Vibration of biological structures is often measured in a reference system that is imposed on the investigator by the accessibility of the object. This imposes a serious handicap on the usability of the results. A method is presented that measures the 3-D components of vibration of the structure and integrates complete 3-D anatomy in the data analysis. A realistic3-D anatomical model of the tested structure is used to determine coordinate transformations and express the motion parameters in intrinsic object reference systems. Results from different experiments can now be unequivocally compared and predictions of mathematical models can accurately be checked. Animations of the vibrating structure can be made to study the motion from all angles, even those not accessible during the experiments. One can also calculate the ratio of vibration amplitudes at different landmark points, check whether the structure has a fixed rotation axis, or calculate the vibration along an observation axis that was used in experiments with a completely different experimental approach. We present as an example a study on the vibration of the malleus. The application of our procedure is not limited to problems in the biomedical research area, but it is of general use in [bio-] engineering applications.

The use of artificial heart valves is more and more diffused in the medical practice in particular in Europe and US where the average age of the people is continuously increasing. In the engineering point of view they present several problems that can be faced by a deep knowledge of the behaviour in operative conditions. Such problems are mainly related to the compatibility with the patient body and the reliability of the valve itself, and both are related to the possibility of a continuative and extended application in real cases. The compatibility is mainly related to the material choice and to the fluid-dynamic behaviour. The reliability can be basically improved by a smart and simplified design of each component, which imposes a really intensive evaluation of the response to operative inputs. Fatigue is one of the most important effects related to reliability. A mechanical valve is subjected to fluid-dynamics forces and repeatable shocks. due the impact on the constraints, which create dangerous vibrations. The analysis of such vibrations by SLDV[1][2] in both free and operative conditions is the main task of the present work. In this paper an experimental and numerical analysis of the vibrational behaviour of a mono-leaflet valve was performed in order to extract useful information on the optimised design. An in vitro test, simulating operative conditions, was performed in order to verify the real behaviour of the valve.

Authors present a new non-intrusive experimental procedure based on laser techniques for the measurement of mechanical proprieties of tendons. In previous works authors described a new methodology based on the measurement of the first resonance frequency of the tendon by laser vibrometry during in-vitro tensile experiments, with the final aim of establishing a measurement procedure to perform the mechanical characterization of tendons by extracting parameters, as the resonance frequency, achievable also during in-vivo investigation. In this work the experimental procedure has been updated with a measurement technique for the non-invasive determination of tendon cross-sectional area during tensile vibration tests at different load levels. Test procedure is based on a tensile machine, which measure tendons longitudinal elongation generated by a known load. Sample cross-section area is measured and stress-strain curve can be obtained. The cross-section area is measured with a new non-contact procedure based on optical displacement sensor, in such a way as to determine its perimeter. From the perimeter, the area can be easily extracted by integration. At each load level, resonance frequency, damping, area and tensile force are measured, allowing thus a complete mechanical characterization of the tendon. Stress —strain relations have been correlated to the first resonance frequency of the tendon measured using a single-point laser Doppler vibrometer.

The use of Laser Doppler Vibrometer (LDV) technology has been at the fore front of Micro Electro-Mechanical Systems (MEMS) research since the early 1990's. The art of the technology has culminated in our latest Micro Scanning Vibrometer (MSV) system for automated scan measurements on MEMS. One MEMS application driving our product development is the use for testing optical MEMS devices, such as optical switches used in the telecommunications industry. To exemplify this, we present measurements made in collaboration with Applied MEMS on their MEMS DuraScanTM mirror. For Applied MEMS, LDV characterization was important for validating the design intent for two-axis rotation of a single-gimbaled structure. Scan measurements reveal distinct, isolated rotational modes about x- and y-axes that can be used to constrain mirror motion in either direction. A key feature of the LDV is that it measures real-time transient response in typical operating conditions where both electrical and mechanical effects are present. Characterization of settling time performance shows that the mirror can be optimized for fast, accurate beam steering needed for applications like optical switching.

For a life time optimized construction the knowlegde of dynamical assemblies load is one of the basic requirements. This fact is especially relevant for smart electronic structures. To analyze the load vibration investigations and vibration tests are necessary. For such investigations ofelectronic structures contactless working lasertechniques are used. In the last few years experimental modal analyses based on laser vibrometers have been established. The results of such analyses show eigenfrequencies, vibration amplitudes and mode shapes. Based on this structural modifications concerning a vibrational optimization are inferable.

We describe an advanced interferometric testing system that we have built at the Berkeley Sensor & Actuator Center (BSAC) at the University of California, Berkeley. The system provides live dynamic views of microelectromechanical devices as well as precise measurements of their motions in three dimensions. A high-speed interface feeds these signals to an ultra-high-performance network (SuperNet), which can deliver them to remote locations where they can, for example, be compared to simulations. An illustrative example using a nonlinear oscillating microactuator demonstrates the utility of the system.

