Fundamental Shear Horizontal Mode Research Articles

Ultrasonic guided wave monitoring of dendrite formation at electrode–electrolyte interface in aqueous zinc ion batteries

The formation of dendrite affects the cycling life of a battery and lead to malfunctions such as internal short-circuiting and thermal runaway events. However, existing methods to observe dendrite formation, such as X-ray computed tomography and scanning electron microscopy are either prohibitively complicated or unsuitable for long-term, in-situ monitoring. In this study we present a method which uses the fundamental shear-horizontal mode (SH0*) guided ultrasonic waves to independently monitor the status of the electrodes in a symmetric aqueous zinc-ion battery. Experimental measurements show that the velocity and attenuation of the ultrasonic wave on the opposing electrodes vary in the opposite senses during the cycling. While the velocity and attenuation changes can be partially reversed, a monotonic drift can also be observed with increasing number of cycles. Coupled with optical microscopy, the partially reversible oscillations can be associated with zinc stripping/plating. The irreversible drifting can be associated with the formation of ‘dead’ zinc dendrite. The technique shows clear sensitivity to the formation of dendrite, especially in the early stages (∼10 cycles) of charging and discharging processes. This work should inspire future research to enable quantitative assessment of the technique sensitivity and to improve its resolution.

Excitation of unidirectional SH wave within a frequency range of 50 kHz by piezoelectric transducers without frequency-dependent time delay

Unidirectional generation of a pure guided wave mode is of practical importance in structural health monitoring (SHM). Currently, unidirectional propagation guided waves can only be generated by using transducer array in a phased array form, which is limited within a very narrow frequency range. If a variable-wavelength unidirectional wave source is required, both the transducer spacing and time delay usually need to be changed with frequency, which is against the permanent arrangement demand of transducers in SHM. In this work, inspired by the unique features of bidirectional SH0 wave (the fundamental shear horizontal mode) piezoelectric face-shear and thickness-shear transducers, a new method was proposed for generating unidirectional SH0 wave. Two types of transducer configurations (double-side and single-side) were designed to unidirectionally generate SH0 wave without frequency-dependent time delay. Both finite element simulations and experiments were conducted to validate the unidirectional features of the proposed double-side and single-side transducer configurations. Results shows that the double-side transducer configuration is capable of generating unidirectional propagation SH0 wave at the frequency range from 100 kHz to 150 kHz, while the corresponding working frequency range for the single-side one is from 100 kHz to 140 kHz. The proposed method provides a cheap way for generation of the unidirectional SH0 wave within a certain frequency range without adjusting the relative transducer spacing and the time delay with frequency, so it will have great potential applications in SHM.

Quantification of defects in an aluminum plate using direction-tunable shear horizontal wave imaging

The quantification of damage, in plates, pipes and such like structures, is one of the current research areas. In this study, to estimate the notch size, shape, and orientation was carried out experimentally based on fundamental shear horizontal mode, SH0 mode. Using least number of transmitters, the reconstruction algorithm for the probabilistic inspection of damage (RAPID) has been used to carry out fast and efficient investigation of scattered waves using SH0wave interaction with notch at various incident angles. An approach of ultrasonic guided waves and (RAPID) algorithm, using a direction-tunable shear-horizontal mode array magnetostrictive patch transducer (DT-SHMA-MPT), the notch in a thin aluminum plate is experimented. Firstly, the RAPID algorithm, based on SH0mode, is used here to quantitatively study a notch in a thin aluminium plate. Secondly, the imaging application using DT-SHMA-MPT is achieved. Experiments were conducted using an array of eight DT-SHMA-MPTs based on a pitch-catch mode to utilize the scattered waves at the notch. The results obtained through experiments reveal the effect of directionality of the scattered waves and have find out the optimal transducers configuration. The localization, quantification and orientation at the same time are obtained using only two or three transmitters. To improve the accuracy of imaging, a threshold value was selected. The presented approach can be used to detect, locate and image the surface defects in aluminum plate.

