Dictionary:Hydrophone

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A detector that is sensitive to variations in pressure, as opposed to a geophone that is sensitive to particle motion. Used when the detector can be placed below a few feet of water, as in marine or marsh work or as a well seismometer.

Some hydrophones operate because of magnetostriction (q.v.) but most are piezoelectric (q.v.). Piezoelectric hydrophones include benders, disc hydrophones, and cylindrical hydrophones.

FIG. H-12. Piezoelectric hydrophones. (a) A piezoelectric disk generates a voltage across opposite faces when bent. (b) Acceleration-canceling feature of the disc hydrophone. (c) Bender geophone. (d) Cylindrical hydrophone.

The sensing element is usually a piezoelectric ceramic material such as barium titanate, lead zirconate, or lead metaniobate. Piezoelectric hydrophones are high-impedance devices and signals may be passed through preamplifiers or impedance-matching transformers before transmission through the streamer to the recording instruments. Compare geophone.

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