SH0 Mode Research Articles

SH1 mode plate wave resonator on −27°YX LiTaO3 single crystal plate with phase velocity of 12 km s−1

Abstract This study presents a first shear horizontal (SH1) mode plate acoustic wave resonator on a −27°YX LiTaO3 (LT) thin plate. The SH1 wave is generated when a backside electrode is formed on the opposite side of an interdigital transducer (IDT). Two resonators, one with Cu and the other with an Al backside electrodes, along with a Cu IDT were simulated and fabricated. Both fabricated SH1 resonators exhibited high phase velocities of 12 km s−1 and bandwidth (BW) of around 4.5%. The temperature coefficient of frequency is −38 ppm °C−1 at resonance and −56 ppm °C−1 at anti-resonance on a 0.13λ thick LT plate. Although the backside electrode is necessary for high coupling of the SH1 wave, it increases the clamp capacitance of the devices, resulting in low impedance characteristics of around 10 Ω and low impedance ratios around 30 dB. Additionally, the suppression of spurious responses is necessary for filter application.

On the nature of hydrogen bonding in the H2S dimer

Hydrogen bonding is a central concept in chemistry and biochemistry, and so it continues to attract intense study. Here, we examine hydrogen bonding in the H2S dimer, in comparison with the well-studied water dimer, in unprecedented detail. We record a mass-selected IR spectrum of the H2S dimer in superfluid helium nanodroplets. We are able to resolve a rotational substructure in each of the three distinct bands and, based on it, assign these to vibration-rotation-tunneling transitions of a single intramolecular vibration. With the use of high-level potential and dipole-moment surfaces we compute the vibration-rotation-tunneling dynamics and far-infrared spectrum with rigorous quantum methods. Intramolecular mode Vibrational Self-Consistent-Field and Configuration-Interaction calculations provide the frequencies and intensities of the four SH-stretch modes, with a focus on the most intense, the donor bound SH mode which yields the experimentally observed bands. We show that the intermolecular modes in the H2S dimer are substantially more delocalized and more strongly mixed than in the water dimer. The less directional nature of the hydrogen bonding can be quantified in terms of weaker electrostatic and more important dispersion interactions. The present study reconciles all previous spectroscopic data, and serves as a sensitive test for the potential and dipole-moment surfaces.

Band edge modulation for high-performance LL-SAW resonators on LiNbO3/SiC by introducing an ultra-thin intermediate oxide layer

With the exploding demand of rapid information transmission, high-frequency acoustic filtering devices are becoming an immediate need. Longitudinal leaky surface acoustic wave (LL-SAW) devices with unique advantages can be a promising platform. In this paper, we introduce a 100 nm intermediate oxide layer into the X-cut lithium niobate on silicon carbide (LiNbO3/SiC) to improve the in-band performance of LL-SAW resonators. First, the dispersion curves of the structures are analyzed by finite element method. In this part, we successfully interpret the intrinsic low quality factor (Q) of LL-SAW on LiNbO3/SiC in general design, and predict the enhancement of Q by introducing an intermediate oxide layer without degradation on spurious response. Then, one port resonators considered in the simulation are fabricated and measured. As a result, enhancements in Bode Q among the whole passband are confirmed. Compared with devices state of art, resonators with leading performances are demonstrated. The fabricated resonators have peak-valley admittance ratio of 63.87 dB, Bode Q of ∼300 at fr and ∼530 at far, keff2of 15.66 % and phase velocity of 6187.3 m/s. Additionally, the resonant frequency of SH1 mode shifts to higher frequency. This work enables the design of next generation high frequency mobile communication filters.

Guided wave tomography for quantitative thickness mapping using non-dispersive SH0 mode through geometrical full waveform inversion (GFWI)

Guided wave tomography plays a significantly important role in quantitatively mapping thickness variations in plate-like structures and pipelines in the petrochemical industry for accurate measurement of corrosion, as guided waves enable rapid screening of large areas without needing direct access. Several inverse algorithms have been implemented in guided wave tomography; however, almost all of them use a primary assumption: the three-dimensional (3D) guided wave thickness reconstruction is simplified as a two-dimensional (2D) acoustic wave velocity inversion, which is then mapped to thickness variation using the dispersive nature of guided waves. Although this assumption simplifies the inverse procedure, it makes it impossible to use non-dispersive modes in reconstructions. Geometrical full waveform inversion (GFWI) is promising to overcome this limitation since it can reconstruct corrosion profiles through geometry optimization using a data-fitting procedure, where velocity-to-thickness mapping is not needed. In this work, GFWI-based guided wave tomography is developed in plate-like structures, and is applied to reconstruct thickness maps in a series of corrosion defects using the non-dispersive SH0 mode, demonstrating high performance and achieving an improved reconstruction resolution.

