This PDF file contains the front matter associated with SPIE Proceedings Volume 7098, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Metrology as the art of careful measurement has been understood as uniform methodology for measurements in natural sciences, covering methods for the consistent assessment of experimental data and a corpus of rules regulating application in technology and in trade and industry. The knowledge, methods and tools available for precision measurements can be exploited for measurements at any level of uncertainty in any field of science and technology. A metrological approach to the preparation, execution and evaluation (including expression of uncertainty) of measurements of translational and rotational motion quantities using laser interferometer methods and techniques will be presented. The realization and dissemination of the SI units of motion quantities (vibration and shock) have been based on laser interferometer methods specified in international documentary standards. New and upgraded ISO standards are reviewed with respect to their suitability for ensuring traceable vibration measurements and calibrations in an extended frequency range of 0.4 Hz to higher than 100 kHz. Using adequate vibration exciters to generate sufficient displacement or velocity amplitudes, the upper frequency limits of the laser interferometer methods specified in ISO 16063-11 for frequencies ≤ 10 kHz can be expanded to 100 kHz and beyond. A comparison of different methods simultaneously used for vibration measurements at 100 kHz will be demonstrated. A statistical analysis of numerous experimental results proves the highest accuracy achievable currently in vibration measurements by specific laser methods, techniques and procedures (i.e. measurement uncertainty 0.05 % at frequencies ≤ 10 kHz, ≤ 1 % up to 100 kHz).

Laser techniques are commonly used to measure structural vibration responses with high spatial resolution over an extended area. Forced mode shapes will generally be similar to natural mode shapes and undamped mode shapes, if the damping is not too great nor the modal spacing too close. When this is not the case, the real components of forced mode shapes of close modes, and of the response at an off-resonant frequency, can be combined to reveal the corresponding natural mode shapes. These components are combined in proportions calculated to fit natural mode shape data extracted from frequency responses, measured at a relatively small number of suitable points within the scanned area. Procedures may be varied to suit different measurement techniques; continuous-scan LDV techniques offer the possibility of fitting to line-scan polynomial coefficients instead of the amplitudes at specific points thus reducing the time needed for the data acquisition. All the techniques promise considerable economies in test measurement timescales.

Conventional scanning laser Doppler vibrometer (LDV) systems cannot be effectively employed with impact excitation because they typically measure a structure's response at only one point at a time. This necessitates exciting the structure at multiple points to create a multi-input-single-output modal test data base, which is not only tedious, but prone to errors due to variations in the impact characteristics from one point to the next. Previous works have demonstrated that an LDV can be used to measure the mode shapes of a structure over a surface by scanning the laser spot continuously as the structure's response decays. The author recently presented a procedure that allows one to post-process continuous-scan LDV (CSLDV) measurements of the free decay of a structure using standard modal parameter identification techniques. Using this approach, one can find the natural frequencies, damping ratios and mode shapes of a structure at hundreds of points simultaneously from a few free responses. The procedure employs a novel resampling approach to transform the continuous-scan measurements into pseudo-frequency response functions, fits a complex mode model, and then accounts for the time delay between samples to obtain the mode shapes. This paper extends the previous work by presenting an algorithm that uses the input force spectrum, measured by an instrumented hammer, to mass normalize the mode shapes obtained using the continuous-scan LDV process. Other issues such as the effect of the scan frequency on the procedure and on speckle noise are also briefly addressed.

The reliance of the aerospace industry on finite element models during the design of new products requires the best possible models for the prediction of the dynamic behaviour. A major aim of current experimental research is to provide a more complete set of data from a single test in a reduced amount of time, so as to increase the overall efficiency of the Finite Element updating process. To this end, a new continuously-scanning laser Doppler vibrometery measurement technique for cylindrical structures was introduced recently which allows the measurement of the dynamic behaviour of a cylindrical structure with a so-far unachieved spatial resolution in a much shorter time than with conventional measurement techniques. The new measurement system consists of several distinct parts and, as a results, shows therefore a high sensitivity towards the measurement setup. To estimate the influence of each part of the setup on the measurement results, a simulation of the measurement system will be presented in this paper. The aim of the simulation is to gain a better understanding of the sensitivity of different components and parameters to the overall quality of the measurement data. The investigation uses a sensitivity analysis of the critical parameters to weight their influence on the accuracy of the measurement and provides a procedure, based on the modal assurance criterion (MAC), to optimize the alignment parameters for a specified accuracy of the system. The results of the analysis for an aero engine casing component highlight the strong influence of the alignment parameters on the overall measurement accuracy of the 'Lighthouse' system but also shows the high accuracy that can be achieved with such a measurement system.

The mathematical model of the velocity sensed by a laser beam incident in an arbitrary direction on a rotating target undergoing arbitrary vibration is now well established. The model combines a three-dimensional description of the velocity of the point of incidence on the target with knowledge of the orientation of the incident beam and any known point along the line of incidence of that laser beam. For scanning LDV, where the beam is deflected through the use of optical devices, recent work has introduced a general mathematical procedure for determination of the final beam orientation following successive reflections and refractions through an optical system. This paper describes this work, including how inevitable translational and angular misalignments can be incorporated and, for the first time, how Doppler shifts on transmission through or reflection from rotating / oscillating optical components can be calculated. Demonstration of the application of this procedure is seen in the proposal of a novel, scanning LDV arrangement in which rotating wedge prisms are used to track a rotating component. Preliminary experimental results are shown for this arrangement. The versatility of the mathematical procedure is shown by application to a tracking LDV arrangement using a rotating Dove Prism. The predictions show how angular and translational misalignments distort the desired scan path and how the whole body rotation of the target can result in measurement of small velocity components at integer multiples of the prism rotation frequency.

