Fly-inspired microphones with piezoelectric readout

The directional hearing capabilities of the fly Ormia Ochracea have been known and utilized in MEMS devices since the 1990s. The fly locates crickets by listening to their chirps—an amazing feat when one considers the size of the fly’s ear compared to the wavelength of audible sound. This work will focus on the design, modeling, fabrication, and testing of a biologically inspired microphone that harnesses this fly’s hearing ability. Recent prototypes are 1/16th the size of previously fabricated devices of similar design and match the true size of the fly’s hearing mechanism. The device consists of a two-sided cantilever beam that rotates about torsional pivots, resulting in two main frequency modes that can be used in the sound localization process for in-plane directivity: a gradient mode that causes the two sides of the beam to move out-of-phase, and a symmetrical mode that causes the two sides of the beam to move in-phase. The microphones are fabricated on a silicon-on-insulator wafer with a 2-μm-thick device layer. A 500-nm-thick aluminum nitride film is the piezoelectric transduction material. The main sensing modes are shown in multipoint scans and are accurately modeled with the finite element method.The directional hearing capabilities of the fly Ormia Ochracea have been known and utilized in MEMS devices since the 1990s. The fly locates crickets by listening to their chirps—an amazing feat when one considers the size of the fly’s ear compared to the wavelength of audible sound. This work will focus on the design, modeling, fabrication, and testing of a biologically inspired microphone that harnesses this fly’s hearing ability. Recent prototypes are 1/16th the size of previously fabricated devices of similar design and match the true size of the fly’s hearing mechanism. The device consists of a two-sided cantilever beam that rotates about torsional pivots, resulting in two main frequency modes that can be used in the sound localization process for in-plane directivity: a gradient mode that causes the two sides of the beam to move out-of-phase, and a symmetrical mode that causes the two sides of the beam to move in-phase. The microphones are fabricated on a silicon-on-insulator wafer with a 2-μm-thick...