Shear Surface Waves Research Articles

Phase velocity shifts of shear surface waves in flexoelectric wave-guide clamped on piezomagnetic base

Surface acoustic wave devices featuring periodic layers of piezomagnetic and piezoelectric-flexoelectric layers are subject to intense investigation. In miniaturized devices, large strain gradients are possible that produce significant flexoelectric fields in piezoelectric components. In the present theoretical research, surface acoustic wave transference has been manifested in a flexoelectric waveguide clamped over a piezomagnetic base. This endeavor involves the formulation and solution of coupled magneto-electro-elastic field equations governing the structure’s behavior. Coupled magneto-electro-elastic field equations for the structure have been derived and solved utilizing analytical techniques. By accounting for pertinent boundary conditions, the dispersion relations characterizing the velocity of surface waves, both in scenarios with and without electrodes have been obtained. Based on proper numerical examples, the frequency and phase velocity spectrum have been plotted offering insights into key parameters i.e. modal frequency, phase velocity, and wave attenuation. The outcomes of the theoretical study may be helpful in providing insights into mechanical wave propagation in coupled piezoelectric/piezomagnetic structures.

Synthesis and Application of Polymer SXFA in the Detection of Organophosphine Agents with a SAW Sensor.

The effective detection of isopropyl methylfluorophosphonate (GB, sarin), a type of organophosphine poisoning agent, is an urgent issue to address to maintain public safety. In this research, a gas-sensitive film material, poly (4-hydroxy-4,4-bis trifluoromethyl)-butyl-1-enyl)-siloxane (SXFA), with a structure of hexafluoroisopropyl (HFIP) functional group was synthesized by using methyl vinylpropyl dichlorosilane and hexafluoroacetone trihydrate as initial materials. The synthesis process products were characterized using FTIR. SXFA was prepared on a 200 MHz shear surface wave delay line using the spin-coating method for GB detection. A detection limit of <0.1 mg/m3 was achieved through conditional experiments. Meanwhile, we also obtained a maximum response of 2.168 mV at a 0.1 mg/m3 concentration, indicating the much lower detection limit of the SAW-SXFA sensor. Additionally, a maximum response standard deviation of 0.11 mV with a coefficient of variation of 0.01 and a maximum recovery standard deviation of 0.22 mV with a coefficient of variation of 0.02 were also obtained through five repeated experiments. The results show that the SAW-SXFA sensor has strong selectivity and reproducibility, good selectivity, positive detection ability, high sensitivity, and fast alarm performance for sarin detection.

Role of wave scattering in instability-induced Langmuir circulation

We consider a classical problem about dynamic instability that leads to the Langmuir circulation. The problem statement assumes that there is initially a wind-driven shear flow and a plane surface wave propagating in the direction of the flow. The unstable mode is a superposition of (i) shear flow and (ii) surface waves, both modulated in the horizontal spanwise direction and (iii) circulation that is made up with vortices forming near-surface rolls whose axes are coaligned along the shear flow streamlines and whose transverse size corresponds to the modulation period. Usually, the Langmuir circulation is understood as the vortical part of the mode slowly varying in time, which is the combination of the first and the last flows. The novelty of our approach is that we, first, take into account the scattering of the initial surface wave on the slow current. Second, we find the interference of the scattered and the initial waves generating a Stokes drift modulated in the same direction. Third, we establish the subsequent effect of the circulation by the vortex force created by the nonlinear interaction of the initial shear flow and the modulated part of the Stokes drift. Leibovich and Craik previously showed that the third part of the mechanism could maintain the Langmuir circulation. We calculate the growth rate that is approximately twice smaller than that obtained by Craik. The vertical structure of the circulation in the mode consists of two vortices, which corresponds to the next mode in Craik's model.

SH Waves in a Half-Space Model of Functionally Gradient Piezoelectric Semiconductors with Initial Stresses

In terms of piezoelectric class (6 mm) crystal semiconductor, the propagation of shear surface waves on the half-space surface under initial stresses is studied. The initial stresses and material parameters are hypothesized to exponentially vary along direction only. Besides, the velocity equations of SH waves can be obtained based on the boundary conditions and the kinematic equations of the initially stressed graded piezoelectric semiconductor material, as well as the traction-free boundary conditions. Based on the numerical results, we explore how the semiconductivity, initial stresses as well as material gradient index impact the dispersive curves.