In the past decade, Continuous Scanning Laser Doppler Velocimetry (CSLDV) has been successfully used in experimental modal analysis and vibration tests. Essentially, this technique consists in the use of a Laser Scanning Velocimeter (LDV) moving continuously across a vibrating surface rather than stepping in a point-by- point fashion. If the structure is undergoing harmonic vibration, its Operating Deflection Shape (ODS) can be recovered in a very short time and without the limitations in spatial resolution typical of discrete point measurements. Recently, this technique has been extended to transient excitation -i.e. the object is swept by the laser transducer during a period of transient free response caused by an impact. The combination of a broadband excitation with a full-field measurement results in a highly complex signal, modulated both by the mode shapes of the structure and by the exponential decays due to damping effects. Thus, the signal contains in its spectrum a mixture of temporal information (the eigenvalues of the structure) and spatial information (the eigenvectors), all in a single time history. This paper presents a mathematical model of this new concept, first applied to a simple one-dimensional scan and then to a rectangular 2-D area scan. The numerically-simulated signals of the 1-D case are compared with actual measurements, both in time and frequency domains. Finally, an analysis of the measurement parameters involved in this method is provided.

The Blade Tip-Timing (BTT) method is largely used to measure vibrations of rotating turbomachinery bladed disks under operating conditions. Other measurement methods, for example strain gauges, might be intrusive, or unsuitable because of inadequate optical access such as is required by Scanning Laser Doppler Vibrometer (SLDV) systems which may be commonly used in laboratory-based rotating test rigs. This paper presents the use of BTT method for measuring out-of-plane vibrations of a rotating 24-bladed disk and the design of mechanical components to accommodate BTT probes. Examples of measured data, using both BTT and SLDV system, will be presented.

This article describes the development and application of a 16x16 array (matrix) laser vibrometer based on a parallel architecture which supports fast 2D measurement of arbitrary (steady state, non-steady state, transient) solid body vibrations without beam scanning. The small size and low weight of the measurement probe, which is linked to a remote detector/processor unit via a flexible armoured fibre-optic umbilical, enables deployment in areas with restricted access. Incorporating aspects of high-speed electronic speckle pattern interferometry (ESPI) and laser Doppler vibrometry (LDV), the design is based on a hybrid fiber-optic/bulk optic interferometer which operates at a wavelength of 1550 nm. Test data illustrate high-speed capture of transient vibrations, showing the full 2D temporal evolution of surface deformation, including multiple resonant modes, of a center-pinned metal plate excited by a 1-50 kHz frequency chirp of 109 ms duration. We discuss preliminary data showing detection of sub-surface defects in composite materials, based on non-contact (frequency chirped) acoustic resonance of the locally damaged structure. For large area NDT the probe can be mounted on a lightweight XY gantry for automated multi-frame measurements.

Several new applications for optical ultra-high frequency (UHF) measurements have been evolved during the last decade by advancements in ultra-sonic filters and actuators as well as by the progress in micro- and nanotechnology. These new applications require new testing methods. Laser-based, non-influencing optical testing is the best choice. In this paper we present a laser-Doppler vibrometer for vibration measurements at frequencies up to 1.2 GHz. The frequency-shifter in the heterodyne interferometer is a slow-shear-mode Bragg cell. The light source in the interferometer is a green DPSS (diode pumped solid state) laser. At this wavelength the highest possible frequency shift between zero and first diffraction order is a few MHz above 300 MHz for a slow shear-mode Bragg cell and, therefore, the highest possible bandwidth of the laser-Doppler vibrometer should usually be around 300 MHz. A new optical arrangement and a novel signal processing of the digitized photo-detector signal is employed to expand the bandwidth to 1.2 GHz. We describe the utilized techniques and present the characterization of the new ultra-high-frequency (UHF) vibrometer. An example measurement on a surface acoustic wave (SAW) resonator oscillating at 262 MHz is also demonstrated. The light-power of the measurement beam can be switched on rapidly by a trigger signal to avoid thermal influences on the sample.

The middle ear ossicles transmit sound from eardrum to inner ear under largely varying ambient pressure conditions. To protect the structures within the cochlea from excessive footplate incursions the configuration of the ossicles changes with pressure. Sequences of micro CT-scans were acquired from gerbil temporal bones under static ear canal pressures ranging from -450 to +450 daPa. These image stacks were used to track the 3D motion and deformations of the ossicles as a function of pressure using hyperelastic warping. Using the scans for zero pressure, accurate finite-element reference models were generated for each of the ossicles. With the difference between these template images and the target image data recorded in a deformed configuration as a driving force, the warping algorithm displaced and deformed the finite-element models of the ossicles in order to align the deformed template with the target data. Position changes of the ossicles within the middle ear cavity and deformation of the ossicles and the tympanic membrane were all measured in a same preparation. For each static pressure load a finite-element ossicular chain model is obtained in the run and can be used for further analysis under acoustic stimulation.

A novel system for using a single-point Laser Doppler vibrometer (LDV) to measure surface normal velocity components of non-planar targets has been developed. A description of this measurement system is presented, along with a discussion of results and relative merits compared with conventional scanning LDV systems. Data from sample measurements taken on an anti-tank landmine buried in sand are presented. It is shown that measurements of the same surface wave using this system and a conventional system can differ by as much as 75%.

The multichannel WDM (Wavelength Division Multiplexing) technique inspired the concept of vibration measurements for many points of a vibrating object. The N-independent WDM separated 15XX nm fibre coupled laser diodes (used for optical fibre telecommunication) form coherent system of sources for multipoint measurement of vibrations according to the rule one wavelength - one point. The scattered light from the object coupled into the fibre, filtered coherently, after special signal processing, allows analysing amplitudes and phases of many vibrating points in real time. Some experiments and results of such system will be demonstrated.

A new capability of TV holography, also known as electronic speckle pattern interferometry (ESPI), is presented for locating and imaging slightly thinned or thickened areas in metallic plates. It is based on the measurement of the wavenumber variation of narrowband Lamb waves as they propagate through these plate-thickness inhomogeneities. The relation between frequency and phase velocity of all Lamb modes depends on the elastic constants of the material the plate is made of (two parameters in isotropic materials) and on the plate thickness. Therefore, the associated dispersion curve of each mode present wavenumber changes that are sensitive to a thickness reduction. We have formerly developed a double-pulsed TV holography system which allows the full-field measurement of the instantaneous out-of-plane displacement field induced by surface acoustic waves and, by further processing, to calculate maps of the acoustic amplitude and phase. A method based on further analysis of the acoustic complex-displacement map is therefore proposed to locate and characterize such smooth thickness reductions. In particular, we calculate a map of the local wavenumber of the acoustic wave as the modulus of the two-dimensional gradient of the mechanical phase. Hence, as the variations in the wavenumber correspond to variations in the plate thickness, the local thickness reductions and increments can be detected in this map. Within the resolution limits imposed by the wavelength of the Lamb wave, this method allows also to contour the shape of the inhomogeneities. The technique is demonstrated herein by imaging a X-shaped recess machined on an aluminium plate.

