The primary aim of the proposed research is to develop a miniature microphone diaphragm for hearing aids that achieves second-order directional sensitivity to sound over the frequency range that is important for speech. A hearing aid that can achieve second-order directional sensitivity can be capable of over 9 dB of attenuation of unwanted sounds that interfere with speech. Existing approaches to achieving this noise reduction are based on the processing of signals from three nondirectional microphones. The effectiveness of these systems has been hampered by the effects of microphone self-noise, and sensitivity to mismatches between the microphones. In addition, the space required to house the three microphones limits the application of these devices to larger behind-the-ear hearing aids. The approach of the proposed study avoids these difficulties by developing a single miniature microphone diaphragm that has the potential of achieving second-order directional response over much of the audible range of frequencies. Miniature microphone diaphragms will be designed and fabricated that comprises an extension of the successful first-order directional microphone diaphragms we have developed under our current NIH BRP award. The designs will be optimized to ensure that the 2nd order directional response dominates over as wide a range of frequencies as possible. The designs will be fabricated using silicon microfabrication technology and the directional acoustic response will be verified experimentally. The acoustic characterization of the fabricated diaphragms will be accomplished by comparing the 2nd order response with measurements of the 2nd derivative of the response obtained using measurements of the sound pressure at an array of locations in the vicinity of the diaphragm. This effort will demonstrate the feasibility of creating a miniature 2nd order microphone diaphragm that can be incorporated into hearing aids. Having demonstrated a practical microphone diaphragm design, an electronic read-out will be developed in a follow-on study to transduce the diaphragm motion into an electronic signal.
An estimated 500 million people worldwide suffer hearing loss, making it the number one disability in the world (Phonak, Sep 2006.) Hearing aids remain the primary form of treatment, yet the number one complaint of users is difficulty understanding speech in noisy environments. About half of those who could benefit from an aid do not use them because of design, stigma and cost issues;however a smaller hearing aid is their second most preferred solution. This proposed research will lead to a dramatic improvement in miniature, second-order directional microphone technology that will help users communicate in complex acoustical environments and attract new users.
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