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10TH INTERNATIONAL CONFERENCE ON VIBRATION MEASUREMENTS BY LASER AND NONCONTACT TECHNIQUES - AIVELA 2012 Date: 27–29 June 2012 Location: Ancona, Italy ISBN: 978-0-7354-1059-6 Editor(s): Enrico Primo Tomasini

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Select this Article		Preface: 10th International Conference on Vibration Measurementsby Laser and Noncontact Techniques Enrico Primo Tomasini AIP Conf. Proc. 1457, pp. 1-1; doi:http://dx.doi.org/10.1063/1.4730624 (1 page) Full Text: Download PDF
		Abstract Unavailable

ADVANCES IN LASER VIBROMETRY I

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Are rotating wedges a feasible alternative to dual mirrors for scanning and tracking LDV?

Steve J. Rothberg and Mario Tirabassi

AIP Conf. Proc. 1457, pp. 5-13; doi:http://dx.doi.org/10.1063/1.4730537 (9 pages)

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An LDV scanning head is proposed based on a pair of rotating optical wedges. Modelling demonstrates how the wedges can be configured to scan point-by-point, in a line and in a circle. The circular scan is considered for the tracking application and shown to offer certain advantages over alternative systems based on dual mirrors and a Dove prism in terms of lower apparent velocities at key rotation orders.

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07.10.-h	Mechanical instruments and equipment
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy

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Advanced techniques in vibrometry by using spatial light modulators

S. Mayer, B. Tibken, and C. Rembe

AIP Conf. Proc. 1457, pp. 14-23; doi:http://dx.doi.org/10.1063/1.4730538 (10 pages)

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Vibrometry is a modern contactless measurement technique to analyze vibrations in different applications. It is extremely important for industry and research. Since spatial light modulators (SLM) have been developed, new techniques in vibrometry are possible. This paper presents two applications which use the SLM as actor instead of a galvanic mirror. Both techniques modify the phase of the wave front of a laser beam by using an SLM. On the one hand, it allows varying the focus plane and repositioning of a spot without any mechanical device. For that, special patterns have to be written to the SLM. On the other hand, overlay patterns can be used to reduce speckle drop-outs nearly without changing position and focus of the spot. For both applications an optimized signal level is the key to get sufficient results in a rougher environment.

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07.10.-h	Mechanical instruments and equipment
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy
42.79.Hp	Optical processors, correlators, and modulators

Select this Article		Generalized Laser Doppler Vibrometer noise maps Patrick O'Malley, Joseph Vignola, and John Judge AIP Conf. Proc. 1457, pp. 24-34; doi:http://dx.doi.org/10.1063/1.4730539 (11 pages) Full Text: Download PDF
	+ -	Show Abstract In a previous work[1], the authors presented preliminary data showing how noise can be mapped as a function of beam focus and standoff distance. This analysis builds on the previous work, but presents a method of mapping laser Dopopler vibrometer (LDV) noise which can be broadly generalized. The apparatus used in the experiments is a Polytec OFV505 with a custom servo-actuated attachment to the focus ring, which is mounted to linear positioning stages to control standoff distance and dither location. A high resolution grid of measurement locations is generated to create a map of signal strength as a function of both standoff distance and "focus error" - a description of the degree to which the beam is defocused, expressed in terms of how the standoff would need to be adjusted in order to move the beam into focus. Using this approach, the particular optics of the LDV system are no longer directly a factor, as determining the relationship between the focus adjustment and standoff distance should be possible with any system. Further noise maps from experiments which dither the horizontal location of the measurement beam show how the signal field can change for nearby measurement locations on a rough surface and highlight the importance of averaging LDV measurements.

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Demodulator electronics for laser vibrometry

G. Dudzik, A. T. Waz, P. R. Kaczmarek, A. J. Antonczak, J. Z. Sotor, K. Krzempek, G. Sobon, and K. M. Abramski

AIP Conf. Proc. 1457, pp. 35-40; doi:http://dx.doi.org/10.1063/1.4730540 (6 pages)

