A microphone consisting of a hollow cylinder whose flexible, circular endplates are bonded to pairs of flat spiral wound coils of optical fiber is described. When the endplate/disk is deformed due to a pressure difference, the outer and inner fiber coils experience opposite strains resulting in a "push-pull" optical path length difference which is detected in an all-fiber Michelson interferometer. The close proximity of the interferometric fiber coils, separated by the thin thermally conducting end plate, rejects thermal gradient induced signals. The addition of a second identical endplate and fiber coil pair at the opposite end of the cylinder doubles the acoustic sensitivity while canceling acceleration induced signals. The calculated and measured optical strain of a single plate, single coil sensor using static pressure, acoustic pressure, and acceleration are in good agreement and yield a sensitivity of 21 milliradians per Pascal per meter of optical fiber for an 8.0 cm diameter, 3.0 mm thick plate below its resonance frequency of 3 KHz.
David A Brown,
S. L. Garrett,
"Fiber Optic Flexural Disk Microphone", Proc. SPIE 0985, Fiber Optic and Laser Sensors VI, (1 February 1989); doi: 10.1117/12.948847; https://doi.org/10.1117/12.948847