Shear Horizontal Wave Research Articles

Metasubstrate-based SH guided wave piezoelectric transducer for unidirectional beam deflection without time delay

Focusing the energy of a guided wave along a desired direction is of great significance in structural health monitoring (SHM), since it can improve the sensitivity to defects and reduce the complexity of signal interpretations. The phased array method is the most common approach for beam deflection, which requires a high uniformity of each element and the support of expensive and complex electronics. Moreover, the mirrored wave beam cannot be avoided for a linear array, resulting in the difficulty of distinguishing the defects at the symmetric positions. In this work, a metasubstrate-based piezoelectric transducer (MSBPT) is developed for unidirectional SH0 wave (the fundamental shear horizontal wave) beam deflection under a single driving source. The proposed MSBPT is constituted by a metasubstrate and two columns of thickness-shear mode PZT wafers. The metasubstrate is designed to provide the required phase gradient for unidirectional beam deflection, so no extra time delay is needed during excitation and reception. An analytical model is proposed to guide the design of the transducer to obtain the desired wave beam. The beam deflection properties of the MSBPT are validated by finite element simulations and experiments. It is observed that the MSBPT can concentrate the energy of the generated SH0 mode only in one desired direction with a small divergence angle. Moreover, the MSBPT can also serve as a sensor that only receives the SH0 mode propagating from the deflection angle and filters out the wave energies from other incident angles. Due to the simple configuration, the proposed MSBPT will be helpful in the controllable generation and reception of SH0 mode in SHM.

In-Motion Railcar Wheel Inspection using Magnetostrictive EMATs

Due to cyclic mechanical loading, railcar wheels are subject to the development of internal fatigue cracks in the rim underneath the tread surface. Off-line inspections are extremely laborious and require extended out-of-service time, and most existing in-line inspection systems that use conventional ultrasonics or electromagnetic acoustic transducer (EMAT) techniques have several drawbacks that limit their full-scale deployment in service. This paper discusses the work performed on the initial research and development of a proof-of-concept novel magnetostrictive EMAT sensor for in-motion railcar wheel inspection. Wheelsets with known internal discontinuities and a 3.7 m long panelized track were used to demonstrate the feasibility of the developed approach and methods. The results obtained from these tests have shown that the magnetostrictive EMAT sensor that generates 5 mm wavelength shear horizontal waves detects both surface defects and internal fatigue cracks with an excellent signal-to-noise ratio. Different wavelengths can also be added to the sensors to enhance or complement the detection of fatigue cracks at different depths. A total of four or five sensors located at standard concrete crosstie spacing along each rail would be able to provide complete coverage on wheels ranging from 711 to 965 mm in diameter with ±90° wheel coverage per sensor, and a theoretical inspection speed of 56 kph can be achieved using this approach.

Enhancing Shear Horizontal Wave Generation With a Multilayer Coil Electromagnetic Acoustic Transducer

Enhancing Shear Horizontal Wave Generation With a Multilayer Coil Electromagnetic Acoustic Transducer

Soft magnetostrictive patches for guided wave ultrasonics using Wiedemann effect-based MPTs and EMATs

Magnetically soft and malleable magnetostrictive (MS) alloys are highly promising as low-cost solutions for high-efficiency generation of guided waves in industrial applications and a variety of magnetostrictive patch transducers (MPTs) have been described in the literature. This work focuses on understanding the mechanisms and behaviour of soft MPTs used in the Wiedemann effect geometry, generating shear horizontal (SH) guided waves using FeCo alloy patches. MPT operation is explored in relation to patch geometry, size, magnetic field directions and guided wave wavelength. MPTs are compared with electromagnetic acoustic transducers (EMATs) and EMATs are also placed on MS and copper foil patches bonded to large glass plates for some of the measurements. Periodic permanent magnet (PPM) array EMATs operating on MPTs bonded to ferritic steel samples produced significant enhancements in the generated wave amplitude and the detected signal amplitude when compared to directly generating on the steel substrate, which primarily operates through the Lorentz mechanism. This enhanced performance was investigated and was found to be due to the magnetic fringing fields at the magnet edges. Moreover, EMAT lift-off behaviour was significantly improved when an EMAT was placed above a magnetostrictive patch, with 50 mm lift-off between the EMAT and the patch demonstrated for SH wave generation at a 22 mm nominal wavelength at a 170 kHz excitation frequency on a glass plate sample.

Enhancing the Performance of a Large Aperture Ultrasound System (LAUS): A Combined Approach of Simulation and Measurement for Transmitter-Receiver Optimization.

