Shear Horizontal Wave Research Articles

Propagation of shear horizontal (SH) waves in a functionally graded piezoelectric substrate with periodic gratings

Propagation of shear horizontal (SH) waves in a functionally graded piezoelectric substrate with periodic gratings

Lowest remnant thickness estimation using Staircase Magnetostrictive Patch (ScaMP) Transducer

Wall thickness reduction, which typically results from corrosion, erosion, or operating conditions, is a significant challenge in many industries. In order to generate a broadband pure shear horizontal wave mode in plate structures, this paper proposes a magnetostrictive patch transducer called the Staircase Magnetostrictive Patch (ScaMP) Transducer. For ScaMP transduction, an optimised patch width offers a broadband frequency response is employed. The lowest remnant thickness of the sample was estimated using the wideband SH1 dispersive guided wave mode's cut-off property. The broad frequency excitation method enabled measurement over a range of wall thinning up to 80% of the nominal thickness with a single data acquisition. Experiments were carried out on an 8 mm nominal wall thickness aluminium plate with gouge defects to evaluate the proposed sensor's broad frequency response. The measurement of remnant thickness was estimated with a maximum error of 5.5%.

Magnetic skyrmion dynamics induced by surface acoustic waves

Magnetic skyrmions are promising information carriers for high-density memories. The dynamical motion of magnetic skyrmions have been extensively investigated in the development of magnetic racetracks. In this study, a surface acoustic wave (SAW) is theoretically investigated to drive skyrmions by using micromagnetic simulations. The in-plane type and out-of-plane particle displacement components of SAWs generate different magnetoelastic effective fields. The shear horizontal (SH) wave mode SAW drives skyrmions flow movement by the magnetoelastic coupling effect. Increasing the acoustic wave amplitude and magnetoelastic coupling constants, as well as a reduced wavelength, are beneficial for an enhanced skyrmion motion velocity. The skyrmion motion trajectory can be controlled by designing the geometry of magnetic films. Interestingly, in a circular magnetic film, the skyrmions driven by SH waves show clockwise or counterclockwise movement trajectories depending on the sign of topological charges. Our results provide an energy efficient approach to drive skyrmion dynamics including rotational motion, thus paving the way for low-power spintronics.

Analysis of wave-particle drag effect in flexoelectric semiconductor plates via Mindlin method

In this paper, the infinite power series of two-dimensional (2D) differential equations for flexoelectric semiconductor plates are derived by extending the Mindlin method. The zeroth-order and first-order theories are systematically presented and applied to the plate made of cubic crystals of class m3m, identifying explicitly the coupling among wave modes and charge distributions. More specifically, it is observed that the extensional and thickness-stretch waves are coupled with axial motions of free carriers; bending and fundamental shear are coupled with the thickness motions of free carriers, showing the dynamic phenomena of the flexoelectric electronic (flexoelectronic) effect; and the shear-horizontal waves, such as face-shear and thickness-twist, are decoupled. Furthermore, when comparing with the three-dimensional (3D) dispersion relations in the flexoelectric semiconductor plate which are also derived for the first time in this paper, the simple 2D theory is shown to be amazingly accurate. For instance, for an infinite plate of thickness 2h = 0.2 µm, the extension, bending, and shear modes predicted from the present 2D theory agree well with the 3D benchmarks when the actual wavelength is larger than 1.26 µm, i.e., wavelength is at least more than six times of the thickness. To illustrate the flexoelectricity-based wave-particle drag effects, the wave modes and charge distributions are plotted. Due to its simplicity and computational efficiency, the present 2D theory provides us a powerful tool in understanding the physical mechanism of wave-particle drag in flexoelectric semiconductor plates and analyzing acoustoelectric devices when the flexoelectric effect is involved.