Numerical methodology for the investigation of structures in the virtual reality is developed. This methodology is based on the principles oftime averaging laser holographic interferometry. Ability to vary the parameters ofthe virtual optical experiment enables smooth transfer to the smaller dimensions and levels of amplitudes up to the nanoscale investigations. Such type of analysis can be successfully used for different applications, starting from biological investigations of cells, up to the design of microelectronics components.

Micro electro-mechanical systems (MEMS) devices are being developed for a broad range of applications. In most cases, the sensitivity of the final device is a function of the intrinsic dissipation of mechanical energy, or Q-1. We use laser Doppler vibrometery (LDV) and finite element modeling to examine and quantify a variety of different dissipation mechanisms that are important for the room temperature operation of MEMS oscillator devices. In this work we examine dissipation mechanisms that include phonon-phonon scattering, thermoelastic dissipation, acoustic radiation, viscous drag and attachment loss. We examine three different systems experimentally and analytically to demonstrate that different loss mechanisms are dominant in each case at room temperature. Full-field LDV measurements are used to show that resonant reflectors are responding as predicted by finite element modeling and reduce the torque that the oscillator imposes on its foundation. This result shows that the attachment loss can be mitigated with the use of resonant reflectors and by careful design and fabrication. However, this reduction in the attachment loss does not reduce the Q-1 at room temperature for this device. From this we conclude that for these oscillators, attachment loss is not an important dissipation mechanism at room temperature, and the loss is due to some other intrinsic mechanisms mentioned above. We find that at pressure greater than 1O-2 Ton acoustic radiation dominates for our MEMS paddle oscillators, while for a diamond oscillator, 10-3 Ton is the low-pressure for when radiation damping is dominant.

Micro-Electro-Mechanical Systems (MEMS) devices present many difficult characterization challenges. In an environment where dimensions are measured in microns and mechanical resonant frequencies are measured in kilohertz, conventional measurement and characterization techniques cannot be used. Laser Doppler Vibrometer (LDV) technology offers many unique advantages for MEMS characterization and troubleshooting. One of the key problems in characterizing and troubleshooting MEMS devices is the separation of electrical and mechanical effects. By definition, MEMS devices have integrated electrical and mechanical components to form electro-mechanical systems. When characterizing and troubleshooting these devices it is often difficult to determine whether an observed behavior is purely mechanical, purely electrical, or inherently electro-mechanical. Because LDV measurements are electrically inert and do not introduce mechanical artifacts, they are ideally suited for this application. Applied MEMS and Polytec PT have successfully developed LDV based measurement techniques that allow detailed characterization and rapid troubleshooting of MEMS devices. Three real-world examples of MEMS characterization using a LDV are presented including, an optical micro-mirror, a robust low-noise accelerometer and a hermetic ceramic sensor package.

In the present work the development of a customised vibrometer able to work on Microsystems is shown. The system is based on a commercial Laser Doppler vibrometer, in which the optical set-up, the mechanical arrangement and the processing software and hardware were modified and developed to measure vibrations of small object with a resolution in the micro scale. The main characteristics of this system is a very versatile platform, in which laser Doppler Vibrometry, two-axis stages micropositioner, digital signal processing and image acquisition and processing can work together in order to obtain the integration of vibration measurements with other experimental techniques. The system developed, which represents the first step in this project, has been applied to a typical test case in order to verify performances and limits. A discussion about main features and limits is presented.

Recent technological advances in magnetic storage suggest the feasibility of extremely high-density magnetic recording up to 1 terabit per square inch (1 Tbit = 10-12 bits) areal densities. Modeling indicates that approximately 3 nanometers (nm) of physical head-disk spacing is required for such high recording densities. When the recording slider is flying at such ultra low spacing over a high-speed rotating disk, it is experiencing disturbances from various different sources and of a wide frequency range. These disturbances may cause the recording slider to vibrate significantly, a condition that is known as fly-height modulation (FHM), which may result in data loss. A significant source of excitation is from the surface irregularities of the rotating disk and is termed dynamic microwaviness. The term dynamic microwaviness has been introduced recently to differentiate from regular topographical microwaviness that is measured statically. In this paper, the procedure for making reliable dynamic microwaviness measurements of disk media used in hard disk drive (HDD) systems is described. Furthermore, such measurements are made on different magnetic disks that are intended for extremely high recording densities using non-contact laser vibrometry. The source of the dynamic microwaviness and its interaction with system dynamics are also investigated

The dynamics of a contact type system is analyzed in the regimes of singular and periodic shock processes. Governing equations of motion and their analysis is presented for one-dimensional system model. Examples of the design of different contacting elements is presented together with the numerical modeling results. The construction of the contacting elements, particularly the cantilever plate is optimized using numerical and laser holographical analysis.

