Analysis and design of a MEMS (microelectromechanical system) directional microphone diaphragm with active Q control

• Published in: The Journal of the Acoustical Society of America 2010-03, Vol.127 (3_Supplement), p.1944-1944
• Main Authors: Miles, Ronald N., Su, Quang T., Cui, Weili, Homentcovschi, Dorel, Wu, N. Eva
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.3384908

The analysis and design of a MEMS directional microphone are described that incorporates electronic feedback to achieve active Q control. The microphone diaphragm consists of a 1 × 2-mm stiffened plate fabricated out of polycrystalline silicon that is supported on a central hinge. The sound pressure gradient incident on the diaphragm produces a rocking motion about the central hinge. Interdigitated comb fingers at each end of the diaphragm enable both capacitive sensing and electrostatic actuation. The diaphragm has been designed to have its dominant resonant mode have a frequency of approximately 1 kHz. By minimizing sources of passive damping, the thermal noise of the microphone has been shown to be lower than the noise floor of existing two-microphone systems used in directional hearing aids [Miles et al., J. Acoust. Soc. Am. 125 (2009)]. However, this low-passive damping also results in an undesirable resonance within the audible frequency range. To minimize the adverse effects of this resonance, a simple analog electronic feedback system is designed that can result in acceptable performance in both the frequency and time domains. [Work funded by NIH Grant R01 DC009429.]