The paper describes a hybrid technique, aimed at nondestructive inspection of materials, that combines whole-field optic measurements, acoustic excitation and a numerical reconstruction method. The interior of a thick specimen is probed by short bursts of narrowband ultrasonic bulk waves. The acoustic wavefronts that constitute the burst emerge at the opposite face of the sample and induce periodic displacements of its surface. These displacements are measured by TV holography, a whole-field optical technique, also known as electronic speckle pattern interferometry (ESPI). The measurement process yields the complex amplitude (i.e., amplitude and phase) of the acoustic wavefronts at the plane of the surface as a series of 2-D, complex-valued maps. Lastly, a numerical reconstruction algorithm that uses the Rayleigh-Sommerfeld diffraction formula is employed to calculate the amplitude and phase of the acoustic wavefronts at any other plane in the interior of the specimen. This procedure is analogous to the numerical reconstruction of optical object wavefronts in digital holography (with light and free space taking the place of acoustic waves and the material medium, respectively), so the present method could also be designated as digital opto-acoustic holography. If the wavefronts are affected by the presence of inhomogeneities in the medium, information about the shape and position of such defects could be retrieved from the reconstructed wavefront at the appropriate depth. The technique herein proposed was successfully tested in an alluminium specimen with an artificial defect.

This paper discusses some of the relevant aspects that a designer of an on-line test station for washing machine diagnostics based on a single-point laser Doppler vibrometer should consider. In particular, the paper presents a series of experiments useful to answer the two following questions: a) Where to locate the measurement point? b) Does the test need to be done with an external load to be inserted into the rotating drum? Tests have been done on a "good" washing machine and on a machine exhibiting the most frequent defects to be detected in production line. The study of the Operating Deflection Shapes (ODS) of the machine has been used to determine the best area of the machine cabinet where to position the single point laser vibrometer for on-line diagnostics. In order to support the decision whether or not to employ an artificial unbalance load inserted into the drum during the dynamic test, measurements have been repeated with and without load. Results have been analysed to highlight pros and cons of the use of an external load.

Techniques based on holographic interferometry have achieved a mature state of non destructive testing applications in industry and nowadays they are rising as interesting and promising tools in the field of conservation practices; giving information about the condition of structural integration of artworks. In the practice of these techniques it is necessary to generate a relative deformation in the object under study. Depending of the characteristics of the artwork, different methods may be used to achieve the desired displacement; being thermal excitation by means of filament lamps and wave sounds generated by speakers the most common. By applying these methods the deformation process usually involves a large area of the object, which limits the information obtained of a finite region. However, the use of a wave sound emitter of small dimensions, like a low power monotone buzzer, allows to decrease the affected area and to obtain information about the structural integrity of localized points of the surface. In the present study conventional double exposure double way holographic technique based on holographic films was used to obtain an out of plain deformation pattern caused by a sound emitter in an oil painting which has suffered heavy structural damage. Optimization of the excitation sound wave characteristics (frequency and amplitude) and the adjustment and calibration of the experimental set up, in order to obtain precise information about the physical and mechanical integrity of localized points of the painting are reported.

The paper presents the results of modal analysis of four-storey building. In the tests, the structure was excited to vibrate by means of a modal hammer designed for large objects. To excite the whole structure, multiple-point excitation was applied. The parameters of vibration resulting in consequence of this excitation were measured both by piezoelectric accelerometers and a scanning laser vibrometer. Comparison with the results of in-operation modal analysis, in case when the building was excited by rocket engines, was also performed.

We describe a novel instrument for the remote measurement of dynamic deflection shapes of structures several tens of meters long, based on geometrical optics techniques with scanned laser illumination, which we have named Scanner of Dynamic Deflections (SCADD). A set of aligned control points is measured in each scan, each point being defined by a retroreflector attached to the structure. By measuring the delay of the optical signal reflected from each point, the system renders a component of the displacement of that point which is transverse to the illumination direction. The intended application of SCADD is the field data acquisition for diagnosing the structural health of civil infrastructures, either as a stand-alone instrument or integrated in a non-destructive structure testing system comprising several data sources, typically an array of accelerometers and a SCADD unit. The foreseen measurement accuracy and the spatial and temporal sampling density of SCADD are adequate to the application of modal analysis techniques. For the purpose of locating our proposal in its technological context, we include firstly a brief description of the most usual methods (optical and non-optical) for the field measurement of vibrations of civil structures. Then, the SCADD principle of measurement and architecture are detailed. In the experimental section we describe a SCADD prototype and a series of measurements of a control point located 18 m away from the SCADD head, from which we extract the repeatability and a calibration curve of the prototype. Finally, the main advantages of SCADD are detailed.

In this work we present an application of TV holography to the generation of movies showing the propagation of acoustic guided waves in aluminium plates. Each movie shows a wavetrain whose envelope (i.e., the acoustic amplitude) and carrier wave move at the group and phase velocities, respectively. In particular, we use the S0 Lamb mode and the Rayleigh wave to illustrate the behaviour of dispersive and non-dispersive waves. Both wavetrains were generated by means of the classical wedge method and detected with our double-pulsed TV holography system, which renders 2D maps of the instantaneous out-of-plane displacement fields of the plate surface. The snapshots of the movie are obtained from a set of these 2D measurements, taken under repeatability conditions by successively increasing the delay between generation and detection. Then, a processing based on the 3D-FFT is applied to the set; the result is a new set of complex maps that permits to characterize the evolution of the positions of the envelope centre and of a point with a given value of the phase, so that it is possible to compare the phase and group velocities of the wavetrain.

