Linear Thermoelastic Generation of Ultrasound in Metals

Abstract

The incidence of an electromagnetic wave on a metal surface is accompanied by the generation of acoustic waves within the metal.¹ These waves are excited both at the frequency of the incident wave, and at its harmonies. Accordingly, there exist physical mechanisms of linear and nonlinear ElectroMagnetic-Acoustic Transformation — EMAT. The inductive interaction,² as well as the deformation interaction³, are considered to be responsible for the linear EMAT, while non-linear EMAT is supposed to originate from the thermoelastic interaction.⁴ It was shown recently both experimentally, and theoretically that inductive and deformation potential, forces are capable exciting ultrasound at double the frequency of the electromagnet ic wave, i.e. in the nonlinear regime.^5,7 The present work makes this picture complete by deriving formulae which demonstrate the possibility of a linear EMAT due to thermoelastic generation.