Abstract: An improved marsh case is disclosed. The marsh case contains and protects a geophone, which is inserted into the earth in the course of oil exploration. The marsh case provides an cap having an upper opening through which wires pass to the geophone and a lower internally threaded opening that attaches to the body of the case. The body of the case provides an upper externally threaded opening which attaches to the cap, and a lower internally threaded conical surface which allows a threaded cylindrical surface of a spike to be attached. The threads of the body are slightly tapered, thereby relieving some of the stress that would otherwise be applied to the threads. The rim of the upper external threaded opening of the body and an internal annular shoulder in the cap compress an O-ring, thereby making a water-tight seal.

Abstract: A hydrophone array to perform passive and active sound imaging is described. The array is comprised of a plurality of acoustic transducers attached to a cable that may be towed behind a geophysical survey vessel. The cable and acoustic transducers are enclosed within a sheath of essentially constant external dimensions, which extends longitudinally the length of the cable and which is effective in minimizing turbulent noise created by the array during its use. The sheath may be circular or elliptical in cross-section and can enclose a jacket of resiliently flexible and positively buoyant material that encases the cable and transducers.

Abstract: An environmentally sealed acoustic transducer that utilizes a semi-liquid, liquid or paste-like couplant material between a bottom surface of a transducer case and a structure that is to be acoustically vibrated. The transducer case fits into a chamber or well that provides a seal relative to the outer surfaces of the transducer case, and a weep or bleed passageway is provided and opens to the chamber or well. The bleed passageway permits excess couplant material to move out of the chamber through the passageway when the transducer case is inserted into the chamber or well. The bleed passageway has a seal so that the entire unit is environmentally sealed.

Abstract: An underwater sensing device for measuring or sensing an underwater condin proximate the floor of an ocean, lake or similar body of water. The sensing device includes an underwater sensing device mounting member and an underwater sensing device sensor, such as a hydrophone, mounted on the mounting member. The mounting member has known acoustic properties including a thickness and a largest dimension, each of which is a function of an acoustic wavelength in the underwater environment. The sensing device can also include acoustic diffraction reducing members disposed around the edges of the mounting member. The sensing device can also include first and second underwater sensors disposed on either side of the mounting member so that one of the sensors faces away from the underwater floor. An underwater sensing device switch, such as a gravity switch, activates the sensor that faces away from the underwater floor.

Abstract: An acoustic sensor assembly is provided for sensing acoustic signals in a moving fluid such as high speed fluid stream. The assembly includes one or more acoustic sensors and a porous, acoustically transparent screen supported between the moving fluid stream and the sensor and having a major surface disposed so as to be tangent to the moving fluid. A layer of reduced velocity fluid separating the sensor from the porous screen. This reduced velocity fluid can comprise substantially still air. A foam filler material attenuates acoustic signals arriving at the assembly from other than a predetermined range of incident angles.

Abstract: A hydrophone retrieval system is described, which includes: a) a case having an interior chamber adapted to house an anchor fixture within the chamber, the case having at least one sealable opening therein adapted to accept therethrough an electric leader cable and a retrieval cable, in a water-tight manner; b) an anchor fixture disposed within the chamber, where the anchor fixture includes an anchor member portion, wherein a first end of the electric leader cable passes through a first aperture formed in the anchor member portion; c) a first end of the retrieval cable passing through a second aperture formed in the anchor member portion; d) a retrieval cable termination element attached to the first end of the retrieval cable within an interior portion of the fixture, wherein the diameter of the retrieval cable termination element is greater than the diameter of the second aperture; and e) a base member portion, wherein the anchor member and base member portions are rigidly separated from each other at a fix

Abstract: A sound amplification system includes an amplifier and a waterproof microphone. In an exemplary embodiment the microphone includes a transducer within a cavity covered by a resilient waterproof membrane. The system can monitor either the complete frequency range of the microphone or only one or more selected frequency ranges. The system can include one or more noise emitting lures that produce sound in a frequency range corresponding to the one or more selected frequency ranges. The invention also includes a method of waterproofing a miniature microphone. A housing can be provided for the microphone to protect it and to reduce background noise caused by turbulence during towing. The housing has a streamlined shape and can be weighted. One or more fins can be provided to stabilize the housing.