Propagation characteristics of shear horizontal waves in piezoelectric semiconductor nanoplates incorporating surface effect

Elastic wave-based devices made of piezoelectric semiconductors (PSs) find wide applications in modern scientific and technological fields. Elastic waves propagating in PS nanostructures have a rich variety of propagation characteristics due to the interaction between deformation, polarization, and charge carrier, as well as the influence of surface effect. Based on the Gurtin-Murdoch surface model, we conduct an analysis of horizontally polarized shear (SH) waves propagating in an infinite n-type PS plate with nano-thickness in this paper. For the open-circuit and electrically isolated boundary conditions, the analytical frequency and phase velocity spectrum relations and cut-off frequencies of SH waves with anti-symmetric and symmetric modes are presented. The influence of the surface effect, initial electron concentration, and thickness of the PS plate on the propagation characteristics of SH waves, such as frequency spectrum, phase velocity, and cut-off frequency, are elaborated in detail. Numerical results show that propagation characteristics of SH waves are size-dependent, and the macroscopic effective shear rigidity is softened at the nanoscale due to surface effect, which thus leads to the reduction of the frequency and phase velocity of SH waves. Moreover, the propagation characteristics of SH waves can be manipulated by changing the initial electron concentration.

Characterization of the full complex-valued stiffness tensor of orthotropic viscoelastic plates using 3D guided wavefield data

A two-stage inversion scheme is proposed to determine the full set of 9 complex-valued stiffness properties of orthotropic viscoelastic plates using their 3D surface velocity response to a broadband vibrational excitation. A combination of the hybrid TLS-ESPRIT and IWC method is employed to the extract complex-valued wavenumber–frequency pairs corresponding to relevant Lamb wave and shear horizontal plate waves from the data from surface velocity response. Particle swarm optimization is chosen to inversely determine the plate’s orthotropic viscoelastic properties using the semi-analytical finite element method as a forward model to compute the real and imaginary parts of the wavenumbers. The inversion procedure first identifies the elastic parameters by matching the real wavenumber values, followed by the characterization of the viscoelastic properties which are merely linked to the imaginary wavenumber values. To validate the accuracy of the proposed method, a series of numerical simulations of 3D wavefield data using a finite element model (COMSOL) is conducted, as well as broadband experimental measurements obtained by means of a 3D Infrared Scanning Laser Doppler Vibrometer. It is shown that the inverted orthotropic viscoelastic properties based on the virtual wavefield data are in close agreement with the target values, showing a mean relative error of less than 2% and 5% error on the elastic and viscous properties, respectively. Additionally, the median absolute deviations are negligible, showing the robust convergence of the inversion procedure to a global minimum, and giving confidence to apply the method on experimental wavefield data in order to reveal the full (unknown) C-tensor for material characterization. The proposed characterization method can be used for various orthotropic viscoelastic materials, including metal sheets, carbon/epoxy laminates, and wooden plates.

Nondestructive Evaluation of Concrete Compressive Strength Using Shear-Horizontal Waves

Longitudinal (P) waves have been widely employed for estimating concrete compressive strength based on correlation models between wave velocity and strength. However, P-wave based methods show high uncertainty because of the challenge of identifying the weak first arrival of P waves and the sensitivity of P waves to air voids and moisture. Shear-horizontal (SH) waves are superior to P waves because of their velocity stability in concrete at various air void and moisture levels. Moreover, SH waves exhibit a high signal-to-noise ratio without mode conversion after reflection and refraction. In this study, an SH-wave based method was developed to measure the shear-wave velocity (Vs) of concrete directly using SH-wave transducers and then establish a correlation between Vs and compressive strength. The proposed method was verified using concrete specimens produced with four water-to-cement ratios and different strength grades. The results indicate that the proposed method can significantly improve the accuracy of first arrival identification and enhance the preciseness of strength evaluation.

Wave field characteristics and transmission processing of seismic waves in coal seams with non-developing fundamental mode channel waves

