Abstract: A support structure for piezoelectric elements in a marine seismic cable is provided. The support structure comprises upper and lower cylindrical halves, each with channels formed therein. Two axial channels are adapted to retain three piezoelectric elements each. A third axial channel, positioned between the sensor element channels, is adapted to retain a flexible circuit. Transverse channels between the sensor element channels and the circuit channels accommodate extension from the flexible circuit. The piezoelectric elements are mounted within their respective channels with a resilient pad with adhesive on both sides. The piezoelectric elements are graded so that any group of three piezoelectric elements exhibits approximately the same sensitivity as any of the other three groups of piezoelectric elements on the support structure.

Abstract: A support structure for piezoelectric elements in a marine seismic cable is provided. The support structure comprises upper and lower cylindrical halves, each with channels formed therein. Two axial channels are adapted to retain three piezoelectric elements each. A third axial channel, positioned between the sensor element channels, is adapted to retain a flexible circuit. Transverse channels between the sensor element channels and the circuit channels accommodate extension from the flexible circuit. The piezoelectric elements are mounted within their respective channels with a resilient pad with adhesive on both sides. The piezoelectric elements are graded so that any group of three piezoelectric elements exhibits approximately the same sensitivity as any of the other three groups of piezoelectric elements on the support structure.

Abstract: A seismic sensor array includes a means for passive electrical to optical energy transformation and transmission. This transformation is used remotely with traditional sensor arrays, which may include hydrophones, geophones, or a combination of them. The transformation means is used to develop an optical signal in a fiber which then conveys the seismic signals to a recording center or data accumulator.

Abstract: A seismic sensor array includes a means for passive electrical to optical energy transformation and transmission. This transformation is used remotely with traditional sensor arrays, which may include hydrophones, geophones, or a combination of them. The transformation means is used to develop an optical signal in a fiber which then conveys the seismic signals to a recording center or data accumulator. The transformation means preferably comprises a stack of piezoelectric elements capped on each end by a rounded crown to accommodate an optical fiber wound around the stack and the crowns.

Abstract: A geophone includes an optical element capable of changing its refractive index and path length in response to acceleration of the geophone. The sensor component comprises a mass mounted on a fulcrum for rotational movement against the force of a biasing member. An optical fiber is stretched between the casing of the sensor and an extension of the mass, such that rotational movement of the mass about the fulcrum varies the tension in the fiber. Varying the tension in the fiber varies the optical path length and index of refraction of the fiber, and these variations may be detected as a seismic signal. A first set of magnets dampens the vibratory movement of the mass, and a second set of magnets reduces the frequency of the movement of the mass.

Abstract: An element that is sensitive to a pressure or acceleration signal comprises an optical element capable of changing its index of refraction and/or path length in response to a time varying pressure or in response to acceleration and a pliant mounting member supporting the optical element. The mounting member changes its geometrical configuration in response to the time varying pressure or acceleration. Some embodiments of the invention use a mechanical amplifier to achieve the needed sensitivity.

Abstract: An arcuate or flat ferroelectric sensor is incorporated in a seismic streamer. The structure comprises two half-cylinders which are mounted together around a cable. The half-cylinders are coupled together by bolts or pins or any other appropriate means. Each half-cylinder defines a well into which a sensor is mounted. With the sensor in place, the structure is covered over with a sound-transparent material to receive an acoustic signal into the sensor. Electrical leads from the sensor are directed through ports in the half-cylinders, and the leads are connected together to provide a composite sensed signal to the cable in analog form. The sensor in each half-cylinder is a single element hydrophone that, when connected to a sensor in a complementary half cylinder in series or in parallel, forms an acceleration cancelling hydrophone.

Abstract: An arcuate or flat ferroelectric sensor is incorporated in a seismic streamer. The structure comprises an interior cable, a surrounding woven strength member, an overlying foam floatation layer, and an enclosing jacket. One or more elongate channels are formed in the overlying floatation layer, and one or more hydrophones are mounted in the channel(s). The elongate channel enlarges the acoustic aperture for the reception of seismic signals.

Abstract: A vertical hydrophone cable includes a support cable, a plurality of hydrophones, and an equal number of delay elements which are tuned to provide synchronization between the seismic and electrical signals. A number of such vertical hydrophone cables are provided. In operation, the vertical array provides a method of seismic exploration comprising the steps of deploying the plurality of vertical hydrophone cables with the integral delay elements, generating a seismic signal, and receiving reflected return signals at the plurality of hydrophones with synchronism between the electrical and sound signals, so that the vertical cable functions in the manner of a traveling wave antenna.

Abstract: A fiber optic hydrophone structure comprises a casing around which is wound an optical fiber. The casing includes complementary top and bottom diaphragm members that mesh together and which are separated by a spacer ring. The spacer ring is tapered to knife edges which abut the inside surfaces of the top and bottom diaphragm members. The spacer thus acts as a fulcrum when a seismic signal causes motion of the diaphragms.

Abstract: A magnetic drive device couples the drive motor of a depth control device or bird, with the axle of the depth control wings. The magnetic drive includes a plurality of permanent magnet pieces mounted in respective drive blocks on either side of a magnetically permeable membrane of the main body of the drive mechanism. The magnet pieces are mounted side by side in alternating polarity to capture as much of the magnetic flux of the magnets as possible to minimize stray flux from escaping the drive. Pole pieces either side of the drive blocks also serve to capture stray flux. To the maximum extent possible within the constraints of mechanical durability, the drive mechanism is made of non-magnetic or non-ferrous materials which would interfere with the heading sensor of the bird. Thus, this invention avoids reducing the accuracy of the heading sensor of the bird, while eliminating a major source of seawater inleakage into the bird.