This investigation concerns the application of different techniques, including optical fibre strain sensing puIsed Digital Speckle Pattern Interferometry (DSPI), traditional modal analysis and finite element model updating procedures to the study of vibrating composite structures. A prototype system for condition monitoring of composite structures is being developed which relies on the on-line measurement of dynamic strains in order to detect any deterioration in performance due to damage. A range of carbon-fibre reinforced composite specimens that incorporate innovative Fabry-Perot interferometric long gauge-length strain sensors have been produced and tested. The optimal design of fibre sensor network configurations for the identification of different damage parameters is being aided through the development of a software simulation tool and the use of a p-version FEM package. Vibration modes of the excited structures have also been determined using an out-of-plane pulsed-DSPI system, employing a dual-cavity frequencydoubled Nd:YAG pulsed laser with a 25Hz repetition rate. In general, experimental results compare favourably with finite element predictions. The data derived from the strain sensors is used to update a parameterised FE model of the composite structure, allowing the determination of the position and extent of damage present.

Mechanical hysteresis problems associated with pressure sensors based on interferometric measurements of diaphragm deflection are discussed. The source and importance of each contribution to the net hysteresis is calculated and compared with experimental results. Possible methods to decrease hysteresis effects are presented. Based on these suggested methods, new sensors have been manufactured and their hysteresis evaluated. The results demonstrate that significant reductions in hysteresis can be achieved with minimum cost. Future sensor development will focus on materials selection and manufacturing methods to fully realize these improvements.

A very thin taper fiber has been produced for a vibration sensing. Frequency characteristics of the sensor up to 2000Hz are measured and the possibility for optical remote sensing a an acceleration measurement tools is discussed.

A highly sensitive pressure sensor based on two Mach-Zender interferometers is described.The interferometer measuring and reference channels are made of single-mode W-lightguides.The measured sensitivity was shown experimentality to be 65.10-2 dB.Pa-1.m-1.

A novel technique for extending the unambiguous range for differential measurements of linear surface deflections is presented. The principle utilises a new type of spatial heterodyne system, where a common-path interferometer probes the axial displacement of three points on the object surface simultaneously. The system is based on a single laser diode with all the optical functions of the system implemented in a single holographic optical element (HOE). The common-path scheme combined with the HOE provides a system that is inherently stable, since the HOE operates both as transmitter and receiver in the system. The HOE at the same time provides a simple and all passive quadrature phase measurement without the need for any active elements or polarising optics. The system is compact, robust, and has the potential for being mass-produced at a low cost and is thus well suited for industrial use. The demonstrated system can measure vibrations or tilt with an unambiguous dynamic range of approximately 1:14,000. Furthermore, the system can easily be reconfigured for a desired sensitivity and dynamic range.

This study concerns the application of a novel digital CMOS-DSP camera in full-field interferometry for vibration analysis and quasi real time processing in optical metrology. Characterisation tests on the digital camera have been performed. Both quasi-static and carrier-based approaches have been considered and will be presented in this paper. The CMOS-DSP camera is a primary component of a compact and low cost system for classical image processing and an innovative element for full field vibration measurement using a single pixel carrier based approach.

The evaluation of the time dependent speckle modulation [2-3] due to optical path difference changes can be extended to vibration measurement. For a sinusoidal signal evaluation with varying frequency: from zero at its reversal point, to maximum frequency at its medium position with maximum speed. For both cases we assume a harmonic vibration. For evaluation, the distance of two adjacent zero frequency points is determined, giving half the mechanical time base, and the maximum frequency, giving the maximum mechanical speed, or, assuming a harmonic vibration, the mechanical amplitude.

Review of current and emerging methods ofholography and speckle metrology is given. Advanced holographic rapid access system (RAS) is presented. It is very simple, compact, portable and user-friendly. Holographic RAS is elegantly devised and requires minimal hardware. Holographic RAS has several modifications and spin-offs. Ultra high resolution silver halide media are used in this RAS. The unique features of holographic RAS enable the possibility to avoid any liquid baths for photoprocessing ofthe medium and to work in real time in situ. For the first time it is possible to obtain holograms, holographic interferogams and specklegrams outdoors in any brightly lit natural environments, including sunlit ones. It means that even extremely strong polychromatic exposures can be tolerated during rapid production of a hologram. Onboard research by means of holography and speckle metrology is analysed. The innovative holographic RAS suits ideally for monitoring of various physical processes, studying of vibrations and static deformations, testing of microelectronics and MEMS in microgravity. A novel very small holographic device is presented. It is portable device with no lenses and no alignment problems. The hardware is so simple that it can be operated by an astronaut having practically no skill in optics. One of the early variants of holographic RAS invented by this author was used to obtain the first ever holograms and holographic interferograms ofdifferent physical phenomena aboard navigating spacecraft. Experimental data properly illustrating novel vast possibilities for onboard space research are presented. The photographs from holographic interferograms and holograms are shown. Holographic images obtained in extremely unpromising outdoor environments are given.

A system based on digital holographic interferometry in combination with a rigid and a flexible endoscope is described. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulses, are captured at separate video frames of the CCD-camera, transferred in a frame grabber and further processed in a PC. If during the interval between the two laser pulses (usually in the range of 5-600 ?s) the object undergoes a vibration, a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to quantitatively evaluate the vibration. Two compact systems (using rigid and flexible endoscopes) have been developed to be used for many applications, both mechanical and biological, where measurements need to be performed at "hidden" surfaces or inside more or less closed objects. The quality of the results obtained by using mechanical objects is usually better, this can be easily explained by the fact that a biological surface is much more complex, in particular some parts reflects well the light and some other absorb it. Experimental results are presented.

