Showing papers on "Laser Doppler vibrometer published in 2018"

Modeling and optimization of tool vibration and surface roughness in boring of steel using RSM, ANN and SVM

Abstract: In this paper, statistical models were developed to investigate effect of cutting parameters on surface roughness and root mean square of work piece vibration in boring of stainless steel. A mixed level design of experiments was prepared with process variables of nose radius, cutting speed and feed rate. According to design of experiments, eighteen experiments were conducted on AISI 316 stainless steel with PVD coated carbide tools. Surface roughness, tool wear and vibration of work piece were measured in each experiment. A laser Doppler vibrometer was used to measure vibration of work piece in the form of acousto optic emission signals. These signals were processed and transformed in to different frequency zones using a fast Fourier transformer. Analysis of variance was used to identify significant cutting parameters on surface roughness and root mean square of work piece vibration. Predictive models like response surface methodology, artificial neural network and support vector machine were used to predict the surface roughness and root mean square of work piece vibration. Cutting parameters were optimized for minimum surface roughness and root mean square of work piece vibration using a multi response optimization technique.

The Application of Tactile, Audible, and Ultrasonic Forces to Human Fingertips Using Broadband Electroadhesion

Abstract: We report an electroadhesive approach to controlling friction forces on sliding fingertips which is capable of producing vibrations across an exceedingly broad range of tactile, audible, and ultrasonic frequencies. Vibrations on the skin can be felt directly, and vibrations in the air can be heard emanating from the finger. Additionally, we report evidence from an investigation of the electrical dynamics of the system suggesting that an air gap at the skin/surface interface is primarily responsible for the induced electrostatic attraction underlying the electroadhesion effect. We developed an experimental apparatus capable of recording friction forces up to a frequency of 6 kHz, and used it to characterize two different electroadhesive systems, both of which exhibit flat force magnitude responses throughout the measurement range. These systems use custom electrical hardware to modulate a high frequency current and apply surprisingly low distortion, broadband forces to the skin. Recordings of skin vibrations with a laser Doppler vibrometer demonstrate the tactile capabilities of the system, while recordings of vibrations in the air with a MEMS microphone quantify the audible response and reveal the existence of ultrasonic forces applied to the skin via electronic friction modulation. Implications for surface haptic and audio-haptic displays are briefly discussed.

Analysis of the dynamic performance of a complex ultrasonic horn for application in friction stir welding

Abstract: Simple and complex ultrasonic horns used in ultrasonic vibration-assisted friction stir welding are designed and analyzed using the finite element method. Modal analysis of the designs shows that the computed frequency in axial direction comes out ~ 19.5 kHz, that is close to the intended working frequency. The frequencies in the axial and non-axial direction make a large gap, eliminating the possibility of modal coupling. Safe design of the ultrasonic horn depends on amplitude and stress concentration at its end face. Harmonic response analysis of the designs reveals that the maximum ultrasonic amplitude occurs at the horn’s small end. Besides, the maximum amplitude in case of the complex horn is lower than that of the simple horn, and the reduction in amplitude is appropriately discussed. The maximum von Misses stress on the horns is confined to a narrow region while the magnitude of maximum stress is lower than the yield strength of the respective material. The simulation results suggest that the designed simple and complex horns are safe within the design and metallurgical limits and are validated by real-time monitoring using laser vibrometer.

Thin film piezoelectric acoustic transducer for fully implantable cochlear implants

