SLOW ACOUSTIC WAVES WITH THE ANTI-PLANE POLARIZATION IN LAYERED SYSTEMS

Abstract

This paper theoretically investigates the three-partial slow surface Zakharenko-type waves (SSZTW3) with the anti-plane polarization possessing single mode and propagating in layer-on-substrate systems. The dispersive SSZTW3 can exist with the conditions on both the shear elastic constants [Formula: see text] and the bulk shear wave velocities [Formula: see text], where the superscripts L and S belong to the layer and substrate, respectively. The SSZTW3 mode starts with zero-phase velocity and approaches the maximum velocity [Formula: see text] for infinite layer thicknesses. The SSZTW3 phase and group velocities were calculated for many layered structures with Vtm < 1000 m/s , for example, for Au/Paratellurite structure, where the Paratellurite is a common acousto-optic crystal. The velocities' first and higher derivatives were also obtained in order to better understand their behavior for different applications in SAW filters and sensors. The calculations of derivatives were carried out for the Au/Ftorapatite structure with the smallest value of Vtm ~ 210 m/s that is lower than any known acoustic wave velocity in tough materials. It is thought that SSZTW3 usage in MEMS-(CMUTs) technical devices can simplify technological processes. The effective masses were also calculated for different layered structures in the limit of zero-phase velocity Vph, where the dispersion relations correspond to those for free quasi-particles in a vacuum. It was found that the masses are smaller than the mass of a free electron. Hence, it is expected that the SSZTW3 appearance with Vph → 0 can be caused by electrons.