Abstract: A flextensional sonar transducer comprising a first cavity defined by an elliptical shell and end plates covering the two ends of the shell, vibration drive means inside the cavity and coupled between portions of the shell wall at opposite ends of the major axis of the shell, a further cavity connected to the first cavity and an opening between the two cavities for coupling the two cavities for the further cavity to affect the resonant frequency of the first.

Abstract: A sonar projector having a pair of opposed oscillating pistons driven by an electromagnetic assembly is rendered capable of operating at reduced resonant frequency by providing liquid mass loading for the pistons. The mass loading is achieved by utilizing a structure which constricts a body of liquid on one side of the piston. The constricted liquid may be sea water or liquid sealed within the body of the unit. In accordance with a further aspect of the invention, a seal assembly is provided for the moving pistons which not only provides a sealing function but which also acts to radially center the pistons and to provide an axially directed restoring force thereto during piston oscillation. The electromagnetic assembly, in accordance with still a further aspect of the invention, is formed with a permanent magnet structure arranged in a cylindrical configuration with the opposed pistons on opposite axial ends thereof to reduce magnetic leakage losses.

Abstract: A sonar transducer wherein a plurality of transducer modules are affixed along the length of a mounting member in the form of an elongated bar. The bar is contained within a protective housing and the mid point of the mounting member is affixed to the back wall of the housing in a manner that the mounting member stands off from the back wall of the housing. The mounting member is cantilevered on either side of the mounting position and is totally enclosed within the outer housing which is affixed along its entire length to a host structure so as to isolate and protect the alignment of the transducer modules from distortions.

Abstract: A self-orienting vertically sensitive accelerometer is disclosed for measuring a vertical component of acceleration independently of the orientation of the accelerometer. The accelerometer of the present invention includes a spherical plastic shell having a plurality of perforations disposed therein and a thin film of metallic coated piezoelectric polymer bonded to the exterior thereof, forming a small diaphragm at each perforation. In response to acceleration a dynamic pressure is developed within a fluid mass partially filling the spherical plastic shell which creates a strain and resultant charge in each small diaphragm of piezoelectric polymer. The vast difference in density between the fluid mass and the air in the remaining volume of the spherical plastic shell permits the charge developed in each small diaphragm under fluid pressure to be attributed solely to the vertical component of acceleration applied to the fluid mass.

Abstract: A transducer array designed for towing at an extended distance behind a sace vessel includes electroacoustical transducer elements connected in opposition to the active elements of the array. A surrounding acoustic isolation structure effectively isolates the dummy transducer elements from the ambient noise field while permitting cancellations of self-induced noise.

Abstract: A signal sensor automatically compensates for the variations of the static pressure of the medium in which it is placed. The signal sensor comprises one or two assemblies each formed of a piezoelectric sensitive element applied against one face of a flexible plate. The other face of the plate is shielded from the variations of the dynamic pressure to be measured by a material absorbing the vibrations but fairly flexible so as to transmit any variation of the ambient static pressure. This material which may be a porous foam or a fibrous substance impregnated with liquid, fills a tubular apertured sleeve.

Abstract: The apparatus of the present invention detects the resonant frequency of a vibratory member in contact with a fluid. The detection of the resonant frequency enables the device to be used to detect the density of a fluid which it is in contact with and thereby calculate the flow rate of the fluid. The vibratory member is mounted in a housing in such a way that the chambers on either side of the vibratory member have equal volumes. The fluid enters the device through a conduit and then divides into two equal tubes on either side of an extension of a vibratory member extending down these tubes. The apparatus for measuring the resonant frequency of the vibratory member is mounted on the vibratory member and is comprised of a piezoelectric element coupled to a driver circuit in a feedback loop.

Abstract: A tubular piezo-electric sensor has at least one sensitive element disposed against an outer surface of a tubular support. A substance whose acoustic impedance is very different from that of the material forming the tubular support is disposed therein and a remaining volume of the tubular support is filled with liquid. Glass fiber cords or open cell foams, for example, are used as the substance, and the liquid may, for example, be that which fills a seismic streamer and, in this case, the tubular support is left open. The tubular support may also be closed at both ends by sealed caps and included in a protective sheath. The dimensions of the tubular support and the material from which it is made are chosen so as to optimize the sensitivity of the piezo-electric sensor.

Abstract: An acoustic transmitter for use in a borehole logging tool employs multiple Helmholtz resonators stacked such that apertures in opposite sides of each of the resonators are in linear alignment so as to provide increased acoustic energy output over a broad band of low frequency seismic frequencies.

