Non-stationary elastic wavefields from an apodized normal transducer. Near-field asymptotics and numerics

Abstract : We simulate non-stationary radiating near-field of a normal transducer acting at the surface of an isotropic homogeneous elastic half-space. The transducer is assumed large compared to the characteristic wavelength. Effects of non-constance of distribution of pressure over the aperture of the transducer on the wavefield are considered in detail. These are i) excitation of a plane S-wave, ii) anomalous polarization in the plane P-wave, and iii) suppression of edge waves by an apodization of the pressure distribution. Asymptotic formulas are tested against a numerical method based on new mixed finite elements. The agreement is found excellent within the bounds of the asymptotic theory.