The proposed research is to develop an integrated micro-electromechanical systems (MEMS)-based miniature microphone system for directional sensing of sound based on a biological model. The design follows that used by the Ormia ochracea fly. This fly employs a unique coupled mechanical bar system operating at the critical damping to extract the direction of sound. The Ormia ochracea fly has ears separated by only about 500um yet has remarkable sensitivity to direction of sound. The separation of the fly's ears is too small for it to sense the direction of a sound source if it uses traditional human techniques such as the difference in arrival times or the amplitudes of sound at each ear. The fly's unique ear structure helps to magnify the difference in amplitude as well as phase of the sound wave. The proposed MEMS device uses two flapping wings which are textured to achieve critical damping to mimic the fly's ear system. An initial finite element simulation shows the proposed design replicates the directional sound response of the fly's biological system. The displacement of the membrane due to typical sound pressure is on the scale of nanometers and requires a highly sensitive position measurement approach to determine the amplitude. Such a position sensitivity can be achieved by optical means using two diffraction gratings at the edges of the wings. A diffractive interferometer using fixed and moving gratings can provide subnanometer displacement sensitivity. By placing the gratings at the outer edges of the membrane, a maximum displacement can be achieved. This translates into angular resolution of the direction of sound to about 1-2 degrees. The proposed tasks include the design, fabrication and characterization of the sensor performance. Intellectual merit: The proposed research provides an opportunity to combine the advances in MEMS technology with unique functionalities of biological systems to develop a novel sound sensor. The findings of the research will enable us to understand how the fly's hearing system achieves such a remarkable directional sensitivity and to fabricate an electromechanical equivalents. A set of such sensors can be used for pinpointing explosions by monitoring the direction of sound which can be deployed using micro air vehicles. In addition, a network of these sensors can be used for unattended movement monitoring. Other applications of such sensors include use in low noise hearing aids. The principal investigators and research staff have extensive experience in MEMS design, fabrication and testing. The Naval Postgraduate School has state-of-the-art MEMS design facilities as well as an anechoic chamber with experienced staff for acoustic testing. Broader impact: This research will accomplish two goals. First, it will significantly expand current knowledge on the inner workings of the Ormia ochracea fly's unique hearing system and on the design and fabrication of electromechanical equivalent for applications involving pinpointing sources of sound. Second, the graduate students participating in this investigation will gain valuable knowledge and experience in this multidisciplinary area of research. The Naval Postgraduate School also provides research opportunities for promising local high school students. Current plans are to include high school students in the research, where possible, in order to enhance their skills in mathematics and science and to encourage them to pursue mathematics, science, and engineering in higher education. The findings of the research will be published in scholarly journals and conferences.
