Acoustic Wave Measurements Research Articles

Optical polarimetric measurement of surface acoustic waves

A surface acoustic wave (SAW) is utilized in diverse fields ranging from physics, engineering, to biology for transducing, sensing, and processing various signals. Optical measurement of the SAW provides valuable information since the amplitude and the phase of the displacement field can be measured locally with the resolution limited by the spot size of the optical beam. So far, optical measurement techniques rely on modulation of the optical path, phase, or diffraction associated with SAWs. Here, we demonstrate that SAWs can be measured with an optical polarimeter. We show that the slope of the periodically tilting surface due to the coherently driven SAW is translated into the angle of polarization rotation, which can be straightforwardly calibrated when polarimeters work in the shot-noise-limited regime. The polarimetric measurement of SAWs is, thus, beneficial for quantitative studies of SAW-based technologies.

Nondestructive Evaluation of Electroplating-Induced Hydrogen Embrittlement in Cadmium-Coated High-Strength Steel Using Ultrasonic Surface Waves

Development of a nondestructive evaluation (NDE) method to detect nascent hydrogen embrittlement (HE) in electroplated high-strength steel parts is becoming important for the aerospace industry. This research investigates the feasibility of surface acoustic waves (SAWs) measurements to distinguish between cadmium (Cd) plated SAE 4340 steel samples with low and high HE susceptibilities. SAWs were generated with a 10 MHz piezoelectric transducer and detected by line scans via a laser Doppler vibrometer setup. Using signal processing algorithms in MATLAB, SAW velocities as well as attenuation coefficients were estimated. Depth profiles of steel hardness near coatings were also evaluated using Vickers microindentation tests. Average steel hardness in not-baked samples was slightly increased. Cd coatings were characterized by laser and optical microscopy methods. Small variations found in thickness and surface roughness of the Cd coatings among the samples did not significantly affect the NDE results. On average, samples in the not-baked condition (high HE risk) exhibited lower SAW attenuation coefficients compared to immediately baked and late-baked conditions (low HE risk). However, it was not possible to distinguish between the manufacturing conditions of individual samples due to overlaps in attenuation measurement results. SAW velocities as estimated by the cross-correlation method were found to be not sensitive to manufacturing conditions.

Detection and numerical simulation of blasting-induced damage in shallow-buried twin tunnels with small spacing

In order to study the damage effect of blasting load on the surrounding rock of shallow-buried small spacing twin tunnels, the shallow-buried tunneling section of the south extension project of Shunhe Expressway is taken as the engineering background. Firstly, based on the dynamic damage evolution and Hoffman failure criterion, an anisotropic dynamic damage constitutive model for rock materials is established. Then, by using the secondary development function of the LSDYNA software, the constitutive model is applied to the numerical simulation of the tunnel blasting damage. Finally, based on the acoustic wave measurement theory, the wave velocities in the surrounding rock of the shallow-buried small spacing twin tunnels before and after blasting were measured by using non-metallic ultrasonic detectors, and the damage of the surrounding rock is evaluated from changes in wave velocity. The applicability of the anisotropic dynamic damage constitutive model and the accuracy of the numerical results are verified by comparing the numerical simulation results with the field test results. The numerical simulation results show that the maximum damage radius of single-hole blasting is 0.58 m, and the maximum damage depth is 1.88 m. According to the damage threshold of the rock mass, the horizontal failure range of the rock mass can reach 0.14 m, and the failure depth is 1.70m. According to the field test, the damage degree of the middle intercalated rock is higher than that of the other parts of the surrounding rock in the alternate blasting excavation of the double track tunnel. The damage depth of the surrounding rock caused by blasting excavation is about 0.5 m, which is close to the simulation results, and verifying the accuracy of the anisotropic dynamic damage constitutive model. The research results have a certain guiding role on the blasting excavation and damage control of shallow-buried twin tunnels with small spacing..

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

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.