Laser ultrasonic inspection for mechanical properties of materials at high temperature

The measurement of mechanical properties of high-temperature resistant materials at high temperatures is particularly critical, and laser ultrasonic non-destructive testing technology is a prospective approach for measuring mechanical properties in high-temperature environments. Laser ultrasonic propagation models are constructed by finite element analysis, which reveals the effects of different excitation mechanisms on acoustic velocity measurements. It is found that the shear wave in the main propagation direction is hardly detected, and the distinction between shear waves and surface waves in the time domain signal is difficult. Based on the conclusions, the relationships between surface waves, longitudinal waves, and mechanical properties of materials are established by theoretical derivation. According to the propagation characteristics of surface waves and longitudinal waves, the eccentricity detection scheme of the same side and the concentricity detection scheme of the opposite side are, respectively, designed. The velocities of surface waves and longitudinal waves are measured, considering the thermal expansion coefficient and density changes with temperature. The mechanical properties of materials at different temperatures (25–1000 °C) are successfully calculated, and the experimental results are well in accordance with the reference values. It gives a reliable basis for efficient measurement of mechanical properties of materials at high temperatures.

Dispersion of surface elastic waves on Z-LiNbO3 films on Z-sapphire

Epitaxial thin films of lithium niobate with a thickness of 160 nm, oriented along the crystallographic c axis, were grown by direct liquid injection chemical vapor deposition on c-sapphire substrates. Different families of very high-frequency surface acoustic waves with general polarization exist in such piezoelectric films on high-velocity substrates. Surface Brillouin light scattering measurements, complemented with fast finite element analysis of wave dispersion, demonstrate Rayleigh, leaky shear, and leaky longitudinal surface waves, excited at frequencies between 10 and 30 GHz. The Brillouin technique reveals dispersion and anisotropy of propagation without the implementation of high-frequency surface acoustic wave transducers.

Dispersion of Shear Surface Waves in an Elastic Substrate Imperfectly Bonded with an Elastic Layer

Исследовано распространение поверхностной поперечной волны для слоистой структуры, состоящей из упругого слоя, лежащего на упругом полупространстве с поверхностью неполного упругого контакта. Рассмотрены две различные модели неполного упругого. Получены дисперсионные уравнения, описывающие зависимость фазовой скорости поверхностной волны от волнового числа. На основе анализа дисперсионных уравнений показано, что несовершенство границы раздела может существенно уменьшить или увеличить фазовую скорость поверхностной волны. Առաձգական կիսատարածության վրա գտնվող և թերի կոնտակտ ունեցող առաձգական շերտ բաղադրյալ կառուցվածքի համար ուսումնասիրված է մակերևութային լայնական ալիքի տարածումը: Դիտարկվել են թերի կոնտակտի երկու տարբեր մոդելներ: Ստացվել են դիսպերսիոն հավասարումներ, որոնք նկարագրում են մակերևութային ալիքի ֆազային արագության կախումը ալիքային թվից: Դիսպերսիոն հավասարումների հետազոտումով ցույց է տրվել, որ բաժանման եզրի անկատարությունը կարող է էապես մեծացնել, կամ փոքրացնել մակերևութային ալիքի ֆազային արագությունը: The surface shear wave is studied in layered bi-material structure consisting from an elastic layer lying on an elastic half-space with an imperfectly bonded interface. The two models of the imperfect “slip” and “scattering” interface are considered. The dispersion equations are obtained describing the surface wave phase speed versus wavenumber. Based on the analysis of dispersion equations it is shown that the interface imperfectness can sufficiently decrease in “slip” case or increase in “scattering” case the surface wave phase speed.

Modelling of coupled magnetoelastic waves in structure containing thin antiferromagnetic films on an elastic substrate

In this work we present a model explaining the properties of magnetoelastic waves propagation in the heterostructure containing an antiferromagnetic layer on a non-magnetic elastic substate. Horizontally polarized shear surface waves (SH-waves) propagating in thin film are Love waves. The dispersion characteristic of magnetoelastic waves in such structure was obtained, and the effect of variation of the thickness of the antiferromagnetic layer and the external magnetic field on the frequency of the magnetoelastic resonance was also studied. It was found that an increase in the magnetic field magnitude leads to the increase in the magnetoelastic resonance frequency, and, on the contrary, with an increase in the thickness of the AFM layer the magnitude of the magnetoelastic resonance frequency decreases. The obtained results can be used to develop devices for generating and processing signals in the GHz and THz frequency ranges.