The Large Aperture Ultrasound System (LAUS) developed at BAM is known for its ability to penetrate thick objects, especially concrete structures commonly used in nuclear waste storage and other applications in civil engineering. Although the current system effectively penetrates up to ~9 m, further optimization is imperative to enhance the safety and integrity of disposal structures for radioactive or toxic waste. This study focuses on enhancing the system's efficiency by optimizing the transducer spacing, ensuring that resolution is not compromised. An array of twelve horizontal shear wave transducers was used to find a balance between penetration depth and resolution. Systematic adjustments of the spacing between transmitter and receiver units were undertaken based on target depth ranges of known reflectors at depth ranges from 5 m to 10 m. The trade-offs between resolution and artifact generation were meticulously assessed. This comprehensive study employs a dual approach using both simulations and measurements to investigate the performance of transducer units spaced at 10 cm, 20 cm, 30 cm, and 40 cm. We found that for depths up to 5 m, a spacing of 10 cm for LAUS transducer units provided the best resolution as confirmed by both simulations and measurements. This optimal distance is particularly effective in achieving clear reflections and a satisfactory signal-to-noise ratio (SNR) in imaging scenarios with materials such as thick concrete structures. However, when targeting depths greater than 10 m, we recommend increasing the distance between the transducers to 20 cm. This increased spacing improves the SNR in comparison to other spacings, as seen in the simulation of a 10 m deep backwall. Our results emphasize the critical role of transducer spacing in achieving the desired SNR and resolution, especially in the context of depth imaging requirements for LAUS applications. In addition to the transducer spacing, different distances between individual sets of measurement positions were tested. Overall, keeping the minimal possible distance between measurement position offsets provides the best imaging results at greater depths. The proposed optimizations for the LAUS in this study are primarily relevant to applications on massive nuclear structures for nuclear waste management. This research highlights the need for better LAUS efficiency in applications such as sealing structures, laying the foundation for future technological advances in this field.

New Shear Horizontal (SH) Surface-Plasmon-Polariton-like Elastic Surface Waves for Sensing Applications.

The advent of elastic metamaterials at the beginning of the 21st century opened new venues and possibilities for the existence of new types of elastic (ultrasonic) surface waves, which were deemed previously impossible. In fact, it is not difficult to prove that shear horizontal (SH) elastic surface waves cannot exist on the elastic half-space or at the interface between two conventional elastic half-spaces. However, in this paper we will show that SH elastic surface waves can propagate at the interface between two elastic half-spaces, providing that one of them is a metamaterial with a negative elastic compliance s44(ω). If in addition, s44(ω) changes with frequency ω as the dielectric function ε(ω) in Drude's model of metals, then the proposed SH elastic surface waves can be considered as an elastic analogue of surface plasmon polariton (SPP) electromagnetic waves, propagating at a metal-dielectric interface. Due to inherent similarities between the proposed SH elastic surface waves and SPP electromagnetic waves, the new results developed in this paper can be readily transferred into the SPP domain and vice versa. The proposed new SH elastic surface waves are characterized by a strong subwavelength confinement of energy in the vicinity of the guiding interface; therefore, they can potentially be used in subwavelength ultrasonic imaging, superlensing, and/or acoustic (ultrasonic) sensors with extremely high mass sensitivity.

Characteristics of Shear Horizontal Waves in a Microstructural Layer Imperfectly Bounded Between an Initially Stressed Half-Space and an Inhomogeneous Half-Space

Characteristics of Shear Horizontal Waves in a Microstructural Layer Imperfectly Bounded Between an Initially Stressed Half-Space and an Inhomogeneous Half-Space

High performance SAW resonator with spurious mode suppression using double-layer electrode transverse modulation

This work aims to solve the problem of tradeoff between various properties and spurious mode suppression in surface acoustic wave (SAW) resonators. A high-angle rotated Y-cut LiNbO3 (LN)/SiO2/Si multilayered structure was proposed to balance the electromechanical coupling coefficient (K 2) and temperature coefficient of frequency (TCF), and the propagation characteristics of Rayleigh mode were simulated by the finite element method. For the widely existing spurious modes, the shear-horizontal wave and longitudinal modes were eliminated by optimizing the cut angle of LN and electrode thickness, and a method of double-layer electrode transverse modulation was proposed to suppress the transverse modes. This method reduces the mass loading effect by replacing the electrode from Cu to Cu/Al. Moreover, the Al thicknesses in different regions are changed to perform the transverse modulation, and thus a widespread suppression of transverse modes is achieved by exciting the piston mode and enhancing the energy constraint, with a significant improvement on quality factor at the resonance frequency. Eventually, the spurious-free SAW resonator has the K 2 of 9.5% and the TCF close to zero. This work provides a feasible scheme for the design of high performance SAW resonators with spurious mode suppression.

