Acoustic waves guided by a fluid layer on a piezoelectric substrate

Abstract

This paper theoretically studies the propagation and the generation of leaky acoustic waves in a fluid layer enclosed between the half-infinite YZ-LiNbO3 (lithium niobate) substrate coated with a thin SiO2 (silicone dioxide) layer and the half-infinite domain occupied by silicone rubber. The plane wave spectrum in the structure is computed, and the specific features of the behavior of the real and imaginary parts of the leaky wave velocity depending on the fluid layer thickness and the electric boundary conditions are analyzed. Besides, the numerical estimations are made of the coupling-of-mode (COM) parameters describing a periodic grating deposited on the LiNbO3 substrate under the SiO2 layer. The dependence of the COM parameters is investigated on characteristics and conditions specifying the structure, such as the fluid layer thickness, the SiO2 coating thickness, and the presence or the absence of projections on the SiO2 coating face in contact with the fluid. In particular, it is found that the reflection and the transduction coefficients remain high enough even when the fluid layer is several wavelengths thick provided that the frequency is close to the value f0=vl0′∕2p, where vl0′ is the real leaky wave velocity at the zeroth thickness of the fluid layer and p is the grating period. It is also found that projections on the SiO2-fluid interface significantly increase the reflection coefficient.