| 摘要 |
PROBLEM TO BE SOLVED: To provide a microphone which can improve a directivity without making a construct large-scale. SOLUTION: Either of a measurement optical path of an interferometer and a reference optical path is formed on at least a part of a surface which a wave front of a detected sound wave enters in phase. When a geometric optical path difference between the measurement optical path and the reference optical path is constant, an intensity of the detected sound wave is detected based on an interference signal outputted from the interferometer. Firstly, when the detected sound wave enters either of the optical path, a refractive index of the optical path changes, thereby resulting an interference signal at the interferometer. If no change occurs in the geometric optical path difference between the measurement optical path and the reference optical path at this time, the interference signal indicates the change of the refractive index in either of the optical path, i.e., the detected sound wave. COPYRIGHT: (C)2003,JPO
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