Shear horizontal wave in a p-type Si substrate covered with a piezoelectric semiconductor n-type ZnO layer with consideration of PN heterojunction effects

Shear horizontal wave in a p-type Si substrate covered with a piezoelectric semiconductor n-type ZnO layer with consideration of PN heterojunction effects

Scattering-free modulation of elastic shear-horizontal waves based on interface-impedance theory

Scattering-free modulation of elastic shear-horizontal waves based on interface-impedance theory

Internal and External Pipe Defect Characterization via High-Frequency Lamb Waves Generated by Unidirectional EMAT

Periodic permanent magnet(PPM) electromagnetic acoustic transducers (EMATs) are commonly employed for axial defect inspection in pipelines. However, the lowest-order shear horizontal waves (SH0) guided waves have difficulties in distinctly differentiating internal and external defects. To enhance the signal-to-noise ratio and resolution, a unidirectional electromagnetic acoustic transducer (EMAT) based on Circumferential Lamb waves (CLamb waves) is developed. Through structural parameter optimization and excitation frequency adjustment, high-amplitude and low-dispersion CLamb waves are successfully generated in the high-frequency-thickness product region of the dispersion curve. Finite element simulations and experimental validation confirm the capability of this EMAT in exciting CLamb waves for the detection of crack-like defects. Experimental results demonstrate that the excitation efficiency of the CLamb EMAT exceeds that of the periodic permanent magnet electromagnetic acoustic transducer by more than tenfold. The defect reflection signal of the CLamb EMAT exhibits higher resolution and more significant amplitude compared to the PPM EMAT. The integration of this method with SH0 mode detection allows for the inspection of both internal and external defects in pipelines, offering a new avenue for EMAT applications in pipeline inspection.

Vibration Response of Soil under Low-Frequency Vibration Using the Discrete Element Method

The vibration response of soil is a key property in the field of agricultural soil tillage. Vibration components of tillage machinery are generally used to reduce tillage resistance and improve work efficiency, and the pressure variation under low-frequency vibration will affect the fragmentation and dispersion of farmland soil. However, the gradient of pressure variation, frequency domain response, and effective transmission range is unclear. A new method based on the DEM (discrete element method) is presented to study the vibration response and pressure transmission under low-frequency vibration. Bench test results have shown that peak pressure positively correlates with the vibration frequency and attenuates rapidly at a vibration distance of 100 to 250 mm. The resulting data were also selected to determine the simulation model’s parameters. Amplitude, vibration frequency, and soil depth were used as test factors in single-factor simulation tests, and their effects on the peak pressure, frequency domain response, and effective transmission distance were analyzed. The results showed a positive relationship between the peak pressure and the test factors. The peak pressure increased with a maximum gradient of 19.02 kPa/mm at a vibration distance of 50 mm. The amplitude, vibration frequency, and soil depth positively correlated with the dominant frequency amplitude. The main frequency was independent of amplitude and soil depth. At a vibration distance of 250 mm, the dominant frequency was approximately twice the vibration frequency at 7–11 Hz and approximately equal to the vibration frequency at 13–15 Hz. Multiple exponential functions were used to fit the peak pressure attenuation function, obtaining an effective transmission distance range of 347.15 to 550.37 mm for the 5 kPa cut-off pressure. For a soil depth of 300 mm, the vertical shear wave diffusion angle was greater than the horizontal shear wave diffusion angle. This study clarifies the vibration response of soil under low-frequency vibration, which helps to design vibration-type, soil-engaging components of tillage machinery and match vibration parameters for energy-saving and resistance reduction purposes in soil tillage.

