This research is to develop a low-cost, low-power-consuming, active-noise-cancelling technology for hearing aids, using MEMS resonant-microphones and microspeaker, so that the wearers of the hearing aids will hear speech clearly without being hampered by undesirable sounds and noises. The proposed approach is to integrate a microspeaker and a resonant microphone array in a same package, and drive the microspeaker with signals picked up by the resonant microphone array (specifically designed to be extremely sensitive to any undesirable sounds or noises) after a summing and inverting amplifier (with automatic gain control) in order to produce 180 out-of-phase sound for active cancellation of any undesirable sounds. The proposed technology will be very inexpensive, as it is based on MEMS microspeaker and resonant microphone array, and also will consume very low power, since the microspeaker and resonant microphone array are based on piezoelectric transduction and because the signal processing and drive electronics is ultra-low power consuming without any power hungry digital signal processing. The innovation of this project is centered on (1) the bank of acoustically filtering MEMS microphones based on a high Q resonance of the microphone diaphragm and (2) a microspeaker that provides active noise cancellation. The former is to replace the electrical filter banks (that emulate human cochlea) with a bank of the Q-enhanced/filtered microphones. The latter is to actively cancel out the undesired sounds by generating the noise-canceling sound waves (with the same magnitude but 180 out of phase of the undesired sounds). The basic microphone structure will be a piezoelectric unimorph built on a 0.3 ? 10 mm2 support diaphragm (about 1 - 10 m thick) with its one edge clamped, electrically-insulating films and Al electrode films in a silicon substrate. A typical frequency response of such a resonant microphone shows a peak with Q of about 40 at the fundamental resonant frequency of the diaphragm. The microspeaker will be built on a tens-of- mm2 square PZT bimorph-diaphragm (with a bulk-micromachined silicon top-cover) that has already shown a flat diaphragm displacement from DC to 11 kHz. A low-cost, low-power-consuming microspeaker will be designed for a targeted sound output level of 95 dB SPL (into 2 cc volume) per 1 Vzero-to-peak. During the 2 years of the proposed research, the main focus will be on (1) design and fabrication of various resonant microphones and microspeakers and (2) demonstration of active noise cancellation that suppresses any undesirable sounds or noises by 40 dB SPL. By the end of the research period, we expect to pave clear paths to a low-cost, ultra-low-power-consuming, active-noise-cancelling technology based on MEMS resonant-microphones and microspeaker, ideally suited for hearing aids.
This proposed research is to develop an active noise cancellation technology for hearing aids through low-cost MEMS-based resonant-microphones and microspeaker. Array of high Q (quality factor) resonant microphones will be developed for acoustic filtering, while a microspeaker will be developed for active noise cancellation. Successful completion of the research will pave a path to a very low-cost, ultra-low-power- consuming, and active-noise-cancelling hearing aid that allows its wears to hear clear speech without being hampered by noises and undesirable sounds
