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Journal ArticleDOI

A two-stage finite element model of a meander coil electromagnetic acoustic transducer transmitter

07 Apr 2011-Nondestructive Testing and Evaluation (Taylor & Francis Group)-Vol. 26, Iss: 02, pp 101-118
TL;DR: In this article, a two-stage numerical model of a meander coil electromagnetic acoustic transducer transmitter operating on the Lorentz force principle is presented, which is used to predict the ultrasonic A-scan signals for bulk (longitudinal and shear) and guided (Rayleigh) waves in isotropic homogeneous materials.
Abstract: This paper presents a two-stage numerical model of a meander coil electromagnetic acoustic transducer transmitter operating on the Lorentz force principle. This model was used to predict the ultrasonic A-scan signals for bulk (longitudinal and shear) and guided (Rayleigh) waves in isotropic homogeneous materials. The simulation results agree with the experimental results. The grating effects of the meandering coil, for different coil spacings, are also discussed in this paper.
Citations
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TL;DR: A unidirectional EMAT with two meander-line coils is proposed, and a finite element model is used to simulate the directivity of the Rayleigh and shear vertical waves generated by these EMATs.
Abstract: The elastic waves generated by traditional meander- line coil electromagnetic acoustic transducers (EMATs) propagate in two directions, overlapping the echo signals from defects with the same distances, and the defect echo signal is hard to distinguish from the edge-reflected signal when the EMATs are near the edge of a specimen. In this paper, a unidirectional EMAT with two meander-line coils is proposed. A finite element model is used to simulate the directivity of the Rayleigh and shear vertical waves generated by these EMATs. Six transducers are fabricated using the printed circuit technique. The unidirectional Rayleigh wave and shear vertical wave are tested, and the results agree well with the simulation.

45 citations

Journal ArticleDOI

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TL;DR: This paper presents a method which combines electromagnetic simulation and ultrasonic simulation to build EMAT array models and radiation pattern obtained with Hilbert transform on time domain waveforms is proposed to characterise the sensor in terms of its beam directivity and field distribution along the steering angle.
Abstract: This paper presents a method which combines electromagnetic simulation and ultrasonic simulation to build EMAT array models. For a specific sensor configuration, Lorentz forces are calculated using the finite element method (FEM), which then can feed through to ultrasonic simulations. The propagation of ultrasound waves is numerically simulated using finite-difference time-domain (FDTD) method to describe their propagation within homogenous medium and their scattering phenomenon by cracks. Radiation pattern obtained with Hilbert transform on time domain waveforms is proposed to characterise the sensor in terms of its beam directivity and field distribution along the steering angle.

30 citations


Cites background from "A two-stage finite element model of..."

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TL;DR: A new means of generating higher-order mode clusters of guided waves (HOMC-GW) using a meander-coil (MC) electromagnetic acoustic transducer (EMAT) in plates at frequencies significantly higher than the lower-order plate modes.
Abstract: This paper reports on a new means of generating higher-order mode clusters of guided waves (HOMC-GW) using a meander-coil (MC) electromagnetic acoustic transducer (EMAT) in plates at frequencies significantly higher than the lower-order plate modes. These wave modes are considerably less dispersive and they occur at much higher frequency-thickness (f x d) products. Our studies cover the f x d range of 13 to 20 MHz·mm. Experimental measurements were carried out on Al plate samples of different thicknesses using three different EMAT coil periods. To understand the generation and propagation characteristics of HOMC-GW with EMATs, several simulations were carried out using 2-D finite element models at different f x d products. These simulations captured all features observed in the experiments. The time-frequency smoothed pseudo Wigner-Ville distribution (SPWVD) was used to analyze the HOMC-GW modes. Defect detection measurements using HOMC-GW generated using EMATs were made on Al plates with machined defects.

29 citations


Cites methods from "A two-stage finite element model of..."