Abstract: This paper reports the development of a single cantilever thin film PLD-PZT transducer prototype. The device was experimentally characterized by attaching it on an acoustically vibrating membrane resembling the behavior of the eardrum. Acceleration characteristic of the sensor attached on the membrane was obtained by using a Laser Doppler Vibrometer (LDV) as the output voltage was measured by an oscilloscope. A voltage output of 114 mV was obtained, when the device was excited at 110 dB Sound Pressure Level (SPL) at 1325 Hz. This is the highest value for a thin film piezoelectric transducer in the literature to our knowledge. Using the results of a finite element analysis for this single-channel prototype, which are within 92% agreement with the experimental results, we performed an optimization study to propose a multi-frequency acoustic sensor to be placed on the eardrum for fully-implantable cochlear implant (FICI) applications. The proposed multi-channel transducer consists of eight cantilever beams. Each of these beams resonates at a specific frequency within the daily acoustic band (250–5000 Hz), senses the eardrum vibration and generates the required voltage output for the stimulation circuitry. The total volume and mass of the transducer are 5 × 5×0.2 mm3 and 12.2 mg, respectively. High sensitivity of the transducer (391.9 mV/Pa @900 Hz) enables transmission of strong signals to be the readout circuit, which can easily be processed. Expected to satisfy all the requirements (volume, mass, and stimulation signal at the hearing band) of FICI applications for the first time in literature, the proposed concept has a groundbreaking nature and it can be referred to as the next generation of FICIs since it revolutionizes the operational principle of conventional CIs.

Experimental Control of Turbulent Boundary Layers with In-plane Travelling Waves.

Abstract: The experimental control of turbulent boundary layers using streamwise travelling waves of spanwise wall velocity, produced using a novel active surface, is outlined in this paper. The innovative surface comprises a pneumatically actuated compliant structure based on the kagome lattice geometry, supporting a pre-tensioned membrane skin. Careful design of the structure enables waves of variable length and speed to be produced in the flat surface in a robust and repeatable way, at frequencies and amplitudes known to have a favourable influence on the boundary layer. Two surfaces were developed, a preliminary module extending 152 mm in the streamwise direction, and a longer one with a fetch of 2.9 m so that the boundary layer can adjust to the new surface condition imposed by the forcing. With a shorter, 1.5 m portion of the surface actuated, generating an upstream-travelling wave, a drag reduction of 21.5% was recorded in the boundary layer with Re τ = 1125. At the same flow conditions, a downstream-travelling produced a much smaller drag reduction of 2.6%, agreeing with the observed trends in current simulations. The drag reduction was determined with constant temperature hot-wire measurements of the mean velocity gradient in the viscous sublayer, while simultaneous laser Doppler vibrometer measurements of the surface recorded the wall motion. Despite the mechanics of the dynamic surface resulting in some out-of-plane motion (which is small in comparison to the in-plane streamwise movement), the positive drag reduction results are encouraging for future investigations at higher Reynolds numbers.

Measurement and prediction of cavitating flow-induced vibrations

Abstract: The objective of this paper is to investigate the unsteady cavitation behaviors and the corresponding cavitating flow-induced vibrations. Results are presented for the modified NACA66 hydrofoils made of stainless steel and POM Polyacetate respectively at Re = 6.0×105 for various cavitation regimes. The high-speed camera and the single point laser Doppler vibrometer (LDV) are used to observe the transient cavitating flow patterns and measure the vibration velocities. The results showed that the vibration amplitude increases dramatically for the cloud cavitation due to the development of large-scale cloud cavity. The main flow-induced frequencies, which are in accordance with the cavity shedding frequency, decrease with the decrease of the cavitation number. As for the effect of the hydroelastic response on the vibration behavior, the lift coefficient for the POM Polyacetate hydrofoil fluctuates more significantly with a larger mean value than that for the stainless steel hydrofoil. Compared with the vaporous cavity along the suction side of the stainless steel hydrofoil, the cavity for POM Polyacetate hydrofoil appears to be fragmentized. The main vibration frequencies for the POM Polyacetate hydrofoil are larger than that for the stainless steel hydrofoil, with the chaotic hydroelastic response with high frequency.

The Feasibility of Using Laser Doppler Vibrometer Measurements from a Passing Vehicle for Bridge Damage Detection

Abstract: This paper investigates the feasibility of detecting local damage in a bridge using Laser Doppler Vibrometer (LDV) measurements taken from a vehicle as it passes over the bridge. Six LDVs are simulated numerically on a moving vehicle, collecting relative velocity data between the vehicle and the bridge. It is shown that Instantaneous Curvature (IC) at a moving reference, which is the curvature of the bridge at an instant in time, is sensitive to local damage. The vehicle measures Rate of Instantaneous Curvature (RIC), defined as the first derivative of IC with respect to time. A moving average filter is found to reduce the effects of noise on the RIC data. A comparison of filtered RIC measurements in healthy and damaged bridges shows that local damage can be detected well with noise-free measurements and can still be detected in the presence of noise.

