Circuit-field coupled finite element analysis method for an electromagnetic acoustic transducer under pulsed voltage excitation

tation and considers the non-uniform distribution of the biased magnetic fleld. A complete model of EMATs including the non-uniform biased magnetic fleld, a pulsed eddy current fleld and the acoustic fleld is built up. The pulsed voltage excitation is transformed to the frequency domain by fast Fourier transformation (FFT). In terms of the time harmonic fleld equations of the EMAT system, the impedances of the coils under difierent frequencies are calculated according to the circuit-fleld coupling method and Poynting’s theorem. Then the currents under difierent frequencies are calculated according to Ohm’s law and the pulsed current excitation is obtained by inverse fast Fourier transformation (IFFT). Lastly, the sequentially coupled flnite element method (FEM) is used to calculate the Lorentz force in the EMATs under the current excitation. An actual EMAT with a two-layer two-bundle printed circuit board (PCB) coil, a rectangular permanent magnet and an aluminium specimen is analysed. The coil impedances and the pulsed current are calculated and compared with the experimental results. Their agreement verifled the validity of the proposed method. Furthermore, the in∞uences of lift-ofi distances and the non-uniform static magnetic fleld on the Lorentz force under pulsed voltage excitation are studied.