Autonomous Machine Learning Algorithm for Stress Monitoring in Concrete Using Elastoacoustical Effect.

The measurement of stress in concrete structures is a complex issue. This paper presents a new measurement system called a self-acoustic system (SAS), which uses frequency measurements of acoustic waves to determine the condition of concrete structures. The SAS uses a positive feedback loop between ultrasonic heads, which causes excitation to a stable limit cycle. The frequency of this cycle is related to the propagation time of an acoustic wave, which directly depends on stresses in the test object. The coupling mechanism between acoustic wave propagation speed and stress is the elastoacoustic effect described in this paper. Thus, the proposed system enables the coupling between the limit cycle frequency and the stress degree of the concrete structure. This paper presents a machine learning algorithm to analyse the frequency spectrum of the SAS system. The proposed solution is a real-time classifier that enables online analysis of the frequency spectrum from the SAS system. With this approach, an autonomous system for stress condition identification of concrete structures is built and described.

Temperature field estimation of an axisymmetric laminar flame via time-of-arrival measurements of acoustic waves, and machine learning

In this study, temperature field estimation was performed via time-of-arrival measurements of acoustic waves and using machine learning. An axisymmetric combustion field created by a McKenna burner was chosen as the measurement region. Electrical discharges served as the acoustic point source, and the acoustic travel times were measured using microphones installed along the periphery of the measurement region. In particular, acoustic waves refract under a temperature gradient, which makes it difficult to obtain an explicit analytic expression for the solution. Hence, a model that predicts the profile from the acoustic travel times was acquired through machine learning. As the number of acoustic paths with different travel times was four, the radial temperature profile was first parameterized by four variables. Then, big data of acoustic travel times corresponding to a set of variable values were produced using a simulator that calculates acoustic trajectories and the corresponding travel times. Finally, the model, in the form of the simplest artificial neural network with a single hidden layer, was trained with the generated big data. The temperature fields were obtained from the measured acoustic travel times using the model and found to match well with those measured using a thermocouple.

Research on Temperature Monitoring Method and System Design for Key High Voltage Equipment of Wind Farm

This paper focuses on the temperature detection of high-voltage equipment in wind power plant, puts forward the surface acoustic wave measurement method, and deeply studies the design process of surface acoustic wave sensor device and the design scheme of monitoring system. In different process materials of piezoelectric substrate and antenna design mode, there will be great differences in the transmission efficiency and anti-interference ability of surface acoustic wave. Therefore, the influence of surface acoustic wave on the performance of surface acoustic wave sensor device is possible Testing and setting the surface measurement parameters can improve the measurement performance. In the aspect of detection system, the typical key temperature monitoring equipment of high voltage switch cabinet in wind farm is selected to form a practical deployment scheme, which realizes the integrated functions of automatic temperature measurement, parameter optimization and adjustment, alarm and so on. The research and design method in this paper has great practical application value in the operation and control of new energy system.

Love wave transference in piezomagnetic layered structure guided by an imperfect interface

The problem presents an analytical study of the wave transference in piezo-composite layer lying over an elastic substrate. The interface of the geometry is assumed to be imperfect. The imperfection is characterized by Linear Spring Model. Dynamics of the media taken are framed in form of direct Sturm–Liouville problem. Dispersion relations are found for both magnetically open and magnetically short case. Velocity profile of Love wave has been delineated through graphs for different affecting parameters (i.e., imperfection at the interface, layer thickness and heterogeneity in the substrate). It has been shown that the increase in these parameters increases the phase velocity of the Love wave. Further, layer thickness is noted to have a less effect on the velocity profile of the wave as compared to heterogeneity in the substrate. Moreover, a comparative study has been shown between the aforementioned cases with the variation in imperfect parameter. The velocity in open case is found to be higher than that of short case. The obtained results may provide guidance towards optimization of Surface Acoustic Wave devices and measurement of imperfections.

