Measuring and testing – Vibration – Sensing apparatus
Patent
1978-08-21
1980-11-25
Kreitman, Stephen A.
Measuring and testing
Vibration
Sensing apparatus
350 9629, G02B 514
Patent
active
042351138
ABSTRACT:
This invention relates to an optical fiber acoustical sensor for sensing acoustic vibrations and in combination with an incoherent or coherent source of light such as a LED or a laser and a photo detector to determine the frequency and amplitude of the sound pressure variations. The invention consists of an element of optical fiber without cladding surrounded by a liquid or plastic potting material permeable to sound pressure and having an index of refraction slightly less than the fiber. The intensity of a light beam transmitted by means of fiber optic waveguides, single or multi-mode, from a source of light through the sensor to a photo detector varies with the variation of sound pressure to which the sensor is subjected. If the sensor is in water, the transmitted light intensity varies with the acoustical pressure in the water because the changes in liquid or plastic index of refraction changes with the sound pressure.
Generally the fiber sensor is in an element preferably surrounded by a fluid which has an index of refraction close to but less than that of the fiber, and the coil thickness is small relative to the wavelength of the sound to be detected.
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J. A. Bucaro, et al., Applied Optics, "Optical Fiber Acoustic Senser," vol. 16, pp. 1761-1762, Jul. 1977.
J. H. Cole, et al., J. Acous. Soc. Am., "Fiber-Optic Detection of Sound," vol. 62, pp. 1136-1138, Nov. 1977.
J. A. Bucaro, et al., J. Acoust. Soc. Am., "Fiber-Optic Hydrophone," vol. 62, pp. 1302-1303, Nov. 1977.
B. Culshaw et al., Electronics Letters, "Acoustic Sensitivity of Optical-Fibre Waveguides," vol. 13, pp. 760-761, Dec. 1977.
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