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One of the most important parts of a fiber-laser vibrometer is demodulation electronic section. The distortion, nonlinearity, offset and added noise of measured signal come from electronic circuits and they have direct influence on finale measuring results. Two main parameters of an investigated vibrating object: velocity V(t) and displacement s(t), influence of detected beat signals. They are: the Doppler frequency deviation f(t) and phase shift φ(t), respectively. Because of wide range of deviations it is difficult to use just one demodulator. That is the reason why we use three different types of demodulators. The first one is the IQ demodulator, which is the most sensitive one and its output is proportional to the displacement. Each IQ channel is sampled simultaneously by an analog to digital converter (ADC) integrated in a digital signal processor (DSP). The output signals from the two FM demodulators are proportional to the frequency deviation of heterodyne signals. They are sensitive directly to the velocity of the object. The main disadvantage of scattered light interferometry system is a “speckle effect”, appearing in relatively large amplitude fluctuation of a heterodyne signal. To minimize “speckle effect” influence on quality of beat signals we applied the automatic gain control (AGC) system. Data acquisition, further signal processing (e.g. vibration frequency spectra) and presentation of results is realized by PC via USB interface.

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06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
06.30.Gv	Velocity, acceleration, and rotation
07.10.-h	Mechanical instruments and equipment
07.60.Ly	Interferometers
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy
42.81.Wg	Other fiber-optical devices

BLADE TIP TIMING

Select this Article		Tip timing measurement chain validation with the Universal Tip Timing Calibrator UTTC, approach and experience Uwe Pfeifer and Michael Zidorn AIP Conf. Proc. 1457, pp. 43-51; doi:http://dx.doi.org/10.1063/1.4730541 (9 pages) Full Text: Download PDF
	+ -	Show Abstract The presentation will outline the motivation, results and experience of the development and application of a Universal Tip Timing Calibrator (UTTC) by the Siemens Tip Timing expert group. Due to the importance of the Tip Timing blade vibration measurement technology for the development of new gas turbine frames it is indispensible to calibrate these systems to international traceable standards. The very complex matter of tip timing signals does not allow to refer to simple physical and easy available laboratory standards in a standard working procedure. Even very sophisticated and expensive arbitrary wave and pattern generators are not able to generate signals to be used as calibration signals for multi-sensor tip timing systems of the last generation. So far, these 3^rd and 4^th generation Blade Vibration Tip Timing Measurement (BVTTM) systems could not be tested and calibrated completely within their dedicated application range regarding blade vibration amplitude, frequency and dynamic response. Based on this situation, the Siemens Tip Timing expert community decided the development of a universal and wide range application Tip Timing Simulator and Calibrator four years ago. Meanwhile, this device exists and is widely used for BVTTM system development, field system set up, data validation and off-line data evaluation. Inside the paper, the technical features and the software capabilities as well will be described in detail. Finally, two application examples with two different BVTTM systems are presented and the results are being discussed. As a summary it can be expressed, that the UTTC was found as a very helpful instrument for an optimal Tip Timing system setup.

Select this Article		Data acquisition and processing for tip timing and operational modal analysis of turbomachinery blades Danilo Sabbatini, Bart Peeters, Ton Martens, and Karl Janssens AIP Conf. Proc. 1457, pp. 52-60; doi:http://dx.doi.org/10.1063/1.4730542 (9 pages) Full Text: Download PDF
		Abstract Unavailable

Select this Article		Development and experimental characterization of a new non contact sensor for blade tip timing Jean-Francois Brouckaert, Roberto Marsili, Gianluca Rossi, and Roberto Tomassini AIP Conf. Proc. 1457, pp. 61-68; doi:http://dx.doi.org/10.1063/1.4730543 (8 pages) Full Text: Download PDF
	+ -	Show Abstract Performances of blade tip timing measurement systems (BTT), recently used for non contact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor characteristics. The sensors used for BTT generate pulses, to be used also for precise measurements of turbine blades time of arrival. All the literature on this measurement techniques do not address this problem in a clear way, defining the relevant dynamic and static sensor characteristics, fundamental for this application. Till now proximity sensors used are based on optical, capacitive, eddy current and microwave measuring principle. Also pressure sensors has been used. In this paper a new sensing principle is proposed. A proximity sensor based on magnetoresistive sensing element has been assembled end tested. A simple and portable test bench with variable speed, blade tip width, variable clearance was built and used in order to characterize the main sensor performances.

