Multiphysics Modeling of a Lorentz Force-Based Meander Coil Electromagnetic Acoustic Transducer via Steady-State and Transient Analyses

Huang

et al. 2017

J. Sens. Sens. Syst.

Self Cite

Abstract. Electromagnetic acoustic transducers (EMATs) are noncontact transducers generating ultrasonic waves directly in the conductive sample. Despite the advantages, their transduction efficiencies are relatively low, so it is imperative to build accurate multiphysics models of EMATs and optimize the structural parameters accordingly, using a suitable optimization algorithm. The optimizing process often involves a large number of runs of the computationally expensive numerical models, so metamodels as substitutes for the real numerical models are helpful for the optimizations. In this work the focus is on the artificial neural networks as the metamodels of an omnidirectional EMAT, including the multilayer feedforward networks trained with the basic and improved back propagation algorithms and the radial basis function networks with exact and nonexact interpolations. The developed neural-network programs are tested on an example problem. Then the model of an omnidirectional EMAT generating Lamb waves in a linearized steel plate is introduced, and various approaches to calculate the amplitudes of the displacement component waveforms are discussed. The neural-network metamodels are then built for the EMAT model and compared to the displacement component amplitude (or ratio of amplitudes) surface data on a discrete grid of the design variables as the reference, applying a multifrequency model with FFT (fast Fourier transform)/IFFT (inverse FFT) processing. Finally the two-objective optimization problem is formulated with one objective function minimizing the ratio of the amplitude of the S0-mode Lamb wave to that of the A0 mode, and the other objective function minimizing as the negative amplitude of the A0 mode. Pareto fronts in the criterion space are solved with the neural-network models and the total time consumption is greatly decreased. From the study it could be observed that the radial basis function network with exact interpolation has the best performance considering its accuracy of approximation and the time required to build the metamodel.

Section: S Wang Et Al: Optimizations Of An Emat With Ann Metamodelsmentioning

confidence: 59%

Accelerated optimizations of an electromagnetic acoustic transducer with artificial neural networks as metamodels

Huang

et al. 2017

J. Sens. Sens. Syst.

Self Cite

“…Ludwig conducted transient analysis of a meander coil EMAT placed on isotropic non-ferromagnetic half-space, assuming uniform static magnetic field [7]. Jafari-Shapoorabadi studied in detail the controlling eddy current equations and argued that the previous work using the total current divided by the cross section area of the conductor as the source current density is equivalently applying the incomplete equation, and this means ignoring the skin effect and proximity effect [8], while we proved the opposite in [9]. Dhayalan used the FEM package COMSOL to build the electromagnetic model of a meander EMAT, and the simulated Lorentz force was exported to another package Abaqus as the driving force to excite Lamb waves [10].…”

Section: Introductionmentioning

confidence: 67%

A multi-objective structural optimization of an omnidirectional electromagnetic acoustic transducer

et al. 2017

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In this paper an axisymmetric model of an omnidirectional electromagnetic acoustic transducer (EMAT) used to generate Lamb waves in conductive plates is introduced. Based on the EMAT model, the structural parameters of the permanent magnet were used as the design variables while other parameters were fixed. The goal of the optimization was to strengthen the generation of the A0 mode and suppress the generation of the S0 mode. The amplitudes of the displacement components at the observation point of the plate were used for calculation of the objective functions. Three approaches to obtain the amplitudes were discussed. The first approach was solving the peak values of the envelopes of the time waveforms from the time domain simulations. The second approach also involved calculation of the peaks, but the waveforms were from frequency domain model combined with the forward and inverse Fourier transforms. The third approach involved a single frequency in the frequency domain model. Single and multi-objective optimizations were attempted, implemented with the genetic algorithms. In the single objective optimizations, the goal was decreasing the ratio of the amplitudes of the S0 and A0 modes, while in the multi-objective optimizations, an extra goal was strengthening the A0 mode directly. The Pareto front from the multi-objective optimizations was compared with the estimation from the data on the discrete grid of the design variables. From the analysis of the results, it could be concluded that for a linearized steel plate with a thickness of 10mm and testing frequency of 50kHz, the point with minimum S0/A0 could be selected, thus the multi-objective optimization effectively degenerated to the single objective optimization. While for an aluminum plate with a thickness of 3mm and frequency of 150kHz, without further information it would be difficult to select one particular solution from the Pareto front.

“…1 and a 2-D space is considered here. The permanent magnet is located on the top of the coil and the specimen, the S-pole of the magnet is 6 on the top with the N-pole underneath. The liftoff of the coil in the model is only 25 m, which can increase the weak coupling efficiency of the EMAT.…”

Section: Model Configurationmentioning

confidence: 99%

“…Therefore, it has a wide range of applications for the EMAT such as rough material surface, high temperature and high speed available, etc. [5,6] Typically, the sensitivity of EMATs is affected by the transmit power, coil turns, constant external magnetic field, electrical conductivity, magnetic permeability and acoustic impedance, which is about 40 dB lower than that of PZTs. The weak transduction efficiency is currently the main challenge of EMATs in practical applications, so different types of signal processing techniques are required to enhance the signal and isolate noise .…”

Section: Introductionmentioning

confidence: 99%

Numerical evaluation of focal position selection by line-focusing electromagnetic acoustic transducer with experimental validation

Huang

Sun

et al. 2019

JAE

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2019) 'Numerical evaluation of focal position selection by line-focusing electromagnetic acoustic transducer with experimental validation.', International journal of applied electromagnetics and mechanics., 61 (3). pp. 341-355.Abstract-As the focal position of a line-focusing electromagnetic acoustic transducer (LF-EMAT) affects the intensity of the focal signal, we measure the displacement signal and the slection method of the focal line position is then studied in this work to improve the signal intensity and detection precision for a shear-vertical (SV) wave LF-EMAT. We calculate the magnetostatics filed and bulk wave propagation utilizing the finite element method (FEM). We simulate the characteristics of the SV wave, and we find that the radiant distance and propagation direction has a great influence on the amplitude of the displacement of the specimen. The superposition area of SV waves from different sources possesses better focusing ability, and the triangular area (normalized amplitude of the SV waves lower than 10%) near the surface of a specimen should be avoided to be chosen when designing the meander line coils. As for the line-focusing EMAT described in this manuscript, the selection of focal positions for different thickness specimens or detection depth is completely different. Moreover, we perform an experiment to validate the simulation results and lead to a conclusion that the position of the focal point is required to be appropriately close to the excitation coils to enhance the intensity of the signal, while the best focal position should be calculated.