Studies on a Piezoelectric Cylindrical Transducer for Borehole Dipole Acoustic Measurements

In this article, a novel design of a piezoelectric dipole transducer is proposed for formation acoustic velocity measurement in the vicinity of a borehole with a frequency range of 0.4–6 kHz. The transducer which actuates a cylindrical shell to generate a pure dipole mode wave by using multiple piezoelectric bender bars is analyzed theoretically and simulated numerically by using the finite element method (FEM). Moreover, the transducer is fabricated and tested to compare with the numerical simulation results, which shows that the test and simulation results are in good agreement. Finally, compared with numerical simulation results of the traditional dipole transducer, it is shown that the proposed dipole transducer has higher transmitting sensitivities than commonly used ones, especially in low frequency responses. This work lays a foundation for the new development of the transducer in borehole dipole acoustic shear wave measurements. Especially, in a slow formation where the shear wave velocity is lower than that of compressional wave in the borehole fluid, the transducer could be used for highly efficient shear wave velocity measurements.

Principle Analysis and Experimental Measurement of Sound Wave Frequency Attenuation

Acoustic wave measurement; Frequency attenuation; Sensors

An active source seismo-acoustic experiment using tethered balloons to validate instrument concepts and modelling tools for atmospheric seismology

SUMMARYThe measurements of acoustic waves created by a quake are of great interest for planets with hot and dense atmospheres, like Venus, because surface deployments of seismometers will last only a few hours, whereas freeflying balloons could fly many days. Infrasound sensors can also be used to constrain subsurface properties during active seismic experiments. This study presents a controlled source seismo-acoustic experiment using infrasonic sensors and accelerometers mounted on a tethered helium balloon. Both the acoustic waves generated below the balloon by seismic surface waves, and the ones generated by strong ground motions above the seismic source are clearly observed and separated on the records of the various instruments. This data set allows various validations and investigations. First, it validates the ground to air coupling theory and our numerical modelling tools. Then, it allows us to demonstrate that antenna processing of infrasound sensors deployed below the balloon can estimate the arrival incidence angle of the acoustic waves within 10°. Finally, a polarization analysis of the accelerometers taped on the balloon envelope is presented. It demonstrates that accelerometer records are strongly dependent on their location on the balloon due to its deformations and rotations. However, the different acoustic signals can be distinguished through their polarization, and a best sensor location is estimated at the bottom of the balloon envelope. These results are a first step towards detecting and locating seismic activity using airborne acoustic sensors on Venus and elsewhere. However, some observations of earthquake signals in a more realistic geometry are still missing.

Recovering piecewise constant refractive indices by a single far-field pattern

We are concerned with the inverse scattering problem of recovering an inhomogeneous medium by the associated acoustic wave measurement. We prove that under certain assumptions, a single far-field pattern determines the values of a perturbation to the refractive index on the corners of its support. These assumptions are satisfied, for example, in the low acoustic frequency regime. As a consequence if the perturbation is piecewise constant with either a polyhedral nest geometry or a known polyhedral cell geometry, such as a pixel or voxel array, we establish the injectivity of the perturbation to far-field map given a fixed incident wave. This is the first unique determinancy result of its type in the literature, and all of the existing results essentially make use of infinitely many measurements.

Dual-laser-induced Breakdown Thermometry via Sound Speed Measurement：A New Procedure for Improved Spatiotemporal Resolution.

Measurement of acoustic waves from laser-induced breakdown has been developed as gas thermometry in combustion atmospheres. In the measurement, two laser-induced breakdown spots are generated and the local gas temperature between these two spots is determined through the measurement of the sound speed between them. In the previous study, it was found that the local gas breakdown can introduce notable system uncertainty, about 5% to the measured temperature. To eliminate the interference, in present work, a new measurement procedure was proposed, where two individual laser pulses with optimized firing order and delay time were employed. With the new measurement procedure, the system uncertainty caused by local gas breakdown can be largely avoided and the temporal and spatial resolutions can reach up to 0.5 ms and 10 mm, respectively. The improved thermometry, dual-laser-induced breakdown thermometry (DLIBT), was applied to measure temperatures of hot flue gases provided by a multijet burner. The measured temperatures covering the range between 1000 K and 2000 K were compared with the ones accurately obtained through the two-line atomic fluorescence (TLAF) thermometry with a measurement uncertainty of ~3%, and a very good agreement was obtained.

