strings, using an analog position sensing detector. The sensor is used to monitor the cable vibrations of a small scale mock-up of a cable structure and to evaluate the performance of an active tendon control algorithm.

The use of transmission grating for measurement of rough body tangential velocity is discussed. The possibility of obtaining narrow component in the spectrum of scattered from rough surface and transmitted through the grating radiation is confirmed both theoretically and experimentally. The availability of a narrow component in the spectrum of scattered radiation with (Delta) f/f < 2 10^-2 enables one to measure tangential velocity of the diffuse object within +/- 0.5% accuracy.

The vibration displacement of a shaker in an accelerometer calibration system is detected by a Michelson type of a phase quadrature laser interferometer. The interferometric signals are stored in a digital storage scope and transferred to a computer for displacement calculation. Due to the high resolution, fast acquisition speed, and large memory capacity of the scope, this system demonstrates a measuring range from about 10 nm to 100 micrometers at the frequency range of DC to 20 kHz. A cyclical signal- preserving algorithm is developed to preserve the signal's phase and amplitude while reducing the drift and random noise level. The standard deviations of the measured displacements are 1.3% for 13 nm and rapidly lower to 0.04% for 500 nm or greater. The measured displacement in conjunction with the vibration frequency and the output voltage of the accelerometer then give its sensitivity. Preliminary results demonstrate that the sensitivities calibrated by both the direct displacement measuring method (our experiment) and the conventional fringe-disappearance method agree within 0.6%.

A laser scanning system is proposed to enable the measurement of dimensions of steel plates used in shipbuilding with the objective being design verification and tolerance monitoring at the early stages of assembly. When the system is combined with a second scanning-viewing system it is demonstrated that depth measurements can be obtained giving the 3D shape of the plate or structure. The precision of the two configurations is discussed and evaluated.