EMAT simulations based on a two- dimensional FEM coupled electro- mechanical formulation

Huang

International Journal of Applied Electromagnetics and Mechanics

et al. 2018

In this work a Multiphysics model of a meander line electromagnetic acoustic transducer (EMAT) to generate S0 mode Lamb waves in an aluminum plate is built and the structural parameters of the transducer are optimized based on the model. Three approaches to solve the amplitude of the in-plane displacement component at an observation point are explored and the single frequency approach is selected because it is the fastest. In the optimization, the objective function to minimize is the negative amplitude of the S0 mode waves, and the design variables are the width and height of the magnet and liftoff values of the magnet and the coil from the top surface of the plate. The liftoff values form a linear constraint of the optimization problem. A genetic algorithm (GA) program capable of handling the linear constraint efficiency is developed. The internal status of the GA program is tracked carefully to avoid unnecessary evaluations of the objective function. With 30 runs of the program, the optimal set of variables leads to the ratio of the width of the magnet to that of the coil of 115.85%.

Section: Introductionmentioning

confidence: 99%

Constrained optimization of a meander line EMAT generating S0 mode Lamb waves with genetic algorithms

Huang

International Journal of Applied Electromagnetics and Mechanics

et al. 2018

A wholly analytical method for the simulation of an electromagnetic acoustic transducer array

Xie

Yin

Sergio

et al. 2016

JAE

This paper presents a wholly analytical method which combines electromagnetic and ultrasonic simulations for the study of an Electromagnetic Acoustic Transducer Array (EMAT). Analytical solutions to the eddy current problem for the meander coil used in an EMAT are adapted from the classic Deeds and Dodd solution, which was originally intended for circular coils. The analytical solution resulting from this novel adaptation exploits the large radius extrapolation and shows several advantages over the finite element method (FEM), especially in the higher frequency regime. The calculated Lorentz force density from the EM solver is then coupled to the ultrasonic simulations, which exploit an analytical solution for generating the distribution of surface waves. Beam features are studied, which can produce performance parameters for an EMAT array, facilitating the optimum design of such sensors. This total analytical approach to an EMAT simulation has not been reported previously to our knowledge. 2

International Journal of Applied Electromagnetics and Mechanics

A Kriging surrogate model of an electromagnetic acoustic transducer (EMAT) generating omnidirectional Lamb waves

Wang¹,

Huang²,

Wang³

et al. 2018

Electromagnetic acoustic transducers (EMATs) are non-contact ultrasonic transducers used to generate ultrasonic waves directly in the tested metal samples, suitable for special situations like testing moving or hot metal solids. EMATs rely on electromagnetic coupling, and the transduction efficiency of EMATs is relatively low, so it’s crucial to improve their performance through building accurate models and implementing structural optimisations. Modern evolutionary optimization algorithms involve a number of evaluations of the objective function of the optimization problem, so it’s necessary to explore surrogate models to reduce the time consumption during evaluation of the computationally expensive objective function, especially when the function corresponds to complex numerical models, like the EMAT model. We focused on the application of Kriging surrogate model (DACE) in EMAT modeling in this work. The formulations of the DACE model were reviewed, then the model of an omnidirectional EMAT was introduced. Three methods to calculate the amplitudes of the displacement components were discussed and compared, including the time-domain method, the multifrequency method (with FFT/IFFT processing), and the single frequency method applying directly the phasors. The DACE model of the EMAT was then built to predict outputs on a discrete grid of the design variables. Finally the obtained DACE model was used as the surrogate model in the optimization of the EMAT driven by the simulated annealing algorithm. With the DACE model, the total time consumption of optimization of the EMAT was reduced greatly.