The concept of an impulse response function (IRF) for interferometers - and especially for common-path mterferometers - will be introduced as a tool for depicting fringe appearance in ESPI systems based on the shearing effect-1.The impulse response function relates the measured phase change at an arbitrary position in the detector plane with a displacement in the object plane. Thus the TRY depicts the function of a specific filter placed in the Fourier plane ofthe common-path interferometer. A suite of filters will be introduced to show the specific way in which the filter will control the fringe interpretatio

Today, the vibration analysis of laminated structures represents an important field in engineering metrology. To perform non-invasive vibration measurements in industrial environments, optical methods are a preferable choice. Electronic Speckle Pattern Interferometry is a method, which permits full field and non-contacting displacement or deformation measurements. The experimental measurement of the resonant frequencies for the piezoceramic material is generally performed by impedance analysis. In this work, Electronic Speckle Pattern Interferometry (ESPI) technique is proposed for studying vibration of piezoceramic/nickel circular laminated plates. The circular membrane is a composite made of a nickel alloy disk with thickness 0. 1 mm and diameter 32 mm, to which a piezoceramic disk, with the same thickness and a smaller diameter (24 mm) is bonded. The time average frame subtraction technique is improved by subtracting two Bessel fringe patterns at two different amplitude levels. A brief analysis of the techniques and some preliminary experimental tests are presented.

Miniature semiconductor laser sources are used in holography for the tasks of 3-dimensional data acquisition and volumic display as well as for interferometric non-destructive diagnosis. Semiconductor lasers enable compact recording and display set-ups. Novel advanced holographic methods and compact devices fit very well for producing high quality optical replicas ofmasterpieces. Rapid holographic techniques and the use ofsemiconductor lasers permit to investigate the masterpieces at their constant locations without the need of transportation to a laboratory. Multiple examples with photographs from holograms and holographic interferograms are given in this work. Successive interferograms taken as snapshots during real time monitoring of artwork subjected to deformations are presented.

Laser Doppler vibrometers are widely used for noise analysis in research and development. Recently laser vibrometer have started to emerge as an important element for inspection and quality control in manufacturing processes. In this paper we present three different applications for non-intrusive inspection of automotive components in a rough production environment The first application is the detection of cracks. Cracks in materials usually result in a change of resonance frequencies and damping . Althoughthe environmental noise on the production floor is very high, it is shown in this paper how to extract the relevant parameters for quality control using impulse excitation and analysis of the acoustic-related vibration response. Another application is the test of a bulb filament commonly used in headlights. By combining a suitable excitation of the bulb with vibro-acoustic signal processing and appropriate classification, bulbs could be detected and removed from the production line that would otherwise have failed prematurely. Small electric motors with gears are common components in automobiles. The vibration signals that are produced when they are activated are measured with a laser vibrometer. Statistical tools are then used to analyse and classify these parts. Motors with defects and unacceptable noise contributions can be extracted. It can be shown that the result has a very high correlation with subjective human response.

This paper presents a comparative study between accelerometer and laser vibrometer measurements aimed at on-line quality control carried out on universal motors of washing machines, which exhibit defects localized mainly in the bearings. The test is designed so to study measurement problems of an on-line station. Bearing defects include faults in the cage, in the rolling element and in the outer and inner ring. A set of no defective and defective motors were analyzed by means of the acceleration signal provided by the accelerometer, and the displacement and velocity signals given by a single point laser vibrometer. Advantages and disadvantages of both absolute and relative sensors and of contact and non-contact instrumentation will be exposed taking into account the applicability in real on line quality control measurements and bringing to evidence the related measurement problems due to the specific environmental conditions of assembly lines and sensor installation constraints.

The combination of ultrasonics with optics has led to the development of emergent technologies for nondestructive testing with outstanding capabilities. In this work we describe a combination that, in our knowledge, was up to now unexplored, directed to the detection of cracks and other types of flaws in metallic plates of medium thickness (several millimeters). We selected a special kind of surface acoustic waves, i.e. Lamb waves, to explore the volume of the plates in the search for flaws, while a whole field interferometric technique, namely double-pulse TV holography, is employed to generate a map of the surface displacements in which the signature of the defects can be seen as a perturbation of the initially smooth wavefronts. Several examples of detection of artificially generated flaws are presented.

Basic and applied research in resonance conditions of structures is now an acquired design procedure providing highly reliable results. However, further research is needed on mathematical models to simulate actual operating conditions and define change mode parameter patterns in relation to external conditions such as temperature. The test procedure described here under is designed to aid in the development of such models. A significant number of spark plug specimens are used to review the mechanism of change in spark plug electrode natural frequencies as a function of operating temperature. Spark plug ground electrode resonance frequency and damping may be a critical parameter for the conect operation of the engine. In particularly in the laboratory of Prototipo S.p.A. has been tested, for statistical approach, eight different types of spark plugs, researching the resonance in fixed temperature range (from 6500Cto 8500 C). For the purposes of verify the influence of the temperature on the damping we used other eight different type of spark plug for the two conditions: 750 ° C and 20 °C.