Abstract: A piezoelectric vibrator comprises a piezoelectric element having a rectangular shape and being provided with at least one input electrode from which an input lead extends and at least one output electrode from which an output lead extends; and a case having a rectangle-like shape for accommodating the piezoelectric element and having at least through holes through which the input and output leads penetrate thereby the leads project to an exterior of the case. The through holes have a size larger than a size of the leads to create a clearance between the leads and inner walls of the through holes so as to allow the leads to show a displacement or a vibration due to the vibration of the piezoelectric element.

Abstract: A protective cover for protecting the sonar transducer of a fishing boat or other recreational watercraft, from damage caused by flying debris during overland towing. The protective cover conforms to the outside shape of the transducer and is secured in place by an elastic strap or a releasable strap using VELCRO.RTM. or snap fasteners.

Abstract: This invention provides a dual gimbal geophone assembly. The geophone is placed in the cavity of a mass member. The mass member is rotatably attached to a frame so that the mass member rotates about a first plane. The frame is rotatably attached to support members so that the frame rotates about a second plane which is orthogonal to the first plane. This geophone provides two degrees of rotation, one along the first plane and the second along the second orthogonal plane. The geophone remains vertical within the tilt tolerance of the geophone regardless of the orientation of the assembly.

Abstract: A geophone is disclosed that has a cylindrical housing closed at one end by a bottom and the other end by a top. A magnet assembly with pole pieces at each end of the magnet is centrally mounted in the housing providing an annular space between the magnet assembly and the housing. A coil form is located in the annular space. Springs support the coil form for axial movement relative to the magnet assembly along the longitudinal axis of the housing. Washers are included on the upper and lower sides of each of the springs to enhance the life span of the springs by reducing the damage caused by torsional forces experienced by the springs during normal operation and rough handling. Also incorporated in the geophone are resilient members mounted between the coil form and the housing to prevent the coil form from directly hitting the housing and thereby reduce the amount of frequency shift experienced by the geophone over its life span.

Abstract: The device comprises instruments for collection and recording of signals in seismic exploration of the substratum off-shore. The device is designed as a pole which is adapted to be forced down into the seabed and comprises a pointed lower end (7), an intermediate approximately cylindrically shaped main portion (6), a vibration-absorbing spacer (14) between the pointed end (7) and the intermediate main portion (6). The other end of the intermediate main portion (6) is connected to a top part (8) designed for inserting/pulling and other ways of handling the device. The pointed end (7) at least comprises geophones (15-17) and a hydrophone (23) is placed in the vicinity of the upper end of the device. The majority of the device's other instruments are placed in the intermediate main portion (6). The device is connected to a main cable (4) which extends to a seismic ship (29, 31).

Abstract: The invention concerns a window including at least a first sheet (16), a second sheet (18), said sheets being joined together by a connecting layer (20), characterised in that it also includes an ultrasonic device (12) placed between said sheets (16,18) and co-operating directly with a first face (24) of said first sheet (16) to detect the presence of foreign bodies on a second face (26) of said first sheet (16) opposite said first face (24), said device (12) comprising a transducer (28) able to emit, via a transmitting/receiving face, an incidental ultrasonic signal of wavelength .lambda. in said first sheet (16), the thickness of said first sheet being equal to K..lambda./2, where K is an integral number, and said transducer being able to receive, via said transmitting/receiving face a reflected ultrasonic signal representative of the presence or absence of said foreign bodies to generate a detection signal.

Abstract: This invention provides a stabilizer for a geophone which reduces the amount of movement of the geophone after deployment in a marine environment subjected to water currents or turbulence. The stabilizer consists of a bulb-shaped body with fin-shaped lobes. An axial cavity for receiving the geophone housing containing the geophone is located at one end of the stabilizer. The other end terminates in a tail designed to promote laminar flow and reduce turbulence coming off the geophone housing and stabilizer. When the geophone is deployed, the stabilizer and attached geophone housing come to rest on a stable, 3-prong base comprised of two adjacent lobes of the stabilizer and the end of the geophone housing opposite the end inserted into the stabilizer.

Abstract: A lightning protection system is disclosed for a seismic data acquisition system having single or multiple geophones positioned at predetermined ground locations over a large area. A surge suppressor is placed across the leads to which the geophones strings are connected. Such surge suppressor preferably comprises a gas discharge arc tube. The base or spike of each geophone is implanted in the ground, A ground lead is connected to the surge suppressor. Electrical energy from a lightning strike affecting the geophones, cables, data acquisition boxes, etc. is dissipated by the surge suppressors through the multiple spikes to the earth thereby to minimize damage resulting from lightning.

