Intrusion detection system

Abstract

A wire comprised of an electrical conductor enclosed within insulation, is loosely positioned relative to an electrically conductive member. This combination is positioned to monitor disturbances caused by the intrusion of the protected area. The relative movement of the wire and the electrically conductive member caused by intrusion disturbances produces an electrical signal which is attributable to a capacitance change. The signal can be realized from either the electret characteristic of the wire or it can be realized by the application of a d-c bias voltage to the combination. A signal developed by the combination in response to a mechanical disturbance includes a low frequency and a high frequency component. The low frequency component, attributable to a "strain mode" of operation, developed by the displacement of the wire relative to the electrically conductive member by mechanical deflection of the conductive member whereas the high frequency component, attributable to an "acceleration mode" of operation, results from the vibration of the wire relative to the conductive member. The high frequency component code is comparable to a "ringing" condition much the same as is experienced by an accelerometer.

I claim:  .[.1. Apparatus for monitoring disturbances caused by mechanical shock, pressure, impact, etc., comprising in combination, a substantially rigid first electrically conductive member adapted to respond to disturbances, a second electrically conductive member disposed in a loose fitting, intermittent contacting relationship with said first electrically conductive member and being mechanically free to move with respect to said first electrically conductive member, electrical insulating material disposed between said first and secod electrically conductive members to establish a capacitance therebetween, disturbance of said substantially rigid first electrically conductive member resulting in mechanical displacement of said second electrically conductive member with respect to said first electrically conductive member, the displacement producing a change in said capacitance..].  .[.2. Apparatus as claimed in claim 1 wherein said insulating material exhibits an electret characteristic, said 
     
        electret characteristic providing an electrical charge..].  3.  Apparatus as claimed in claim .[.1.]. .Iadd.13 .Iaddend.further including a d-c voltage source operatively connected to said electrically conductive members to establish an electrical charge on said insulating material. .[.4. Apparatus as claimed in claim 1 wherein the change in capacitance produced due to the displacement of the second electrically conductive member with respect to the first electrically conductive member is manifested by the development of an electrical signal, said electrical signal consists of a low frequency component corresponding to the capacitance change produced by separation of said first electrically conductive member from said second electrically conductive member and a high frequency component corresponding to the vibration of said second electrically conductive member..].  .[.5. Apparatus as claimed in claim 1 wherein said first electrically conductive member includes a sheet of electrically conductive material, and said second electrically conductive member is a wire resting loosely on said sheet of electrically conductive material with said electrical insulating material disposed therebetween..].  .[.6. In an intrusion detection system for responding to disturbances, the combination of a substantially rigid tubular member exhibiting electrical conductivity characteristics, a flexible, loose fitting electrical conductor having an effective diameter which is substantially less than the inside diameter of said tubular member and being disposed witin said tubular member in an intermittent contacting relationship with an interior surface of said tubular member so as to be substantially closer to one interior surface of the tubular member than to the opposite interior surface of the tubular member, electrical insulating material disposed between said tubular member and said flexible electrical conductor to establish a capacitance therebetween, a disturbance causing displacement of the loosely positioned flexible electrical conductor relative to said substantially rigid tubular member causing a change in said capacitance, said change in capacitance resulting in the development 
     
     
        of an electrical signal indicative of the disturbance..].  7.  Apparatus as claimed in claim .[.6.]. .Iadd.14 .Iaddend.wherein said electrical insulating material is a coating on said flexible electrical conductor, the effective diameter of the combination of said flexible electrical conductor and the coating of electrical insulating material being substantially less than the inside diameter of said tubular member.  .[.8. Apparatus as claimed in claim 7 wherein the insulating material coating 
     
     
        exhibits an electret characteristic..]. 9.  Apparatus as claimed in claim .[.7.]. .Iadd.14 .Iaddend.including a d-c voltage source operatively connected to said flexible electrical conductor and said tubular member to establish a charge condition in said insulating material.  .[.10. Apparatus as claimed in claim 6 wherein said electrical signal is comprised of a low frequency and high frequency component, wherein said low frequency component corresponds to the change in capacitance produced by the displacement of said wire element relative to said tubular member in response to said disturbance and said high frequency component corresponds to the vibration of said wire element relative to said tubular member in response to said disturbance..].  .[.11. Apparatus as claimed in claim 6 wherein said flexible electrical conductor is a wire..]. .Iadd. 12. Apparatus as claimed in claim 14 including, circuit means responsive to said first frequency and second frequency signal components for weighting said first frequency and second frequency signal components and producing an output signal indicative of a combination of predetermined weighted representations of said first frequency and second frequency signal components. .Iaddend. .Iadd. 13. Apparatus for monitoring disturbances caused by mechanical shock, pressure, impact, etc., comprising in combination, a substantially rigid first electrically conductive member adapted to respond to disturbances, a second electrically conductive member disposed in a loose fitting, intermittent contacting relationship with said first electrically conductive member and being mechanically free to move with respect to said first electrically conductive member, electrical insulating material disposed between said first and second electrically conductive members to establish a capacitance therebetween, a disturbance of said substantially rigid first electrically conductive member resulting in a mechanical displacement and a mechanical vibration of said second electrically conductive member with respect to said first electrically conductive member, said mechanical displacement and mechanical vibration producing a change in said capacitance, said change in capacitance being manifested by the development of an electrical signal, said electrical signal consisting of a first frequency component corresponding to the capacitance change produced by said mechanical displacement of said second electrically conductive member and a second frequency component corresponding to the mechanical vibration of said second electrically conductive member, and circuit means responsive to said electrical signal. .Iaddend.  .Iadd. 14. In an intrusion detection system for responding to disturbances, the combination of a substantially rigid tubular member exhibiting electrical conductivity characteristics, a flexible, loose fitting electrical conductor having an effective diameter which is substantially less than the inside diameter of said tubular member and being disposed within said tubular member in an intermittent contacting relationship with an interior surface of said tubular member so as to be substantially closer to one interior surface of the tubular member than to the opposite interior surface of the tubular member, electrical insulating material disposed between said tubular member and said flexible electrical conductor to establish a capacitance therebetween, a disturbance causing a mechanical displacement and a mechanical vibration of said loosely positioned flexible electrical conductor relative to said substantially rigid tubular member, said mechanical displacement and mechanical vibration of said loosely positioned flexible electrical conductor causing a change in capacitance, said change in capacitance resulting in the development of an electrical signal including a first frequency component produced by said mechanical displacement and a second frequency component produced by said mechanical vibration, and circuit means responsive to said electrical signal for identifying said disturbance. .Iaddend.