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
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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.
References
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TL;DR: A finite element model of the elementary transducers has been developed and shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object.
Abstract: Guided wave inspection has proven to be a very effective method for the rapid inspection of large structures. The fundamental shear horizontal (SH) wave mode in plates and the torsional mode in pipe-like structures are especially useful because of their non-dispersive character. Guided waves can be generated by either piezoelectric transducers or electro- magnetic acoustic transducers (EMATs), and EMATs can be based on either the Lorentz force or magnetostriction. Several EMAT configurations can be used to produce SH waves, the most common being Lorentz-force periodic permanent magnet and magnetostrictive EMATs, the latter being directly applied on the sample or with a bonded strip of highly magnetostrictive material on the plate. This paper compares the performance of these solutions on steel structures. To quantitatively assess the wave amplitude produced by different probes, a finite element model of the elementary transducers has been developed. The results of the model are experimentally validated and the simulations are further used to study the dependence of ultrasonic wave amplitude on key design parameters. The analysis shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object. Periodic permanent magnet EMATs generate intermediate wave amplitudes and are noncontact and insensitive to the variations in properties seen across typical steels. Large signal amplitudes can be achieved with magnetostrictive EMATs with a layer of highly magnetostrictive material attached between the transducer and the plate, but this compromises the noncontact nature of the transducer.
149 citations
TL;DR: The design of an electromagnetic acoustic transducer (EMAT) array device for the inspection of large areas of metallic plate-like structures using the S/sub 0/ guided wave mode is described and the limitations of its operation are discussed.
Abstract: The design of an electromagnetic acoustic transducer (EMAT) array device for the inspection of large areas of metallic plate-like structures using the S/sub 0/ guided wave mode is described. The reasons for using the S/sub 0/ mode are discussed and it is shown how the choice of mode determines the nature of the EMAT array elements. A novel array construction technique is shown to be necessary whereby the EMAT coils for adjacent elements are overlapped in order to achieve the required element density. Results are presented that illustrate the operation of the device on steel and aluminum plate specimens in the thickness range from 5 to 10 mm. An area of at least 10 m/sup 2/ can be inspected from a single location. Spurious signals in the results are caused both by the unwanted A/sub 0/ mode and by S/sub 0/ sidelobes, the latter occurring at the same radial distance from the array as the genuine S/sub 0/ signal from a reflector, but in the wrong direction. The signal-to-coherent noise performance of the complete system is determined by the amplitude ratio of the largest genuine S/sub 0/ signal to the largest spurious signal. This is typically around 30 dB. The sensitivity of the device to artificial defects and genuine corrosion patches is demonstrated and the limitations of its operation are discussed. The feasibility of using the device with the S/sub 1/ guided wave mode to inspect a 20 mm thick plate is also demonstrated.
135 citations
TL;DR: In this article, an analytical model for the response of a solid to periodic surface stresses is applied to cases where the stresses arise from Lorentz forces on currents flowing in a static magpetic field.
Abstract: Calculations and measurements of the efficiencies of electromagnetic transducers for Rayleigh and Lamb waves are presented. Existing solutions for the response of a solid to periodic surface stresses are applied to cases where the stresses arise from Lorentz forces on currents flowing in a static magpetic field. Results are presented for both electri- cally insulating and conducting solids. In the former case, the current must be passed through wires bonded directly to the surface, while in the latter case they may be induced in the metal surface by a nearby coil with no physical contact. Included are expressions for the efficiencies of transmitting and receiving transducers along with a brief discussion of ap- propriate reciprocity relations and equivalent circuits. The theoretical predictions are compared to experimental results for the transduction of 130 kHz flexural waves on 3/8-in aluminum and steel plates. With no adjustable parameters, the theory closely predicts the absolute level of performance on the aluminum plate. Data on steel is qualitatively the same but suggests that magnetostrictive coupling is of comparable magnitude to the Lorentz force coupling mechanism. The dependence of transducer performance upon separation from the plate is also found to be accurately described by the model.
134 citations
TL;DR: In this article, the authors compared pure rare earth cobalt (REC) undulators and hybrid undulators, using both REC and steel, with conventional and superconducting undulators.
Abstract: Pure Rare Earth Cobalt (REC) undulators and hybrid undulators, using both REC and steel, are described and compared with each other and with conventional and superconducting undulators.
120 citations
TL;DR: In this article, a noncontact electromagnetic transducer was proposed to generate horizontally polarized shear waves traveling along, or at a predetermined angle to, the surface of a thick metal object.
Abstract: Theoretical and experimental results obtained with a new type of noncontact electromagnetic transducer are presented. The transducer differs from previous configurations in that a periodic permanent magnet and an axially wound coil are combined to produce a transversely directed periodic surface stress. It is demonstrated that this configuration can be used to generate horizontally polarized shear waves traveling along, or at a predetermined angle to, the surface of a thick metal object, horizontally polarized shear modes of a thin plate, or torsional waves in a tube. A model is presented for the radiation resistance of the transducer in semi‐infinite samples and plates and supporting experiments are reported. Some advantages of this transducer in ultrasonic nondestructive evaluation of structural materials are summarized.
115 citations