Abstract: A marine seismic bottom geophone anchor and coupling device comprising two rectangular fabric sections attached along their edges and along a plurality of lines between edges to form a plurality of pockets. The pockets are filled with a weighting material. Connecting means are provided so that when the combined fabric sections are wrapped around a marine seismic bottom geophone, it will be held in a generally cylindrical form to simultaneously anchor the geophones and associated cables at a desired marine bottom location, isolate the sensors from noise sources, and provide good coupling to the marine bottom for receiving desired seismic signals.

Abstract: A device for mounting an ultrasonic transducer on user equipment for operation in a contaminating, ambient environment. A housing has a forwardly extending, profiled inner surface for promoting focusing along an axis of ultrasonic waves emitted by a transducer mounted against a shoulder of the casing. A chamber adjacent to a backside of the transducer is formed by a rearwardly extending portion of the casing and a cap forming an overlap portion therewith. A bladder disposed in the chamber has a port which vents into the overlap portion such that pressure equalization across the transducer is dynamically maintained. A calibrator offset by known displacement from the transducer provides a reflected wave portion to the transducer such that errors caused by temperature dependency of the velocity of propagation of the ultrasonic waves through the ambient environment can be substantially eliminated.

Abstract: There is provided a hermetically sealed dry-coupled transducer apparatus and system adapted for improved measuring of liquid level in a pipe or vessel, or for other instrumentation applications. The transducer system is characterized by having a hermetic seal at the junction of an acoustic window 33' and an outer shell 31' (thereby hermetically sealing a forward aperture of the outer shell), and a thin, compliant, threaded cap 46 enclosing a rearward aperture of the outer shell. The cap provides means for repetitively assembling and disassembling the transducer module, if necessary, prior to welding. In addition, a push rod applies acoustic coupling force to a piezoelectric transducer element to effect dry coupling to a surface, while the compliant cap prevents significant force transmission to the shell. The system exhibits limited reverberation and, moreover, is suitable for use in high-temperature environments.

Abstract: A device including instruments for use on the seabed for the collection and recording of first signals during off-shore seismic exploration.

Abstract: A seismic sensor platform comprises an open frame and a plurality of seismic motion sensors vertically positioned in a common horizontal plane in spaced relationship around the periphery of the open frame. A spike associated with each of the sensors extends beneath the open frame for anchoring each of the sensors in the earth. The frame includes a shield for protecting the sensors from physical damage and for shielding them from seismic noise. Second and third pluralities of horizontally positioned sensors may be provided on the frame, orthogonally positioned with respect to each other to sense orthogonal components of reflected seismic waves. The sensors may each be of a different natural frequency to optimize the multifrequency output of the sensor array.

Abstract: An ultrasonic piezoelectric transducer that is operable in very high and very low temperatures. The transducer has a dual housing structure that isolates the expansion and contraction of the piezoelectric element from the expansion and contraction of the housing. Also, the internal components are made from materials having similar coefficients of expansion so that they do not interfere with the motion of the piezoelectric element.

Abstract: A method and apparatus for recording acoustical and seismic signals at the ocean bottom with minimal noise. A seafloor seismic recorder couples geophones to the water bottom, stores the seismic data, and is retrievable. The device is comprised of a chassis, a ballast ring, an electronics control package, a geophone package, a buoy means, and a leg extension means. The geophone package is disconnectably connected to the portion of the control package housing, so that the geophone package can remain coupled to the seafloor, when the control package and chassis rise toward the surface for a short distance. The buoy means permits the ballast ring and geophone package to become embedded in the sediment upon impact, and allows the chassis, geophone package, and control package to rise to the surface upon release of the ballast ring.

Abstract: An alarm device is placed in the water of a swimming pool for monitoring the swimming pool by triggering an alarm in response to changes in water pressure or sound as a result of persons falling into the swimming pool. The device includes a switch element and wave detector, as well as an acoustic alarm. A covering device or shelf, placed below the water surface and above the detector device is an integral component of the alarm device. The covering device includes a parabolically designed wall which is placed around the detector and is in hydraulic connection with it.