Rapid evaluation of safety-state in hidden-frame supported glass curtain walls using remote vibration measurement

Abstract: The vibration performance of a simulation for a hidden-frame supported glass curtain wall (HFSGCW) was tested using a Laser Doppler Vibrometer (LDV) in this paper. The effect of silicon structural sealant on the first order inherent frequency of HFSGCW and the spectral characteristics per LDV on different points were studied. Meanwhile, the test results of LDV were verified using traditional sensors (DASP modal analysis system) in order to evaluate the feasibility of LDV used for safety state evaluation of HFSGCW. Results show that the first order inherent frequency obtained by LDV matches well with DASP modal analysis results. The first order inherent frequency decreases with an increase of sealant failure，and the first order frequency amplitude scale of structural sealant upper point increases significantly after the structural silicon sealant is destroyed. The safety state of HFSGCW is divided into three levels. Meanwhile, a safety state rapid evaluation model and key detection technologies of HFSGCW based on LDV is proposed.

Plastic Strain Determination With Nonlinear Ultrasonic Waves Using In Situ Integrated Piezoelectric Ultrasonic Transducers

Abstract: The detection of plastic deformation of metallic alloy materials with second-harmonic Rayleigh ultrasonic wave is first investigated using direct-write piezoelectric ultrasonic transducers, in which piezoelectric poly(vinylidenefluoride/ trifluoroethylene) [P(VDF/TrFE)] polymer coatings and electrodes are directly deposited, processed, and patterned on the alloy to be evaluated. Rayleigh ultrasonic signals, generated by the direct-write transducers on titanium alloy specimens, are characterized by a laser scanning vibrometer. The results show that acoustic nonlinearity increases with plastic strain, and an increase of ~40% in the acoustic nonlinearity corresponding to a plastic strain of 5.1%. The measurement data and technical features with the use of the direct-write transducers are compared with the conventional discrete angle beam piezoelectric transducer. The results and analyses show that compared with the conventional discrete angle beam piezoelectric transducers, implementation of the direct-write piezoelectric transducers has significant technical advantages and is promising for applications in determining nonlinear ultrasonic waves and plastic strain of structural materials.

Elastic characterization of wood by Resonant Ultrasound Spectroscopy (RUS): a comprehensive study

Abstract: The main principle of Resonant Ultrasound Spectroscopy (RUS) measurement method is to excite a sample and to deduce its elastic constants from its free mechanical resonant frequencies. The goal of this paper is to propose an application of RUS in the case of wood cubic samples by: (1) using frequencies and mode shapes (or vibration patterns) of the free resonant modes in an iterative numerical procedure to solve the inverse problem for identifying components of the stiffness tensor of the sample’s material, (2) finding the limits and optimizing the robustness of the identification procedure in the case of wood and (3) applying it to a large density range of wood samples. Specific continuous waves have been used as excitation signal in order to experimentally determine the free resonant frequencies and mode shapes of the sample in a faster way by means of Scanning Doppler Vibrometer measurements. Afterward, the stiffness tensor was derived by solving iteratively an inverse problem. The gain of using the mode shapes in the inverse identification procedure is demonstrated to be particularly necessary for wood, especially for pairing each measured frequency with its corresponding theoretically predicted one, as viscoelastic damping causes the resonant peaks to overlap and/or disappear. A sensitivity analysis of each elastic constant on the measured resonant frequencies has thus been performed. It shows that, in its current state of development, not all of the elastic constants can be identified robustly and a modified identification procedure is thus proposed. This modified procedure has been applied successfully to wood samples with a large density range, including softwood and hardwood, and particularly non-homogeneous wood species or with specific anatomical features.