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TL;DR: The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC.
Abstract: This paper presents a new method of improving the ultrasonic signal amplitude from a meander line EMAT by using soft magnetic alloy ribbon (Fe₆₀Ni₁₀V₁₀B₂₀) as a magnetic flux concentrator (MFC). The flux concentrator is a thin soft amorphous magnetic material (Fe₆₀Ni₁₀V₁₀B₂₀) which is very sensitive to a small flux change. The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC. Two dimensional numerical models have been developed for the EMAT with MFC to quantify the improvement of the received signal amplitudes. Model calculations and experiments have been carried out for a wide range of ultrasonic frequencies (500 kHz-1 MHz) in different materials.

26 citations

Journal ArticleDOI

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TL;DR: In this paper, an approach to solve directly the underlying integro-differential equations involved in the eddy current model was proposed, for both steady-state and transient analyses, and the skin effect and proximity effect were observed in a generalized multi-conductor electromagnetic model, both for the complete and incomplete equations.
Abstract: Electromagnetic acoustic transducer (EMAT) is a kind of non-contact ultrasonic transducer, and during its operation, no liquid coupling is required. Despite this advantage, EMAT has low transduction efficiency and its performance depends on the tested object, thus further research of its complex multiphysics transduction mechanism involving both electromagnetic and elastodynamic phenomena is paramount. In this paper, an approach to solve directly the underlying integro-differential equations involved in the eddy current model was proposed, for both steady-state and transient analyses. Skin effect and proximity effect were observed in a generalized multi-conductor electromagnetic model, both for the complete and incomplete equations. Time-varying distributions of the Lorentz force vector were solved from the static bias magnetic field and sinusoidal current density waveforms converted from the corresponding complex phasors of the frequency-domain solution for a meander coil EMAT. For a plate model without any defect and a plate model with a slot defect, the waveforms of displacement component at two points from transient analyses were recorded. The simulated traveling velocities of the wave packets were calculated to compare with the theoretical group velocities of S0 and mode-converted A0 modes of Lamb waves.

25 citations

References
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Book

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25 Nov 1983
TL;DR: In this paper, the authors considered the problem of finite element solutions to the scalar Helmholtz equation and showed that the solution can be found in finite elements in one dimension.
Abstract: 1. Finite elements in one dimension 2. First-order triangular elements for potential problems 3. Electromagnetics of finite elements 4. Simplex elements for the scalar Helmholtz equation 5. Differential operators in ferromagnetic materials 6. Finite elements for integral operators 7. Curvilinear, vectorial and unbounded elements 8. Time and frequency domain problems in bounded systems 9. Unbounded radiation and scattering 10. Numerical solution of finite element equations References Appendices Index.

1,219 citations

Journal ArticleDOI

[...]

TL;DR: The results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40, and the 2-D Fourier transform method is used to quantify Lamb wave interactions with defects.
Abstract: The interaction of individual Lamb waves with a variety of defects simulated by notches is investigated using finite-element analysis, and the results are checked experimentally. Excellent agreement is obtained. It is shown that a 2-D Fourier transform method may be used to quantify Lamb wave interactions with defects. The sensitivity of individual Lamb waves to particular notches is dependent on the frequency-thickness product, the mode type and order, and the geometry of the notch. The sensitivity of the Lamb modes a/sub 1/, alpha /sub 0/, and s/sub 0/ to simulated defects in different frequency-thickness regions is predicted as a function of the defect depth to plate thickness ratio and the results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40. Transmission ratios of Lamb waves across defects are highly frequency dependent. >

865 citations


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576 citations


"A two-stage finite element model of..." refers background in this paper

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Reinhard Lerch1
TL;DR: A method for the analysis of piezoelectric media based on finite-element calculations is presented, which provides deeper insight into the physical mechanisms of acoustic wave propagation in piezoeselastic media.
Abstract: A method for the analysis of piezoelectric media based on finite-element calculations is presented in which the fundamental electroelastic equations governing piezoelectric media are solved numerically The results obtained by this finite-element calculation scheme agree with theoretical and experimental data given in the literature The method is applied to the vibrational analysis of piezoelectric sensors and actuators with arbitrary structure Natural frequencies with related eigenmodes of those devices as well as their responses to various time-dependent mechanical or electrical excitations are computed The theoretically calculated mode shapes of piezoelectric transducers and their electrical impedances agree quantitatively with interferometric and electric measurements The simulations are used to optimize piezoelectric devices such as ultrasonic transducers for medical imaging The method also provides deeper insight into the physical mechanisms of acoustic wave propagation in piezoelectric media >

502 citations

Book

[...]

