Abstract: A multimode perimeter intrusion detection system comprises at least one elongated electret tape mounted on a barrier, such as a fence or wall, along the perimeter of an area to be protected and operated simultaneously in both active and passive modes to detect intruders in proximity to, as well as in contact with, the barrier. The tape is directly mechanically coupled to the barrier above and parallel to the ground or floor and is electrically connected to a sound wave generator and to signal processing apparatus which detects signals produced on the tape by intruders and activates an alarm. In the active mode, the tape radiates sound waves, preferably in the ultrasonic range, outwardly from the barrier and receives doppler-shifted reflections from a person moving in the sound field for transmission to the signal processing apparatus.

Abstract: Drift of the standing wave pattern in an acoustic doppler intrusion detection system with radiating and receiving transducers in a confined space is compensated by changing the operating frequency of the carrier wave generator when the magnitude of the received carrier wave is less than a predetermined threshold level. The magnitude of the received carrier wave is continuously monitored and compared to the threshold level. The generator frequency is incrementally increased until the carrier wave magnitude is optimum. This invention comprehends the apparatus for and method of optimizing signal strength at the receiving transducer by this technique.

Abstract: A tape transducer comprising an inner conductive strip laminate sandwiched between and totally enclosed by identical outer conductive strip laminates. The inner laminate has an inner conductive strip having opposite sides to which thin dielectric layers are bonded, the layers being electrically charged to form electrets having electrical charges of the same polarity on their outer surfaces. Each outer laminate has a conductive foil with marginal side portions overlying the side edges of the inner laminate and sealed together. The portions of the outer laminates aligned with the inner laminate are capable of simultaneously moving toward and away from the inner laminate for advantageously generating sonic waves in a transmitting mode and for efficiently generating an electrical signal in a receiving mode.

Abstract: Apparatus for continuously producing an elongated composite tape transducer having an inner laminate with a conductive dielectric-covered strip and two outer laminates each with a conductive foil comprises two reels containing the outer laminates and one reel containing an inner laminate, a station for electrically charging the dielectric layers on opposite sides of the inner strip, a mold for applying and sealing the outer laminates to opposite sides of the inner laminate to form the composite transducer, and a mechanism for pulling the three laminates through the apparatus. The lead end of the inner strip is electrically grounded. The charging station has two electrodes connected in parallel to a source of high DC voltage and physically positioned to make electrical contact with the dielectric layers, respectively, on opposite sides of the inner strip.

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: The sensitivity of a buried electrostatically charged cable transducer, such as an electret cable, to mechanical disturbances caused by men, vehicles and the like moving on the surface of the ground is greatly improved by disposing the cable loosely in a coextensive rigid hollow member such as a tube. The inside dimension of the tube is larger than the outside diameter of the cable, the cable being supported on the inner surface of the tube at longitudinally randomly spaced points. The cable is thus free to move radially relative to the tube in response to pressure waves or vibrations propagating through the ground and incident on the exterior of the tube so as to bend, twist, compress and/or otherwise stress the cable and generate corresponding electrical signals between the inner and outer conductors of the cable.

Abstract: An improved low-cost line transducer comprises a pair of electret covered conductors twisted about each other to form longitudinal helices and mechanically coupled to a medium that transmits mechanical forces transversely of the conductors. A change in the conductor-electret spacing caused by the mechanical disturbance generates an electrical signal between the conductors which is detected and processed by appropriate circuitry for indicating the occurrence of the disturbance. This simplified line transducer has improved sensitivity to the low frequency disturbances because of the non-symmetrical relation of the two conductors throughout their length. Undesired hum and noise picked up by the unshielded line is reduced or eliminated by appropriate circuits in the signal processor.

Abstract: An active ultrasonic perimeter intrusion detection system comprises an elongated flexible electret tape capable of being stored on and deployed from a reel or the like and connectable when deployed to a signal generator operating at ultrasonic frequencies and to a receiver having a signal processing and alarm capability. The tape comprises an electret layer sandwiched between relatively fixed and movable conductive strips and lies flat on a surface adjacent to the area to be protected such as the walls or ceiling of a room or the perimeter of a ground area. The movable stip produces a substantially undirectional ultrasonic beam outwardly from the tape and along its length so as to illuminate objects that cross over the tape. This causes a reflection of the ultrasonic signal and doppler shifting of its frequency which is detected by the tape, the output of which passes to the receiver for indicating the intrusion.

Abstract: A simplified hydrophone array for use in a towed marine streamer for seismic undersea exploration comprises a longitudinal series of electrically separate sensor sections comprising radially spaced coaxial inner and outer conductors and a plurality of longitudinally extending electret cables tightly fitted in the annular space between the conductors. Each cable has a conductive lead wire insulated by an electret covering, such as electrostatically charged tetrafluoroethylene (Teflon); an electrical signal between inner and outer conductors and across the electret is produced by acoustic energy transmitted to the outer conductor. The outer conductors are electrically insulated from each other and the inner conductor is longitudinally continuous throughout the length of the array and thus is common to all sections.