Fine detection of geological structures in the working face of mines can provide a strong geological guarantee for safe and efficient production. The channel wave seismic method is an effective geological guarantee technology; however, it is only effective for coal seams wherein channel waves develop well. It does not yield acceptable results for coal seams in which channel waves develop poorly or fail to develop. To address this problem, the Kelvin–Voigt viscoelastic model and the staggered grid high-order finite difference method were applied to study the propagation and attenuation characteristics of the seismic wave field in viscoelastic coal seams. Moreover, the causes for the non-development of channel waves were explored. Numerical simulation and a field experiment on transmitted channel waves were performed for fault structure detection in coal seams. The effects of refracted longitudinal waves, multiple shear horizontal (SH) waves, and first-order Rayleigh channel waves on fault structure detection in models with different fault throws were investigated. The results indicate that the coal seam transverse wave quality factor Qs has a significant influence on the absorption attenuation of Love channel waves and fundamental mode Rayleigh channel waves. However, it has minimal influence on refracted longitudinal waves, first-order Rayleigh channel waves, and multiple SH waves. When the fault throw is greater than or equal to the coal seam thickness, the first-order Rayleigh channel waves and multiple SH waves can accurately reflect the fault location and extension shape, and the refracted P waves can accurately locate the faults but cannot accurately reflect the fault extension shape. When the fault throw is half the coal seam thickness, the refracted P waves and multiple SH waves have a poor detection effect, but the first-order Rayleigh channel waves can accurately reflect the fault location and extension shape. For working faces in which fundamental mode channel waves develop poorly, first-order Rayleigh channel waves can replace the fundamental mode channel waves in seismic methods to locate geological structures in coal seam working faces.

Beam-focused SH wave transducer based on YSr3(PO4)3 piezoelectric crystal for high temperature structural health monitoring

Guided-wave-based structural health monitoring (SHM) technology is of great importance for real-time inspection of high-temperature structures. The fundamental shear horizontal (SH0) wave is believed to be an ideal wave mode for developing SHM systems due to its nondispersive characteristics. However, currently very limited SH0 wave transducers can be used for SHM of high-temperature structures due to the limitation of materials. Herein, a novel YSr3(PO4)3 (YSP) piezoelectric crystal in the space group I4¯3d was grown. Experiments show that the face-shear piezoelectric coefficient d14 (d14 = d25 = d36) is 9.7 pC/N and varies little from 25 to 800 °C. Then a beam-focused SH0 wave piezoelectric transducer is developed based on face-shear-mode YSP wafers. Both finite element simulations and experimental results indicate that the YSP-based transducer can excite pure SH0 wave and focus the wave energy along two opposite main directions. Especially, the obtained SH0 wave beam is highly concentrated with a small divergence angle of less than 30°, originating from the high working frequency range from 300 to 400 kHz. The excellent temperature stability of the as-grown YSP crystal makes the proposed SH0 wave piezoelectric transducer very suitable for SHM of high-temperature structures.

Monitoring of thermal stress in metal plates by using bonded shear horizontal wave piezoelectric transducers

Thermal stress is one of the major causes of failure of engineering structures and its measurement has attracted more attention in recent years. The ultrasonic wave method is very promising in stress measurement due to its non-destructive nature and easy manipulation. The traditional ultrasonic wave transducers require a coupling medium which would introduce large repeatability errors in travel time measurement and thus in the measured stress. In this work, a methodology based on bonded shear horizontal (SH) guided wave piezoelectric transducers was developed to monitor thermal stress in metal plates. The adhesive bonding between the transducer and the specimen ensures the repeatability in travel time measurements, and the strain gauges are also employed to monitor the wave path length. The dispersive equation of acoustoelastic SH wave propagating in an isotropic medium under the uniaxial stress is derived. Both the uniaxial tension test and thermal modulation test have been performed in aluminum and steel plates. The results show that the acoustoelastic constants of the SH0 wave are identical to that of the shear bulk wave as predicted by the acoustoelastic theory and the thermal stress measured from −60 °C to 100 °C by the proposed method has a very good repeatability (better than 2 MPa) in both the aluminum and steel plates. Considering the convenience and reliability of the bonded SH0 wave piezoelectric transducer, the proposed method is very promising for monitoring of thermal stress in engineering structures, such as rails, etc.

Selective simultaneous generation of distinct unidirectional wave modes in different directions using dual-array transducer