Acoustic waves in granular packings at low confinement pressure

Elastic properties of a granular packing show a nonlinear behavior determined by its discrete structure and nonlinear inter-grain force laws. Acoustic waves show a transition from constant, pressure-dependent sound speed to a shock-wave-like behavior with an amplitude-determined propagation speed. This becomes increasingly visible at low static confinement pressure as the transient regime shifts to lower wave amplitudes for lower static pressure. In microgravity, confinement pressure can be orders of magnitude lower than in a ground-based experiment. In addition, the absence of hydrostatic gradients allows for much more homogeneous and isotropic pressure distribution. We present a novel apparatus for acoustic wave transmission measurements at such low packing pressures. A pressure control loop is implemented by using a microcontroller that monitors static force sensor readings and adjusts the position of a movable wall with a linear-motor until the desired pressure is reached. Measurements of acoustic waves are possible using accelerometers embedded in the granular packing as well as piezos. For excitation, we use a voice-coil-driven wall, with a large variety of signal shapes, frequencies, and amplitudes. This enables experiments in both the linear and strongly nonlinear regimes.

The Combined Method of Ray Tracing and Diffraction and Its Application to Ultra-wideband Pulse Propagation

In this study the scattered-filed computation using the combined method of ray tracing and diffraction (CMRD) is revisited but with an extension to the backscattering computation. The concept of the equivalent phase object is considered as the key part in the developed CMRD method, and is analyzed mathematically with accurately derived expressions for its amplitude and phase function. A formulated CMRD method for the backscattering computation is developed in this work, which is then used in the forward modeling and numerical computations for ultra-wideband pulse propagation and backscattering from a perfectly conducting circular cylinder. The numerical simulation indicates that reasonable and good agreements can be achieved for comparisons between our CMRD method and exact eigenfunction expansion approach. It is expected that the theoretical model and method of backscattering calculation using CMRD can be applied to the image processing and target identification with measurements of backward-scattered electromagnetic and acoustic waves.

Nanoscale thermal transport and elastic properties of lithiated amorphous Si thin films

Silicon is the heart of modern electronics and due to it is high theoretical storage capacity it also attracted much attention as a possible anode material for the next generation Li-ion batteries. Heat conduction is one of the major properties in the development of Li-ion batteries for energy conversion systems and it is of paramount importance to have comprehensive understanding of heat dissipation on the scale of electrochemical storage device. In this work we report ex-situ study of nanoscale thermal transport and elastic properties of lithiated amorphous Si (a-Si) anode films using picosecond time-domain thermoreflectance (TDTR). Radio frequency (rf) magnetron sputtering was used to deposit a ∼330 nm thick a-Si films on glass substrate. Near-surface nanoscale thermal transport measurements show 40% increase in thermal conductivity of a-Si upon electrochemical lithiation reaching up to 2.2 W m-1K−1. This sizeable increase might be due to Li+ ion-mediated heat conduction during lithiation process. The standard deviation of measured thermal conductivity was slightly higher likely due to inhomogeneous lateral and cross-plane Li+ ions distribution in the sub-surface film region. Nanosecond laser pulsed induced surface acoustic waves (SAWs) measurements showed the decrease in Young’s modulus after lithiation on nanometre scale, which is attributed to volumetric expansion of Si upon Li+ ions insertion.