Abstract: An acoustic damper for substantially reducing the reverberation echoes at the junction between an acoustic signal propagating fluid and a material having an acoustic impedance substantially different from that of the fluid. The damper, which is particularly adapted for use in ultrasonic transducers, is formed of a material having an acoustic impedance which substantially matches the acoustic impedance of the fluid, such material preferably being a foam plastic material having sufficient hardness to be acoustically stable. For preferred embodiments, the damper is formed of a laminate of the layer described above and a second layer of a material which provides high acoustic attenuation, such as cork material.

Abstract: A seismic energy source provides a bias pressure and oscillating pressure force on a piston mounted transversely to the major axis of the well bore and in pressure contact with the wall of the well bore. A seismographic energy wave is generated in the surrounding earth by oscillating the pressure of the piston against the well wall. This apparatus uses the pressure of ambient fluid in the well bore to reduce the power required to provide pressure contact and to oscillate the piston against the wall.

Abstract: An acceleration sensor uses a capsule of mercury filling a rigid enclosure with pressure sensors responsive to inertial forces exerted by the mercury on the walls of the enclosure when it is caused to accelerate. The enclosure may have a flexible lining on its walls or contain a flexible bag for holding the mercury. Means are provided for producing a bias pressure in the mercury. The enclosure may be cubic or tetrahedral, for example, and the outputs of the pressure sensors additively combined to produce outputs representing accelerations in required orthogonal directions when these differ from the directions to which the sensors are responsive. A rotational acceleration sensor is also described.

Abstract: A borehole televiewer uses an acoustic fluid which is lubricating, non-toxic, thermally conductive, electrically insulating, non-reactive, tolerant of high temperatures and pressures, impedance-matched to that of the borehole fluids and the tool window, and which has a low kinematic viscosity at low temperatures.

Abstract: The power output and thus the range of sonar apparatus is limited by caviion of the water surrounding a sonar transducer at high output power levels. The invention "strengthens" the water surrounding a sonar transducer by increasing the hydrogen content to permit a many fold increase in the transducer output power before cavitation occurs.

Abstract: An acoustic energy absorbing baffle comprising a fluid containment means having an acoustic window means, a viscous fluid contained within said fluid containment, a porous material comprising strands of wire and being immersed within said viscous fluid means, a compliant mass means and means for holding said compliant mass means in close proximity of said porous material means such that the motion of said compliant mass means is imparted to said porous material. Incident acoustical energy is transmitted through the acoustic window and translated into energy absorbing motion of the porous material by acoustical excitation of the compliant mass means.

Abstract: A mechanism for compensating an underwater transducer for the ambient hydrostatic pressure. The transducer housing includes a quantity of liquid which may be vaporized in the housing volume. The relative volumes of vapor and liquid depend on the temperature, pressure and type of liquid used. A small heater in the liquid increases the temperature of the liquid so that the pressure of the vapor increases and counteracts the increase in hydrostatic pressure at greater depths. The liquid chosen should have a high critical pressure relative to the operating pressure of the transducer.

Abstract: A pressure gradient sensor is disclosed for optically sensing the direction and magnitude of an acoustic wave propagating through a fluid. Each sensor consists generally of at least three fiber-optic displacement sensors disposed within a circular array oriented perpendicular to the longitudinal axis of a streamer. Each sensor phase-modulates a coherent light signal indicative of the water pressure sensed outside the streamer. The output of the signals include a component due to transient pressure waves and a component due to hydrostatic pressure differences between the sensors.

Abstract: A self-orienting, directionally sensitive particle velocity transducer with an axially magnetized magnet which, displaced by gravity, floats off-center in a chamber filled with ferromagnetic fluid. Wire coils affixed coaxially to the chamber ends asymmetrically intersect the magnet's flux lines. Axial chamber rotation results in gravitationally induced sideways movement of the magnet to maintain its equilibrium position. An impinging sound wave causes relative movement between the low inertia chamber-coil assembly and the high inertia magnet, thereby inducing a voltage in the coils--a relatively high voltage for vertical movement due to vertical assymetry, but a relatively low voltage for horizontal movement due to horizontal symmetry. Axial sensitivity is low because the ferromagnetic fluid filling the narrow gap between the magnet and the chamber ends resists relative axial movement and any induced voltages in the coils cancel.