Shear horizontal (SH) waves are widely used in the non-destructive evaluation and structural health monitoring fields. Conventional periodic permanent magnet electromagnetic acoustic transducers (PPM EMAT) can generate a single SH wave mode, which propagates in both forward and backward directions. Generation in a single direction is usually preferred to ease signal interpretation and increase inspection reliability. Recently, we have proved that a single, either fundamental or high-order, SH wave mode can be unidirectionally generated using a dual PPM EMAT, with carefully designed driving signals. Distinct SH modes present different applicability due to their particular response to features in the structure, such as defects. Hence, unidirectional generation of two different SH modes simultaneously with a dual-array transducer is investigated in this paper. The selectivity of wave modes and the selectivity of the propagation direction are studied by combining pure wave mode excitability with the superposition of optimal excitation signals for unidirectional generation, addressed in the frequency–wavenumber domain. Excitation signals for optimal and simultaneous generation of the SH0 and SH1 modes propagating in the same direction or in opposite directions have been designed. Experiments on an aluminium plate have demonstrated that the two wave modes can be effectively simultaneously generated with only one dual-array transducer and the propagation direction of each wave mode can be flexibly controlled using the designed excitation signals.

Parametric Analysis of SV Mode Shear Waves in Transversely Isotropic Materials Using Ultrasonic Rotational 3-D SWEI.

Ultrasonic rotational 3-D shear wave elasticity imaging (SWEI) has been used to induce and evaluate multiple shear wave modes, including both the shear horizontal (SH) and shear vertical (SV) modes in in vivo muscle. Observations of both the SH and SV modes allow the muscle to be characterized as an elastic, incompressible, transversely isotropic (ITI) material with three parameters: the longitudinal shear modulus μL , the transverse shear modulus μT , and the tensile anisotropy χE . Measurement of the SV wave is necessary to characterize χE , but the factors that influence SV mode generation and characterization with ultrasonic SWEI are complicated. This work uses Green's function (GF) simulations to perform a parametric analysis to determine the optimal interrogation parameters to facilitate visualization and quantification of SV mode shear waves in muscle. We evaluate the impact of five factors: μL , μT , χE , fiber tilt angle [Formula: see text], and F-number of the push geometry on SV mode speed, amplitude, and rotational distribution. These analyses demonstrate that the following hold: 1) as μL increases, SV waves decrease in amplitude so are more difficult to measure in SWEI imaging; 2) as μT increases, the SV wave speeds increase; 3) as χE increases, the SV waves increase in speed and separate from the SH waves; 4) as fiber tilt angle [Formula: see text] increases, the measurable SV waves remain approximately the same speed, but change in strength and in rotational distribution; and 5) as the push beam geometry changes with F-number, the measurable SV waves remain approximately the same speed, but change in strength and rotational distribution. While specific SV mode speeds depend on the combinations of all parameters considered, measurable SV waves can be generated and characterized across the range of parameters considered. To maximize measurable SV waves separate from the SH waves, it is recommended to use an F/1 push geometry and [Formula: see text].

Large-Range Spurious Mode Elimination for Wideband SAW Filters on LiNbO₃/SiO₂/Si Platform by LiNbO₃ Cut Angle Modulation.

A LiNbO3 (LN)/SiO2/Si multilayered structure was recently reported as a new platform for achieving wideband radio frequency (RF) filters. However, the in-band ripples in filters resulting from the spurious Rayleigh mode lead to deteriorated performance, and thus, a wide Rayleigh elimination window (REW) is highly desired for realizing spurious-free wideband surface acoustic wave (SAW) filters with a wide design space and good process tolerance. Here, we investigated the spurious mode suppression on the LN/SiO2/Si platform theoretically and experimentally through modulating the cut angle ( θ ) of LN. The K2 dispersion characteristics of the main mode (shear-horizontal wave) and spurious mode (Rayleigh wave) on LN/SiO2/Si substrates were systematically analyzed by the finite-element method (FEM), along with bulk LN for comparison. It is found that the REW is wider on LN/SiO2/Si than bulk LN, as Rayleigh wave can be totally eliminated with Cu electrode normalized thickness ( [Formula: see text]) ranging from 0.1 to 0.19 when θ is between 19° and 22° on the LN/SiO2/Si platform, in contrast to the quite narrow REW on bulk LN restricted to some specific [Formula: see text]. To verify the simulation results, resonators were prepared on 15°YX-LN/SiO2/Si, 20°YX-LN/SiO2/Si, bulk 15°YX-LN, and bulk 20°YX-LN. In addition, the typical spurious-free wideband SAW filter with [Formula: see text] nm based on the 20°YX-LN/SiO2/Si platform demonstrates high performance with a center frequency ( [Formula: see text]) of 1.27 GHz, a minimum insertion loss (ILmin) of 0.7 dB, and a 3-dB fractional bandwidth (FBW) of ~20.1%. This work provides a workable solution in fabricating spurious-free wideband and low-loss SAW filters for fifth-generation (5G) applications.

