Thermal boundary layer limitations on the performance of micromachined microphones.

This work examines the extent to which thermal boundary layer effects limit the performance of micromachined microphones. The acoustic impedance of the cavity formed by the microphone enclosure is calculated using both analytical and finite-element methods. A thermal correction to the cavity impedance is included to account for the transition of compression and expansion within the enclosure from adiabatic to isothermal when the thermal boundary layer that forms at the walls of the enclosure becomes large compared to the enclosure dimensions.

A transmission-line model of back-cavity dynamics for in-plane pressure-differential microphones.

Pressure-differential microphones inspired by the hearing mechanism of a special parasitoid fly have been described previously. The designs employ a beam structure that rotates about two pivots over an enclosed back volume. The back volume is only partially enclosed due to open slits around the perimeter of the beam.

A rotational capacitive micromachined ultrasonic transducer (RCMUT) with an internally-sealed pivot.

Most capacitive micromachined ultrasonic transducers (CMUTs) are comprised of individual gap-closing parallel plates. We present an unconventional CMUT in which a vacuum-sealed cavity beneath a diaphragm layer comprises a mechanical structure that pivots and has a first rocking or rotational mode of vibration. The general ability to couple individual CMUT pistons under vacuum with mechanical structures to alter vibration mode frequencies and mode shapes is thus demonstrated.

A broadband, capacitive, surface-micromachined, omnidirectional microphone with more than 200 kHz bandwidth.

A surface micromachined microphone is presented with 230 kHz bandwidth. The structure uses a 2.25 μm thick, 315 μm radius polysilicon diaphragm suspended above an 11 μm gap to form a variable parallel-plate capacitance.

Micromachined piezoelectric microphones with in-plane directivity.

Micromachined piezoelectric microphones with in-plane directivity are introduced. A beam rotates about center torsional pivots and is attached to piezoelectrically active end-springs. Rotation of the beam in response to sound pressure gradients produces spring deflections, which, in turn, produce an open-circuit voltage at the piezoelectric films.