Abstract: A pickup device for picking up vibration transmitted through bones or solid members in human, in which a piezoelectric element is mounted like a cantilever within a substantially rigid liquid-tight case filled with a viscous liquid in such a way that the free end of the piezoelectric element can vibrate with respect to the liquid-tight case. The viscosity of the viscous liquid ranges from 30 to 10,000 cs so that the sharpness of resonance of the piezoelectric element can be suitably suppressed.

Abstract: The geophone transducer comprises in combination: a geophone capable of detecting horizontal seismic waves, and a rigid casing having a gimbal chamber. A gimbal is provided inside the chamber on which the geophone is mounted for limited free angular movement in one direction only. The gimbal includes in one preferred embodiment a viscous liquid in which the geophone is only partially submerged while it is supported by a U-shaped bracket which is mounted for rotation about a fixed axis.

Abstract: The invention relates to hydrophones which require liquid backing of the sensing plate, and more particularly, to compliance enhancing means for use in such hydrophones. In a practical embodiment, in which a compliant sensing plate in the form of a thin diaphragm is employed, liquid backing of the sensing plate is provided to balance the hydrostatic pressure across the sensing plate. To increase the compliance of the hydrophone, reduced by the presence of the backing oil, and to do so in a linear manner, a bellows is introduced into the backing chamber having the desired compliance and pressure rating. The invention is applicable to hydrophones having either compliant or stiff sensing plates. An improvement in hydrophone linearity and sensitivity is obtainable over a significant range of hydrostatic pressures.

Abstract: A plurality of transducers, closely conforming to the surface of a low-drag ose, are baffle mounted in close pack configurations to eliminate grating lobes. The baffle assembly is mounted outside a pressure hull within a thin acoustically transparent fairing. A plurality of pressure compensators also attach outside the pressure hull. The cavity between pressure hull and fairing is filled with pressure compensating acoustic fluid. Larger portions of unused volume are first filled with a syntactic foam to minimize the amount of fluid required. The pressure compensators balance fluid pressure against external sea pressure to prevent fairing collapse. This array maximizes available nearby internal nose volume thus allowing beamforming electronics to be located within the pressure hull in close proximity to the array elements, connecting thereto via a plurality of short coaxial cables.

Abstract: A compact subwavelength size monopole underwater sound radiator has chararistics to maximize resistive radiation impedance, minimize reactive radiation impedance, facilitate heat dissipation and minimize compensating air usage. This results in improved efficiency, bandwidth and use factor. The underwater sound radiator uses two back-to-back mounted, frustum shaped, hollow, radiating shells to achieve radiation characteristics approximating those of an equivalent sized pulsating sphere. An elliptically shaped, uniform cross-section magnetostrictive ring crossed by a linear piezoelectric spreader comprises a compact eclectic driver. Both the magnetostrictive ring and the piezoelectric stack contribute to the output through inverse phase cyclic changes in their respective lengths those changes being added and amplified by the flexural-bow type action of the elliptically shaped magnetostrictive ring.

Abstract: An electro-hydraulic (EH) actuator for converting electrical inputs into hydraulic output signals is described. The actuator features a pressure balanced design which permits operation at high absolute pressures without performance degradation. Internal portions of the EH actuator are filled with a non-conducting fluid, while a flexible diaphragm provides a movable interface between the fluid and the environment in order to equalize the internal and external pressures on the actuator.

Abstract: A sonar transducer especially adapted for use when subjected to high hydrostatic pressures and extreme mechanical and explosive shock. The sonar transducer includes a conventional casing, ruggedized to withstand high pressures and a hostile environment. The casing is closed on all sides but one. An array of piezoelectric ceramic stacks are suspended inside of the casing and sandwiched between a single front mass and individual rear masses. The single front mass is positioned closest to the open side of the casing. A flexible cover is sealed over the open side of the casing and pressurized oil is placed inside the housing. Appropriate channels are provided to enable the oil to freely flow throughout the interior of the unit, including flowing inside of and about the ceramic stacks. Electrical connections are made with the ceramic stacks to allow external voltages to electrically stress the stacks, and also to allow external sensing of the voltages generated when the stacks are mechanically stressed.

Abstract: The seismic method comprises in one preferred embodiment, towing a long, flexible member over the earth's surface, the member having liquid-filled geophones mounted thereon or coupled thereto and suitably spaced therealong, and a seismic cable for receiving the individual outputs of the geophones. Each liquid-filled geophone provides an output electric signal having a polarity corresponding to the direction of the earth's motion. In another embodiment of the method of this invention, the geophones are positioned on the earth's surface in a predetermined pattern; their output signals are transmitted to a utilization device; then the geophones are moved to another location, and the detection process is repeated.In a simplified embodiment, the geophone comprises a hollow cylindrical casing defining a chamber therein. A high-density liquid substantially fills the chamber. The chamber has a flexible bottom wall which constitutes a force or pressure transducer.