Abstract: A seismometer system which provides readouts of the time integral (Cumulative Absolute Velocity or CAV) of the acceleration time history of an earthquake. CAV is found to be a measure of the structural damage potential of an earthquake. Three triaxial low frequency acceleration sensors are connected into a digital computer system. Each sensor has a capacitive pickoff, whose capacitances determines the length of an electrical pulse; the pulse gates high-frequency clock cycles into a counter. The counts are summed to give the time integral. A microprocessor provides for periodic re-zeroing and other calibration functions, and for the actuation of alarms, relays and electrical pulses for utility shutoff and the like at predetermined levels of CAV. The acceleration time history of the earthquake is stored in the memory for later retrieval if desired. The whole system is contained in a small inexpensive package.

Abstract: A hydrophone is provided for use with a hydrophone array enclosed in a streamer cable that is deployed in a body of water. The active transducer elements of the hydrophone are electrically isolated from the sealed metal case in which they are mounted. The signal input and output terminals are protected from short-circuiting due to water invasion of a faulty streamer cable jacket.

Abstract: In accordance with illustrative embodiments of the present invention as disclosed herein, a leader cable is anchored to a post on the upper end of a geophone case having a spike on its lower end that penetrates the ground to hold the case in an upright postion. The anchor is formed by a continuous stress member in the cable that is looped around the post to isolate the electrical conductors in the cable from strains imposed on the cable. The post can be an integral part of a block located at the upper end of the case, or a bobbin that is captured by a cap that closes the top of the case.

Abstract: A hydrophone with crossed pairs of geophones is provided with a strong light weight housing allowing use at several thousand feet deep in the ocean while still maintaining good sensitivity. The cruciform housing has a cylindrical portion conforming to each of the four geophones so that each cylindrical wall has small diameter and requires small thickness. The cylindrical portions are joined to a central body to complete the housing.

Abstract: An apparatus and method of high resolution reverse vertical seismic profile (VSP) measurements is shown. By encapsulating the seismic detector and heaters in a meltable substance (such as wax), the seismic detector can be removably secured in a borehole in a manner capable of measuring high resolution signals in the 100 to 1000 hertz range and higher. The meltable substance is selected to match the overall density of the detector package with the underground formation, yet still have relatively low melting point and rigid enough to transmit vibrations to accelerometers in the seismic detector. To minimize voids in the meltable substance upon solidification, the meltable substance is selected for minimum shrinkage, yet still having the other desirable characteristics. Heaters are arranged in the meltable substance in such a manner to allow the lowermost portion of the meltable substance to cool and solidify first.

Abstract: In accordance with an illustrative embodiment of the present invention, a water-proof geophone housing assembly includes a lower body member housing a seismic transducer, a cap member closing the upper end of the lower body member, an upper body member molded over the cap member and an upper portion of the lower body member, there being a molecular bond between all confronting surfaces of the members to prevent entry of moisture. The electrical lead wires extending from the transducer through the cap member and upwardly out of the upper body member are water blocked to prevent migration of water therealong.

Abstract: A light weight and compact geophone assembly for detecting transient seismic signals along orthogonal axes. The geophone assembly having a plurality of geophones arranged within close proximity of each other within a compact housing. The geophones are interconnected to a conductor cable passing through the housing in a unique water-tight sealing arrangement. At the cable entrance into the housing, the conductor cable is surrounded by a tapered boot compressed about the cable by a sleeve which in turn is fixed in place by a locking nut. The locking nut is received by complementary threads at the cable entrance into the housing. When tightened, the locking nut forces the compression sleeve over the tapered surface of the boot, compressing the boot about the cable. In addition, the locking nut and compression sleeve urge the boot in compression between the cable and the housing. Located atop of the housing is a bubble leveling device.

Abstract: A geophone and a geophone planting tool adapted to engage the outer case of the geophone, to hold it securely during aligning, leveling and implanting into the earth and to release it upon lifting the geophone planting tool from the geophone have matable surfaces which enable forces to be transmitted from the geophone planting tool to the geophone.

Abstract: A transducer (700) of great sensitivity is disclosed which incorporates a magnetohydrodynamic (MHD) cell (738) exposed to the flow of a electrically conductive fluid (712) within a channel (704). Flexible diaphragms (722) form the ends of the channel (704) and deflect with the fluid motion. The deflection is sensed by strain gauges (724) and the signals from the MHD cell and strain gauges are processed. In addition, an MHD power generator is contemplated which generates power from a moving electrically conductive fluid, such as sea water in geophysical motion. A strong magnetic field is established normal the direction of fluid flow. Electrodes are positioned normal to both the magnetic field and fluid flow to complete a circuit to transfer the power generated by the movement of the electrically conductive fluid through the magnetic field.

