Abstract: An acoustic sensor, such as a hydrophone, is deployable in a fluidic media having high temperature, high pressure, and/or potentially caustic chemicals. The hydrophone includes a housing filled with an internal fluid and containing a sensing mandrel. The sensing mandrel senses the acoustic pressure transmitted to the internal fluid through a diaphragm. The sensing mandrel preferably includes a polymer tubular mandrel having a coil of optical fiber wound and bonded to its outer surface. The sensing mandrel can be suspended within the housing instead of being rigidly attached thereto. To relieve pressure created by thermal expansion of the internal fluid, the flexible diaphragm, a filler member, a pressure compensator, or combinations thereof can be used. The filler member is mounted in the hydrophone and reduces the amount of internal fluid required in the housing. The compensator may be a bellows or a buffer tube.

Abstract: A method and apparatus for reducing the difficulty of controlling the length of a section of optical waveguide wrapped around a mandrel separating Bragg gratings forming an interferometric sensor are provided. The section of optical waveguide may be wrapped on a mandrel having at least two different outer diameters. The mandrel may also include one or more bores for receiving and protecting the Bragg gratings.

Abstract: A pressure compensated hydrophone for measuring dynamic pressures is disclosed. The hydrophone includes a compliant hollow mandrel with a single optical fiber coiled around at least a portion of the mandrel. The mandrel further includes at least one pressure relief valve for compensating for changes in hydrostatic pressure. The pressure relief valve includes a micro-hole, which allows hydrostatic pressures or low frequency pressure events to couple into the interior of the mandrel to provide compensation against such pressure. Higher frequencies pressure events of interest do not couple through the micro-hole and therefore only act only on the exterior of the mandrel, allowing for their detection. Because (quasi) hydrostatic events are compensated for, the mandrel may be made particularly compliant, rendering the singular fiber optic coil particularly sensitive to the detection of the higher frequency signals of interest.

Abstract: A pressure compensated hydrophone for measuring dynamic pressures is disclosed. The hydrophone includes a compliant hollow mandrel with a single optical fiber coiled around at least a portion of the mandrel. The mandrel further includes at least one pressure relief valve for compensating for changes in hydrostatic pressure. The pressure relief valve includes a micro-hole, which allows hydrostatic pressures or low frequency pressure events to couple into the interior of the mandrel to provide compensation against such pressure. Higher frequencies pressure events of interest do not couple through the micro-hole and therefore only act only on the exterior of the mandrel, allowing for their detection. Because (quasi) hydrostatic events are compensated for, the mandrel may be made particularly compliant, rendering the singular fiber optic coil particularly sensitive to the detection of the higher frequency signals of interest.

Abstract: An acoustic sensor, such as a hydrophone, is deployable in a fluidic media having high temperature, high pressure, and/or potentially caustic chemicals. The hydrophone includes a housing filled with an internal fluid and containing a sensing mandrel. The sensing mandrel senses the acoustic pressure transmitted to the internal fluid through a diaphragm. The sensing mandrel preferably includes a polymer tubular mandrel having a coil of optical fiber wound and bonded to its outer surface. The sensing mandrel can be suspended within the housing instead of being rigidly attached thereto. To relieve pressure created by thermal expansion of the internal fluid, the flexible diaphragm, a filler member, a pressure compensator, or combinations thereof can be used. The filler member is mounted in the hydrophone and reduces the amount of internal fluid required in the housing. The compensator may be a bellows or a buffer tube.

Abstract: A pressure compensated hydrophone for measuring dynamic pressures is disclosed. The hydrophone includes a compliant hollow mandrel with a single optical fiber coiled around at least a portion of the mandrel. The mandrel further includes at least one pressure relief valve for compensating for changes in hydrostatic pressure. The pressure relief valve includes a micro-hole, which allows hydrostatic pressures or low frequency pressure events to couple into the interior of the mandrel to provide compensation against such pressure. Higher frequencies pressure events of interest do not couple through the micro-hole and therefore only act only on the exterior of the mandrel, allowing for their detection. Because (quasi) hydrostatic events are compensated for, the mandrel may be made particularly compliant, rendering the singular fiber optic coil particularly sensitive to the detection of the higher frequency signals of interest.

Abstract: An improved reduced distortion spring spider for geophones is disclosed that has the desired ratio of spurious resonant frequency to the natural frequency of the geophone and can absorb the sharp lateral forces imposed on the geophone during destructive testing and field usage.