APPLICATION OF LDV TO MEMS

Select this Article		Dynamical topography measurements of MEMS up to 25 MHz, through transparent window, and in liquid by Digital Holographic Microscope (DHM) Yves Emery, Nicolas Aspert, and François Marquet AIP Conf. Proc. 1457, pp. 71-77; doi:http://dx.doi.org/10.1063/1.4730544 (7 pages) Full Text: Download PDF
	+ -	Show Abstract DHMs have unique features especially relevant for MEMS characterization. They provide 3D topography for large vertical ranges with interferometric resolution, in a single acquisition, without any lateral or vertical scanning. Any standard microscopic objective can be mounted on them, including those with correction for cover glass thickness. In this paper, DHM is operated in conjunction with a laser pulsed stroboscopic module providing synchronization of camera acquisition and shutter, laser pulses with length down to 7.5 ns, and MEMS excitation signal up to 25 MHz. These systems can measure fast movements over large vertical amplitude, in-and out-of-plane motions of device with complex geometry, provide a statistical analysis of multiple single devices, and can measure under vacuum or in liquid and/or through transparent window. This is illustrated with the presentation of the measurements of a cantilever, an ultrasonic transducer, a variable capacitor, and a gyroscope.

Select this Article		There is plenty of room at the bottom to approach sub-femtometer vibrometry Christian Rembe AIP Conf. Proc. 1457, pp. 78-87; doi:http://dx.doi.org/10.1063/1.4730545 (10 pages) Full Text: Download PDF
	+ -	Show Abstract One challenging application field of optical vibrometry is micro-and nanometrology. Since small structures resonate at high frequencies and with small vibration amplitudes this application area requires high spatial resolutions, high amplitude resolutions, and high measurement bandwidths. In addition, small structures are sensitive to heating because even a small heating energy can raise temperatures dramatically. Laser-Doppler technique provides amplitude resolutions down to the range of a few fm/, but for some applications even lower resolutions are required. In this paper, I summarize interferometric measurement solutions from basic physics science branches where amplitude-noise levels in the attometer regime have been demonstrated empirically and I discuss if these resolutions can be transferred to industrial applications. In addition, I propose heterodyne interferometry for the broad bandwidth measurements of the electrical field vector of light and I derive the theoretic resolution limit for in-plane-vibration measurements for a new detection method for the first time.

Select this Article		Measuring MEMS vibration with novel quasi-heterodyned laser interferometry Adam Styk, Patrick Lambelet, Roman Paris, and Małgorzata Kujawińska AIP Conf. Proc. 1457, pp. 88-94; doi:http://dx.doi.org/10.1063/1.4730546 (7 pages) Full Text: Download PDF
	+ -	Show Abstract The paper presents novel interferometric measurement technique applied for MEMS dynamic properties measurements. The method was developed especially for multi-channel interferometer developed under SMARTIEHS EU project. The method employs sinusoidal modulation of light and novel smart-pixel camera detector. The measurement results obtained with developed measurement system and commercial Polytec system, obtained while measuring reference objects, are in good correspondence showing usefulness of proposed method.

ADVANCES IN LASER VIBROMETRY II

Select this Article		A universal laser interferometer for high linearity measurements Grzegorz Budzyn, Tomasz Podzorny, and Janusz Rzepka AIP Conf. Proc. 1457, pp. 97-104; doi:http://dx.doi.org/10.1063/1.4730547 (8 pages) Full Text: Download PDF
	+ -	Show Abstract In the paper we present the idea and measurement results of a modified laser interferometer with improved measurement linearity and measurement resolution. Presented solutions allow for linearity increase below 1nm mark with measurement resolution even of single picometers (depending on the noise parameters of the laser source and detection electronics) in the basic heterodyne configuration of the optical elements.

Select this Article		Simultaneous 3D-vibration measurement using a single laser beam device Christian Brecher, Alexander Guralnik, and Stephan Baümler AIP Conf. Proc. 1457, pp. 105-112; doi:http://dx.doi.org/10.1063/1.4730548 (8 pages) Full Text: Download PDF
	+ -	Show Abstract Today's commercial solutions for vibration measurement and modal analysis are 3D-scanning laser doppler vibrometers, mainly used for open surfaces in the automotive and aerospace industries and the classic three-axial accelerometers in civil engineering, for most industrial applications in manufacturing environments, and particularly for partially closed structures. This paper presents a novel measurement approach using a single laser beam device and optical reflectors to simultaneously perform 3D-dynamic measurement as well as geometry measurement of the investigated object. We show the application of this so called laser tracker for modal testing of structures on a mechanical manufacturing shop floor. A holistic measurement method is developed containing manual reflector placement, semi-automated geometric modeling of investigated objects and fully automated vibration measurement up to 1000 Hz and down to few microns amplitude. Additionally the fast set up dynamic measurement of moving objects using a tracking technique is presented that only uses the device's own functionalities and does neither require a predefined moving path of the target nor an electronic synchronization to the moving object.