Abstract: A method of measuring the shear modulus profile of a seabed floor using one or more bottom shear modulus profilers, each having a seisometer package to measure the seabed motion in three dimensions and a sensor for measuring the pressure at the seabed floor, placed on or below the seabed floor, and a means for converting the measurements derived therefrom into a shear modulus profile.

Abstract: A hydrophone mount for use in a marine seismic cable having a central core, such mount comprising: a first housing portion having first and second apertures, first and second edges, and a cavity adapted for holding a hydrophone; a second housing portion having first and second apertures and first and second edges, the first and second housing portions being sized and shaped so that the first and second housing portions can be positioned adjacent to the core to form a housing around the core with the first edge of the first housing portion interlocking with the first edge of the second housing portion, the second edge of the first housing portion interlocking with the second edge of the second housing portion, and the first and second apertures of the first housing portion axially aligning respectively with the first and second apertures of the second housing portion; and a first member positioned in the aligned first apertures and a second member positioned in the aligned second apertures.

Abstract: An ultrasonic distance sensor transmitting from and receiving an ultrasonic wave with a single ultrasonic transmitting and receiving element to measure proximate distances such as vehicle floor heights or distances to obstacles or pedestrians approaching relative to a vehicle. The ultrasonic transmitting and receiving element is accommodated by means of a resilient member having beads, under pressure in a casing and secured therein, thus attenuating residual vibration which disturbs accurate measurement of the proximate distances. The beads also serve to prevent water from invading into the case. The sensor incorporates a protection circuit for preventing burn-out of an output transistor due to accidental prolonged transmission.

Abstract: A housing adapted for receiving a sonic transducer capable of projecting and receiving a sonic pattern having a primary lobe and a secondary lobe. The housing has an end wall for receiving the sonic transducer and a restrictive wall for intercepting the secondary lobe of the sonic pattern in one quadrant and reflecting that portion of the secondary lobe into the opposite quadrant. A pair of side walls substantially intercept and reflect the secondary lobe in quadrants adjacent the one quardant to provide more uniform sonic pattern. The side walls may be disposed at an angle outward from the direction of projection of the primary lobe having a value of from 0.2 to 0.3 of the value of the angle the secondary lobe makes with the primary lobe.

Abstract: An accelerometer for blast monitoring comprises at least one piezoelectric transducer having a piezoelectric membrane attached along the edge thereof to the sidewall of a suitable container and mounted for free movement in such container for generating a high impedance electrical output signal upon deformation of the piezoelectric membrance by vibration during a blast, a high to low impedance converter connected to the piezoelectric membrane for converting the high output impedance of the piezoelectric membrane into a low impedance signal for transmission through long cables to recording equipment, and means for encapsulating the piezoelectric transducer and converter into epoxy or other solid material to minimize response of the transducer to surrounding acoustic signals.

Abstract: In an acoustic ground vibration detector for the detection of infrasound ground vibrations, comprising at least one three-component geophone probe, the three individual geophones of said geophone probe are electrically connected in series and act upon an operation amplifier whose output signal activates a Reed relay. The activated Reed relay switches on a sound signal transmitter which produces an audible acoustic signal for the duration of the ground vibration signal. The acoustic ground vibration detector is intended in particular for locating buried persons. Moreover, it serves to protect important objects by registering infrasound ground vibrations produced by footfall sound.

Abstract: A geophone designed to measure the vibrations of bodies, especially vibrations in the earth's crust, comprises two-strip sensors made of piezoelectric polymer, embedded by one end in the geophone casing and resting freely, by one side, on the inertial mass of the geophone, thus enabling the making of geophones with a very wide pass-band.

Abstract: An apparatus for implanting and positioning a geophone assembly into the earth is disclosed. The geophone implanting apparatus includes a receptacle for receiving and retaining a geophone assembly. A magnetic compass and a cylindrical bubble level are mounted concentrically approximately one meter from the receptacle so that the ferromagnetic properties of the geophone do not induce errors in the azimuth measurement. A pair of radially disposed handles are utilized to rotationally manipulate the geophone into a proper orientation during implantation. After the geophone assembly has been implanted and leveled a release mechanism is utilized to release the geophone from the receptacle by deforming a spring grip mechanism which is utilized to retain the geophone. In the depicted embodiment, a geophone assembly having a radially non-symmetric case is utilized in conjunction with a matching receptacle so that a unique orientation of the geophone may be accomplished.