DISPERSION OF LAMB WAVES IN MULTILAYER STRUCTURES

Low cost, the possibility of online monitoring and high sensitivity distinguish the method of structural monitoring using Lamb waves from other available methods. Structural analysis based on Lamb waves in heterogeneous materials requires fundamental knowledge of the behavior of Lamb waves in such materials. This basic knowledge is critical for signal processing in determining possible damage that can be detected by the propagating wave. Recently, Lamb wave methods have been used to simultaneously survey large areas of composite structures. However, such methods are more complex than traditional ultrasonic testing because Lamb waves have dispersive characteristics, namely, the wave speed varies depending on the frequency, modes and thickness of the plates. Experimentally measured group velocities of Lamb waves in composite materials with anisotropic characteristics do not coincide with theoretical group velocities, which are calculated using the dispersion equation of Lamb waves. This discrepancy arises because in anisotropic materials there is an angle between the direction of the group velocity and the direction of the phase velocity. This work investigates the propagation characteristics of Lamb waves in composites, focusing on group velocity and characteristic wave curves. For symmetric laminates, a robust method is proposed by imposing boundary conditions on the mid-plane and top surface to separate symmetric and antisymmetric wave modes. The dispersive and anisotropic behavior of Lamb waves in two different types of symmetrical laminates is theoretically studied in detail. The dispersion of Lamb waves was studied for 10 symmetric and asymmetric modes. It is shown that only fundamental modes are not characterized by a cutoff frequency, which indicates the interaction of fundamental modes with composite layers in the low-frequency range. A high level of group velocity dispersion was discovered for the SH0 and S0 modes. It is concluded that in isotropic laminates, dispersion is characteristic of symmetric modes. It is shown that the frequency dependence of the group velocity of Lamb waves of laminar composites can be represented in polynomial form.

A new theoretical model for high-order harmonics of SH0 mode ultrasonic guided waves based on magnetostrictive mechanism

In recent years, it was found that magnetostrictive ultrasonic guided wave transducers experimentally excited nonlinear harmonic components under a certain combination of dynamic and static magnetic fields. However, a satisfactory model for the relevant excitation mechanisms is not available. In this study, a new magnetostrictive guided wave excitation model was established and the causes for harmonics generation were analyzed. In addition, the calculation results of the model were obtained under different magnetic field parameters. We firstly changed the calculation conditions of magnetostrictive strain in the model and then theoretically calculated the odd and even harmonics of SH0 mode ultrasonic guided waves for the first time. Furthermore, the accuracy of the model was experimentally verified. By changing the strength ratio of the dynamic magnetic field to the static magnetic field (HD/HS), the excitation amplitudes of odd and even harmonics could be regulated with a magnetostrictive sensor. As the ratio of HD/HS increased, the normalized amplitude of the second harmonic firstly increased and then decreased, whereas the normalized amplitude of the third harmonic showed an exponential growth with different curvatures. This study enriched the theory of magnetostrictive guided wave excitation and provided a theoretical basis for the applications of magnetostrictive sensors.

Enhancement in performance of SAW resonator on LN/SiC substrate by take slowness asymmetry into account

Abstract Layered structures comprising high-coupling lithium niobate (LiNbO3, LN) piezoelectric thin plates bonded to high-velocity SiC substrates have attracted much attention of high-performance surface acoustic wave (SAW) devices. However, such these layered structures exhibit severe Rayleigh mode spurious responses that degrade the performances of SAW devices. This paper explores the generation mechanism of spurious modes on LN/SiC layered structure, and proposes an optimized layered structure with suppressed Rayleigh spurious modes. The investigation involves deriving the Euler angle range of LN by analysing the slowness surface of both LN and SiC. In addition, it is worth noting that slowness surface overlaps at some Euler angle ranges, which will cause coupling between different modes, thus generating spurious mode. Simulation result shows the frequency characteristics of SAW resonator at resonant and anti-resonant frequencies of 4.3 GHz and 4.88 GHz of SH mode, achieving a K 2 of up to 26.5% and a quality factor Q of 828. It is proved that the optimization structure offering larger K 2, higher velocity and improved Q values and Rayleigh spurious mode suppression, which is favourable for wideband and high frequency SAW devices applications.