Select this Article		Remote-sensing vibrometry at 1550 nm wavelength A. Dräbenstedt, J. Sauer, and C. Rembe AIP Conf. Proc. 1457, pp. 113-121; doi:http://dx.doi.org/10.1063/1.4730549 (9 pages) Full Text: Download PDF
	+ -	Show Abstract Laser-Doppler vibrometry (LDV) is a proven technique for vibration analysis of mechanical structures. A wavelength of 633 nm is usually employed because of the availability of the relatively inexpensive Helium-Neon laser source which has a good coherence behavior. However, coherence break-down through the beat of multiple longitudinal modes and the limited detector carrier-to-noise-ratio (CNR) at a measurement laser power of 1 mW have prevented a wide use of LDV in remote sensing applications. Such applications in civil engineering are bridges, towers or wind turbines. The lower photon energy of IR light at 1550 nm wavelength increases the CNR by a factor 2.4. This helps especially in the condition where the carrier power decreases below the FM threshold. We have designed a heterodyne interferometer which allows the shot noise limited detection at 1550 nm wavelength close to the theoretical possible CNR. We present calculations of the fundamental noise contributions in interferometric light detection for a comparison of the achievable CNR between common HeNe vibrometers and IR vibrometers. The calculations are backed by measurements that show the devices working close to the theoretical limits. The achievable noise level of the demodulated velocity signal is shown in dependence from the standoff distance. Our novel heterodyne interferometer has been transferred to the Polytec product RSV-150. An application example of this new sensor will be demonstrated.

SELF MIXING VIBROMETRY

Select this Article		Digital to analog conversion methodology applied to self-mixing displacement signals Antonio Luna Arriaga, Francis Bony, and Thierry Bosch AIP Conf. Proc. 1457, pp. 125-131; doi:http://dx.doi.org/10.1063/1.4730550 (7 pages) Full Text: Download PDF
	+ -	Show Abstract An adaptive algorithm has been designed to treat interferometric self-mixing signals for weak and moderate laser feedback. With regard to the creation of an embedded displacement sensor, the reconstruction process is inspired from the interpolation feature found in digital-to-analog converters. By using an adaptive filter as the central process, the algorithm presents a high potential of parallelism to meet timing restrictions. A validation for different signal scenarios was carried out. The obtained precision and ease of maintainability enlightens its capabilities to be coupled with other signal processing methods to produce better system reliability.

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Optical feedback interferometry for measuring dynamic stress deformation of beams

Reza Atashkhooei, Francisco Azcona, Santiago Royo, and Lluis Gil Espert

AIP Conf. Proc. 1457, pp. 132-138; doi:http://dx.doi.org/10.1063/1.4730551 (7 pages)

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An optical feedback interferometer has been used as a sensor for measuring the deformation of the beams under dynamic loading. The compactness, non-contact nature, high accuracy (below half wavelength of the laser) and the cost-effectiveness of this sensor makes it a suitable choice for material deformation measurements. A general procedure of the measurement is described in detail, including the proposed solution to deal with the speckle effect which appears when large deformations are presented. The performance of the proposed sensor has been compared and validated with a commercial contact LVDT sensor showing measurement differences below 20μm (2.9%).

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07.60.Ly	Interferometers
46.80.+j	Measurement methods and techniques in continuum mechanics of solids

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Error analysis due to laser beams misalignment of a double laser self-mixing velocimeter

Bendy Tanios, Francis Bony, and Thierry Bosch

AIP Conf. Proc. 1457, pp. 139-147; doi:http://dx.doi.org/10.1063/1.4730552 (9 pages)

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In this paper, we present a self-mixing double-head laser diode velocimeter. Analyzes are performed to evaluate the sensitivity to misalignment for this setup and calculate errors due to this misalignment. The analyses and calculations are verified by experimental results.