Machine learning techniques for estimating seismic site amplification in the Santiago basin, Chile

Seismic site amplification and seismic hazard maps are crucial inputs for decision making and risk evaluation in places where seismicity imposes a significant risk to human life and infrastructure. In this work, we propose a novel machine learning (ML) based methodology to integrate qualitative and quantitative data to map the degree of seismic amplification in an area of Chile, one of the most seismically active countries on Earth. Our method uses measurements of surface shear wave velocities (Vs30) and predominant frequencies (f0) combined with gravity anomaly maps to update the geographic extension of seismic amplification classes. Additionally, we trained the predictive models to interpolate and extrapolate Vs30 and f0 to the unsampled sites. Applying this method to the Santiago basin resulted in (i) a refined seismic amplification map, and (ii) maps of Vs30 and f0 estimated with improved accuracy. The best predictions, obtained by ML techniques and validated through cross-validation, are possibly due to the inclusion of spatial covariates for algorithm training, enhancing the ability of the model to capture the spatial correlations of geological, geophysical and geotechnical data. The estimation of predominant frequencies (f0) is improved considerably by including gravity as a covariant. The accuracy of the f0 predictions apparently depends more on the choice of covariates than on the algorithm used, while the Vs30 predictions are more sensitive to the chosen algorithm. These results illustrate the great potential of machine learning predictive algorithms in digital soil mapping, which surpass traditional geostatistical techniques. The major contribution of this work is to introduce a novel methodology, based on artificial intelligence models, to extend local measurements of site-specific dynamic properties. This information can be used to quantitatively estimate seismic hazard over a regional scale.

Imaging of Love Waves and Their Interaction with Magnetic Domain Walls in Magnetoelectric Magnetic Field Sensors

AbstractThe complex behavior of horizontally polarized surface shear waves in magnetoelectric surface acoustic wave based magnetic field sensor devices is revealed by time‐resolved magnetooptical microscopy with picosecond temporal and submicron spatial resolution. The imaging of the propagating waves in the magnetoelectric composites is realized through the functional soft‐magnetic layer by coupled magnetoelastic interactions. Partial surface wave reflections, wave front dephasing, and secondary wave generation occur, which originate from structures and magnetic domain walls. Closure domain structures bend and reflect the magnetic surface waves. Strain stimulated magnetic domain walls display dynamic periodic expansions, which propagate along the domain walls and change the magnetomechanical response also in the surrounding regions. The revealed spatial and temporally varying nondeterministic response restricts the noise performance of the surface acoustic wave based magnetic field sensors and thus confines the sensor's limit of detection. Magnetic time‐resolved optical imaging is shown to be a powerful method for the operando characterization of magnetoelectric devices and in‐plane displacement surface acoustic wave fields that are not accessible by other methods.

Role of odd viscosity in falling viscous fluid

The aim of the present study is to investigate the linear and nonlinear wave dynamics of a falling incompressible viscous fluid when the fluid undergoes an effect of odd viscosity. In fact, such an effect arises in classical fluids when the time-reversal symmetry is broken. The motivation to study this dynamics was raised by recent studies (Ganeshan &amp; Abanov, Phys. Rev. Fluids, vol. 2, 2017, p. 094101; Kirkinis &amp; Andreev, J. Fluid Mech., vol. 878, 2019, pp. 169–189) where the odd viscosity coefficient suppresses thermocapillary instability. Here, we explore the linear surface wave and shear wave dynamics for the isothermal case by solving the Orr–Sommerfeld eigenvalue problem numerically with the aid of the Chebyshev spectral collocation method. It is found that surface and shear instabilities can be weakened by the odd viscosity coefficient. Furthermore, the growth rate of the wavepacket corresponding to the linear spatio-temporal response is reduced as long as the odd viscosity coefficient increases. In addition, a coupled system of a two-equation model is derived in terms of the fluid layer thickness $h(x,t)$ and the flow rate $q(x,t)$. The nonlinear travelling wave solution of the two-equation model reveals the attenuation of maximum amplitude and speed in the presence of an odd viscosity coefficient, which ensures the delay of transition from the primary parallel flow with a flat surface to secondary flow generated through the nonlinear wave interactions. This physical phenomenon is further corroborated by performing a nonlinear spatio-temporal simulation when a harmonic forcing is applied at the inlet.