Electronic speckle pattern interferometry (ESPI) is a full-field measurement technique, capable of displaying vibrational mode shapes. A simple optical set-up for an ESPI system using a holographic optical element (HOE) is presented. The HOE is designed to create a speckled reference beam in the interferometer. A partially reflective glass plate provides illumination of the object along the normal to its surface, ensuring that the system is sensitive only to out-of-plane displacement of the object. It is demonstrated that the HOE-based system can be used for vibration measurements. Phase shifting can be implemented for fringe analysis. A big advantage of the system is its simplicity. It requires a small number of components: a coherent light source, a holographic optical element, a glass plate and a CCD camera. Introducing holographic optical elements in ESPI gives the advantage of large aperture optical elements at relatively low cost.

We present our investigation on the separation of mechanical vibrations from rigid body displacements. Pairs of digital holograms acquired between two consecutive time intervals from this type of events produce phase maps that contain both the vibration and rigid body motion information, or even further fully decorrelated phase maps after computer processing. In order to compensate for body displacements, a conjugate object-image experimental arrangement for digital holography is used to measure the mechanical vibrations in a rectangular flat plate. This is achieved by including an extra lens with variable focal length adjustments in front of the typical lens-aperture combination used in the optical head of a digital holographic set up. Out of plane data is obtained from a framed metal plate subjected to a known modal vibration that is also allowed to move perpendicularly to its surface. We will demonstrate that due to the power adjustment of the added lens the angular phase change in the digital hologram from the known object motion allows the separation of the vibration mode at the image plane. The proposed lens addition into a new optical head arrangement in digital holography combined with an a priori knowledge of the rigid body displacement is able to accurately separate the mechanical vibrations making it a promising method in experiments performed under noisy environments. This research suggests the inclusion of adaptive lenses to control the effective focal length when there is a need to separate two distinctive motion types, i.e., vibration from rigid body motion.

An important area of application of holographic optical elements (HOEs) is in optical and electronic speckle pattern interferometry. The design, fabrication and characterization of holographic optical elements (HOEs) for electronic speckle pattern interferometry are presented. Reflection HOEs (RHOEs) were fabricated for use in electronic speckle pattern interferometers (ESPI) and laser Doppler vibrometers (LDV). The HOE-based interferometer is sensitive to out-of-plane displacements only. The results obtained are promising for future applications of the system for modal analysis.

Some optical features of electronic speckle pattern interferometer has been considered in this paper. Optical software was used for this aim. Resolution of objective and camera chip were considered. Modulation transfer function as one of most important characteristics was considered as a tool for that end.

Ultrasonic dental scalers are clinically used to remove deposits from tooth surfaces. A metal probe, oscillating at ultrasonic frequencies, is used to chip away deposits from the teeth. To reduce frictional heating, water flows over the operated probe in which a bi-product, cavitation, may be generated. The aim of this study is characterise probe oscillations using scanning laser vibrometry and to relate the recorded data to the occurrence of cavitation that is mapped in the course of this research. Scanning laser vibrometry (Polytec models 300-F/S and 400-3D) was used to measure the movement of various designs of operating probes and to locate vibration nodes / anti-nodes at different generator power settings and contact loads (100g and 200g). Cavitation mapping was performed by photographing the emission from a luminol solution with a digital camera (Artemis ICX285). The scaler design influences the number and location of vibration node / anti-node points. For all ultrasonic probes, the highest displacement amplitude values were recorded at the tip. The highest amounts of cavitation around the probes were recorded at the second anti-node measured from the tip. Broad, beaver-tale shaped probes produced more cavitation than slim shaped ones. The design also influences the amount of inertial cavitation around the operated instrument. The clinical relevance is that broad, beaver-tale shaped probes are unlikely to reach subgingival areas of the tooth. Further research is required to design probes that will be clinically superior to cleaning this area of the tooth.

Recently, a measurement set-up was presented to detect small nonlinear distortions in the vibration of acoustically driven mechanical systems. A speaker generates a specially designed multisine excitation signal that drives the vibration of a test object. The generated sound pressure is measured with a probe microphone in front of the test object, and an heterodyne vibrometer measures the corresponding vibration. Due to the high degree of linearity of the heterodyne technique, very small nonlinear distortions can be detected. In this paper the set-up is used to verify whether small nonlinear distortions are present in the vibration of the middle ear system, which is classically considered to be a completely linear system. In vitro measurements on the right ear of an adult male gerbil proved that nonlinear distortions are present in the vibration of the tympanic membrane. Similar results were seen in measurements on the left ear. The influence of post-mortem changes on the nonlinear behaviour of the middle ear was verified in a number of successive measurements. These indicated that the nonlinear behaviour of the middle ear decreases in time.

In this paper we report experimental data obtained using a novel, non contact and unified approach for the monitoring of some important vital parameters: Heart Rate, Heart Rate Variability, Respiration Rate, Filling Time, Pulse Transit Time. The measurement approach - named optical vibrocardiography (VCG) - has been recently described by some of the authors for what concerns the assessment of a single parameter or measurement and technical aspects. Here, we discuss the experimental setup realized to operate optical VCG in order to measure the previously cited vital parameters. We present two novel configurations for the assessment of the respiration rate and the pulse transit time. The quantities measured by optical VCG have been compared with the ones measured with golden standard instrumentations; the comparison reference instruments has shown differences with no statistical and clinical significance. Optical VCG therefore can be considered a valid, fully non-contact measurement method for the assessment of vital signs, with the additional advantage that such parameters can be assessed using one single instrument instead of a set of dedicated devices.

The interaction of Ultrasound waves with bone material has always been of great interest for the scientific community. This is due to the fact that ultrasonic waves are non-ionizing, cheap, and easy to generate and to detect. The use of multi-input interleaved multisine offers new applications for ultrasonic testing in bone specimens, where identification of material properties by means of ultrasound pulses often suffers from poor S/N ratio. The research reported here, describes a novel application a of scanning Laser Doppler Vibrometer (LDV) to the analysis of bone specimens by means of underwater visualization of multisines acoustic fields. The results demonstrate that this new non-invasive acoustic measurement technique can successfully visualize and measure reflected acoustic fields, as well as diffraction effects.