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06.30.Gv	Velocity, acceleration, and rotation
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy

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Robust real-time self-mixing interferometric laser vibration sensor with embedded MEMS accelerometer

Usman Zabit, Olivier D. Bernal, and Thierry Bosch

AIP Conf. Proc. 1457, pp. 148-155; doi:http://dx.doi.org/10.1063/1.4730553 (8 pages)

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In this paper, we present a real-time implementation of a Self-Mixing (SM) interferometric laser diode (LD) based vibration sensor coupled with an embedded MEMS (microelectromechanical system) accelerometer. Such a sensor allows measuring correct target movements even when the LD based SM sensor is subject to extraneous movements. This results in a vibration sensing system that can be used for embedded applications as there is no more need of keeping the sensor stationary. Such an approach opens the way for the use of such laser sensors in conditions where the use of anti-vibration support is not available or possible. The proposed data fusion between a MEMS accelerometer and a LD based SM sensor results in a robust, compact and low-cost sensing system.

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07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm	Micromechanical devices and systems
07.60.Ly	Interferometers
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy

Select this Article

Nanovibration amplitude measurement using semiconductor laser autodyne

Dmitry A. Usanov, Anatoly V. Skripal, Evgenii O. Kashchavtcev, and Michael Yu. Kalinkin

AIP Conf. Proc. 1457, pp. 156-161; doi:http://dx.doi.org/10.1063/1.4730554 (6 pages)

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Effect analysis of external optical feedback on waveform and spectrum of semiconductor laser autodyne signal has been performed. The method of nanovibration amplitude determination has been described. The method involves measuring ratio of the first spectral components of nanovibration autodyne signal to one of the additional mechanical vibrations, taking into account the level of external optical feedback. It has been experimentally shown, that taking into account external optical feedback can significantly improve the accuracy of nanovibration measurements.

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07.10.-h	Mechanical instruments and equipment
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy

METROLOGY AND CALIBRATION

Developed in Collaboration with Dr. H. J. von Martens

Select this Article		The problem of calibrating Laser-Doppler Vibrometers at high frequencies M. Winter, H. Füser, M. Bieler, G. Siegmund, and C. Rembe AIP Conf. Proc. 1457, pp. 165-175; doi:http://dx.doi.org/10.1063/1.4730555 (11 pages) Full Text: Download PDF
	+ -	Show Abstract The new international standard 16063-41:2011 provides well-defined rules for the calibration of laser-Doppler vibrometers up to 50 kHz. Recent research work addresses the enhancement of the methods defined by the standard to the frequency range up to a few hundreds of kilohertz. However, the newest generation of vibrometers can measure frequencies up to the GHz range which requires completely new approaches for calibration. Here, we demonstrate the overall characterization of the photodetector, connection cable, and analog-digital (A/D) converter transfer characteristics. This is an important step towards calibration of high-frequency vibrometers up to the GHz range.

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Calibrating angular transducer using sinusoidal and shock excitation

Li Zhang and Jun Peng

AIP Conf. Proc. 1457, pp. 176-180; doi:http://dx.doi.org/10.1063/1.4730556 (5 pages)

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Primary angular vibration calibration system and primary angular shock calibration system are developed by Changcheng Institute of Metrology and Measurement (CIMM). The both systems using laser interferometer and grating measure rotational angle, angular velocity and angular acceleration, which are traceable to the International System of Units (SI). This paper will study the dynamic performance of an angular accelerometer and a gyro under the excitation of sinusoidal and shock using the calibration systems. It shows that the angular transducers should be calibrated using both sinusoidal and shock excitation to obtain more detailed dynamic information.

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06.20.fb	Standards and calibration
06.30.Gv	Velocity, acceleration, and rotation
07.07.Mp	Transducers
07.10.-h	Mechanical instruments and equipment