Analytical and numerical investigation of finite and infinite periodic lattices for mitigation of seismic waves in layered grounds

This paper studies periodically arranged seismic barriers consisting of finite and infinite lattices to mitigate seismic surface waves in layered soils. Using Bloch-Flouquet theory, three different configurations of periodic barriers are examined. Rayleigh, Love, and shear surface waves are quantitatively identified using three conceptions: depth of energy, sagittal polarization ratio, and sound cone. The performed analyses suggest that if barriers increase the surface stiffness of existing ground, Rayleigh modes will be located above the sound cone, thus providing energy dissipating channels through bulk modes. Numerical modeling of finite barriers in time and frequency domains validates the concept of Rayleigh modes’ energy dissipation to bulk modes. The results indicate that the designed barriers effectively reduce the amplitude of surface seismic waves, thus mitigating damage from seismic events.

Optical coherence elastography to evaluate depth-resolved elasticity of tissue.

Skin-elasticity measurements can assist in the clinical diagnosis of skin diseases, which has important clinical significance. Accurately determining the depth-resolved elasticity of superficial biological tissue is an important research direction. This paper presents an optical coherence elastography technique that combines surface acoustic waves and shear waves to obtain the elasticity of multilayer tissue. First, the phase velocity of the high-frequency surface acoustic wave is calculated at the surface of the sample to obtain the Young's modulus of the top layer. Then, the shear wave velocities in the other layers are calculated to obtain their respective Young's moduli. In the bilayer phantom experiment, the maximum error in the elastic estimation of each layer was 2.2%. The results show that the proposed method can accurately evaluate the depth-resolved elasticity of layered tissue-mimicking phantoms, which can potentially expand the clinical applications of elastic wave elastography.

3-D synthetic modelling and observations of anisotropy effects on SS precursors: implications for mantle deformation in the transition zone

SUMMARY The Earth's mantle transition zone (MTZ) plays a key role in the thermal and compositional interactions between the upper and lower mantle. Seismic anisotropy provides useful information about mantle deformation and dynamics across the MTZ. However, seismic anisotropy in the MTZ is difficult to constrain from surface wave or shear wave splitting measurements. Here, we investigate the sensitivity to anisotropy of a body wave method, SS precursors, through 3-D synthetic modelling and apply it to real data. Our study shows that the SS precursors can distinguish the anisotropy originating from three depths: shallow upper mantle (80–220 km), deep upper mantle above 410 km, and MTZ (410–660 km). Synthetic resolution tests indicate that SS precursors can resolve $\ge $3 per cent azimuthal anisotropy where data have an average signal-to-noise ratio (SNR = 7) and sufficient azimuthal coverage. To investigate regional sensitivity, we apply the stacking and inversion methods to two densely sampled areas: the Japan subduction zone and a central Pacific region around the Hawaiian hotspot. We find evidence for significant VS anisotropy (15.3 ± 9.2 per cent) with a trench-perpendicular fast direction (93° ± 5°) in the MTZ near the Japan subduction zone. We attribute the azimuthal anisotropy to the grain-scale shape-preferred orientation of basaltic materials induced by the shear deformation within the subducting slab beneath NE China. In the central Pacific study region, there is a non-detection of MTZ anisotropy, although modelling suggests the data coverage should allow us to resolve at least 3 per cent anisotropy. Therefore, the Hawaiian mantle plume has not produced detectable azimuthal anisotropy in the MTZ.