Mode conversion of fundamental guided ultrasonic wave modes at part-thickness crack-like defects

Guided ultrasonic waves can be employed for efficient structural health monitoring (SHM) and non-destructive evaluation (NDE), as they can propagate long distances along thin structures. The scattering (S0 mode) and mode conversion of low frequency guided waves (S0 to A0 and SH0 wave modes) at part-thickness crack-like defects was studied to quantify the defect detection sensitivity. Three-dimensional (3D) Finite Element (FE) modelling was used to predict the mode conversion and scattering of the fundamental guided wave modes. Experimentally, the S0 mode was excited by a piezoelectric (PZT) transducer in an aluminum plate. A laser vibrometer was used to measure the out-of-plane displacement to characterize the mode-converted A0 mode, employing baseline subtraction to achieve mode and pulse separation. Good agreement between FE model predictions and experimental results was obtained for perpendicular incidence of the S0 mode. The influence of defect depth and length on the scattering and mode conversion was studied and the sensitivity for part-thickness defects was quantified. The maximum mode conversion (S0-A0 mode) occurred for ¾ defect depth and the amplitude of the mode-converted A0 and scattered S0 modes mostly increased linearly as the defect length increased with an almost constant A0/S0 mode scattered amplitude ratio. Similar forward and backward scattering amplitude was found for the mode converted A0 mode. The mode conversion of the S0 to SH0 mode has the highest sensitivity for short defects, but the SH0 mode amplitude only increased slightly for longer defects. Employing the information contained in the mode-converted, scattered guided ultrasonic wave modes could improve the detection sensitivity and localization accuracy of SHM algorithms.

3.2 GHz first shear horizontal-mode plate wave resonator on a 175°YX LiNbO3 thin plate showing 24.6% bandwidth

In this study, a first shear horizontal (SH1) mode plate wave resonator for HF and wide-band filters was investigated. From FEM simulation, the SH1 mode plate wave exhibited a high phase velocity of 23 km s−1 and a high electro-mechanical coupling factor (k 2) of 37% on (0°, 85°, 0°) LiNbO3 (LN) with a thickness of 0.1λ (λ: wavelength). The SH1 mode resonator was fabricated on a 0.5–0.57 μm thick LN film. An 80 nm Al IDT electrode was formed with λ varied from 4–16 μm. Finally, 50 nm thick Al was deposited to form an electrically short bottom plane, which was required to generate a SH1 mode wave. The fabricated device exhibited a resonance frequency (f r) of 2.24 GHz, an anti-resonance frequency (f a) of 2.8 GHz, a wide fractional bandwidth (FBW) of 20%, an impedance (Z) ratio of 35.4 dB, and TCF of −90.8 ppm/°C at f r and −74.8 ppm/°C at f a.

Key factors governing the direction of SH0 mode guided waves generated by FeCo strip-based magnetostrictive sensor

Magnetostrictive sensors (MsS) are widely used to generate ultrasonic guided waves of SH0 mode for the purpose of detecting defects in plate-like structures. An MsS commonly employs a rectangular magnetostrictive strip and a sensor unit (including detection coil and magnet) to generate SH0 waves. However, the effect of coverage range of static magnetic field (Ls) and dynamic magnetic field (LD) on the SH0 wave generation direction has not been fully explored. So far, the cases of LS<<LD and LD>>LS are seldom discussed in the development of MsS for generating SH0 mode. In this study, the key factor governing the direction of SH0 mode generated by FeCo strip-based MsS was experimentally clarified. The transition phenomenon in the generation direction of SH0 wave was observed while the combination parameters crossing the control line of Ls≈LD. The phenomenon could be interpreted by the alterations in the operation mechanism of Wiedemann effect and reversed Wiedemann effect. As a result, the generation direction of SH0 mode could be tuned along the static magnetic field (Ls<<LD), the dynamic magnetic field (Ls>>LD) or the direction of both static and dynamic magnetic fields (Ls≈LD). The findings in this study is of benefit for guiding the design of MsS array with the tunable generation direction of SH0 mode.

