Showing papers on "Laser Doppler vibrometer published in 2021"

Experiments on a Thin Panel Excited by Turbulent Flow and Shock/Boundary-Layer Interactions

Abstract: An experimental methodology was designed to study the effects of turbulent flow and shock/boundary-layer interaction (SBLI) on the postflutter response of a thin, buckled panel. The approach combin...

Nonlinear vibrations and damping of fractional viscoelastic rectangular plates

Abstract: Damping is largely increasing with the vibration amplitude during nonlinear vibrations of rectangular plates. At the same time, soft materials present an increase in their stiffness with the vibration frequency. These two phenomena appear together and are both explained in the framework of the viscoelasticity. While the literature on nonlinear vibrations of plates is very large, these aspects are rarely touched. The present study applies the fractional linear solid model to describe the viscoelastic material behavior. This allows to capture at the same time (i) the increase in the storage modulus with the vibration frequency and (ii) the frequency-dependent nonlinear damping in nonlinear vibrations of rectangular plates. The solution to the nonlinear vibration problems is obtained through Lagrange equations by deriving the potential energy of the plate and the dissipated energy, both geometrically nonlinear and frequency dependent. The model is then applied to a silicone rubber rectangular plate tested experimentally. The plate was glued to a metal frame and harmonically excited by stepped sine testing at different force levels, and the vibration response was measured by a laser Doppler vibrometer. The comparison of numerical and experimental results was very satisfactorily carried out for: (i) nonlinear vibration responses in the frequency and time domain at different excitation levels, (ii) dissipated energy versus excitation frequency and excitation force, (iii) storage energy and (iv) loss factor, which is particularly interesting to evaluate the plate dissipation versus frequency at different excitation levels. Finally, the linear and nonlinear damping terms are compared.

Modal identification of vibrating structures using singular value decomposition and nonlinear iteration based on high-speed digital image correlation

Abstract: This study aims to develop an effective method to identifying modal parameters of vibrating structures using digital image correlation (DIC) technique, in which singular value decomposition (SVD) and nonlinear least square iteration are integrated. The proposed approach was first used to measure modal parameters of a cantilever plate to verify its effectiveness and accuracy. The obtained results were compared with those measured with the forced normal mode test, operating deflection shape measurement, accelerometer, Laser Doppler Vibrometer and finite element techniques. In the experiment, synchronization of the hammer hitting and high-speed camera signals was achieved via the data acquisition cards and Labview program. Natural frequency and damping ratios were obtained through the enhanced frequency response functions with a nonlinear least square algorithm; and the mode shapes were determined through singular value decomposition. The experimental modal parameters of the cantilever plate identified by the present method agreed well with those identified by the Polymax modal estimator in the commercial code LMS test.lab and rational fraction polynomial. It is demonstrated that use of DIC technique for vibration analysis is of considerable advantages in comparison with the accelerometer and LDV techniques. Finally, a real-life case study was performed for vibratory modal analysis of a passenger car bonnet in this study. It is shown that the experimental modal parameters of the real car bonnet identified by the present method agreed well with those identified by the forced normal mode and the accelerometer tests. The proposed technique is anticipated to provide an effective approach for identification of modal parameters of vibrating structures in practical applications.

Doppler velocimeter and vibrometer FMCW LiDAR with Si photonic crystal beam scanner.

Abstract: In this paper, we propose and demonstrate a frequency-modulated continuous-wave light detection and ranging (LiDAR) with a Si photonic crystal beam scanner, simultaneously enabling scanning laser Doppler measurements. This nonmechanical solid-state device can reduce the size of conventional scanning laser Doppler vibrometers, making LiDAR a multimodal imaging sensor, which can measure the distributions of distance, velocity, and vibration frequency. We fabricated this device using Si photonics process and confirmed the expected operations. Distance and velocity resolutions were less than 15 mm and 19 mm/s, respectively. The detection limit of the vibration amplitude determined by the signal-to-noise ratio was 2.5 nm.

Accuracy of cardiac-induced brain motion measurement using displacement-encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI): A phantom study.