One of the primary methods for analyzing roof stability in underground mines is the age-old method of "roof sounding" where a miner taps on the roofand listens for the hollow sound of loose blocks of rock. This paper looks at the feasibility of using noncontact laser-based vibration measurements to detect roof fall hazards with the ultimate vision of improving, expanding and automating procedures for mine roof inspection. Vibration measurements made on loose blocks of rock in underground mines are summarized and compared to estimates of fundamental resonance frequencies for rock slabs of the size responsible for highly hazardous "skin failures." Both laser Doppler vibrometry and full-field interferometric methods are examined and are considered to be feasible methods for detecting anomalous vibrations in loose roofrocks. Results from simple laboratory experiments using laser vibrometry demonstrate some of the proposed application concepts. While considered a challenge to move these techniques from the laboratory to heavy industrial or outdoor environments, the potential for success in the current application is enhanced by the reduced requirements of qualitative analyses.

A paper presents the original methodology for laser-based profilometry suitable for board spectrum of industrial applications. Based on simple hardware and software its advantages over existing profilers are numerous and include the exclusion of frame grabbers, strong processors, large memory requirements, high communication speed, mechanical parts, and complex computation algorithms. Also, some practical examples of its implementation are presented.

The typical means of time-frequency analysis (TFA) and the system the authors have developed recently are introduced in this paper. The TFA system has powerful functions such as short time Fourier transform (STFT), Wigner distribution (WD), wavelet transform (WT) and multi-resolution time-frequency analysis (MRTFA). This paper introduces the theory of main functions and the design of the TFA system. Practical application indicated that MRTFA proposed by the authors is more advantageous in analyzing the signal with small or large scale components than other typical means of TFA.

The statistical properties ofphotodetector current in laser Doppler velocimeter are studied. The analysis of zero crossing counting shows that it overestimates by certain amount velocity and displacement measurements. The dispersion of zero counts in the presence of additive shot noise is also studied. The simple analytical expression for dispersion of zero counts is obtained in absence of additive shot noise. It shows that the relative accuracy of velocity or displacement measurement is inversely proportional to the square root ofmeasured distance. The relative dispersion ofzero counts less than 0.005 % can be achieved while measuring 5 mdisplacement if certain requirements concerning signal-to-noise ratio are met.

This paper presents robust methods for filtering the optoelectronic current generated by laser signals in case of vibration measurements. First is presented a general procedure for obtaining signals corresponding to certain spatial vibrations by using diffracting grating. The diffracting grating is attached to the body supposed to present vibrations, and a set of four photodetectors is placed in the measuring area in symmetrical positions as related to a point of maximum intensity for the received light. The photoelectric current generated by this set is further filtered and processed, so as three electronic signals corresponding to displacements of the body along all three rectangular spatial coordinates axes to be obtained. Then is presented a method for determining the derivative of the spatial coordinates of the body as related to tune, in conditions of low-amplitude vibrations overlapped to a general translation ofthe body along a certain direction, under the influence of an external force. It is shown that such a structure is suitable for controlling the position of material bodies, due to the fact that the derivative of the position as related to time represents the acceleration of the body (proportional to the external force acting upon it).

In this paper, we present a phase error correction algorithm for passive phase demodulation in Michelson interferometers. The key feature of the passive demodulation scheme is the incorporation of a grating (Ronchi) filter placed in front of optical detector. The filter is split into four quadrants and each of the quadrants imposes a 900phase shift. This quadrature feature offers single-step detection of phase information from the interference fringes, which are created by the superposition of the object and reference light beams. Our signal processing scheme incorporates first a diagonal subtraction, then followed by appropriate filtering and root mean square. In addition, this scheme can remove spurious intensity fluctuations induced by microphonics and unstable light source. An experimental setup has been constructed for demonstrating the operation ofthe proposed scheme. Simulation ofpossible errors due to grating misalignment and the effects on signal recovery will also be presented.

This paper outlines a newly developed laser interferometer for calibration of vibration and acceleration pick-ups at the National Metrology Institute of Japan. The developed laser interferometer is a homodyne, phase shifted Michelson type which has quadrature outputs. This interferometer satisfies the requirement for the sin-approximation method for vibration and acceleration pick-up calibration described in the international standard (ISO 16063-11"Methods for the calibration of vibration and shock pick-ups. Part 1 1 : Primary vibration calibration by laser interferometry"). In this report, the requested performances of the laser interferometer under ISO 16063-11 are discussed. Design concepts of the optical and electric parts to achieve those performances are described. The scope and the features of the developed laser interferometer are also verified and discussed. The developed laser interferometer can be applied for vibration calibration up to 1 m/s in velocity, in both amplitude and phase shift evaluation. The interferometer is currently used for the national standard of vibration and acceleration pick-up calibration system.