SH-wave based defect imaging method for CFRP plates with variable thickness

ABSTRACT Classical guided wave imaging methods find applicability in uniform-thickness plates or quasi-isotropic plates. To be compared with, the method presented in this paper advances damage imaging accuracy for both uniform-thickness and variable-thickness anisotropic plates by incorporating new compensation terms grounded in the theoretical excitation directivity of the quasi-SH0 mode in anisotropic material. Specifically, the nondispersive nature of the wave speed and skew angle of the quasi-SH0 mode in the low- fd states (frequency-thickness-product lower than the cut-off value of SH1 mode) is established through dispersion curves and wave structure calculations. Additionally, employing the elastic dynamics reciprocity theorem reveals that the directivity of this mode is also nondispersive in the low- fd states. Therefore, the quasi-SH0 mode is theoretically insensitive to thickness variation. Experiment validated these theoretical calculations. On this basis, this paper proposed an integrated imaging method that utilises transmitted and reflected wave information by incorporating matching pursuit algorithm, cross-correlation analysis, probabilistic reconstruction and delay-and-sum method that incorporates new compensation terms based on the quasi-SH0 mode theory. Experimental validation of uniform-thickness carbon fibre-reinforced polymer (CFRP) plates and variable-thickness CFRP plates shows the insensitivity of this method to structural thickness variation, enabling effective imaging of damage in such anisotropic structures.

Weak bond evaluation of lap bonding structures by SH guided waves using EMATs

ABSTRACT In this research, simulations and experiments were conducted for the bonding quality evaluation of an aluminum bonding structure, based on the SH guided wave analysis. In order to simulate the propagation of SH waves in the bonded structure, a 3D finite element model was established based on interfacial spring stiffness modeling. The frequency-wavenumber diagram was obtained by doing Fourier transform along the spatial axis in the time frequency domain simulation results. At the same time, the influence of the bonding interface weakening on the propagation characteristics of the guided wave was analyzed. The simulated dispersion curves of SH-guided waves in different bonding states were in good agreement with the theoretically results. In addition, a periodic permanent magnet electromagnetic acoustic transducer (PPM-EMAT) 3D finite element model was established. An optimized transducer was fabricated to excite pure SH0 mode. Then, a series of aluminum lap bonding structures with different bonding states were prepared. The effect of bonding interfaces on the propagation characteristics of SH waves was investigated. The interfacial spring stiffness can be determined when the STFT of the SH waves matches the theoretical dispersion curves. Thus, this method demonstrated an ultrasonic way to distinguish the weakening of the bonding structures.

On-chip topological phononic crystal acoustic waveguide based on lithium niobate thin films

This Letter introduces an on-chip topological phononic crystal (PnC) acoustic waveguide employing lithium niobate thin films. Utilizing a C3v symmetry-breaking mechanism, the topological PnC acoustic waveguide is achieved, operating at frequencies exceeding 430 MHz. A SH0 mode acoustic transceiver is designed, enabling highly efficient on-chip acoustic wave transmission and reception. The fabricated topological PnC waveguide demonstrates a propagation loss of 11.3 dB/mm at the edge mode. An acoustic beam splitter utilizing topological edge mode has been demonstrated, showing the configurability of the topological PnC acoustic waveguide. These results offer significant promise for advancing the development of hybrid phononic circuits tailored for high-frequency acoustic information processing, sensing, and manipulation.

Excitation of Odd Harmonics of SH0 Mode Ultrasonic Guided Waves Using Magnetostriction-Based EMAT: Theoretical Modeling

ABSTRACT Magnetostriction-based electromagnetic acoustic transducer (M-EMAT) is a promising tool for generating fundamental shear-horizontal (SH0) mode guided waves in plate. Though the M-EMAT possesses high-order harmonics excitation ability in nature, its conventional way can only generate a fundamental component of SH0 mode. The analytical modeling was performed in this study to releasing the ability of M-EMAT in generating odd harmonics of SH0 mode. First, the inaccurate conditions of magnetic fields for relative permeability calculation in the existing model are corrected in the proposed model. Second, the error of the existing model in predicting the spectrum of the SH0 mode generated in Nickel plate is estimated. Third, numerical solutions are provided by the improved model to examine the key factors governing the ability of M-EMAT in generating odd harmonics of SH0 mode. The conclusions demonstrated that the intensity ratio (H S /H D ) of static and dynamic magnetic fields is adjusted below 1 and the ability of M-EMAT in generating odd harmonics of SH0 mode can be activated. The normalized amplitude of 3rd harmonics decays exponentially with the increase of H S /H D , which is independent of geometrical parameters of M-EMAT. The improved model can effectively optimize excitation parameters of M-EMAT and generate odd harmonics of SH0 mode in plate.

