A low-frequency dual-band operational microphone mimicking the hearing property of Ormia Ochracea

Zhang, Yansheng; Bauer, Ralf; Jackson, Joseph C.; Whitmer, William M.; Windmill, James F. C.; Uttamchandani, Deepak

Abstract

This paper introduces a directional MEMS microphone designed for hearing aid applications appropriate to low-frequency hearing impairment, inspired by the hearing mechanism of a fly, the female Ormia ochracea. It uses both piezoelectric and capacitive sensing schemes. In order to obtain a high sensitivity at low frequency bands, the presented microphone is designed to have two resonance frequencies below the threshold of low-frequency hearing loss at approximately 2 kHz. One is around 500 Hz and the other is slightly above 2 kHz. The novel dual sensing mechanism allows for optimization of the microphone sensitivity at both frequencies, with a maximum open-circuit (excluding pre-amplification) acoustic response captured via differential piezoelectric sensing at approximately -46 dB (V) ref. 94 dB (SPL) at the resonance frequencies. The corresponding minimum detectable sound pressure level is just below -12 dB. The comb finger capacitive sensing was employed due to a lower electrical response generated from a ground referenced single-ended output by the piezoelectric sensing at the first resonance frequency compared with the second resonance frequency. The capacitive sensing mechanism, connected to a charge amplifier, generates a -28.4 dB (V) ref. 94 dB (SPL) acoustic response when the device is excited at either of the two resonance frequencies. Due to the asymmetric geometry and the 400 μm thick substrate, the device is predicted to perform as a bi-directional microphone below 3 kHz, which is shown by the measured directional polar patterns.

• Journal Article Type: Article
• Acceptance Date: Jun 3, 2018
• Online Publication Date: Jun 20, 2018
• Publication Date: Aug 31, 2018
• Deposit Date: Sep 10, 2018
• Publicly Available Date: Sep 10, 2018
• Journal: Journal of Microelectromechanical Systems
• Print ISSN: 1057-7157
• Electronic ISSN: 1941-0158
• Publisher: Institute of Electrical and Electronics Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 27
• Issue: 4
• Pages: 667-676
• DOI: https://doi.org/10.1109/jmems.2018.2845680
• Keywords: Microphones; Resonant frequency; Auditory system; Micromechanical devices; Sensors; Biomembranes; Frequency conversion
• Public URL: https://nottingham-repository.worktribe.com/output/1067742
• Publisher URL: https://ieeexplore.ieee.org/document/8390909/