A study of the Q and modes of SAW resonators using metal "waffle-iron" and strip arrays

Comparison is made between surface acoustic wave (SAW) resonators using conventional metal-strip array reflectorosn LiNiO3 and analogous "waffle-iron" reflectors consisting of arrays of metal rectangles. Measurements made at 34 MHz with the transducers outside of the resonator indicated that waffle-iron arrays have roughly a fifth of the dissipation loss that analogous strip arrays have. Using either strip or waffle-iron reflectors, when the resonator was operated as a two-port resonator with unapodized transducers between the reflectors, the resonator unloaded Q was dominated by loss mechanisms associated with the transducers. Data is presented comparing the reflection properties of strip and waffle-iron arrays for various dimension ratios. The electric potential field distributions for various modes in resonators using waffle-iron and strip array reflectors were measured using an electrostatic probe. The measured resonant frequencies and corresponding mode patterns for resonators using waffle-iron arrays were compared with computed data obtained using a relatively simple theory. Good agreement was observed. Resonators with waffle-iron arrays are found to have a simpler mode pattern for the dominant mode than that for resonators with corresponding open-circuited strip arrays.