03 Dec 2010
TL;DR: In this paper, the authors present a survey of EMAT techniques and their applications in the industrial domain, including on-line texture monitoring of steel sheets and in-situ monitoring of Dislocation Mobility.
Abstract: Preface. Introduction: Noncontact Ultrasonic Measurements. Brief Historical Sketch of EMAT. Electromagnetic Acoustic Resonance - EMAR. Part I: Development of EMAT Techniques. 1: Coupling Mechanism. 1.1. Background. 1.2. Generation Mechanism. 1.3. Receiving Mechanisms. 1.4. Comparison with Measurements. 2 : Available EMATS. 2.1. Bulk-Wave EMATs. 2.2. Longitudinal-Guided-Wave EMAT for Wires and Pipes. 2.3. PPM EMAT. 2.4. Meander-Line Coil SH-Wave EMAT. 2.5. SH-Wave EMAT for Chirp Pulse Compression. 2.6. Axial-Shear-Wave EMAT. 2.7. SH-Wave EMAT for Resonance in Bolt Head. 2.8. Rayleigh-Wave EMAT. 2.9. Line-Focusing EMAT. 2.10. Trapped-Torsional-Mode EMAT. 2.11. EMATs for High Temperature Measurements. 3: Brief Instruction To Build EMATs. 3.1. Coil. 3.2. Magnets. 3.3. Impedance Matching. Part II: Resonance Spectroscopy with EMATs -EMAR-. 4: Principles of EMAR for Spectral Response. 4.1. Through-Thickness Resonance. 4.2. Spectroscopy with Analog Superheterodyne Processing. 4.3. Determination of Resonance Frequency and Phase Angle. 5: Free-Decay Measurement For Attenuation And Internal Friction. 5.1. Difficulty of Attenuation Measurement. 5.2. Isolation of Ultrasonic Attenuation. 5.3. Measurement of Attenuation Coefficient. 5.4. Correction for Diffraction Loss. 5.5. Comparison with Conventional Technique. Part III: Physical-Acoustics Studies. 6: In-Situ Monitoring Of Dislocation Mobility. 6.1. Dislocation-Damping Model for Low Frequencies. 6.2. Elasto-Plastic Deformation in Copper. 6.3. Point-Defect Diffusion toward Dislocations in Deformed Aluminum. 6.4. Dislocation Damping after Elastic Deformation in Al-Zn Alloy. 6.5. Recovery and Recrystallization in Aluminum. 7: Elastic Constants and Internal Friction of Advanced Materials. 7.1. Mode Control in Resonance Ultrasound Spectroscopy by EMAR. 7.2. Inverse Calculation for Cij and Qij-1. 7.3. Monocrystal Copper. 7.4. Metal-Matrix Composites (SiCf/Ti-6Al-4V). 7.5. Lotus-Type Porous Copper. 7.6. Ni-Base Superalloys. 7.7. Thin Films. 7.8. Piezoelectric Material (Langasite: La3Ga5SiO14). 8: Nonlinear Acoustics. Part IV: Industrial Applications. 9: On-Line Texture Monitoring Of Steel Sheets. 9.1. Texture of Polycrystalline Metals. 9.2. Mathematical Expressions of Texture and Velocity Anisotropy. 9.3. Relation between ODCs and r-Values. 9.4. On-Line Monitoring with Magnetostrictive-Type EMATs. 10: Acoustoelastic Stress Measurements. 10.1. Nonlinear Elasticity. 10.2. Acoustoelastic Response of Solids. 10.3. Birefringence Acoustoelasticity. 10.4. Practical Stress Measurements with EMAR. 10.5. Monitoring Bolt Axial Stress. 11: Measurements On High-Temperature Steels. 11.1. Velocity Variation at High Temperatures. 11.2. Solidification-Shell Thickness of Continuous Casting S

276 citations