Acoustic Field and Energy Characteristics of a Slot Mode in a “Delay Line–Vacuum Gap–Resonating Plate” Structure

Abstract— This paper presents some results of theoretical study on a structure including a delay line based on a Y–X cut lithium niobate plate with two interdigital transducers for the generation and reception of an acoustic wave with transverse horizontal polarization within a frequency band of 1.5–2.2 MHz. The thickness of the plate was 0.35 mm. An Y–X-140° cut lithium niobate resonating plate was placed above the delay line between the transducers with a certain gap. Simulation was carried out by the finite element method. When RF voltage was applied to the input transducer, pronounced resonant absorption peaks associated with the excitation of a slot acoustic mode were observed in the frequency dependence of total losses. The velocity of the slot mode was calculated, and the mechanical and electrical fields in the delay line and resonator were found for the first time. It has been shown that, at resonant frequencies, the energy of an acoustic wave is pumped from the delay line into the resonator. At the same time, a standing SH₀ wave containing more than 66% of system’s acoustic energy appears in the resonator to suppress the travelling wave at the output from the delay line. This conclusion is also confirmed by the amplitude distribution of the transverse horizontal component of the mechanical displacement in the delay line and resonator at resonant frequencies and between them.