Optimal design of EMAT transmitters

Huang

et al. 2017

J. Sens. Sens. Syst.

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: 99%

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

Huang

et al. 2017

J. Sens. Sens. Syst.

“…An exhaustive work by Mirkhani et al [2] presented a practical numerical study aiming at enhancing the characteristics of an EMAT set-up (mainly signal-to-noise ratio). The FEA strategy included ANSYS EMAG computation followed by LS-DYNA 2D representation of ultrasonic waves.…”

Section: Emats (Electromagnetic Acoustic Transducers)mentioning

confidence: 99%

“…-the simulation allows for generating scenarios with a full control over all variables and phenomena -it is impractical and in some cases unfeasible to measure electromagnetic parameters (magnetic induction, current density) inside a solid specimen [2], whereas these can be easily retrieved from FEA -the measurement of a detailed distribution of the magnetic and/or electric field around an engineering object is time-consuming and requires painstaking data processing; by contrast, FEA software directly generates the resulting contour plots -FEA tends to be more economic than experiment, especially when generating an array of results for subsequent inverse problem solution Table 1 presents authors' attempt to arrange the techniques by the frequency range and the level of complexity. The latter variable corresponds to both the underlying physics and the practical difficulties in obtaining reliable results by either experiment or simulation.…”

Section: Introductionmentioning

confidence: 99%

Finite Element Method Applied in Electromagnetic NDTE: A Review

Augustyniak

Usarek

2016

J Nondestruct Eval

The paper contains an original comprehensive review of finite element analysis (FEA) applied by researchers to calibrate and improve existing and developing electromagnetic non-destructive testing and evaluation techniques, including but not limited to magnetic flux leakage (MFL), eddy current testing, electromagnetic-acoustic transducers (EMATs). Premium is put on the detection and modelling of magnetic field, as the vast majority of ENDT involves magnetic induction, either as a primary variable MFL or a complementary phenomenon (EC, EMATs). FEA is shown as a fit-for-purpose tool to design, understand and optimise ENDT systems, or a Reference for other modelling algorithms. The review intentionally omits the fundamentals of FEA and detailed principles of NDT. Strain-stress FEA applications in NDT, especially in ultrasonography and hole-drilling methodology, deserve as well a separate study.

AIP Conference Proceedings

“…In order to improve the amplitude of the ultrasonic wave excited by EMAT, a number of analytical and numerical models of EMATs have been extensively studied by many researchers [1,[3][4][5][6]. However, in these papers, they solved for the magnetic vector potential (MVP) but always ignored the displacement current in the differential equation and neglected the effect of the permittivity of air or tested sample during modeling, due to its low permittivity [1,[3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…However, in these papers, they solved for the magnetic vector potential (MVP) but always ignored the displacement current in the differential equation and neglected the effect of the permittivity of air or tested sample during modeling, due to its low permittivity [1,[3][4][5][6]. Nevertheless, in nondestructive testing and evaluation (NDT&E) field currently, more durable dielectric materials are replacing or coating with metals in many applications [7,8] which have a much higher permittivity than air or metal sample so that the displacement current cannot be ignored.…”

Section: Introductionmentioning

confidence: 99%

Analytical solution for the effect of the permittivity of coating layer on eddy current generated in an aluminum sample by EMAT

Sun¹,

Sun²,

Chen³

2016

Abstract. In order to improve the ultrasonic wave amplitude excited by electromagnetic acoustic transducers (EMATs), many researchers have proposed models. But they always ignored displacement current or the effect of the permittivity of the air or the metal sample during modeling, due to its low permittivity. However, more durable dielectric materials are replacing or coating with metals in many applications which have a much higher permittivity than air or metal sample so that the effect of permittivity cannot be ignored. Based on an analytical model, the effect of the permittivity of coating layer on the eddy current generated in an aluminum sample by EMAT has been studied. The analytical analysis indicates that the eddy current density excited by the spiral coil of EMAT slowly increases in the beginning and then decreases rapidly while the permittivity increases, and it has much relation to the thickness of the coating layer and the exciting frequency, which is verified by the simulation result.