Microfabricated VHF acoustic crystals and waveguides

Microfabricated acoustic crystals have been designed and experimentally verified. The acoustic crystals are realized by including tungsten (W) scatterers in a SiO2 matrix. Wide frequency ranges where acoustic waves are forbidden to exist (acoustic bandgaps, ABG) are formed due to the large acoustic impedance and mass density mismatch between W and SiO2. The acoustic crystal structures are fabricated in a 7-mask process that features integrated aluminum nitride piezoelectric couplers for interrogating the devices. Acoustic crystals in a square lattice have been measured at 67 MHz with greater than 30 dB of acoustic rejection and bandwidths exceeding 25% of the midgap. Single and multimode acoustic waveguides have been realized by defecting the acoustic crystals through removal of a subset of the W scatterers. These waveguides achieve relative transmission of up to 100% for the propagating modes.