Select this Article		Applicability of ISO standard methods to vibration measurements at high frequencies and high accelerations Hans-Jürgen Von Martens AIP Conf. Proc. 1457, pp. 181-199; doi:http://dx.doi.org/10.1063/1.4730557 (19 pages) Full Text: Download PDF
	+ -	Show Abstract New and revised laser methods and techniques developed by national metrology institutes and by leading manufacturers in the past two decades have been swiftly specified as standard methods in the ISO 16063 series of international document standards. The first international standard for the calibration of laser vibrometers, ISO 16063-41:2011, specifies the instrumentation and procedures for performing primary and secondary calibrations of rectilinear laser vibrometers in "typical" ranges of frequency (0,4 Hz to 50 kHz) and other conditions, with "typical attainable uncertainties" (0,25% to 5% for different specified conditions). This allows the specified standard methods to apply with refined techniques and procedures achieving even wider measurement ranges and smaller measurement uncertainties than that specified in the ISO standard. Recent theoretical and experimental investigations demonstrate the applicability of the standardized interferometric methods up to frequencies considerably higher than 50 kHz if measurable vibration amplitudes are generated. Sinusoidal vibration was generated by a piezoelectric actuator at frequencies between 63 kHz and 347 kHz and the displacement was measured by different interferometric standard methods applied simultaneously. Their results differed by less than 1% from each other. From the analysis of the results it is expected that frequencies up to 500 kHz are achievable.

Select this Article		Piezoelectric shaker developments for calibration of accelerometers at extended frequencies Bev Payne and David Evans AIP Conf. Proc. 1457, pp. 200-205; doi:http://dx.doi.org/10.1063/1.4730558 (6 pages) Full Text: Download PDF
	+ -	Show Abstract Piezoelectric shakers are well suited to generate motion suitable for use with laser interferometric methods at frequencies of 3 kHz and above. One advantage of piezoelectric shakers is the higher achievable accelerations and displacement amplitudes as compared to electrodynamic (ED) shakers. Another advantage is the use of a solid ceramic construction rather than a compliant suspension system which results in much lower mechanical noise. Piezoelectric shakers have been developed and used at NIST for many years for high frequency calibration of accelerometers. Previous papers have documented the performance of these shakers for the calibration of accelerometers over the range of 3 kHz to 25 kHz using interferometric calibration methods. Piezoelectric shakers with solid ceramic construction coupled with new high resolution data acquisition systems have made it possible to extend the calibration of accelerometers to smaller amplitudes and a broader range of frequencies. These factors have also allowed calibrations to be performed over a wide range of accelerations rather than over a relatively limited range of accelerations. This paper presents these topics and gives examples of the results of calibrations performed using a piezoelectric shaker and a high resolution data acquisition systems.

Select this Article		The application of orthogonal homodyne interferometer in the vibration calibration of ultra-low frequency and large amplitude Da-zhi Zhang, Ying-jie Cao, Li Zhang, Xin-liang Li, and Chun-yan Hu AIP Conf. Proc. 1457, pp. 206-215; doi:http://dx.doi.org/10.1063/1.4730559 (10 pages) Full Text: Download PDF
	+ -	Show Abstract In this paper, a novel measurement technology for ultra-low frequency vibration using orthogonal homodyne interferometer is introduced. The system can calculate the real-time velocity and the acceleration process accurately, and the target displacement under test can reach one meter. The experiment results demonstrate that the proposed method can realize real-time absolute calibration for the transducer undergoing the effects of ultra-low frequency and large amplitude.

ADVANCES IN LASER VIBROMETRY III

Select this Article		Multi-beam Laser Doppler Vibrometer with fiber sensing head P. B. Phua, Y. Fu, M. Guo, and H. Liu AIP Conf. Proc. 1457, pp. 219-226; doi:http://dx.doi.org/10.1063/1.4730560 (8 pages) Full Text: Download PDF
	+ -	Show Abstract Laser Doppler vibrometry (LDV) is a well known technique to measure the motions, vibrations and mode shapes of structures and machine components. Photodetector-based LDV can only offer a point-wise measurement. However, it is possible to scan the laser beam to build up a vibrometric image. These scanning laser Doppler vibrometers (SLDV) assume that the measurement conditions remain invariant while multiple and identical, sequential measurements are performed. This assumption makes SLDVs impractical to do measurement on transient events. In this paper, we introduce a new method of generating multiple laser beams with different frequency shifts. The laser beams are projected on different points, and the reflected beams interfere with a common reference beam. The cross-talk among object beams can be bypassed with a proper selection of frequency shifts. A simultaneous vibration measurement on multiple points is realized using a single photodetector. Based on the proposed spatial-encoding technology, a self-synchronized prototype of fiber-based multipoint laser Doppler vibrometer at 1550nm wavelength is developed. An addition red pilot laser is used for aiming purpose. It has the flexibility to measure the vibration of different points on various surfaces. The prototype is used to measure the vibration of different points on a cantilever beam and a plate. The measured results match well with simulation results using finite element method (FEM).