Methodology of using acoustic emissions for enhancing rodent behavioral analysis

Rodent models of behavior used in the fields of neuroscience and psychology generate a wealth of multimodal data. For instance, as a rodent moves and behaves in its environment, muscle contractions apply subtle forces to any surface the animal contacts. These forces generate acoustic waves that propagate through the waveguide as Lamb and shear horizontal (SH) waves and contain information about the rodent’s physiology, behavior, and underlying psychological state. If the information in these waves were to be tapped, it would provide a novel, non-invasive way to study rodent behavior. This article lays the foundations for using guided ultrasonic waves generated by a mouse’s movement on an aluminum plate for detecting behavior and drawing inferences about acoustic startle responses. The experimental setup involves piezoelectric sensors capturing the waves generated by the rodent’s movement, which are then stored as discrete acoustic emission (AE) hits using an amplitude threshold-based data acquisition system. This method of data acquisition ensures that data collection occurs only when the animal moves or behaves, and each movement/behavior is represented by values of features within the generated wavepackets (AE hits). Through open field tests with C57BL/6J mice, utilizing piezoelectric sensors and the DAQ system, it was observed that every movement/behavior of the animal generated Lamb wavepackets within the frequency range of 20 kHz to 100 kHz. Furthermore, rearing behavior in the animals also led to the generation of SH wavepackets in the frequency range of 75 kHz to 230 kHz. This criterion was subsequently employed to detect rearing behavior. In the acoustic startle response test, where the animals’ responses to intense sound pulse were recorded, AE hits’ features proved useful in quantifying the response. These experimental findings validate the proposed technology’s practicality and demonstrate its capability to enhance studies of rodent behavior.

Exact analytical solution for shear horizontal wave propagation through locally periodic structures realized by viscoelastic functionally graded materials

The paper presents a novel comprehensive exact analytical solution for modeling linear shear-horizontal (SH) wave propagation in an isotropic inhomogeneous layer made of functionally graded material, using local Heun functions. The layer is a composite of two materials with varying properties represented by spatial variations following the square of the sine function. The Voigt–Kelvin model is used to account for material losses. The study focuses on SH waves incident at a specific angle and employs the wave splitting technique to analyze forward and backward waves, facilitating the computation of reflection and transmission coefficients at any point in the inhomogeneous structure. The proposed solution utilizes the periodic nature of material functions and employs the Floquet–Bloch theory to derive an exact analytical solution. This approach is particularly suited for cases where SH waves encounter locally periodic functionally graded material. A Riccati equation-based verification is conducted to compare the frequency-dependent modulus of the reflection coefficient obtained from the analytical solution with numerically solved results. The presented work provides a comprehensive and versatile analytical solution for studying linear SH wave propagation in locally inhomogeneous isotropic layers, contributing to the theoretical understanding of elastic wave fields and practical applications.

Resonance with surface waves induces forbidden velocity bands in dislocation glide

We use molecular dynamics simulations to demonstrate a pronounced influence of free surfaces on the mobility of dislocations at near-sonic velocities. By correlating instantaneous velocities v and resolved stresses τ, we show that the mobility relations of both edge and screw characters are composed of multiple ranges of stable uniform motion separated by bands of forbidden velocity. The lower limiting velocity for uniform motion of both edge and screw dislocations is the Rayleigh wave speed, cR. When forced to propagate at an average velocity greater than cR, dislocations exhibit cyclic, intermittent jumps in instantaneous velocity between cR and higher velocity branches of the mobility relation. Bands of forbidden velocity may be calculated directly from the velocity dependence of dislocation drag functions, which contain peaks near cR and—in the edge case—one other characteristic surface wave speed, which we associate with shear-horizontal (SH) waves. We propose that peaks in the drag function are due to resonance of free surface vibrations forced by nearby moving dislocations.

A shear horizontal phased array steering excitation technique for remnant wall thickness quantification

Precise wall loss quantification in pipe and plate structures is a critical and challenging task, especially in cases where direct access to the component is limited. Accurate knowledge of the remaining wall thickness allows for timely maintenance or replacement to avoid catastrophic failures. In this work, wall loss quantification is performed utilizing the cut-off frequency of mode SH1. The approach requires the excitation of SH1 across a range of frequencies. For this reason, a novel excitation technique using guided wave phased array steering is developed. Specifically, an array generating shear horizontal waves is employed. The influence of the array’s length, pitch, element width, and mode excitability on excitation is investigated. By appropriately phasing the elements of the array, mode SH1 is targeted and dynamically excited over a wide frequency-wavelength range. The directionality of SH1 is also studied, as in certain conditions, this can be critical for the success of the quantification. Simulation results show the technique can accurately quantify a 65 % wall thinning defect, offering a 15 % increase compared to established techniques. This is critical, as commonly, wall loss defects above 50 % are considered severe. Additionally, using electronic steering, rapid quantification can be achieved. Experiments using an EMAT and synthetic steering on an intact area and an artificially machined corrosion-like defect validate the technique.