Abstract: Purpose The goal of this study was to determine the accuracy of displacement-encoding with stimulated echoes (DENSE) MRI in a tissue motion phantom with displacements representative of those observed in human brain tissue. Methods The phantom was comprised of a plastic shaft rotated at a constant speed. The rotational motion was converted to a vertical displacement through a camshaft. The phantom generated repeatable cyclical displacement waveforms with a peak displacement ranging from 92 µm to 1.04 mm at 1-Hz frequency. The surface displacement of the tissue was obtained using a laser Doppler vibrometer (LDV) before and after the DENSE MRI scans to check for repeatability. The accuracy of DENSE MRI displacement was assessed by comparing the laser Doppler vibrometer and DENSE MRI waveforms. Results Laser Doppler vibrometer measurements of the tissue motion demonstrated excellent cycle-to-cycle repeatability with a maximum root mean square error of 9 µm between the ensemble-averaged displacement waveform and the individual waveforms over 180 cycles. The maximum difference between DENSE MRI and the laser Doppler vibrometer waveforms ranged from 15 to 50 µm. Additionally, the peak-to-peak difference between the 2 waveforms ranged from 1 to 18 µm. Conclusion Using a tissue phantom undergoing cyclical motion, we demonstrated the percent accuracy of DENSE MRI to measure displacement similar to that observed for in vivo cardiac-induced brain tissue.

Analysis of quadcopter propeller vibration based on laser vibrometer

Abstract: An unbalanced propeller can affect a quadcopter’s performance due to vibration, also decreasing its thrust’s yield. Analyses were conducted to determine the correlation between vibration in the dyn...

Nondestructive assessment of cross-laminated timber using non-contact transverse vibration and ultrasonic testing

Abstract: Cross-laminated timber (CLT) is a new generation of engineered wood product developed initially in Europe and has been used in North America for various applications. CLT is composed of at least three layers of lumber boards stacked crosswise in orthogonally alternating orientation to the adjacent layers. CLT has been gaining popularity and increasing application areas in the construction industry, such as building systems, mats for construction and temporary road applications as well as temporary bridges. It is especially identified as the prevailing material in modular construction for the future building industry. However, CLT as a relatively new structural material has limited studies related to their durability and long-term performance. Moreover, nondestructive evaluation methods to understand their mechanical behavior after exposure to harsh environment are lacking. This paper contributes to the development of a rapid nondestructive evaluation method to assess the mechanical properties using transverse vibration method and ultrasonic testing. The free vibration response triggered by the impulse excitation is captured using contact accelerometer and non-contact laser Doppler vibrometer (LDV). The LDV measurement is proven to respond similar to conventional accelerometers but more convenient as a rapid assessment method. While the longitudinal wave speed is measured by ultrasonic testing (UT) in a through-transmission mode, the modulus of elasticity was calculated in terms of measured wave speed. By investigating the different structural states and dimensions of CLT samples, the laboratory and the manufacturing facility, the influences of aging on effective dynamic modulus of elasticity (MOE) and damping are shown. The numerical and experimental results indicate the increase in moisture content decreases the fundamental frequency. Therefore, moisture content should be measured in order to examine the coupled effects of moisture content and aging on the fundamental frequency. The damping ratio extracted using half-power bandwidth method is shown as an additional information related to the moisture content. The non-contact transverse vibration method and UT are shown as an efficient nondestructive evaluation method for assessing the CLT structural state right after the manufacturing as a quality assurance method or after their service in field as a diagnostic tool.

Avoiding transduction-induced heating in suspended microchannel resonators using piezoelectricity.

Abstract: Calorimetry of single biological entities remains elusive. Suspended microchannel resonators (SMRs) offer excellent performance for real-time detection of various analytes and could hold the key to unlocking pico-calorimetry experiments. However, the typical readout techniques for SMRs are optical-based, and significant heat is dissipated in the sensor, altering the measurement and worsening the frequency noise. In this manuscript, we demonstrate for the first time full on-chip piezoelectric transduction of SMRs on which we focus a laser Doppler vibrometer to analyze its effect. We demonstrate that suddenly applying the laser to a water-filled SMR causes a resonance frequency shift, which we attribute to a local increase in temperature. When the procedure is repeated at increasing flow rates, the resonance frequency shift diminishes, indicating that convection plays an important role in cooling down the device and dissipating the heat induced by the laser. We also show that the frequency stability of the device is degraded by the laser source. In comparison to an optical readout scheme, a low-dissipative transduction method such as piezoelectricity shows greater potential to capture the thermal properties of single entities.