Scanning laser Doppler vibrometer measurements are characterized by a high spatial resolution and the fact that the structure is measured (or scanned) point by point. These measurements can be processed with the exciting generic modal parameter estimators. However, more accurate modal parameter estimates can be obtained by exploiting the spatial "smoothness" of high spatial-resolution measurements. To do so, the mode shape will be represented by a generalized parametric Fourier-based model. In this contribution, this generalized parametric Fourier-based mode-shape smoother will be integrated inside the modal parameter estimation procedure resulting in a fully (spatial as well as temporal) parameterized modal model.

This paper presents a comprehensive study between accelerometer, laser vibrometer and microflown probe measurements aimed at comparison of modal model quality assessment. Object of an investigation was a large composite fuselage panel. An extensive test campaign was performed with application of SIMO, MIMO, random and harmonic excitation, velocity and acceleration sensors, contact and non-contact measurement techniques. Advantages and disadvantages of applied instrumentation are discussed taking into account test data variability and the trade-off between workload and test data quality. Presented are real-life measurement problems related to the specific set up conditions. Finally a statistical analysis of estimated models is evaluated to bring to light general assessment of test campaign. Such assessment has a vital importance of successful fault detection based on modal parameters observation as well as in uncertain non-deterministic numerical model updating.

With the development of optical measurement techniques it is possible to obtain vast amounts of data. In vibrometry applications in particular operational deflection shapes are often obtained with very high spatial resolution. Fortunately, many techniques exist to reduce (approximate) the measurement data. One of the most common techniques for evaluating optical measurement data is by means of a Fourier analysis. However, this technique suffers from what is known as leakage when a non-integer number of periods is considered. This gives rise to non-negligible errors, which will obviously hamper the accuracy of the synthesized shape. Another technique such as a Discrete Cosine Transform, used in the widely spread -jpeg standard does not suffer these anomalies but can still prove erroneous at times. One of the more recent approaches is via a so-called Regressive Discrete Fourier Series (introduced by Arruda) which suffers one disadvantage. The problem statement is non-linear in the parameters and needs a priori information about the deflection shape. This can be resolved by using the Optimized Regressive Discrete Fourier Series (ORDFS), introduced in this article, which uses a non-linear least squares approach. In this article the method will be applied in particular to the reduction of data for laser vibrometer measurements performed on an Inorganic Phosphate Cement (IPC) beam (1D), as well as on a car door (2D). The proposed technique will also be validated on simulations to illustrate the properties concerning compression ration and synthesized mode shape error. The introduced method will be bench marked for compression ratio and synthesized deflection shape error with all prior mentioned techniques as well as to the more novel generalized regressive discrete Fourier series (GRDFS).

The focus of this paper is to disclose sources of measurement error in laser Doppler vibrometers (LDV) and to suggest specifications, suitable to describe their impact on measurement uncertainty. Measurement errors may be caused by both the optics and electronics sections of an LDV, caused by non-ideal measurement conditions or imperfect technical realisation. While the contribution of the optics part can be neglected in most cases, the subsequent signal processing chain may cause significant errors. Measurement error due to non-ideal behaviour of the interferometer has been observed mainly at very low vibration amplitudes and depending on the optical arrangement. The paper is organized as follows: Electronic signal processing blocks, beginning with the photo detector, are analyzed with respect to their contribution to measurement uncertainty. A set of specifications is suggested, adopting vocabulary and definitions known from traditional vibration measurement equipment. Finally a measurement setup is introduced, suitable for determination of most specifications utilizing standard electronic measurement equipment.

Optical interferometry for the absolute calibration of standard accelerometers is based on displacement amplitude measurements considering a uniaxial sinusoidal excitation movement at a given frequency. In reality, the movement generated by a shaker also contains components perpendicular to the oscillation axis, introducing a rocking motion effect. In the primary calibration of vibrations by laser interferometry, the rocking motion is a critical issue to be considered for high accuracy measurements. The knowledge of the impact of this effect in the performances of acceleration amplitude measurement is fundamental for the definition of a robust calibration approach. Generally, this effect increases with the excitation frequency and, beyond a certain threshold, its influence in the final result may become quite relevant. In this work, we study the influence of the rocking motion in the calibration of one accelerometer with two shaker models. The study comprises a nominal acceleration of 100 m.s^-2 for frequencies between 1 kHz and 9 kHz, considering a sinusoidal excitement. An interferometric system based on heterodyne detection was used for the high frequency regime. Measurements were performed for 12 incidence points equally spaced along the border of the surface of a dummy mass attached to the standard accelerometer, and the corresponding average was estimated, allowing the characterisation of the rocking motion effect and the estimation of the corresponding component in the expanded uncertainty budget.

Sinusoidal force calibration method based on electrodynamic shaker and interferometric system was studied several years before at Physikalisch-Technische Bundesanstalt (PTB). In that system a load mass are screwed on the top of force transducer, the sinusoidal forces realized by accelerated load masses are traceable to acceleration and mass according to the force definition F(t) = ma(t), where m is the total mass acting on the sensing element of the force transducer and a is the time and spatial-dependent acceleration of the mass, which is directly measured by a laser interferometer. This paper will introduce a new dynamic force calibration system developed at Changcheng Institute of Metrology and Measurement (CIMM). It uses electrodynamic shakers to generate dynamic force in the range from 1N to 20kN, and heterodyne laser interferometers are used for acceleration measurement. A new air bearing system is developed to increase the performance of shakers and an active vibration isolator is used to reduce enviromental disturbance to the interferometric system.

Primary angular acceleration calibration system is developed by Changcheng Institute of Metrology and Measurement (CIMM) to generate angular vibration and shock, which are traceable to the International System of Units (SI). It can be used to calibrate angular transducers, i.e. angular accelerometer, angular velocity transducer, and rotational angle transducer. Two kinds of system are used in the measurement of angular movement, one is based on circular grating and scanning heads, another is based on laser interferometer with diffraction grating. This paper introduce the comparison results of the two measurement systems in the measurement of angular movement under sinusoidal and shock excitation. The results of the investigations show a good accordance of the newly developed method of using grating and scanning heads measuring angular acceleration in comparison with the laser interferometer method.

