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.
1 citations
DOI•
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.
References
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TL;DR: In this article, an analysis of the radiation from a body force shows that it is equivalent to the radiation generated by a series of surface stresses defined by the moments of the body force taken with respect to the depth coordinate.
Abstract: An analysis of the radiation from a body force shows that it is equivalent to the radiation from a series of surface stresses defined by the moments of the body force taken with respect to the depth coordinate. As the body force becomes localized near the surface, the zeroth moment of the force dominates the radiation and is often thought of as an equivalent surface stress. However, under certain conditions, this can vanish, and the other moments must be considered. It is found that, as the order of the moment of a particular force component increases, the resulting radiation patterns alternate between those characteristic of a compressive surface stress and those characteristic of a shear surface stress, which have considerably different angular variations. Results of experiments in the development of EMAT transducers for nondestructive testing that support these results are cited, and important consequences in the design of inspection systems are indicated.
26 citations
TL;DR: In this article, the discovery, early development and theory of the electromagnetic generation of pure shear and quasicompressional ultrasonic waves in metals is reviewed. And the four equations of Quinn lead to a satisfactory explanation of the periodic ionic displacements excited electromagnetically in metals in the presence of a static magnetic field over a wide range of temperature, frequency and magnetic field.
24 citations
TL;DR: In this paper, a 3-D multi-physics finite element model was developed to investigate the physics of the interaction of SH modes with a tri-layer structure and different cases of interfacial adhesion ranging from perfect bond, intermediate and weak bond, were simulated.
Abstract: This study aims to develop a shear horizontal guided wave based technique to evaluate the interfacial adhesion of aluminium-epoxy-aluminium tri-layer in a lap shear joint. A 3-D Multi-physics finite element model was developed to investigate the physics of the interaction of SH modes with a tri-layer structure. By employing the boundary stiffness approach, different cases of interfacial adhesion-ranging from perfect bond, intermediate and weak bond, were simulated. Frequency-wavenumber analysis reveals that at the bond overlap region, the incident SH0 wave mode-converts to fundamental (SH0-like) and first-order(SH1-like) modes. The dispersion characteristics of first-order mode (SH1-like) was found to be dependent on the adhesion level, and this influences the time responses collected on a receiver plate in guided wave through-transmission configuration. Experiments were carried out on aluminium-epoxy-aluminium lap shear joints using PPM-EMAT transducers. The analysis shows that this technique can detect and quantify different levels of adhesion, rather than merely classifying as good or bad bonds.
20 citations
TL;DR: It is shown that a signal dominated by the SH1 mode can be generated using a single permanent periodic magnet (P PM) electromagnetic acoustic transducer (EMAT) (PPM EMAT) and all predictions are then backed up by experimental measurements.
Abstract: Inspection is a key part of the asset management process of industrial plants and there are numerous plate-like structures that require inspection. Ultrasonic guided waves have been extensively used to detect various types of defect by monitoring reflected and transmitted signals because they enable faster screening of large areas. However, ultrasonic guided wave testing becomes difficult for very shallow, sharp defects as current inspection techniques suffer from a lack of sensitivity to such features. Previous studies, obtained by comparing various inspection techniques, suggest that the SH1 mode in particular, at around 3 MHz $\cdot$ mm, would be suitable when testing for shallow defects; however, it is clear that both the SH0 and SH1 modes can exist at this frequency–thickness product. This can complicate the inspection process and, therefore, limit defect detectability. This article investigates the possibility of a single-mode excitation of the SH1 mode at around 3 MHz $\cdot$ mm. The ability of this method toward detecting very shallow defects (<10% cross-sectional thickness loss) has also been studied. By means of analytical predictions and finite element, it is shown that a signal dominated by the SH1 mode can be generated using a single permanent periodic magnet (PPM) electromagnetic acoustic transducer (EMAT) (PPM EMAT). All predictions are then backed up by experimental measurements. It is also shown that, by studying the reflection coefficient of the SH1 mode, the pure SH1 mode can be used to detect defects as shallow as 5% thickness loss from a 500-mm stand-off. These defects would otherwise be missed by standard, lower frequency guided wave testing.
18 citations
TL;DR: In this paper, the directivity patterns of a wide range of electromagnetic acoustic transducers (EMATs) have been determined experimentally using a second, spiral coil EMAT as the detector around a cylindrical surface.
11 citations