PROPAGATION OF ULTRASONIC BEAMS IN FERROELECTRIC CERAMICS IN AN EXTERNAL ELECTRIC-FIELD

The propagation of Gaussian, ultrasonic beams in segnetoelectrics set in a homogeneous electric field is discussed. Conditions that give ris e to electrically induced fold and cusp catastrophes on acoustic wave surfaces are found. For isotropic ferroelectric ceramics, these condit ions result in either focusing or channeling of ultrasonic radiation. In the direction of the electrically induced acoustic axis, no conic r efraction is observed; however, the external field results in a redist ribution of acoustic energy over the cross section of the beam.