Surface-Acoustic-Wave Devices Based on Lithium Niobate and Amorphous Silicon Thin Films on a Silicon Substrate

This work presents an acoustic platform using solidly mounted thin-oriented lithium niobate (LiNbO3) film on silicon (Si). A thin layer of amorphous Si eliminates a conductive layer generated in the thin-film bonding processes and contributes to acoustic energy confinement and thermal frequency stability. The gigahertz operating frequency is achieved by resorting to the guided acoustic wave shear-horizontal wave (SH0) in a 400-nm-thick X-cut LiNbO3 thin film. Due to the elimination of the parasitic surface conduction (PSC) effect, the electromechanical coupling of the guide acoustic wave is maximized in the Si-based heterogeneous wafer. Due to the minimized acoustic impedance mismatch between surface material and substrate, longitudinal and higher order spurious modes are suppressed. Due to the stiff substrate with a small temperature expansion coefficient (TEC), the solidly mounted structure features a reduced temperature coefficient of frequency (TCF) and improved power handling. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22.8%, a high loaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1208 at 1.6 GHz, and a TCF of −36 p/min/K. The compressed filter is demonstrated with a minimum insertion loss (IL) of 0.6 dB, a fractional bandwidth (FBW) of 8%, an out-of-band rejection of 30 dB, a TCF of −38.5 p/min/K at roll-off, and a miniaturized footprint of 0.4 mm2. The performance has shown the strong potential of the LiNbO3–Si platform for front-end applications in 5G.

Developing a face-shear lead-free piezoelectric transducer through anti-parallel co-poling and its application to an omnidirectional piezoelectric transducer

Face-shear deformation was observed in various square piezoelectric transducers prepared using the anti-parallel co-poling method, which led to uniform polarization and the generation and receipt of pure fundamental shear horizontal (SH0) waves without any Lamb wave. The amplitude of the SH0 wave was found to be proportional to the piezoelectric charge constant (d33) of the piezoceramic, suggesting that the d33 value can be used as a figure of merit for piezoelectric transducers with strong SH0 waves. The amplitude of the SH0 wave associated with the square piezoelectric transducer is large at 0° and 90° but almost zero at 45°; therefore, a piezoelectric transducer with good omnidirectional properties needs to be developed. A ring-type omnidirectional piezoelectric transducer was produced using eight trapezoidal piezoceramics. The minimum amplitude of the SH0 wave generated and received by the ring type-transducer exceeded 70% of the maximum amplitude. Hence, this ring-type transducer is highly omnidirectional and can be used for nondestructive testing and structural health-monitoring applications.

Shear horizontal wave propagation in multilayered magneto-electro-elastic nanoplates with consideration of surface/interface effects and nonlocal effects

To depict the impact of surface/interface effects and nonlocal effects on Shear Horizontal (SH) waves in Magneto-Electro-Elastic (MEE) coupled nano-structures, a theoretical model is established, motivated by the dual variable and position (DVP) method. The physical mechanism of the material at the nanoscale is distinctive from that of the counterpart material at the macroscale. The above-referenced phenomenon can be mainly attributed to surface effects and nonlocal effects. With the aid of the DVP method, the phase velocity equation concerning surface effects and nonlocal effects is achieved, which shows stable computation in the high-frequency region. After numerical validation, systematic investigations are carried out to illustrate the size-dependent properties of SH waves. It is revealed that SH0 waves, i.e. the fundamental mode of the SH wave, are dispersive, with their phase velocity controlled by the nanoplate thickness if surface/interface effects and nonlocal effects are considered, which is totally different from macro-structures. Additionally, the surface/interface effect increases the structural stiffness so that it enhances the phase velocity, while the non-local constant has the opposite effect. This paper establishes a theoretical model and comes up with some qualitative conclusions that pave the way for the design of the structure of MEE nano-devices.

Shear Horizontal Surface Waves in a Layered Piezoelectric Nanostructure with Surface Effects.