Quantitative damage imaging in plates based on SH0 mode tomographic approach

Exploring the non-dispersive property, the fundamental shear horizontal mode SH0 can be widely used in the detection and monitoring of defects in plate like structures. To combine an approach of ultrasonic guided waves and a tomographic technique by adapting a reconstruction algorithm for the probabilistic inspection of damage (RAPID) using a double-turn coil omnidirectional shear horizontal wave magnetostrictive patch transducer (OSH-MPT) with three different kinds of array arrangements is presented here for imaging. SH0 can propagate in a composite material through bonding double-turn coil OSH-MPT. To get the information about a damage, RAPID can be utilized based on direct wave of SH0 mode. It is advantageous to monitor a composite plate where the velocity of direct waves depends on the propagation direction. In this paper, a surface simulated defect, using a small cylinder, in a composite material is quantitatively evaluated by using shear horizontal mode tomographic approach. Using modified approaches, to eliminate the effect of uneven probability distribution of the array (UPDA) in RAPID, imaging is obtained. Three different array setups of transducers have been tested to monitor the influence on the images. It has been presented that the image generated by the proposed approach with the optimal transducer array and shape factor, β, calculation method has great influence on the real defect shape. To improve the imaging results threshold is selected based on the receiver operating characteristic (ROC) curve. The proposed approach can be used to detect, locate and image the surface defects in plate like structures.

Temperature Stability Analysis of Thin-Film Lithium Niobate SH0 Plate Wave Resonators

This work presents an extensive study on the temperature coefficient of frequency (TCF) for thin-film lithium niobate (LiNbO3) resonators. To capture the temperature-frequency behavior for each vibration mode, a one-dimensional (1D) multi-section TCF model is proposed and verified by both the finite-element method (FEM) and experiments. By partitioning the metallized and non-metallized sections of the interdigitated transducers (IDT) as distinct TCF blocks and properly considering the spatial energy distribution, the TCF of each mode can be accurately predicted. Two higher lateral-order resonators based on the fundamental shear-horizontal mode (SH0) are designed and fabricated on a LiNbO3-on-SiO2 wafer to provide odd- and even-order harmonics. TCFs of the first 6 overtones (from 84 to 515 MHz) are calculated using the material properties given in the literature, exhibiting a maximum TCF difference of 3 ppm/K between the theoretical prediction and measurement results. Although only SH0 resonators are selected for experimental verification, the proposed multi-section TCF model can be applied to other plate wave MEMS resonators. [2019-0112]

Ultra-wideband T- and π-type ladder filters using a fundamental shear horizontal mode plate wave in a LiNbO3 plate

A fundamental shear horizontal mode (SH0) plate wave in a thin (0°, 115°–120°, 0°) LiNbO3 plate has electromechanical coupling factor k2 larger than 50%. In this study, ultra-wideband π-type and T-type ladder filters composed of three SH0 plate wave resonators were fabricated and characterized. The interdigital transducer (IDT) pitch (P) ratio of IDTs in the parallel and series arm resonators (PR: IDT pitch of parallel arm resonator (Pparallel)/that of series arm resonator (Pseries)) was experimentally investigated. The 3 dB bandwidth is as large as 33%–61%, depending on the IDT pitch ratio. The insertion loss and shape factor in terms of the IDT pitch ratio are also reported.

Characterization and Design Improvement of a Thickness-Shear Lead Zirconate Titanate Transducer for Low Frequency Ultrasonic Guided Wave Applications.

Thickness-shear transducers for guided wave testing have been used in industry for over two decades and much research has been conducted to improve the resolution and sensitivity. Due to a geometric feature of the current state-of-the art transducer, there is an out-of-plane component in the propagation direction of the fundamental shear horizontal mode which complicates the signal interpretation. In such case, complex signal processing techniques need to be used for mode discrimination to assess the structural health with higher precision. Therefore, it is important to revise the transducer design to eliminate the out-of-plane components in the propagation direction of fundamental shear horizontal mode. This will enhance the mode purity of fundamental shear horizontal mode for its application in guided wave inspection. A numerical investigation has been conducted on a 3 mm thick 2 m circular steel plate to understand the behaviour and the characteristics of the state-of-the-art thickness-shear transducer. Based on the results, it is noted that the redesigning the electrode arrangement will suppress the out-of-plane components on the propagation direction of the fundamental shear horizontal mode. With the aid of this information current state-of-the-art transducers were redesigned and tested in laboratory conditions using the 3D Laser Doppler Vibrometer. This information will aid future transducer designers improve the resolution of thickness-shear transducers for guided wave applications and reduce the weight and cost of transducer array by eliminating the need of additional transducers to suppress spurious modes.