An implementation ofthe sine-approximation method of ISO 16063-11 is described. The quadrature interference signals are generated using an interferometer as described in method 3 of ISO 16063-11. The signal processing required for the successful implementation of this method of ISO 16063-1 1 has been implemented by various Metrology Institutes using various techniques. For the implementation of these techniques, different hardware and software configurations are used, ranging from expensive VAX computer systems to digital storage oscilloscopes. A novel, cost effective, fully PC based system has been developed and is described here-in. The hardware consists of a Pentium 200 with 256 MB of RAM. A commercial, 4 channel AtoD card is used for performing the data capturing, while the signal processing software was developed to run under Microsoft Windows®.

Recent developments in the field of digital signal processing (DSP) hardware and affordable powerful PC platforms enable the realisation of a new generation of laser-Doppler vibrometers, providing outstanding measurement accuracy and resolution. The paper presents both PC based and DSP based solutions for digital Doppler signal processing, utilized within the latest vibrometer models introduced by Polytec GmbH, Waldbroim. It is shown, that heterodyne interferometer technology in combination with high-speed AID conversion and numerical demodulation methods provides superior accuracy and resolution in a wide amplitude and frequency range. Depending on the particular application, either PC based systems or plug-in DSP decoder modules are the preferred solution. Advantages and tradeoffs of both ways are analysed. In addition to digital decoding technology, the presented systems make use of digital signal transmission via a standard S/P-DIF interface, commonly known from digital-audio equipment. This interface allows distortion-free signal recording on digital media and signal acquisition without expensive A/D boards. Based on the described technology, a primary calibration system for accelerometers has been developed in a cooperation project. The aim of this paper is the demonstration of digital signal processing as a powerful alternative to analog technology, that will advance measurement accuracy of future laser-Doppler vibrometers.

Primary vibration calibration according to ISO 16063 can be carried out in several ways using different methods. Because of the wide frequency range and the possibility to calibrate sensitivity magnitude and phase, method 3 of part 21 of the international standard is mostly used in practice. Several requirements for components, system integration and control ofthe system must be met to achieve the goals ofthe standard and obtain low uncertainties in measurement and calibration. Illustrated by the CS18P primary calibration system of SPEKTRA, the main requirements, special problems and well-investigated solutions will be discussed. It will be shown that the all-digital vibrometer of Polytec plays an important part but, in addition to that, system integration and optimization of all components must be implemented with great care by calibration specialists. Our paper comes to the conclusion that, for primary calibration, high quality components alone will not be enough. It is necessary to integrate these components in an optimized system that takes into consideration all requirements and influences and so allows to reduce the uncertainties ofthe calibration procedure to the lowest possible values.

Laser pistonphone for absolute microphone calibration in low frequency range has been realized at UME. According to the operation principle of pistonphone, the motion of a piston, which is driven electro-mechanically in a closed acoustical coupler, produces a sound pressure. Accurate measurements of the piston displacement by laser interferometry enable accurate determination of the sound pressure and, as a result, the pressure sensitivity of the microphone exposed to the sound pressure inside the coupler. Homodyne Michelson interferometer with He-Ne laser was used for displacement measurements. Since the pistonphone is operating at low frequencies, the fringe-counting method was used for the signal processing. Calibrations of LS1P microphones with the uncertainty less that 0. 15 dB have been performed using laser pistonphone. Other possible metrological applications of laser pistonphone are also described in the paper.

National Metrology Institutes (NMIs) worldwide make use of laser interferometry in compliance with the new International Standard ISO 16063-1 1 : 1999 to realize and disseminate the unit and the associated scale of the physical quantity of acceleration. By convention, the dissemination has up to now been carried out by primary vibration calibration of reference standard accelerometers as are used in accredited calibration laboratories to calibrate working standards by comparison. The calibration and measurement capabilities (CMCs) of the NMIs are published in the BIPM Key Comparison Database, Appendix C (cf. http://www.bipm.org, 2001). Recently, special commercial laser vibrometers have been developed which comply with the ISO standard and, consequently, may be applied as reference standards at any level of the traceability chain provided they are traced back to appropriate national standards and are provided with adequate uncertainty budgets. Though it may be expected that all calibration laboratories (NMIs included) establish uncertainty budgets in compliance with the ISO Guide to the Expression of Uncertainty in Measurement (GUM), the accuracy attained can be reliably assessed only by appropriate comparison measurements. A general account is given of the state of the art in vibration measurements and transducer calibration using laser interferometry, focusing on comparison results which have confirmed the lowest measurement uncertainty achieved so far. Results of vibration measurements and calibrations obtained by different interferometric methods will be presented. An analysis of international and regional comparison measurements (accelerometer calibrations) will be reported on.

