Numerical implementation and model predictions of a unified conservation law description of the electromagnetic acoustic transduction process

Abstract

A numerical formulation and computer implementation of the electroacoustic transduction process governing an electromagnetic acoustic transducer are discussed. A multistage finite-element, finite-difference procedure is developed to predict the acoustic wave radiation into an isotropic half space due to an excitation coil driven by a high-frequency pulsed current. To demonstrate the flexibility of this approach, the acoustic wave generation efficiency of constant versus variable lift-off wire pair configurations of a meander coil suspended over a metallic specimen is examined in two dimensions. It is shown for the Lorentz force density induced by 5- and 8-wire-pair meander coils that a variable lift-off creates a more uniform volume force density in the metallic specimen and consequently produces more efficient broadband surface waves as compared to the conventional fixed lift-off arrangement. Furthermore, the directivity patterns of these finite-aperture, pulsed-elastic-wave phenomena exhibit behavior that cannot be adequately predicted by simple analytical formulas.