Flexible Shear Mode Transducer for Structural Health Monitoring Using Ultrasonic Guided Waves

The application of the fundamental shear-horizontal wave mode for guided wave structural health monitoring is undoubtedly beneficial due to its nondispersive characteristics. Existing guided wave shear mode transducers are rigid and brittle, because of these characteristics, bonding them to irregular surfaces (i.e., curved surfaces) is challenging. There is a huge market interest in the development of a flexible shear mode transducer, which eases the transducer bonding process onto irregular surfaces and improves the surface contact between the transducer and the structure. This study presents a flexible shear mode transducer for structural health monitoring using low-frequency guided waves (20–120 kHz). The proposed transducer is manufactured using piezoceramic, and based on the results of this study, it exhibits the directional excitation of fundamental shear-horizontal mode at 20–120 kHz. Finite element analysis and laboratory experiments were conducted to study the behavior of the proposed transducer. Field trials were conducted on a liquid storage tank with an undulated surface (due to corrosion). The performance of the proposed transducer is also compared to the commercially available macro fiber composite transducers. The proposed transducer was driven by the industrialized ultrasonic guided wave inspection system; Teletest Focus+ in line with the application of tank floor inspection using ultrasonic guided waves.

Low-frequency pulse echo reflection of the fundamental shear horizontal mode from part-thickness elliptical defects in plates

Defect characterization using guided ultrasonic waves remains a challenging subject and requires a full understanding of the interaction of guided waves with a realistic representation of the defect. The characteristics of pulse echo reflection of the SH0 mode from part-thickness elliptical defects in plates is studied via finite element analysis and experimental measurements. The study shows that the reflection ratio spectrum of the SH0 mode from an elliptical defect exhibits periodic pattern due to interference between reflections from the two edges of the defect. The pattern of the reflection ratio spectrum is determined by the ratio of defect length in the incidence direction to wavelength, while the magnitude is affected by the maximum depth and the effective aspect ratio of the defect. Both the pattern and magnitude of the reflection ratio spectrum are found to be highly sensitive to the incidence angle, and the form of the variation of the reflection with angle is a strong function of the defect shape. In addition, a study of circular defects with tapered depth profiles reveals that the reflection is a function of average length of the tapered defect to wavelength ratio, and the magnitude of the reflection diminishes as the ratio increases.

Scattering of the fundamental shear horizontal mode in a plate when incident at a through crack aligned in the propagation direction of the mode

A study of the scattering of the fundamental guided wave SH(0) at a through-thickness narrow notch directed along the wave's propagation in a plate is presented. The results are obtained from Finite Element simulations and experimental measurements. Good agreement is found between the simulations and the measurements. The results are shown for a range of crack lengths and shapes. The scattered wave field consists of the reflected and diffracted SH(0) mode and also contributions from mode conversions to the S(0) mode. It is found that the coefficient of direct reflection of the SH(0) mode has an undulating nature depending on the length of the crack. This is caused by interference phenomena that are related to the interaction of different surface wave types generated on the crack surfaces and their diffractions at both tips of the crack. It is shown that the dominating part of this reflection is generated by the delayed "Rayleigh type" surface waves reflected from the far tip of the crack.

Short range scattering of the fundamental shear horizontal guided wave mode normally incident at a through-thickness crack in an isotropic plate

Interaction of the fundamental shear horizontal mode with through-thickness cracks in an isotropic plate is studied in the context of low frequency array imaging for ultrasonic guided wave nondestructive evaluation with improved resolution. Circular wave fronts are used and the symmetric case where a line from the wave source bisects the crack face normally is considered. Finite element simulations are employed to obtain trends subject to analytical and experimental validation. The influence of the crack length and of the location of source and measurement positions on the specular reflection from the crack face is first examined. These studies show that low frequency short range scattering is strongly affected by diffraction phenomena, leading to focusing of energy by the crack in the backscatter direction. Study of the diffraction from the crack edges reveals contributions due to a direct diffraction at the edges and multiple reverberations across the crack length. A simple diffraction model is shown to adequately represent cracks up to moderate lengths, providing an easy means of estimating the far field of the waves. The presence of multiple diffraction components is quantitatively established and surface waves on the crack face are identified as equivalent to low frequency symmetric modes of rectangular ridge waveguides.

Scattering of the fundamental shear horizontal mode from steps and notches in plates.

The scattering of the SH0 mode from discontinuities in the geometry of a plate has been studied. Both finite element and modal decomposition methods have been used to study the reflection and transmission characteristics from a thickness step in a plate, obtaining very good agreement. The significance of nonpropagating modes in the scattering from steps in plates has been specifically investigated. A method to approximate the reflection from rectangular notches by superimposing the reflection from a step down (start of the notch) and a step up (end of the notch) has been proposed. It is demonstrated that it is possible to use this method to obtain the reflection from a notch of any depth and at any frequency. The effect of frequency on the reflection from notches has been examined. The limits of this method in approximating cracklike defects have also been studied.