An Overview of Synthetic Jet Under Different Clamping and Amplitude Modulation Techniques

Abstract: There is generally limited guidance available on the optimum clamping method for the diaphragms used in the synthetic jet actuators (SJAs). This paper describes the effects of clamping methods (O-rings, neoprene rubber washers and metal-to-metal clamping) on the actuator diaphragm displacement using Polytec scan vibrometer (PSV). Once the clamping type was implemented, an optimization study to examine the effect of geometrical parameters for three designs of synthetic jet actuators in quiescent conditions—in particular the number of orifices per cavity, the space between them, and their effects on the jet velocity—was performed. It has also been shown that with use the Helmholtz resonance of the cavity and amplitude modulation of the excitation signal, the actuator can exhibit a more significant “blowing” velocity at a reduced power input.

Lamb waves excited by an air-coupled ultrasonic phased array for non-contact, non-destructive detection of discontinuities in sheet materials

Abstract: Lamb wave excitation in sheet materials is possible using non-contact, non-destructive evaluation methods such as air-coupled transducers, pulsed Laser excitation and electro magnetic acoustic transducers (EMATs). However, these methods are limited to specific groups of materials or lack flexibility when testing specimens with different geometries or compositions. In previous work we demonstrated air-coupled Lamb wave excitation using a custom ultrasonic phased array (UPA). In this work we utilized the UPA for localizing two different discontinuities in a steel sheet specimen. The steering capability of the UPA is used in order to find the optimum coupling angle. The time of flight (TOF) of the Lamb wave, reflected at the discontinuities, is measured using a laser Doppler vibrometer (LDV). The defect location is calculated using the group velocity derived from the coupling angle and the theoretical value from the dispersion diagram. The setup is characterized and our results show mean localization errors of 1.39 mm and 1.42 mm at distances of up to 800 mm using the optimum coupling angle. This can be further optimized using a finer angular step size. This way, the system is suitable for a wide range of non destructive evaluation (NDE) applications.

Test Stand for Metamaterials Dynamic Properties Examination

Abstract: Experiments and computer studies on metamaterial issues allow to improve designing of entire devices using 3D CAD technology and finite element methods. Research and their effects are aimed at replacing the mechanisms by the elements made with additive technology. The technology enables using the same metamaterial producing the device or part with various internal structures. While maintaining identical dimensions, the internal structure of the device affects the properties, particularly dynamic properties. For this purpose, apart an appropriate computer model, the particular test is required for rapid and effective prototyping. Therefore, in the paper, the test stand consisted on: The signal generator, the vibration generator and laser vibrometer are proposed. The following is the post for preliminary experimental research.

New Approach to Concurrent VS and VP Measurements Using Bender Elements

Abstract: Bender elements (BEs) have become a routine geotechnical laboratory tool for seismic wave velocity measurements. Since the 1980s, this testing technique has gained popularity, currently being available in many geotechnical laboratories worldwide in a variety of apparatuses. The advantage of simultaneously measuring small- and large-strain soil stiffnesses in each device and the easiness and low-cost implementation of BE are the main reasons for their common application. Although there is already a standardized procedure for BE testing (ASTM D8295-19, Standard Test Method for Determination of Shear Wave Velocity and Initial Shear Modulus in Soil Specimens Using Bender Elements), the use of high-frequency pulses for the simultaneous measurement of compressional (VP) and shear (VS) wave velocities is not considered. In contrast, the use of high-excitation frequencies is usually discouraged, as they tend to induce spurious participation of high-vibration modes in the BE response. However, this work shows that the use of higher vibration modes can be advantageous to evaluate P-wave velocities from standard BE testing. Thus, this paper presents a new approach for the concurrent measurements of VP and VS using a typical installation of BE. The new approach is first demonstrated by experimental measurements and subsequently validated using high-frequency laser vibrometer measurements of the actual BE deformation (nanometer scale) under different excitation frequencies. The laser vibrometer measurements show the displacements of the transmitter BE as a function of the input frequency in not only the horizontal but also in the vertical directions, demonstrating the generation of P-waves when higher vibration modes are excited. The measured VP values are shown to be in good agreement with the predicted values using Biot’s equations. Thus, the proposed methodology addresses the current knowledge gap in the use of BE for concurrent P-wave and S-wave velocity measurements. The generated wavelengths are large enough to travel through the soil skeleton instead of the pore water only.

