Characterizing Halbach EMAT Configurations for SH0 Ultrasonic Waves
06 Jan 2021-IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control (IEEE)-Vol. 68, Iss: 5, pp 1866-1875
TL;DR: In this paper, the authors explored the Halbach magnet array pattern as an alternate to the conventional periodic permanent magnet (PPM) structure, and compared the amplitude generated from multiple single-row Halbach EMATs with singlerow PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation.
Abstract: Electromagnetic acoustic transducers (EMATs) can efficiently generate the shear horizontal (SH) guided wave modes. In this article, the Halbach magnet array pattern is explored as an alternate to the conventional periodic permanent magnet (PPM) structure. The magnetic field strength of a Halbach array is significantly higher on one side of the structure while it is weak on the opposite side of the array. This magnetic field distribution enables Halbach EMATs to generate ultrasonic waves with relatively large amplitude. To observe this phenomenon, this study compares the amplitude generated from multiple single-row Halbach EMATs with single-row PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation. This article then presents the ultrasonic wave fields generated by various double-row Halbach EMAT configurations using finite-element-based simulation models and experimentally validated for guided fundamental SH0 mode generated in an aluminum plate specimen. It is observed that distinct ultrasonic guided wave beam patterns be associated and predicted for different double-row Halbach EMAT configurations.
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10 Oct 2022
TL;DR: In this article , the authors discussed the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s 0.
Abstract: It is vital to detect material degradation in structures early to ensure their structural safety. Nonlinear ultrasonic techniques in the guided medium are employed to interpret the material nonlinearity by quantifying the harmonic responses from the ultrasonic guided wave. In this work, we discuss the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s 0 ) mode and an orthogonal-shear horizontal $(\mathbf{sh}_{0}^{\perp})$ mode generated on a weekly nonlinear isotropic elastic plate while excited with a primary shear horizontal (SH 0 ) mode. The presence of two dominant second harmonic modes is the reason for terming the phenomenon DMSH. Numerical simulations demonstrate the existence of dual harmonics on a thin aluminium plate. As the DMSH possesses different group velocities, each wave packet was identified in time domain analysis as separate signals. The observation is validated experimentally, and dual-mode harmonics were determined by a short-time Fourier transform (STFT) analysis of the time domain signal. A locally enhanced material nonlinearity study was conducted via numerical simulations, and the responses from DMSH were studied. It was found that the second-harmonic $\mathbf{sh}_{0}^{\perp}$ mode was sensitive to locally enhanced material nonlinearity, while the second harmonic s 0 and primary SH 0 were seemingly unaffected. Improved insights from this work may provide important implications for accurate early-state defect detection in structural health monitoring and non-destructive evaluation applications of critical structures.
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TL;DR: In this article , the authors discussed the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s0) mode and an orthogonal-shear horizontal (SH 0) mode generated on a weekly nonlinear isotropic elastic plate while excited with a primary shear horizontal mode.
Abstract: It is vital to detect material degradation in structures early to ensure their structural safety. Nonlinear ultrasonic techniques in the guided medium are employed to interpret the material nonlinearity by quantifying the harmonic responses from the ultrasonic guided wave. In this work, we discuss the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s0) mode and an orthogonal-shear horizontal $(\mathbf{sh}_{0}^{\perp})$ mode generated on a weekly nonlinear isotropic elastic plate while excited with a primary shear horizontal (SH0) mode. The presence of two dominant second harmonic modes is the reason for terming the phenomenon DMSH. Numerical simulations demonstrate the existence of dual harmonics on a thin aluminium plate. As the DMSH possesses different group velocities, each wave packet was identified in time domain analysis as separate signals. The observation is validated experimentally, and dual-mode harmonics were determined by a short-time Fourier transform (STFT) analysis of the time domain signal. A locally enhanced material nonlinearity study was conducted via numerical simulations, and the responses from DMSH were studied. It was found that the second-harmonic $\mathbf{sh}_{0}^{\perp}$ mode was sensitive to locally enhanced material nonlinearity, while the second harmonic s0 and primary SH0 were seemingly unaffected. Improved insights from this work may provide important implications for accurate early-state defect detection in structural health monitoring and non-destructive evaluation applications of critical structures.
TL;DR: In this paper , an improved periodic permanent magnet electromagnetic acoustic transducer (PPM EMAT) was proposed for defect detection for a U-shaped boom, which has superior frequency response characteristics and acoustic field directivity, which is suitable for detecting large and complex structures.
Abstract: In this research, to solve the problem of the ultrasonic guided wave inspection of a U-shaped boom, an improved periodic permanent magnet electromagnetic acoustic transducer (PPM EMAT) is proposed for defect detection for a U-shaped boom. The acoustic field distribution range of a traditional PPM EMAT is approximately ±20°, and the energy distribution is relatively concentrated. By adjusting the tilt angle between adjacent magnets and coils of a traditional PPM EMAT, an improved PPM EMAT is proposed. The acoustic field distribution range of the improved PPM EMAT is approximately ±30°, and the energy distribution in this range is relatively uniform. The simulation and experimental results show that the improved PPM EMAT has superior frequency response characteristics and acoustic field directivity, which is suitable for detecting large and complex structures. Furthermore, based on the traditional PPM EMAT and the improved PPM EMAT array, combined with the reconstruction algorithm for the probabilistic inspection of damage (RAPID), the damage locations of the double-hole defects of a U-shaped boom are studied. It is shown that the imaging results for defect location using the improved PPM EMATs are better than those found using the traditional PPM EMATs.