Speckle patterns are produced when coherent light scatters from optically rough surfaces. In typical applications, a Laser Vibrometer collects a region of a speckle pattern on its photodetector. However, noise can be generated in the Laser Vibrometer output when surface motions cause changes in the speckle pattern. This paper uses high resolution images to investigate typical intensity profiles in the partially- and fully-developed speckle patterns scattered from target surfaces with roughnesses in the range 11nm to 1μm Ra (≈1/60λ to 1.6λ) and from a surface treated with retro-reflective tape. In-plane and tilt target motions cause changes in the scattered speckle patterns and sequences of images are used to investigate how the speckle patterns behave in response to these motions. In the case of retro-reflective tape, incident beam diameter is also found to have an important effect on speckle pattern changes and different incident beam diameters are considered for other target surfaces and motions too. This qualitative analysis of the speckle pattern intensity profiles is compared with established theoretical understanding of speckle patterns and their motions and related directly to the instrument noise levels ultimately encountered. Such fundamental evaluation of speckle pattern motions provides a greater appreciation of speckle noise generation in the Laser Vibrometer outputs.

Although the Doppler-effect is well known, some recent publications discuss the necessity of relativistic corrections in the measurements of two-beam interferometers. This is remarkable because sensor and detector are in the same reference frame and, therefore, it is not necessary to employ the Lorentz transformation. The whole consideration can be made in one inertial frame even if one reflector is moving in respect to the frame of source and detector. However, the commonly used equation for the Doppler-effect for a reflection at a moving surface is not correct because this equation is derived as a quasi-static solution by using optical path lengths. If the speed of light is considered as finite a different equation containing effects of wave propagation follows. Retardation effects in interferometers are discussed in this paper and its influences to laser-Doppler measurements are derived.

The design, realization and characterization of a new type of laser instrument for non-contact measurement of differential displacements are presented. The operating principle is based on two distinct vibrometers that use semiconductor lasers in the self-mixing interferometric configuration. The differential vibration is obtained by electronic subtraction of the vibration signals supplied by the two channels of the vibrometers. The prototype instrument is made by two compact optical heads (5 cm length, 1 cm diameter) and an electronic unit. The working distance can be varied between 10 and 50 cm, and operation is guaranteed on any diffusive surface. The maximum measurable vibration is in excess of 100 μm, and noise-equivalent differential vibration equals 20 nm. The instrument can be used to measure the differential vibrations of two metal samples kept into contact, revealing the hysteresis cycle in the micro-slip and gross-slip regimes.

Accurate vibration measurement of mechanical structures is a relevant problem in aerospace or automotive industry and sismic detection. Used methods concern for instance non guided optics devices, contact resistive systems, contact mechanical systems. We introduce a modelling and an experimental validation of an intrinsic vibration sensor using polarization modulation of the light propagation in an optical fiber as a result of modulated constraints applied to this fiber. We demonstrate that this method allow measurements of vibration frequencies with a good accuracy and a large dynamic. We first analyze the intrinsic birefringence in telecom monomode fiber. Then, we analyze the extrinsic birefringence coming from twisting and bending the fiber. On this basis, we introduce a polarisation controller. We then apply a static force on the fiber through a spring. With vibration applied to the fiber, this force will become dynamic and will induce a dynamic modulation of the polarization at the output of the fiber that we will read. The optimal signal sensing of sound and vibration is obtained by integrating all the characteristics of the device mentioned above.

A low-cost optical sensing system to measure vibrations up to high frequencies (40 kHz) is presented and validated with experiments. The developed system uses a sensing head made with plastic optical fibers to illuminate the vibrating surface and collect the reflected light; a non-demanding data processing is used to measure the amplitude and frequency of the vibration and to compensate the reflectivity of the vibrating surface. Preliminary measurements, performed on vibrating targets with different surface reflectivity have been performed to assess the performance of the system.

One powerful method for measuring the motion of microelectromechanical systems (MEMS) relies on a Laser Doppler Vibrometer (LDV) focused through an optical microscope. Recent data taken under a very simple and common condition demonstrate that the velocity signal produced by the LDV with an optical microscope may be different from the velocity signal produced by the LDV without a microscope. This is especially important if one wishes to estimate acceleration by differentiating velocity. In this study, the time derivatives of LDV signals are compared against the signal from an accelerometer when the LDV is focused through an optical microscope and without the microscope system. The signal from the LDV without the microscope is almost identical to the accelerometer signal. In contrast, the signal from the LDV with the microscope exhibits a nonlinear relationship with the accelerometer signal. Both the LDV and the accelerometer were measuring a sinusoidal velocity generated by an electromechanical shaker. The Fourier transform of the acceleration from the LDV with the microscope shows a multitude of high harmonics of the excitation frequency, which have much higher amplitudes than the harmonics present in the accelerometer signal. Without the microscope, the LDV gives a much less distorted sinusoidal signal, even after time differentiation. The distortion of the signal from the LDV is periodic, with the same period as the sinusoidal drive signal. The largest distortion occurs near points of maximum negative acceleration, corresponding to the positive displacement peak of the sinusoidal oscillation. Because the measured oscillation is out of plane, pseudo-vibrations caused by speckle noise do not explain the distortion. Instead, the distortion appears to be caused by the optics of the microscope.

A conformal scanning laser vibrometer was used to determine the vibrational modes of a 17-note portion of a C-lead tenor steelpan. The data represents the surface-normal motion of the instrument in response to an impulsive excitation intended to mimic the strike of a mallet. A description of this novel measurement system is presented, followed by the surface velocity data and a summary of response shapes and the frequencies at which those responses occur. The data indicate that individual note areas respond when adjacent or non-adjacent notes are struck, and clearly illustrate the complex vibration of the steelpan and the coupling between notes that produce the rich distinctive nature of the steelpan sound.

The dynamic behaviour of a power transmission V-belt system with two fixed pulleys has been analysed by applying the theory of the forced non-linear response of a moving string driven harmonically by eccentrically mounted pulleys. The model has been validated experimentally with reference data obtained by measuring out-of plane components of the belt vibration. The experimental data have been acquired by means of a single-point laser Doppler vibrometer (LDV), measuring the transverse vibration of the belt. Another experimentally technique applied here, for transverse vibration acquisition, was the continuous scanning LDV (CSLDV) that has been used for the first time in translating objects. From the model and the measurements, it has been found that the frequency crossing diagrams, analogous to the so-called Campbell plot used in rotating machinery, perfectly agree. Essentially, this plot demonstrates that the natural frequencies are strongly dependent on the belt's transport speed. Consequently, the model can be employed as useful tool for identifying the transport speeds at which resonances are expected.

