Engineering of acoustic metamaterials with application to MEMS BAW resonators

In this paper, we demonstrate the novel use of empty inclusions (i.e., “holes”) in bulk materials for engineering their acoustic properties (e.g., Young´s modulus, Poisson´s ratio and mass density) in order to tune and achieve optimal acoustical performance/characteristics. Inclusions have been demonstrated before to produce phononic bandgaps for wave trapping. We focus on the propagation characteristics of the metamaterials brought into being by these inclusions. We implement patterns of holes with different sizes and distributions, to effectively scatter acoustic waves in bar-type bulk acoustic wave (BAW) resonators and to devise the desired resonator properties, e.g., the resonant frequency. The effective material properties (especially the acoustic longitudinal velocity) as extracted from measurements are in good agreement with the theoretical (simulated) values.