Non-contact detection of polyester filament yarn tension in the spinning process by the laser Doppler vibrometer method:

Abstract: The precise detection of polyester filament yarn (PFY) tension in the spinning process is critical to ensure product quality. The laser Doppler vibrometer (LDV) method is proposed to achieve non-co...

Lateral resolution limit of laser Doppler vibrometer microscopes for the measurement of surface acoustic waves

Abstract: The lateral or transverse resolution of single-point interferometers for vibration measurement is especially critical for microelectromechanical systems (MEMS) vibrating up to the gigahertz range. In this regime, the acoustic wavelengths are typically in the range of the size of the laser focus. Thus, a successful vibration measurement requires distinct knowledge about the lateral resolution limit and its dependencies with instrumentation parameters. In this paper, we derive an analytic approximation formula, which allows for estimation of the systematic measurement deviation of the vibration amplitude and, thus, a definition of the lateral resolution limit of single-point interferometers for vibration measurement. Further, a compensation and an optimum numerical aperture are proposed the reduce the measurement deviation. For this, the model includes a laser-interferometer microscope of Mach-Zehnder type with Gaussian laser beams considering the Gouy effect and wavefront curvature. As a measurement scenario, an unidirectional surface acoustic wave (SAW) is regarded. The theoretic findings have been validated in the experiment with a representative vibration measurement on a SAW filter at $$433\,{\mathrm {MHz}}$$ with our heterodyne laser-Doppler interferometer with offset-locked semiconductor lasers. The provided formulas help instrument designers and users to choose suitable instrument parameters, especially the numerical aperture of the utilized microscope objective.

Analysis of Air-Coupled Transducer-Based Elastic Waves Generation in CFRP Plates.

Abstract: In this paper, the analysis of non-contact elastic waves generation in carbon fiber reinforced-polymer (CFRP) plate was conducted. Full non-contact elastic waves generation and sensing methods were also analyzed. Elastic waves generation was based on an air-coupled transducer (ACT) while waves sensing was based on a laser Doppler vibrometer. The excitation frequency was equal to 40 kHz. An optimal ACT slope angle for the generation of elastic waves mode was determined with the aid of dispersion curves calculated by using a semi-analytical model. Due to the stack sequence in the composite plate (unidirectional composite), ACT slope angles were different for waves generation in the direction along and across reinforcing fibers direction. Moreover, experimental verification of the optimal ACT slope angles was conducted. It was possible to generate A0 wave mode in the direction along and across the reinforcing fibers. Optimal angles determined using ACT were equal to 16° (along fibers) and 34° (across fibers). In the case of optimal angles, elastic waves amplitudes are almost two times higher than for the case of ACT oriented perpendicularly to the plate surface. Moreover, experimental results based on ACT showed that it was possible to generate the SH0 mode in the direction across the fiber for optimal angles equal to 10°. Finally, based on the A0 wave mode propagation, the process for localization of discontinuities was performed. Discontinuities in the form of additional mass simulating damage were investigated. A simple signal processing algorithm based on elastic wave energy was used for creating damage maps. Authors compared discontinuity localization for ACT oriented perpendicularly to the plate and at the optimal slope angle. The utilization of non-contact waves excitation at optimal ACT slope angles helped to focus the wave energy in the desired direction. Moreover, in this case, elastic waves with the highest amplitudes were generated.

