Abstract: A method of sensing alternating current in a cable having at least a pair of longitudinal conductors each of the pair carrying a current equal or unequal in absolute value to the other in mutually opposite directions, is comprised of disposing a coil with its lateral plane adjacent the cable in a position whereby electromagnetic fields caused by the currents intersect primarily different portions of the coil and induce current in the coil, and detecting the induced current in the coil.

Abstract: A transducer cable includes an inner conductor, an outer conductor, and dielectric between the inner conductor and the outer conductor. A longitudinal passage and a sense wire loosely disposed therein extend through the dielectric. Movement, (e.g., intruder-caused vibration) of the transducer cable results in movement of the sense wire relative to the outer conductor, causing corresponding changes in characteristic impedance of the sense wire. A carrier signal transmitted down the inner conductor produces an electromagnetic field that couples energy to the sense wire. The change in characteristic impedance causes reflection of some of the coupled energy, which produces a corresponding signal that is sensed by a receiver circuitry. The receiver circuitry produces a signal indicating the occurrence of the intruder-caused vibration.

Abstract: A transducer cable includes an inner conductor, an outer conductor, and dielectric between the inner conductor and the outer conductor. A longitudinal passage and a sense wire loosely disposed therein extend through the dielectric. Movement, (e.g., intruder-caused vibration) of the transducer cable results in movement of the sense wire relative to the outer conductor, causing corresponding changes in characteristic impedance of the sense wire. A carrier signal transmitted down the inner conductor produces an electromagnetic field that couples energy to the sense wire. The change in characteristic impedance causes reflection of some of the coupled energy, which produces a corresponding signal that is sensed by a receiver circuitry. The receiver circuitry produces a signal indicating the occurrence of the intruder caused vibration.

Abstract: A dual leaky coaxial cable comprising a pair of parallel elongated conductors, a dielectric surrounding each of the conductors, separate first external conductive shield apparatus surrounding at least the major portion of each of the dielectrics, separate second external shield apparatus surrounding each of the first external shield apparatus, apparatus associated with the shield apparatus for selectively coupling magnetic fields which may surround each of the elongated conductors through the first and second surrounding external shield apparatus, and apparatus for maintaining the individual respective second external shield apparatus separated by a distance which is a fraction of the diameter of either of the second external shield apparatus.

Abstract: A continuous wave (CW) leaky cable sensor for an intrusion detector uses a pair of elongated parallel cables, one for establishing an RF field and the other for receiving the field. A modulator is connected at an intermediate location of the receiving (or transmitting) cable, subdividing a detection zone into detection regions on each side of the modulator. The modulator selectively modifies a signal received by a portion of the receiving cable connected to its input. By processing the signal at the output of the receiving cable, the detection region for either side of the modulator in which an intrusion has occurred can be determined. The resolution of a CW sensor is thus increased at low cost. Multiple modulators can be used at spaced locations increasing the number of detection regions, and thus the resolution.

Abstract: A leaky cable useful antenna or as an intruder detector sensor either buried in a single trench or above ground substantially reducing sensitivity variations due to the environment. Egression of the electric field from the cable is blocked but magnetic fields escape. The velocity of the externally propagating electromagnetic field is slowed and attenuated. In one embodiment, the leaky coaxial cable is comprised of an inner conductor, a dielectric surrounding the inner conductor, a first external shield having low series impedance at VHF frequencies surrounding the dielectric, means for coupling a magnetic field through the first external shield, a second external shield surrounding the first external shield having high series impedance relative to series impedance of the first external shield and means for limiting VHF conduction current between the shields, which effectively causes separation of the internal and external propagation fields of the cables.

Abstract: The invention relates to a leaky cable intrusion detection system comprising a pair of spaced, parallel, buried, leaky coaxical cables. A radio frequency signal is applied to one of the cables, whereby an electromagnetic field outside said one cable is established, and a radio frequency signal from the field penetrates and is received from the other of the cables whereby disturbances in said field can be detected. The cables are spaced apart a distance such that they are intermediately coupled, being coupled to a greater degree than loosely coupled and to a laser degree than tightly coupled. In the preferred embodiment a longitudinal shield is spaced from and is below the cables. By varying the spacing between the cables and the shield, variations in field shape and sensitivity of the system can be substantially reduced.

Abstract: A sensor for use in a leaky cable intrusion system which is comprised of a pair of parallel buried coaxial cables, each of which has a velocity of propagation factor different from the other. This results in different sensitivity characteristics with length, resulting in a combined sensitivity which has markedly reduced amplitude variation over cables having similar velocities of propagation. It also makes feasible a system having ungraded cables in which the position of intrusion in the field set up by the sensor can be determined.

Abstract: A leaky coaxial cable for use as a sensor in a buried or other medium, which has a conductor located parallel to, and in proximity with the shield along the cable, but insulated therefrom. Preferably the two wire transmission line formed by the external conductor and the shield is terminated with an impedance matching the characteristic impedance of the transmission line (for minimum reflections). The external conductor can be oriented to cause the field in a given direction (e.g. above the surface of the burial medium) to be compensated for field variations caused by variations in the burial medium.

Abstract: This invention is an intrusion detector which uses codirectionally coupled CW leakly cable sensor techniques. Successive sensors are connected serially through R.F. decouplers, and each is polled and is sent power from a control unit via the serial cables, through the decouplers. The detector thus provides both intrusion detection and a secure data link.

Abstract: Disclosed is an automatic video intrusion detection system. The system monitors a given area such as between two parallel fences. The image of the given area is divided into an array of cells each approximately equal in size to the image of a man. The video for each cell is integrated, digitized and stored in an array. Changes in cell values are detected and tracked so that changes in, say, 3 adjacent cells in a given direction, indicate an intruder. A microcomputer implements a tracking algorithm. Filtering discriminates against light level changes. The system is simpler than a known one which analyzes grey values of thousands of points in a video field.