In this work a system for static and dynamic calibration of in-fibre Bragg grating sensors (FBG), is described. Our idea starts from the calibration procedure of strain gauges that is done by applying a pure bending on the sample. The aim of this work is to develop a system that allows as to apply an analogous experimental technique. In this case we use as reference a Laser Vibrometer, and therefore to the sample a dynamic excitation by an electrodynamic actuator. The test bench is used to apply a sinusoidal force in a symmetrical way in order to obtain an alternate pure bending in the area where the sensor is glued on the structure. The greatest excitation frequency, limited by the characteristics of FBG interrogation system, is about 20 Hz.

At Turkish National Metrology Institute (UME), linear acceleration unit has been realized based on laser interferometry with different signal processing techniques. Absolute calibrations of reference accelerometers are performed by using fringe-counting and minimum point method in the frequency range from 20 to 10000 Hz. Dissemination of the linear acceleration unit to the secondary levels is carried out through a comparison calibration of vibration pick-ups by "backto- back" method. Traceability chain for calibrations of the vibration calibrations and measurements performed at UME has been described in this paper.

Three methods of using an LDV to measure the vibration of a bladed disc in a rotating rig are described. I.e. (i) the response of one blade is monitored continuously by diverting the laser beam via a small mirror on the rotating disc, and a fixed, annular, conical mirror. Any of the blades may be targeted, by indexing the rotating mirror. (ii) circular scans give circumferential response mode shapes directly, or (iii) via spectra, as nodal diameter coefficients. Some natural modes of blisks (integral bladed discs) occur in isolated pairs, with amplitude distributions which are sinusoidal around a circular scan line. The natural frequencies increase with the number of sinusoids around the circumference, asymptotically to the cantilever blade frequency. Forced vibration of these modes, in a rotating situation, produces various combinations of standing and rotating waves. With a mistuned blisk, the close modes couple to create natural mode shapes which are very irregular. Excitation frequencies are at multiples of rotation speed, exciting modes with equivalent numbers of nodal diameters, sometimes aliased with the number of blisk blades. The LDV techniques described can cover all these effects, and some example measurements are included to illustrate their potential.

Recent work set out a comprehensive analysis of the velocity sensed by a single laser Doppler vibrometer beam incident in an arbitrary direction on a target that is of substantial interest in engineering — a rotating shaft requiring three translational and three rotational co-ordinates to describe its vibratory motion fully. Six separate "vibration sets", each a combination of motion parameters, appeared in the full expression for vibration velocity sensitivity and the difficulties associated with resolving individual vibration components within a complex motion were highlighted. The velocity sensitivity model can incorporate time dependent beam orientation and this is described in this paper with reference to scanning laser Doppler vibrometry. Continuously scanning strategies, in which the laser beam orientation is a continuous function of time, have recently received considerable attention, including a tracking profile in which the probe laser beam remains fixed on a single point on a target such as a rotating disc. Typically, one beam deflection mirror is driven using a cosine function whilst the other is driven with a sine function, resulting in a slightly elliptical beam trajectory. This and other more significant issues such as the effects of misalignment are easily accommodated in the velocity sensitivity model and a thorough analysis of their influence on the measured vibration signal is reported in this paper.

This work deals with valve motion measurements on cylinder heads of Ducati racing motorbikes, by means of high speed laser Doppler vibrometer. The experimental apparatus is described and some measurement results are presented. The results confirm that the effects of the dynamic phenomena are very important, especially at high speeds, and that the dynamic response gets worse with the increment of backlashes in the cam kinematic pairs. In addition, the measurements make it possible to analyse the valve bumping phenomena. The information retrieved from measurements provides insight into the cam system dynamics and helps the development of elastodynamic predictive models.

A new method of order tracking of rotating machinery based on instantaneous frequency estimation (IFE) is proposed in this paper. Compared with traditional methods of order tracking, this method has some outstanding advantages, such as hardware simplified, which is required by order analysis, and only software depended for order tracking. The simulations and actual tests testify the validity of the method. The algorithms of the tracking and estimation about the instantaneous speed of reference shaft are programmed. This method is an effective supplement to traditional order tracking methods and specially satisfies the requirement of Virtual Instruments (VI).

We present a new type of laser vibrometer based on the self—mixing interference effect in a laser diode. The self—mixing configuration allows for a practical set—up that is by far simpler than conventional laser vibrometer schemes and can be assembled at a low cost. The vibrometer principle relies on locking of the interferometer to half interferometric fringe, and on active phase—nulling technique by wavelength modulation, that permits to achieve an extended dynamic range still retaining a sensitivity in the sub—nm range. A prototype of the vibrometer has been designed and assembled, and it can operate on nearly all rough surfaces. The vibrometer noise floor is 100 pm/?Hz, the maximum measurable vibration amplitude is 600 ?m peak—to—peak, and the instrument covers the 0. 1 Hz—70 kHz frequency range of vibration. The self—mixing vibrometer can find application in modal analysis and noise and vibration measurements in industrial and scientific environments.

