Conventionally, directionality is achieved using multiple microphones separated in space over a relatively large area. For limited aperture applications such as smart watches and hearing assistive devices, single-element, ultra-miniature microphones are highly advantageous. However, these directional microphones pose significant transduction challenges because they vibrate in complex ways – different from omnidirectional microphones. Silicon Audio addresses this challenge by leveraging its expertise in the patterning and microfabrication of piezoelectric materials, which provides a versatile means to transduce the mechanical structure’s vibration at multiple regions.
Our directional microphone technology comprises mechanical structures designed and fabricated with vibration mode shapes that respond to small differences in pressure, rather than absolute pressure. These modes of vibration, depicted in the color mapping of the images to the right, are measured using thin film piezoelectric materials. These materials produce an electrical signal in proportion to sound arriving from preferred directions and serve as the microphone output.
At Silicon Audio, our directional microphone technology offers a 10 dB SNR improvement over the current state-of-the-art directional microphone. In terms of directionality, our pressure-gradient piezoelectric microphone produces a figure-8, or dipole-style, directivity as measured in our anechoic chamber.
Conventional Microphone Recording
Directional Microphone Recording
A major complaint from hearing aid users is the “cocktail party effect,” which refers to a hearing aid’s amplification of unwanted noise (such as background noise at a cocktail party), as well as desired speech intelligibility. Presently, hearing aids are limited in their ability to improve speech intelligibility because of the cocktail party effect, and a high-performance directional microphone can make a significant impact. Silicon Audio demonstrates the difference between a conventional microphone and our directional microphone in a replicated cocktail party setting.
Our directional microphone at Silicon Audio uses a mechanical structure inspired by the hearing organ of a special fly, which was discovered to have the ability to locate crickets by listening for their song.Learn MORE
D. Kim, M. L. Kuntzman, and N. A. Hall, "A Transmission Line Model of Back-Cavity Dynamics for In-Plane Pressure-Gradient Microphones," The Journal of the Acoustical Society of America, 2014 (in review).
D. Kim, N. N. Hewa-Kasakarage, M. L. Kuntzman, K. D. Kirk, S. H. Yoon, and N. A. Hall, "Piezoelectric Micromachined Microphones with Out-of-Plane Directivity," Applied Physics Letters, vol. 103, pp. 013502-5, July 2013.
M. L. Kuntzman, J. G. Lee, N. N. Hewa-Kasakarage, D. Kim, and N. A. Hall, "Micromachined Piezoelectric Microphones with In-Plane Directivity," Applied Physics Letters, vol. 102, pp. 054109-4, February 2013.
Our directional microphone uses MEMS fabrication techniques to incorporate piezoelectric materials into a form factor suitable for applications benefiting from directionality in ultra-small packaging.Our MEMS experience...
Working with special materials to effectively harness piezoelectric effects to create an inherently directional microphone exemplifies our competencies at Silicon Audio.Our PIEZOELECTRIC MATERIALS experience...
The interaction of sound waves with our unique biologically-inspired microphones is somewhat different than in conventional microphones, and these differences are exploited to realize ultra-small microphones with high SNR.Our ACOUSTICS experience...