Numerical investigation on vibration and pressure fluctuation characteristics in a centrifugal pump under low flow rate

Abstract: Vibration characteristic is an important factor in evaluating operation stability of centrifugal pump. The vibration of main shaft was measured using a laser vibrometer, internal flow field was sim...

LDV-induced stroboscopic digital image correlation for high spatial resolution vibration measurement

Abstract: Vibration measurement, particularly mode shape measurement, is an important aspect of structural dynamic analysis since it can validate finite element or analytical vibration models. Scanning laser Doppler vibrometry (LDV) and high-speed digital image correlation have become dominant methods for experimental mode shape measurement. However, these methods have high equipment costs and several disadvantages regarding spatial or temporal performance. This paper proposes a laser Doppler vibrometer induced stroboscopic digital image correction for non-contact mode shape and operational deflection shape measurement. Our results verify that single-point LDV and normal rate cameras can be used obtain high spatial resolution mode shape and operational deflection shape. Measurement frequency range is much higher than the camera capturing rate. We also show that the proposed approach coincides well with time-averaged electronic speckle pattern interferometry.

Vibration-based tool wear monitoring using Artificial Neural Networks fed by Spectral centroid indicator & RMS of CEEMDAN modes

Abstract: In machining processes, various phenomena occur during cutting operation. These phenomena can disturb the production through the reduction of part quality and accuracy. An easy way to control the process is by monitoring incontrollable parameters, such as generated temperature and vibration. The acquired vibration signals can provide information regarding tool life, surface roughness, cutting performances, and workpiece defects. This paper evaluates the possibility of monitoring the tool life during the turning process of AISI 1045 steel using laser Doppler vibrometer (LDV); the surface roughness has been measured along with the tool wear until reaching its limit value of 300μm. Furthermore, this paper also outlines the application of CEEMDAN technique to process the acquired signals for the monitoring processes. RMS and SCI indicators have been used to describe the wear progress, then, the artificial neural network has been adopted to achieve a real-time wear monitoring. The obtained results show that the CEEMDAN helps for isolating tool vibration signature. The RMS indicator does not provide enough information about the wear behavior; however, good results have been achieved by SCI indicator. The ANNs fed by SCI deliver accurate results allowing for real-time wear monitoring.

Experimental Study on Impact Force Identification on a Multi-Storey Tower Structure Using Different Transducers

Abstract: This paper presents the identification of both location and magnitude of impact forces applied on different positions of a multi-storey tower structure using different types of transducers, ie, an accelerometer, a laser Doppler vibrometer, and a triangulation displacement sensor Herein, a model-based inverse method is exploited to reconstruct unknown impact forces based on various recorded dynamic signals Furthermore, the superposition approach is employed to identify the impact location Therein, it is assumed that several impact forces are applied simultaneously on potential locations of the multi-storey tower structure, while only one impact has non-zero magnitude The purpose is then to detect the location of that non-zero impact The influence of using different hammer tip materials for establishing the transfer function is investigated, where it is concluded that the hammer with a harder tip leads to a more accurate transfer function An accuracy error function is proposed to evaluate the reconstruction precision Moreover, the effect of sensor type and location on the accuracy of the reconstruction is studied, where it is shown that the proximity between the impact and sensor locations is a dominant factor in impact force reconstruction In addition, the efficacy of using different transducers is studied for the impact localization, where it is demonstrated that reducing the degree of under-determinacy by using a combination of system responses of the same type can improve the localization accuracy

A fundamental study for long-distance noncontact shallow underground exploration technology by acoustic irradiation-induced vibration

Abstract: A fundamental study was conducted to investigate the possibility of shallow underground exploration from a long distance by acoustic irradiation-induced vibration. To detect buried objects in shallow underground, our method is proposed to excite the ground surface directly from above with sound waves and measure the vibration velocity distribution with a laser Doppler vibrometer. From the experimental results, it was found that the detection frequency is inversely proportional to the size of the buried object, but does not change much even if the buried depth is changed. It was also clarified that the buried object can be detected even if the grazing angle of the laser is about 20 degrees, and that it can be explored even at a distance of about 20 m. From these experiment results, it became clear that there is a possibility of shallow underground exploration using an unmanned aerial vehicle equipped with a small sound source.