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 geophone apparatus capable of detecting both horizontal shear and compressional seismic waves has a pair of geophones mounted such that, when in use, said geophones will be inclined at an angle of about 45.degree. in opposite directions from vertical. The output signals generated by the two geophones are summed to yield a compressional wave trace and/or are subtracted one from the other to yield a horizontal shear wave trace.

Abstract: A seismic detector assembly is disclosed that includes a housing and a seismic detector or geophone located in the housing. The geophone has a pair of external terminals that are positioned asymmetrical to the longitudinal axis of the geophone. A printed circuit board having conductive strips for connecting the terminals to leader cables is located in the housing above the geophone. The printed circuit board has a pair of asymmetrical openings through which the asymmetrical terminals can extend only when the printed circuit board is oriented in one position relative to the geophone. Marks on the printed circuit board indicate which conductive strip should be connected to which terminal and the proper orientation of the printed circuit board relative to the truck that receives the output of the geophone.

Abstract: A seismic detector housing assembly is disclosed having a housing open at one end, a seismic detector having an outer case with generally flat end walls, and a pair of terminals extending out of the case through one end wall located in the housing with the terminals extending outwardly from the open end of the housing. A seal member of elastomeric material having openings, through which the terminals extend, covers the end of the detector and closes the open end of the housing. A PC board for connecting the terminals to leader wire conductors covers the seal member. A cup-shaped cap is attached to the housing to enclose the terminals and an outer edge to engage the PC board and compress the seal member into sealing engagement with the cap and the housing.

Abstract: An apparatus for supplying the power requirements of an Ocean Bottom Seismometer is disclosed wherein the power supply is separate from the power consuming devices of an Ocean Bottom Seismometer and mounted on the weight holding the Ocean Bottom Seismometer on the ocean floor during recording.

Abstract: The insulation resistance between the electroded surfaces of an underwater transducer and the water within which the transducer is immersed is greatly improved by coating the electroded surface of the transducer with a layer of air-free, high-resistance waterproof material before bonding an elastomer covering over the assembly to serve as the outer housing.

Abstract: Magnetohydrodynamic (MHD) perturbation sensing apparatus. A rigid, shock resistant enclosure provides a housing having a sealed interior, in which a magnetohydrodynamic sensor and associated electronics are disposed. A hollow tubular conduit having an internal channel containing an electrically conductive fluid such as mercury or an electrolyte is of preferably ring shaped dimensions. The electrically conductive fluid is subject to perturbation-responsive movement within the ring. A very strong magnetic field is set up perpendicularly with respect to the plane occupied by the conduit by at least one pair of spaced apart magnets which have opposite poles disposed in a line generally normal to the plane of the conduit. One or more pairs of electrodes are secured to the conduit in a position normal to the magnetic field whereby to sense perturbations.

Abstract: A speaker system having a magnet and voice coil are mounted within a dome-shaped enclosure in such a way as to be capable of transmitting sonic vibrations and audio waves through a liquid medium or solid structure, the dome-shaped enclosure cooperating with the magnet and voice coil in such a way as to greatly enhance the waves and sonic vibrations generated to the other medium or structure.

Abstract: A piezoelectric transducer in which a casing is mounted in a sealing manner on a base member for supporting two rod-shaped terminals, a piezoelectric element is bonded to the inner surface of said casing, and electrodes on the front and back surfaces of said piezoelectric element are electrically connected to said terminals. The transducer is supported at the position of a node of the free oscillation mode or the forced oscillation mode. The interior of the casing in the transducer is filled with nitrogen gas.

Abstract: A method and apparatus are disclosed for detecting seismic waves and electromagnetic waves at the same location in making geophysical measurements. A seismic wave is generated at a first location and the seismic wave and electromagnetic waves generated by said seismic wave are detected at a spaced-apart second location. The seismic wave may be detected by a single apparatus that also detects the magnetic field. Alternatively, the seismic wave may be detected by two spaced-apart apparatus that also measures the magnetic field at the two spaced-apart locations as well as measuring the electric field between the two apparatus.