Acoustic waves generated by pulsed microwaves in viscoelastic rods: Modeling and experimental verification

The acoustic wave generation in a specimen irradiated by a pulsed microwave is predicted theoretically. The specimen is a viscoelastic rod inserted in to a wave guide. The model is based on Maxwell's equations, heat equation a nd thermoviscoelasticity theory. Computations show the presence of temperat ure oscillations due to the electromagnetic interferences in the irradiated rod if its electromagnetic absorption is low. An experimental method to in fer indirectly the detailed behavior of microwave-generated acoustic waves in polymer rods, including the influence of electromagnetic wave reflection at the rod ends, is presented. The method consists of measuring the oscill ations in the particle acceleration detected at the end of the rod that are induced by variations in the polymer rod length. The oscillations are caus ed by changing electromagnetic standing-wave conditions within the rod. It is found that these oscillations are in agreement in period, amplitude, and phase, with independent values of the complex dielectric constant and comp lex acoustic slowness of the polyvinyl chloride samples used in the study. (C) 2001 Acoustical Society of America.