Shear horizontal wave propagation on a piezoelectric semiconductor substrate under slight ridge or thin metal strip gratings

In the present work, analytical solutions for shear horizontal (SH) waves propagating in an n-type piezoelectric semiconductor (PSC) substrate under periodic slight ridge or thin metal strip gratings are obtained. The solutions of the various physical fields can be expressed as a summation of infinite harmonic waves by using the Bloch–Floquet theorem due to the existence of the periodic ridge or metal grating. Based on the numerical calculations, the effects of the width, height and shape of the ridge, the doping density of the PSC substrate and the material properties of the metal grating on the dispersion and attenuation curves of the SH waves are investigated. The results show that both the periodic ridge and metal grating have evident effects on the propagation characteristics and displacement mode shapes of the SH waves and the effects are closely related with the ratio of the wavelength to the structure period. In addition, the metal gratings can better control the propagation characteristics of SH waves than the ridges, namely, the effects of the metal gratings are more obvious and flexible than that of the ridges.

A new chevron electromagnetic acoustic transducer design for generating shear horizontal guided wave

Guided wave electromagnetic acoustic transducers (EMATs) have a significant role in non-destructive testing and structural health monitoring. It can generate horizontally polarized shear waves propagating axially or circumferentially to characterize the shape and orientation of pipeline defects. This work proposes a new Chevron pattern-like coil structure design with a periodic permanent magnet (PPM) EMAT configuration. This specific design of the EMAT coil can generate a bi-directional shear horizontal wave (SH-wave) and reduce the side lobes. An optimal Chevron angle of coil wires assists in generating orthogonal propagatingwaveforms. These phenomena lead to the constructive interference of propagating waves and develop a resulting wave along the horizontal direction. A 3D FEM modeling and simulation have been carried out and validated with experimental results. The proposed EMAT results are compared with the conventional racetrack PPM EMAT model, which shows a significant improvement over conventional EMATs. A prototype of this proposed EMAT has been developed. It can be used to inspect surface defects in applications such as fuel transportation pipelines.

Systematic investigations on frequency mixing response of ultrasonic shear horizontal and Rayleigh Lamb waves

The study of self- and cross-interactions of shear horizontal (SH) waves has garnered significant attention in the field of nonlinear ultrasonic practice. This interest stems from the potential high sensitivity of SH waves to microdamage and their low out-of-plane attenuation characteristics. However, due to the dispersive nature and intricate mechanisms governing guided wave propagations and interactions, the nonlinear responses of SH waves, particularly the third-order harmonic generation and wave mixing with Rayleigh Lamb (RL) waves, remain largely unexplored. This study presents a comprehensive investigation into the ultrasonic harmonic wave generation of SH guided waves. The research approach combines theoretical considerations and finite element modeling to investigate and discuss guided wave mixing involving SH and RL waves. Six cases of phase-matched wave mode pairs are developed based on deduced synchronism and symmetry conditions. A nonlinear material constitutive model, encompassing both the third- and fourth-order elastic constants, is incorporated into the simulation. The results of the numerical analysis reveal the existence of newly generated higher and combined harmonic waves in an intuitive manner. Specifically, the interactions between ultrasonic SH and RL guided waves are observed to generate second- and third-order combined harmonic waves at the mixing frequencies under internal resonant conditions. The nonlinear waves have a cumulative effect during the mixing period, with their amplitude remaining constant after passing through the mixing zone. This study provides the first observation of mode conversion and third-order combined harmonic generation of SH waves. The insights gained from the numerical perspective offer understandings of the frequency mixing response of SH waves.

Classification of solutions for guided waves in fluid-loaded viscoelastic composites with large numbers of layers.

Guided ultrasonic waves are used for the inspection of multilayered composite aerospace structures. Calculating the corresponding dispersion diagrams is challenging for thick-walled composites with more than 100 layers, such as in modern rocket booster pressure vessels. The Dispersion Calculator (DC) is an open source software for calculating such dispersion diagrams and mode shapes of guided waves. Attenuation caused by viscoelasticity and fluid-loading makes the dispersion curve tracing much more difficult than in the nonattenuated case because the modal solutions are sought in the complex wavenumber plane. The tracing problem is mastered by a reliable algorithm. Whereas leaky Lamb and Scholte waves in coupled and decoupled cases are modeled using the stiffness matrix method, shear horizontal (SH) waves are traced using the transfer matrix method without facing the numerical instability. Through implementation of mode family specific dispersion equations in both matrix techniques for nonattenuated and attenuated cases, symmetric, antisymmetric, and nonsymmetric leaky Lamb, Scholte, and SH waves can be traced separately with better efficiency and robustness. The capabilities of DC are demonstrated by calculating dispersion diagrams and mode shapes for a viscoelastic composite with 400 layers immersed in water. Results are compared against DISPERSE (Imperial College London, London, UK) for selected cases.