Phase resonance in the reflection of acoustic waves by a system of piezocrystalline layers separated by cladding layers with screening properties

摘要

We discuss the reflection of a transverse elastic wave incident from a substrate onto a system consisting of a periodic system of piezocrystalline layers with identical material properties, one side of which is bounded by the substrate and the other by a mechanically free surface. The layers are separated by superconducting or metallized cladding layers, depending on whether the layers are made of piezomagnetic or piezoelectric material, respectively. Because these cladding layers screen the quasistatic magnetic or electric fields that accompany the elastic wave, they cause a reflection of the wave at the layer boundaries that is weak due to the smallness of the magneto- or electromechanical coupling parameters. The presence of the mechanically free surface ensures total reflection at any angle of incidence, so that the amplitude of the reflection coefficient is always unity. This allows us to study the effects of diffraction on the phase of the reflection coefficient for a wave reflected from the boundary of the substrate-layered structure against this constant (unity) amplitude background. We have analyzed the spectral dependence of the phase change of the reflected wave due to multiple reflection at the boundaries between layers, which adds to the path length of the wave. We show that this diffraction-induced phase shift has a characteristic resonance behavior, attaining a maximum value near Bragg-forbidden zones that is roughly twice the increase in the maximum background level. We discuss several possible wave effects based on the concept of phase resonance.