Acoustic field and energy characteristics of the slot mode in the structure “delay line — vacuum gap — resonating plate”

The article presents the results of a theoretical study of a structure including a delay line based on a Y–X cut lithium niobate plate with two interdigital transducers for excitation and reception of an acoustic wave with shear-horizontal polarization in the frequency range of 1.5–2.2 MHz. The plate thickness was 0.35 mm. A resonant Y–X-140° cut lithium niobate plate was located above the delay line between the transducers with a certain gap. The simulation was performed using the finite element method. When an RF voltage was applied to the input transducer, pronounced peaks of resonant absorption associated with the excitation of a slot acoustic mode were observed on the frequency dependence of total losses. The velocity of the slot mode was calculated and mechanical and electric fields in the delay line and in the resonator were found for the first time. It is shown that at resonant frequencies, the energy of the acoustic wave is pumped from the delay line to the resonator. In this case, a standing SH wave appears in the resonator, which contains more than 66% of the acoustic energy of the system, which leads to the suppression of the traveling wave at the output of the delay line. This conclusion is also confirmed by the distribution of the amplitude of the transverse-horizontal component of the mechanical displacement in the delay line and in the resonator at resonant frequencies and between them.