Abstract: Apparatus for suppression of water flow noises in connection with a keel nted sonar dome. A solution of water soluble polymer is ejected through a series of holes along the leading edge of the sonar dome under forward movement of the ship. The concentration and flow rate is chosen to "bathe" the dome in a very dilute dispersion (of the order of 10 parts per million by weight) of the polymer.

Abstract: A housing for an electroacoustic transducer includes a filling or access port for introducing an inert liquid into the chamber defined by the housing. The access port includes a bubble trap and a vent for extracting gaseous bubbles from the fluid fill. The structure of the access port also comprises a substantially zero spring pressure expansion cavity for the fluid.

Abstract: A window for a sonar transducer housing is formed of an elastomeric plate which is bonded to a mounting ring for securing the window to the housing. The plate is bowed with a convex shape during the molding and the curing of the elastomer. During assembly of the housing, the convex surface of the plate faces inwardly and is depressed to a substantially planar configuration by the pressure of oil within the housing. The compression of the elastomer against the mounting ring inhibits separation of the elastomer from the ring.

Abstract: The damping of transducers having a mass oscillating in the manner of a piston in a cylinder containing damping fluid on both sides of the cylinder is rendered adjustable by the provision of a conduit through the mass for the flow of damping fluid from and to either side of the oscillating mass. An adjustable valve is preferably provided in a part of that conduit for damping control through regulation of damping fluid flow.

Abstract: A dipole hydrophone having a differential pressure sensing unit, for example, a multi-laminar bender disc, within a liquid filled housing. Two liquid filled acoustic waveguides form extensions of the housing and include pressure sensing ports. A mass of predetermined value is connected to the sensing unit and with a predetermined separation between sensing ports, the mass value is chosen so that the sensing unit response to acceleration is very nearly equal and opposite to its response due to the inertial mass of the liquid.

Abstract: 1. A tuned electrolytic detector cell comprising an inert plastic casing of enerally cylindrical configuration, a pair of diaphragms closing the ends of said casing, an interior wall portion disposed transversely within said casing and having an opening for fluid communication therethrough, a compliant diaphragm secured to said wall portion and having an aperture centrally disposed therein, an orificed cathode box having a mass therein, attached to the central portion of said compliant diaphragm with the orifice thereof aligned with said aperture thereby to establish fluid communication therethrough, and an anode in said casing.

Abstract: A fiber optic hydrophone for use as an underwater electroacoustic standard. The hydrophone includes a fiber optic acoustic wave detector in one end of the hydrophone which is subjected to incident acoustical waves. A similar fiber optic is in an acoustically isolated compartment where the optic fiber is not affected by the incident acoustical wave. Comparison of light passing through each coil will determine incidence of an acoustical wave on the detector fiber.

Abstract: The utility of a coaxial electret cable transducer as a hydrophone at shallow depths (low hydrostatic pressure) is extended for operation at substantially greater depths (high hydrostatic pressure) by the combination of the electret with a polymer material having piezoelectric properties, i.e., a piezoid. The electret and piezoid are separate flexible materials radially stacked within the cable or alternatively and preferably constitute a single material formed to have both electret and piezoelectric properties. One substance useful as the piezoid or as the electret-piezoid combination is polyvinylidene fluoride (PVF.sub.2).The invention also comprehends the method of measuring underwater soundings at either low or high hydrostatic pressures with the aforementioned coaxial cable as an electrostatic transducer by measuring electrical signals generated across the cable conductors when the ambient pressure is low and as a piezoelectric transducer across the conductors when such pressure is high.

Abstract: A pressure-balanced hydrophone having a low cut-off frequency which inclu a pair of piezo-ceramic tubes, wired in series, and having one end of each tube secured to a metal block in the center. The second end of one of the ceramic tubes is covered by means of a solid metal end cap and the second end of the other ceramic tube is covered by a porous sintered metal end cap. The unit is enclosed in an elastomeric cylindrical boot which is closed at the open end by a metallic disc. A pair of fill plugs are provided to fill the interior and the exterior of the piezo-ceramic tubes with a suitable oil. The unique feature of subject device is that a plurality of pores in the porous sintered metal end cap act as a plurality of capillaries for pressure balancing and thus make the hydrophone insensitive to hydrostatic pressure variations.