Perbandingan Peta Percepatan Tanah di Permukaan sebagai Dasar Perencanaan Tata Ruang Berbasis Mitigasi Bencana di Provinsi Riau

Spatial planning has an important role in disaster mitigation efforts. The availability of earthquake maps is very useful in spatial planning. The need for spatial planning today is micro spatial planning. Therefore, the 2017 national earthquake map needs to be detailed into a micro zonation map at the district or city scale. The ground acceleration presented in the national earthquake map was the acceleration at bedrock, while in spatial planning it is the necessary acceleration at the surface. Therefore, the purpose of this research was to obtain a map of the earthquake at the surface with a micro-scale. Determination of the acceleration value at the surface was carried out by two models. Model-1, the surface acceleration was obtained by multiplying the results of the PSHA analysis at bedrock by the amplification factor based on SNI-1726. While Model-2, the acceleration value at the surface was directly obtained from the results of PSHA analysis using the average surface shear wave velocity (Vs30) based on data from the USGS. The result of this study showed that from the 2 analytical models used, Model-2 has a higher surface acceleration value than Model-1. Riau Province has 12 districts. in general, the 12 districts were included in the low to moderate risk index class, but there was one district that was close to the high index class, namely Rokan Hulu district.

Horizontal-to-Vertical Spectral Ratio of Ambient Vibration Obtained with Hilbert-Huang Transform.

The Horizontal-to-Vertical Spectral Ratio (HVSR) of ambient vibration measurements is a common tool to explore near surface shear wave velocity (Vs) structure. HVSR is often applied for earthquake risk assessments and civil engineering projects. Ambient vibration signal originates from the combination of a multitude of natural and man-made sources. Ambient vibration sources can be any ground motion inducing phenomena, e.g., ocean waves, wind, industrial activity or road traffic, where each source does not need to be strictly stationary even during short times. Typically, the Fast Fourier Transform (FFT) is applied to obtain spectral information from the measured time series in order to estimate the HVSR, even though possible non-stationarity may bias the spectra and HVSR estimates. This problem can be alleviated by employing the Hilbert–Huang Transform (HHT) instead of FFT. Comparing 1D inversion results for FFT and HHT-based HVSR estimates from data measured at a well studied, urban, permanent station, we find that HHT-based inversion models may yield a lower data misfit by up to a factor of 25, a more appropriate Vs model according to available well-log lithology, and higher confidence in the achieved model.

Shear surface wave propagation in stratified media with slip interfaces

Shear surface wave propagation in stratified media with slip interfaces

Shear surface wave propagation in stratified media with slip interfaces

The surface shear wave propagation is studied in elastic semi-spaces separated by elastic layer with an imperfectly bonded interface between layer and semi-spaces. The dispersion equations are obtained analytically describing the surface wave phase speed. Based on the dispersion equation analysis it is shown that the interface imperfectness sufficiently decreases the phase speed and can increase the number of shear wave modes too.

Green’s function and surface waves in a viscoelastic orthotropic FGM enforced by an impulsive point source

Abstract Analytical and numerical approach are taken into consideration to analyze the propagation behavior of horizontally polarized shear surface waves (SH-wave) influenced by an impulsive point source in pre-stressed heterogeneous Voigt-type viscoelastic orthotropic functionally graded (FGM) layered structure. The mechanical properties of the material of viscoelastic functionally graded layer vary with respect to a certain depth as a hyperbolic function, while it varies as a quadratic function for the viscoelastic functionally graded half-space. The complex wave velocity of SH-wave has been achieved by the method of Green’s function and Fourier transformation under the appropriate boundary conditions of the adopted model. The derived wave velocity of SH-waves has been reduced to the classical equation of Love wave when both the viscoelastic orthotropic FGM layer and half-space are considered to be homogeneous isotropic elastic, as depicted in the section of particular cases and validation. Moreover, numerical computation of the obtained velocity equation has been performed and the substantial effects of viscoelasticity and heterogeneity on phase velocity as well as attenuation coefficient for both the cases of absence and presence of initial stress in the media have been perceived by the means of graphs. The final results of this work may be relevant to understand the useful information of SH-wave propagation in the considered layered structure.

Numerical simulation of laser-generated ultrasonic waves for detection surface defect on a cylinder pipe

The non-destructive detection of cylindrical pipe defects is still open to research. In this letter, we report a study of the detection method for the surface defect in the cylindrical pipe by using the laser ultrasonic wave. In this study, the propagation characteristics of laser-generated ultrasonic waves in a cylindrical pipe have been analyzed by the finite element method. The simulation results indicated that the laser-generated surface wave and shear wave converted to surface wave can be used to detect the surface defect in the cylindrical pipe. The maximum negative peak of reflected surface waves due to surface defects increases as the depth of surface defects increases. The position of surface defects through B-scan images can be detected. The proposed method may provide a useful way to detect of the surface defect in the cylindrical pipe.