Holographic measurement of surface acoustic wave parameters in crystals

The theoretical basis of a specialized technique for applying digital holographic interferometry to measure the parameters of surface acoustic waves is presented, a measuring system for visualization and quantitative analysis of the parameters of ultralow-amplitude high-frequency oscillations arising in electronic devices using surface acoustic waves is developed, and experimental results of the study of surface acoustic waves in crystals of lithium niobate are obtained. In this case, to ensure the possibility of recording precision double-exposure interferograms of high-frequency surface acoustic waves, a picosecond pulsed laser with two-stage frequency multiplication was used as a radiation source, and to increase the spatial resolution of the system with the possibility of observing a wide field of view, an adjustable optical zoom of the incoming image was applied to the matrix input (based on charge-coupled devices) of the recording camera and digital zoom was used for obtained interferogram. We achieved the measuring sensitivity of the surface acoustic waves amplitude and spatial-temporal resolution allowing visualization and measurement of surface acoustic waves with amplitudes of the order of 1 nm and frequencies of the order of 10 MHz, which is far beyond the capabilities of standard methods of holographic interferometry.

Spherical microcavity-based membrane-free Fizeau interferometric acoustic sensor.

The monitoring of acoustic waves is essential for a variety of applications, ranging from photoacoustic imaging to industrial non-destructive evaluation and monitoring. Optical acoustic sensors have many advantages over electrical counterparts such as passivity and immunity to electromagnetic interference, and can be quite compact with all-fiber structures. A common approach is to optically detect the acoustically induced mechanical movement of a cantilever or a reflective membrane. However, sensors based on moving mechanical parts have limitations, because they are influenced by the mechanical properties of the structures involved that behave as a coupled spring-mass system. Here a new type of optical acoustic sensing concept based on a spherical microcavity fiber Fizeau interferometer is described. The sensor is fabricated by inserting a section of single-mode fiber into a spherical microcavity to form a Fizeau interferometer. Thanks to the elasto-optic effect, the sound pressure modifies the refractive index of the microcavity; then a corresponding change in the interferometric spectrum can be observed. The sensor was successfully used to detect acoustic waves under the whole audible region, from 20Hz to 20kHz. The experimental results show that the sensitivity can be improved via altering the length of microcavity. The structure is membrane-free, and the sensitivity will not be limited by these size restrictions which makes the technology an interesting alternative to conventional transducers for acoustic wave measurement.

Surface acoustic wave pressure sensor and its matched antenna design

Interdigital transducer and signal transmission in surface acoustic wave pressure sensor design is one of the difficulties in sensor design. The transmission antenna is an important design indicator to determine the wireless function of the sensor. In this paper, we simulated the design of the interdigital transducer of surface acoustic wave pressure sensor through COMSOL and analyzed the relationship between the eigenfrequency of the single-pair interdigital model and the interdigital electrode. Then, we obtained the design of the interdigital electrode with error of 0.01 MHz. We also simulated the size, bandwidth, impedance matching, and other parameters of antenna through high frequency structure simulator, and a matching dipole transmission antenna was designed and miniaturized. When the bandwidth is satisfied, the control matching impedance error is within [Formula: see text], and it is verified that the antenna satisfies the signal transmission requirement of the surface acoustic wave pressure sensor. This design provides a more comprehensive approach to the design of interdigital transducers and signal transmission for the field of surface acoustic wave measurement pressure.

A high-frequency hydrophone using an optical fiber microknot resonator

We propose a compact fiber-optic hydrophone and use it for acoustic wave measurements. The sensor probe comprises a microresonator formed by simply tying a tapered fiber into a loop structure. When the round-trip phase of light is an integer multiple of 2π, a well-defined resonance spectrum is produced by the resonator, with a quality factor as high as 104. Using spectral filtering technology for power interrogation, the steep linear resonance slope leads to sensitive operation of the sensor for high-frequency acoustic wave detection (of the order of several megahertz). After fabricating the sensor, the knot exhibits low-absorption loss underwater and, thus, the device can possibly be used as a hydrophone. The simple fabrication and small size structure of the sensor make it a good candidate for high-resolution scanning imaging.