Following the EU directive 2006/40/EC proscribing from 2011 that refrigerant fluids must have a global warming potential not higher than 150, it will not be allowed anymore to employ the current R134a on car air conditioning systems. Maflow s.p.a (automotive hose maker) is developing products for each possible new refrigerant. This paper is focused on hoses for CO₂ refrigerants operating in the worst conditions because of the high pressures and temperatures at which they are working (with R134a the high pressure is 18 bar and low pressure is 3 bar; with CO₂ the high pressure is 100 bar and low pressure is 35 bar). Therefore the noise emission control of the CO₂ air conditioning systems is very important. The aim of this study is to develop a standard measurement method for the vibro - acoustic characterization of High Pressure (HP - Shark F4) and Low Pressure (LP - ULEV) hoses to reduce noise emission and raise car passenger comfort; in particular deep research on high pressure hose. The method is based on the measurement of the vibration level of the hoses in a standard test bench by means of a Laser Doppler Vibrometer (LDV) and its acoustic emission by a sound intensity probe.

Vibrodiagnostics of technological machine with bearings of sliding friction and of roll is done in this work. Researching technological machine is described; the main characteristics of work and photo are given. Experimental vibrodiagnostics measurements are done. Primary signals of measurement are got doing vibrodiagnostics measurements. Primary results of measurement are systematized and its analysis is done. Dependence of work characteristics between rotary systems with bearings of sliding friction and of roll is ascertained. Generalization of research results is done and conclusions are formulated.

It is analyzed the statistical dispersion of characteristic features measured by Laser Doppler Vibrometry (LDV) in on-line diagnostic applications, with reference to on-line detection of mechanical defects of washing machines. The paper presents two complementary approaches: a) experimental evaluation of repeatability of measured features according to the Guide to the Expression of Uncertainty in Measurement-GUM; b) Montecarlo simulation of uncertainty propagation across the on-line test station. Experiments consist in a test bench which simulates the vibration of a washing machine, by playing back on a shaker a real signal acquired on-line and taking repeated measurements, so that a statistical analysis is performed about dispersion of diagnostic features. The analysis is repeated by varying the scattering characteristics of the vibrating surface, so to evaluate the effect of signal quality. The Montecarlo approach consists in modeling the propagation of uncertainty across the various elements of the measurement chain, up to the computation of features. The influence of LDV, Data Acquisition device (DAQ) and processing software have been taken into account. Results allow to estimate Repeatability and Reproducibility (R&R) of a typical set of characteristic features used in industrial diagnostics and to discuss uncertainty of similar diagnostic procedures.

It is shown, that interpretation of spectra is very simple and can be used for construction of diagrams of total micro - displacements. The spectral analysis was used also for: studying of interaction of a man - made and natural biological membrane with solutions, researches of periodic change of speckle brightness, arising at movement of water in a cuvette and at plastic deformation of materials.

In this paper, we discuss the realization of an optical microphone array using fiber Bragg gratings as sensing elements. The wavelength shift induced by acoustic waves perturbing the sensing Bragg grating is transduced into an intensity modulation. The interrogation unit is based on a fixed-wavelength laser source and - as receiver - a photodetector with proper amplification; the system has been implemented using devices for standard optical communications, achieving a low-cost interrogator. One of the advantages of the proposed approach is that no voltage-to-strain calibration is required for tracking dynamic shifts. The optical sensor is complemented by signal processing tools, including a data-dependent frequency estimator and adaptive filters, in order to improve the frequency-domain analysis and mitigate the effects of disturbances. Feasibility and performances of the optical system have been tested measuring the output of a loudspeaker. With this configuration, the sensor is capable of correctly detecting sounds up to 3 kHz, with a frequency response that exhibits a top sensitivity within the range 200-500 Hz; single-frequency input sounds inducing an axial strain higher than ~10nε are correctly detected. The repeatability range is ~0.1%. The sensor has also been applied for the detection of pulsed stimuli generated from a metronome.

The aim of this work is to develop and validate a measurement technique for investigating and analysing stress and strain on civil structures reinforced with carbon fibre composites. The proposed sensing elements are Bragg's fibre grating strain sensors. In order to verify the performances of the proposed method, a comparison was made with the results obtained using a laser Doppler vibrometer. The measurement technique was used to study two historical buildings still in use. The vault of the "Elmi - Pandolfi" building in Foligno, and the wooden floor of the "Siaz Building" in Trevi, both located in the province of Perugia, Italy. Both buildings were reinforced with Carbon Fibre Reinforced Plastic (CFRP) after an earthquake.

A fiber Bragg grating sensor for simultaneous static and dynamic strain detection is hereby presented. The principle of operation of the interrogator is based on direct intensity detection: a fixed-wavelength laser source is filtered through the sensing element, and the output power is detected with a photodiode. Multiple sensing for matched-wavelength gratings is performed by splitting the source into multiple channels. The exploitation of cheap components for optical telecommunications results in a low-cost hardware solution that matches several budget-constrained applications. The optical sensor is complemented by signal processing techniques (adaptive filters, spectral estimation, data modeling), capable of improving performances of the system without changing the optical layout. The system has been tested both in static interrogation, as a temperature sensor, and as vibration detector in a typical structural monitoring context. The maximum interrogation range is ~200με, depending on the grating shape, with a resolution <<1 με, and a repeatability of ~1%. A 1% stability over long time has been assessed with a long-term test. The adaptive filtering improves the signal-to-noise ratio of 5.3 dB. The resolution-unlimited spectral estimator resolves resonance peak detection for a vibration of 0.1με.