Our aim while developing a sensor exploiting spectral properties of optically disturbed laser diodes, was to introduce an alternative to already existing speed sensors. Production over assembly lines and other industrial applications can require contactless measurement of moving targets' velocity. Optical interferometry is already a possibility, but a sensor using Self-Mixing interferometry in a laser diode for industrial application can be an innovative solution. Optical feedback interferometry based sensors (with single laser diode or double laser diode architecture) propose low-cost and self-alignment. This paper presents two different architectures, the first one to validate theory and the other one to filter some perturbations we identified from the first set-up.

Laser Doppler velocimetry uses the Doppler shift of light scattered from moving particles. In self-mixing laser Doppler velocimetry some of the scattered light is allowed to re-enter the laser cavity and here it is mixed with the originally generated cavity mode. This interference results in a fluctuation of the laser intensity with a frequency equal to the Doppler shift (self-mixing interference or back-scattered modulation), according to ?f=2nv(cos?? )/?. Here ?f , n , v, ? and ? stand for the Doppler frequency shift, the refractive index of the medium, the velocity of the scatterer, the angle between the velocity vector and the optical symmetry axis, and the wavelength of the laser light in vacuum. The laser Doppler self-mixing velocimeter has been statically calibrated, using a rotating disk covered with white paper. Authors report about the Doppler signal amplitude of the velocimeter as function of the characteristics and colour of the target surface. Dependence of the Doppler peak amplitude from the target distance and the angle between target and optical axis of the sensor are also reported. Results regarding dynamic characteristics of the sensor are reported and it is shown its capability to be used as a laser Doppler vibrometer.

The research results of autodyne signal formed under reflection of semiconductor laser radiation from vibration reflector have been presented. The influence of feedback coefficient and distance to vibration object on autodyne signal form has been shown. The method of reverse problem solution in autodyne interferometry of nonharmonical vibrations has been described. The suggested method allows to restore the amplitude and form of mechanical vibrations for autodyne system developed for interference system separated from the light source.

It has been shown in previous publications that it was possible to obtain from complex velocity maps obtained by optical measurements (Holography, LDV, etc. .) and wave number processing, useful quantities to study energy flows in structures: intensity, power flow, forces, localisation of sources and sinks of energy. In this paper, scanning laser vibrometer measurements on two-plate assembly are used to determine the dissipating power by the joints from these energetic quantities. The proposed method compute the average power flow over lines parallel to the junction to check a one dimensional model of power flow distribution along the other dimension. An approximate energy conservation law of flexural vibration which gives good results on beam structures is used to determine the dissipation characteristics of joints.

A new method for non-interactively measuring and visualising turbulences, e.g. vortexes, and acoustic sound waves in gases is described. The measuring effect is based on the path difference ?? between two interfering laser beams. This difference results from changes of the refractive index n, caused by pressure fluctuations p(t) in a measuring volume. The method is practicable in both the audio and the ultrasonic ranges, as well as for spatially small turbulences. It is adequate for the investigation and demonstration of numerous acoustic, fluidic and fluid-acoustic phenomena.

In this paper an experimental analysis of the energy transmission in vibrating structures is considered. The classical discretization techniques (FEM, BEM) fail when one tries to solve high-frequency dynamic problems. At present, SEA is the most acknowledged theory for providing such kind of solution, giving information on the stored mechanical energy and on the dissipated mechanical power between the modal subsystems. Aim of the present work is to study the vibrating behavior of three coupled plates and compare the SEA solution with the experimental results. The experimental test is performed suspending the system by soft springs to simulate free boundary conditions and exciting the plates by a white random noise. A grid of points is selected on the three plates. The energy values are obtained by measuring the velocity of the grid points by a laser vibrometer.

Electric guitars have received far less attention than acoustical/classical ones from research teams, mainly for the reason that they are essentially considered as mere electro-mechanical transducers and little attention has been paid to their vibrational behavior. However, every guitarist knows from his/her experience how important are typical vibrational parameters such as resonances, damping, construction materials but usually lack the technical knowledge to express it in scientific terms. Also lute-makers usually work only by experience and tacit knowledge and even big companies do not use scientific research to improve their instruments. Following a research line devoted to modem music instruments, in this article we will present some experimental results derived from a series of measurement sessions on two electric guitars, aimed at identifying typical resonance frequencies, modal shapes, and sound characteristics. Experimental set ups have been implemented trying to simulate as much as possible real life situations, in particular excitation has been obtained mainly by acoustical sources and a mechanical device resembling a plastic plectrum. Moreover, in order to better correlate vibrational results with musical properties of electric guitars and traditional making experience, examined guitars have been played in an anechoic chamber and acoustical signals acquired.

The experimental results of excitation of longitudinal surface acoustic waves (LSAW) in solid isotropic bodies by ruby laser pulse are presented. The dependence of generation efficiency from excitation deepness under surface of propagation was investigated. Experimental measurements confirmed that LSAWs of 1 .8 MHz frequency have maximum propagation energy in (1 .5 - 2)? deepness (where ? is wavelength in solid body). It was shown that using laser pulses we can generate with high efficiency LSAW from distance in solid bodies without special processing of their surfaces. The Poisson's ratio coefficient of bodies was 0.26