GHz surface waves in Al/LiTaO3/Si composite: Effect of the Drude electrode on dispersion, attenuation and mode shapes

In fifth generation (5G) mobile communication, radio frequency is in the super high frequency range (3–30 GHz). Thus, different from Ohm law, electrode loss at GHz frequency becomes frequency-dependent. As such, many properties, especially attenuation of piezoelectric acoustic devices, should be reevaluated. In this paper, the attenuation of GHz surface wave propagating in composite structure made of metal electrode, piezoelectric film and elastic half space is investigated based on the loss model of Drude electrode. Specifically, the Al/LiTaO3/Si composite is considered where Rayleigh mode and SH mode are fully coupled. Based on the Stroh-type formalism, the dispersion equations of the composite with the Drude electrode are derived, and compared with the traditional perfect conductor electrode which is under the short circuit boundary condition. The phase velocity, attenuation and wave mode shapes are obtained successfully by the multidimensional moduli ratio convergence method. Numerical results are presented to reveal some interesting intrinsic features, which include two analytical upper bounds of phase velocity, nonexistent validation of intersection points in dispersion curves, and relations among veering, attenuation jumps and wave-mode conversions. These features and relations provide an in-depth insight for GHz wave motion properties in piezoelectric composites.

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.

High-Precision Corrosion Detection via SH1 Guided Wave Based on Full Waveform Inversion.

Corrosion detection for industrial settings is crucial for safe and efficient operations. Due to its high imaging resolution, the guided-wave full-waveform inversion tomography technique has significant potential for corrosion detection of plate metals. Limited by the long wavelengths of A0 and S0 mode waves, this method exhibits inadequate detection resolution for the earlier shallow and small corrosion defects. Based on the relatively short wavelength characteristics of the SH1 mode wave, we propose a high-precision corrosion detection method via SH1 guided wave using the full waveform inversion algorithms. By conducting finite element simulations of ultrasonic-guided waves on aluminum plates with varying corrosion defects, a comparison was made to assess the detection precision across A0, S0, and SH1 modes. The comparison results showed that, whether for regular or irregular defects, the SH1 mode wave always exhibited higher imaging accuracy than the A0 and S0 mode waves for shallow and small-sized defects. The corresponding experiments were conducted on an aluminum plate with simple or complex defects. The results of the experiments reconfirmed that the full waveform inversion method using SH1 guided wave can effectively reconstruct the shape and size of small and shallow corrosion defects within aluminum plates.

Cut-Off Thickness Identification of Defects with Single and Two-Step Geometries Using SH1 Mode Conversion

Cut-Off Thickness Identification of Defects with Single and Two-Step Geometries Using SH1 Mode Conversion

Ultrasonic guided wave defect detection method for tank bottom plate based on SH0 mode multichannel magnetostrictive sensor

To address the challenge of ultrasonic detection of multiple defects in large-scale tank bottom plates, a multi-channel magnetostrictive sensor was designed and developed to effectively excite SH (Shear Horizontal) mode guided waves. The optimal overall scheme of the sensor was obtained by considering the sensor excitation energy, coupling efficiency, and fabrication process. Through experimental tests, the consistency of each channel of the sensor is evaluated, and the center frequency and detection range of the sensor are measured. To detect defects of varying sizes and depths in steel plates, a rotating total focus imaging method is proposed. And we conducted experiments using a multi-channel magnetostrictive sensor to achieve SH0 guided wave imaging of multiple defects across the full domain. Our experimental results demonstrate that, across 8 rotations, we achieved a minimum relative position error of 4.32% and a minimum absolute angle error of 2.16°. Our research provides an effective solution for ultrasonic detection of tank bottom plates, and the proposed method is also applicable for defect detection in other large plate-like structures.

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.