Abstract: An active element in a hydrophone includes a piezoelectric hydrophone crystal mounted to a backing plate. The piezoelectric crystal may be divided into separate segments. If so segmented, the polarities of the segments are oriented in the same direction. Whether or not segmented, the center portion or segment of the crystal is in abutting contact with a motion limiter, which acts as a spring between the piezoelectric crystal and the casing surrounding the crystal and backing plate. The portions or segments or the crystal are connected to electrical signal leads with the minimum amount of solder necessary to ensure secure electrical and mechanical coupling, thereby reducing the effects of the solder connection on the stress flux profile in regions of the crystal close to the solder.

Abstract: A folded acoustical horn is disclosed, having an acoustical transmission path that is generally arcuate about an axis, including a pair of arcuate mouths that are longitudinally spaced apart a selected distance and directed radially outwardly. A horn tuner is operable to selectively adjust the acoustical path to match selected sound frequencies.

Abstract: An active element in a hydrophone includes a piezoelectric hydrophone crystal mounted to a backing plate. The piezoelectric crystal may divided into separate segments. If so segmented, the polarities of the segments are oriented in the same direction. Whether or not segmented, the center portion or segment of the crystal is supported in part by a center pin at its center. Thus, in the presence of a downward pressure, the end portions or segments develop a concave flexure and the center segment, due to the center pin support, develops a convex flexure. With this reverse flexing phenomenon, the center portion segment develops an electrical signal of opposite polarity from those of the end segments. By carefully selecting the areas of the end segments, and electrically coupling the segments so that the harmonics of the various segments are added out of phase, the distortion introduced the harmonics of the various phases subtract.

Abstract: A hydrophone structure comprises a hydrophone casing within which is mounted a conductive substrate. Sound pressure signals are conducted into the interior of the substrate, on which are mounted piezoelectric crystals on the exterior of the substrate. The volume between the casing and the substrate is nearly filled with a fluid, preferably oil. One or more bubbles of air remain in the volume between the casing and the substrate to permit vibration of the substrate and consequently the piezoelectric hydrophone element.

Abstract: A hydrophone transducer is prepared by depositing a piezoelectric material upon a conductive substrate or support structure, and then etching the material into selected regions or segments. The center segment, which provides most of the fundamental signal, is polarized in a first direction by the introduction of a polarizing voltage. The end segments are polarized in the opposite direction by the imposition of a polarizing voltage in the opposite direction. The conductive substrate then serves as one terminal of the output of the hydrophone while the upper surfaces of the segments together serve as the other terminal. The relative strengths of the signals from the segments may tailored by adjusting the areas of the segments.

Abstract: A system and method provide a low distortion hydrophone. A first known piezoelectric element is mounted so as to receive a pressure signal. A second piezoelectric element is provided with a means of receiving and enhancing the same pressure signal. Since a piezoelectric element is a capacitor, another capacitor is coupled in parallel with the second element to serve as a divider. The output voltage of the combination of the two elements is taken as the difference between the positive terminals of the two elements. Thus, the effect of the pressure enhancer and capacitance divider is to provide a difference in potential between the fundamentals from the two elements, while rendering the amplitude of the second harmonics equal. The two equal second harmonics cancel each other out at the output terminals, while retaining a useful fundamental for further signal processing.

Abstract: The present invention provides an apparatus for enhancing the low frequency response of a loudspeaker. At low frequencies the mechanical and electrical inefficiencies of loudspeakers limit the intensity of the sound output by the loudspeakers. Previous attempts to correct the inefficiencies have been hampered by the non-ideal circuit elements used in conventional feedback circuits. To enhance the low frequency response of a loudspeaker there is provided an apparatus which includes a feedback circuit which is operably connected to an audio amplifier and which is tuned to substantially match the impedance of the loudspeaker within a predetermined frequency range. The apparatus further includes a transformer having a primary winding and a secondary winding. The primary winding is adapted to connect to the drive coil of a loudspeaker, and the secondary winding is connected to the feedback circuit.

Abstract: An applanation tonometer for sensing the intraocular pressure of the eye. The tonometer includes coaxial inner and outer probes which are placed in contact with the eye. The difference in longitudinal forces applied by the eye to the inner and outer probes is measured and the intraocular pressure is determined therefrom. The total pressure applied to the eye by the tonometer is not measured as only the differential pressure on the two probes is needed. The tonometer may include a feedback mechanism to oppose relative longitudinal movement between the probes, thus improving the linearity, accuracy and stability of the instrument. The differential-pressure sensing circuitry includes a sample-and-hold circuit for receiving the measured result and supplying it to an indicating meter. The circuitry also includes compensating means for compensating for the force effects of gravity on the masses of the device.

Abstract: An apparatus and method for detecting gas concentration using an infrared absorption gas detector. Noise due to vibration is substantially reduced by integrating the voltage produced by the gas detector with an integrator having an adjustable time constant. The time constant is adjusted to a long value during times when the gas concentration is remaining relatively constant. When the gas concentration is changing substantially, the time constant is adjusted to a relatively short value to allow the output of the integrator to better follow the changes.