We present a solid material characterisation method using a very acccurate polarimetric fiber optic sensor. This very accurate and sensitive transductor permits us to measure the rigidity modulus G of several solid materials presenting several differents geometries. The G determination, in the first part, is achieved by measuring the torsion angle optically and by a non destructive method. The rigidity modulus of Aluminum, Plexiglas and Steel shaft presenting different geometries has been experimentally achieved: we obtained (2.013±0.008)×10¹⁰, (1.384±0.025)×10⁹ and (1.040±0.012)×10¹¹N.m^-2 for the Aluminum, Plexiglas and Steel respectively. The second part of our study presents the dependance of the torsion angle as function of an applied torque for different shaft lengths (from 5 to 32 cm). The comparison between the theoritical and experimental results shows us a good validation criteria of this non destructive optical characterisation method.

High performances of calibration systems for vibration and acoustic sensors to be used in laboratory applications can be achieved only with adequate vibration or shock exciters and other sub-systems, too. Leading manufacturers such as SPEKTRA have recognized the need for the design and development of improved and new techniques, in particular for generating rectilinear vibration and shock motion. Special hardware, software and system concepts have been jointly developed for the mass production of MEMS. Since in sensor production and some metrological applications extreme requirements for sine and shock levels and frequency ranges have to be met, SPEKTRA has decided to design special exciters of their own. The paper will present new designs, measurement results and examples of applications to calibration systems. The extended capabilities of the High-frequency vibration exciter SE-09 with air bearing will be discussed in more detail. Applications to primary and secondary calibration systems will be demonstrated and measurement results will be given. For the High-shock exciters of types HOP-S and HOP-P, theoretical considerations of how to scale up their shock acceleration peak values without compromising highest quality signal waveforms and excellent stability of mechanical excitation will be discussed and compared with practical measurement results. The refined laser interferometer techniques used for the accredited calibration laboratory of SPEKTRA as well as for the commercial calibration systems of SPEKTRA will be presented. Finally an outlook on further developments of vibration and shock exciters for use in calibration and sensor production will be given.

In this study, the effect of demodulator unit characteristics on the calibration of a laser vibrometer is investigated. For this purpose, two commercial available laser vibrometers with analogue demodulator units are used in the experiments. The demodulator units are electrically calibrated using simulated frequency-modulated signals, which are equivalent to output signals obtained from laser optics during laser vibrometer calibration. The calibration results of the demodulator units show extremely similar characteristics to laser vibrometer calibration results carried out in accordance with the new proposed draft (ISO16063-41). Although both calibration results had a large deviation of more than 0.5 % from the nominal sensitivity, a smaller deviation within 0.5 % was obtained by correction on the basis of the demodulator calibration results. The calibration results for both commercially availbale laser vibrometers indicate same amount of deviation after correction.. Most of the large deviation in the laser vibrometer calibration is due to the demodulator characteristics. In ISO16063-41 draft, laser vibrometer calibration is carried out by applying actual vibration to the laser vibrometer. However, the acceleration amplitude range applicable for calibration is limited due to the capability of the vibration exciter. Therefore, the measurable dynamic range of the laser vibrometer is not always sufficiently covered in the calibration. To overcome this problem, our investigation suggests the applicability of a combination of individual component calibrations.

Manufacturers and users of laser vibrometers exploit the wide frequency and intensity ranges of laser techniques, ranging over many decades (e.g., from 0.1 Hz to 100 MHz). Traceability to primary measurement standards is demanded over the specified measurement ranges of any measurement instrumentation. As the primary documentary standard ISO 16063-11 for the calibration of vibration transducers is restricted to 10 kHz, a new international standard for the calibration of laser vibrometers, ISO 16063-41, is under development. The current stage of the 2nd Committee Draft (CD) of the ISO standard specifies calibration methods for frequencies from 0.4 Hz to 50 kHz which does not meet the demand for providing traceability at higher frequencies. New investigations will be presented which demonstrate the applicability of the laser interferometer methods specified in ISO 16063-11 and in the 2nd CD also at higher frequencies of 100 kHz and beyond. The three standard methods were simultaneously used for vibration displacement and acceleration measurements up to 100 kHz, and a fourth high-accuracy method has been developed and used. Their results in displacement and acceleration measurements deviated by less than 1 % from each other at vibration displacement amplitudes in the order of 100 nm. In addition to the three interferometer methods specified in ISO 16063-11 and 16063-15, and in the 2nd Committee Draft of 16063-41 as well, measurement results will be presented. Examples of laser vibrometer calibrations will bedemonstrated. Further investigations are aimed

Laser interferometry is the preferred method currently used by National Metrology Institutes for primary calibration of accelerometers. Highly accurate calibrations require well controlled environmental conditions. Laboratories usually focus on the control of ambient air temperature and humidity. Another important source of influence is the vibration exciter, which besides uniaxial motion can generate undesirable secondary effects. This paper will treat the problem of differential heating of an accelerometer under calibration, when caused by a rise in temperature of the vibrator moving element. A simple device used to evaluate the change in the charge sensitivity of an accelerometer due to heating through its mounting base is presented. The sensitivity to differential heating can then be determined by the use of accurate interferometric methods. The knowledge of this sensitivity enables the calibration laboratory to correct the calibration results obtained with vibration exciters, which exhibit significant temperature variations. For instance, some commercial models can present variations higher than 20 °C, when the Bessel function J1 minimum-point method is applied. The experimental setup, which has been developed at INMETRO to evaluate this characteristic is described and some measurement results are presented.

Primary angular shock calibration system is developed by Changcheng Institute of Metrology & Measurement (CIMM). It uses brushless servo motor driving the air bearing system to generate rotational angle, angular velocity and angular acceleration. Both grating and heterodyne laser interferometer with diffraction grating is used to measure the angular movement, which are traceable to the International System of Units (SI). It can be used to calibrate angular transducers, i.e. angular accelerometer, angular velocity transducer, and rotational angle transducer to obtain sensitivity by angular shock or other kinds of excitation. Heterodyne laser interferometer with diffraction grating is successfully used in the measurement of angular acceleration. The method of using grating and scanning heads measure angular acceleration is developed. One characteristic of this system is that it could generate different kind of excitation signals, which include half sine, trapezoidal, sinusoidal, etc. and it can work as a high performance rate table to generate constant angular velocity. The preliminary test shows the uncertainty in calibrating angular accelerometer should be better than 2%. This paper introduces the mechanic system, control system and measurement system of the angular shock calibration system.