Fiber optic flexural disk microphone

An interferometric fiber optic microphone consisting of a 10‐m‐long, 4‐cm‐diam, flat‐wound (spiral) single mode optical fiber bonded to a simply supported, 8‐cm‐diam, 3‐mm‐thick aluminum disk will be described. In the presence of a pressure difference across the plate or an acceleration of the plate, the surface strain induced in the plate is transmitted to the optical fiber. The optical phase shift induced by the strain is detected in an all‐fiber Michelson interferometer. The calculated strain [A. E. H. Love, A Treatise on the Mathematical Theory of Elasticity (Dover, New York, 1944), 4th ed., Sec. ♯309] and optical strain measured using static pressure, acoustic pressure, and a calibrated aecelerometer, are in good agreement (± 10%) and yield a sensitivity of 30 milliradians per Pascal per meter of optical fiber below the plate resonance frequency of 3 kHz. [Work supported by the Office of Naval Research and Office of Naval Technology.]