Static and dynamic performance of bistable MEMS membranes

Abstract: This paper reports on the characteristic behaviour of bistable MEMS membranes before, during and after switching between the two ground states. For this purpose, silicon membranes with a diameter in the range of 300–800 μm and a thickness in the range of 2–5 μm were investigated. To achieve bistability, hydrogenated amorphous silicon carbide layers with different thicknesses in the range of 50 nm–400 nm were deposited on the silicon membranes using an inductively-coupled plasma-enhanced chemical vapour deposition process. With this bi-layered approach, an initial deflection of 2.5–8.1 μm was achieved which results in a total switching displacement of 5–16.2 μm A setup for bulge testing in combination with a Whitelight interferometer was used to analyse the membrane behaviour before the bi-stable switching. The pressure difference required to initiate switching between the ground states was in the range of 20–320 mbar. Both parameters (i.e. static deflection and switching pressure) are in excellent agreement with an analytical model. When increasing the pressure the membranes deflect up to 2.4 μm before switching, strongly depending on the diameter of the membranes. The dynamic measurements with the laser Doppler vibrometer showed switching times in the range of 5–20 μs, maximum velocities in the range of 1.5 to 4.3 m∙s−1 and high maximum accelerations between 2 to 11∙106 m∙s-2 depending on membrane properties such as diameter, thickness and mechanical stress. Finally, with fast Fourier transform analyses of the measured velocity signal characteristics Eigenmodes of the membrane are determined dominating the oscillation behaviour after switching, thus indicating approaches for effective damping with integrated actuators.

Learning to See the Vibration: A Neural Network for Vibration Frequency Prediction.

Abstract: Vibration measurement serves as the basis for various engineering practices such as natural frequency or resonant frequency estimation. As image acquisition devices become cheaper and faster, vibration measurement and frequency estimation through image sequence analysis continue to receive increasing attention. In the conventional photogrammetry and optical methods of frequency measurement, vibration signals are first extracted before implementing the vibration frequency analysis algorithm. In this work, we demonstrate that frequency prediction can be achieved using a single feed-forward convolutional neural network. The proposed method is verified using a vibration signal generator and excitation system, and the result compared with that of an industrial contact vibrometer in a real application. Our experimental results demonstrate that the proposed method can achieve acceptable prediction accuracy even in unfavorable field conditions.

Non-contact ultrasonic inspection of impact damage in composite laminates by visualization of Lamb wave propagation

Abstract: This study demonstrates a rapid non-contact ultrasonic inspection technique by visualization of Lamb wave propagation for detecting impact damage in carbon fiber reinforced polymer (CFRP) laminates. We have developed an optimized laser ultrasonic imaging system, which consists of a rapid pulsed laser scanning unit for ultrasonic generation and a laser Doppler vibrometer (LDV) unit for ultrasonic reception. CFRP laminates were subjected to low-velocity impact to introduce barely visible impact damage. In order to improve the signal-to-noise ratio of the detected ultrasonic signal, retroreflective tape and a signal averaging process were used. We thus successfully visualized the propagation of the pulsed Lamb A0 mode in the CFRP laminates without contact. Interactions between the Lamb waves and impact damage were clearly observed and the damage was easily detected through the change in wave propagation. Furthermore, we demonstrated that the damage could be rapidly detected without signal averaging. This method has significant advantages in detecting damage compared to the conventional method using a contact resonant ultrasonic transducer due to the absence of the ringing phenomenon when using the LDV.

Optical Measurement of Ultrasonic Fourier Transforms

Abstract: This paper presents a framework for a highperformance ultrasonic Fourier transform. By virtue of the properties of ultrasonic wave propagation, the Fourier transform of a transducer pattern can be retrieved from the wave diffraction pattern at the far-field. The computational complexity of an ultrasonic Fourier transform can be approximated by O(N), taking advantage of the fact that the field from each of the pixels is propagated and added in parallel. In the paper, we demonstrate this principle with a single CMOS compatible aluminum nitride transducer pixel on a silicon substrate. The transducer is driven by a pulsed gigahertz electric signal. The displacement of the backside silicon is detected by an optical UHF-120 vibrometer. The measured displacement pattern in the far field of a square transducer is compared to the predicted ultrasonic field distribution and the analytical Fourier transform.