Electromagnetic generation of Rayleigh waves at MHz frequencies

A Green's function calculation of the far field radiation patterns of EMAT's is presented. The approach is based upon (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMAT, which react to produce the driving Lorentz forces and (b) a Green's function derived from the steepest descent approximation to the far field response of an arbitary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMAT's and horizontally polarized shear waves as radiated by the latter. ABSTRACT A Green's function calculation of the far field radiation patterns of EMAT's is presented. The approach is based upon (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMAT, which react to produce the driving Lorentz forces and (b) a Green's function derived from the steepest descent approximation to the far field response of an arbitary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMAT's and horizontally polarized shear waves as radiated by the latter.

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Electromagnetic generation of electronically steered ultrasonic bulk waves

Moran

Panos

1976

Journal of Applied Physics

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The frequency dependence of the propagation direction of ultrasonic shear and longitudinal waves generated by a meander-line electromagnetic transducer (EMAT) at MHz frequencies has been determined. The results are found to agree well with theory and demonstrate that electronic beam steering is possible using EMAT’s. The relative efficiency of generation in aluminum was also studied and, for a specific meander-line geometry with a permanent magnet providing the necessary static magnetic field, it was found to be relatively flat versus frequency. Efficiency for shear-wave generation (frequency range, 5–9 MHz) was about 4 dB per conversion less than the Rayleigh-wave generation efficiency at 4.6 MHz, and for longitudinal waves (frequency range, 10–24 MHz) about 10 dB less.

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Electromagnetic generation of Rayleigh waves at MHz frequencies

Cited by 11 publications

References 1 publication

Electromagnetic Ultrasonic Transducers

Electromagnetic Ultrasonic Transducers

Half-space radiation by EMATs

Electromagnetic generation of electronically steered ultrasonic bulk waves

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