This work aims to provide a fundamental understanding on the dispersive behaviors of shear horizontal (SH) surface waves propagating in a layered piezoelectric nanostructure consisting of an elastic substrate and a piezoelectric nanofilm by considering the surface effects. Theoretical derivation based on the surface piezoelectricity model was conducted for this purpose, and analytic expressions of the dispersion equation under the nonclassical mechanical and electrical boundary conditions were obtained. Numerical solutions were given to investigate the influencing mechanism of surface elasticity, surface piezoelectricity, surface dielectricity, as well as the surface density upon the propagation characteristics of SH surface waves, respectively. The results also reveal the size-dependence of dispersive behaviors, which indicates that the surface effects make a difference only when the thickness of the piezoelectric nanofilm stays in a certain range.

Coupled Resonance Mechanism of Interface Stratification of Thin Coating Structures Excited by Horizontal Shear Waves

The coupled resonance mechanism of interface stratification of thin coating structures excited by horizontal shear waves is investigated by the forced vibration solution derived from the global matrix method, the integral transformation method, and the plane wave perturbation method. The interface shear stress reaches the peak at coupling resonance frequencies which are an inherent property of the structure, and decreases with the increase of coating thickness or the increase of shear wave velocity difference between the substrate and coating. At the coupling resonance frequency, the thin coating structure is more easily stratified at the interface. The result could provide a theoretical basis for the popularization and application of ultrasonic deicing/defrosting/de-accretion technology.

An ultrasonic wave‐based framework for imaging internal cracks in concrete

Nondestructive detection and sizing of internal cracks initiated in reinforced concrete have been critical problems. Geometric characterization of internal cracks and delaminations contributes to predicting their propagation path and failure pattern followed by structural prognostics. There have been limited studies on quantitative detection and characterization of vertical cracks in concrete using wave-based NDE techniques. This study focuses on solving the problem of imaging deep internal crack planes in the concrete medium by leveraging the ultrasonic shear horizontal (SH) waves from a transducer array. Post-processing the array full matrix capture (FMC) data with both total focusing method (TFM) and plane wave imaging (PWI) reveals their efficiency in mapping planar defects inclined between 0° and 60°. However, their performance on vertical/near-vertical defects is found to be inferior with imaging limited to the tip of the defect planes. Further, half-skip modes of wave dispersion have been adopted in addition to the directly scattered pulses for imaging the vertical and near-vertical cracks. We propose an imaging framework based on the outcomes of our investigation on the best suitable methodology to detect and map planar defects like cracks inclined in the range of 0–90°. Statistical quantification of defect inclinations from the reconstructed images is compared to the ground-truth orientations, and they are found to be 94%–99% accurate. Besides accuracy, the computational efficiency of the proposed techniques makes them desirable and reliable for quick on-site inspections on built infrastructure.

Dynamic response of pile embedded in unsaturated soil under SH waves considering effect of superstructure

Soil is usually treated as one-phase or two-phase media in previous soil-pile dynamic studies. However, the air inside the soil pores can induce strong matrix suction to the skeletons, which would significantly affect the propagation of the shear horizontal waves within the soil. In addition, the superstructure's effect on the soil-pile system's dynamic response is often neglected. This can result in the underestimation of the dynamic impedance of a pile, which would further lead to the overdesign of the pile dimensions. In this study, a novel unsaturated soil–pile–superstructure model induced by vertically propagating shear horizontal waves is established to investigate the seismic performance of a pile under the influence of superstructures. The analytical solutions of the kinematic amplification and interaction factors (IU and AU, respectively) are derived using the Laplace transform and variable separation method. The developed solution is verified by comparing results from the hybrid boundary element method and the dynamic Winkler model in previous studies. Based on the obtained solutions, a parametric study is conducted to investigate the effects of pile and soil properties on the system's seismic response. The main conclusions can be drawn as follows: (1) When 0.2 < a0 (normalized frequency) < 0.7, IU and AU decrease with the increase of soil water saturation. This trend becomes extremely evident when the saturation is above 0.95. (2) Resonance appears at 0 < a0 < 0.7, and the resonance frequency decreases with the increase of the superstructure mass. (3) The vibration of the free-field soil has a non-negligible effect on reducing the system's seismic response.