The present invention provides an inexpensive security sensor cable, a
method for manufacturing of same and an overall security system for using
that sensor cable. The sensor cable consists of a central conductor, an
air separator, a polyethylene dielectric tube, an outer conductor and an
outer protective jacket. The central conductor is loosely centered in the
coaxial cable and thus freely movable relative to the dielectric tube.
The sensor cable has application either in a passive sensing system or in
an active ranging sensing system to determine the location of an
intrusion along the cable. For the passive sensing function, when the
center conductor moves, it contacts a suitable dielectric material from
the triboelectric series, such as polyethylene, which can be processed to
produce a charge transfer by triboelectric effect that is measurable as a
terminal voltage. In an active system, the central conductor moves within
the dielectric in response to a vibration to provide an impedance change
that can be sensed. Conventional radio grade cable may be modified in its
construction by removing its dielectric thread to manufacture the sensor
cable, thus enabling the center conductor to move freely in the air gap
within the dielectric tube. An inexpensive method of manufacturing sensor
cable is provided as the cable parts are readily available. Such a sensor
cable is advantageous in that the passive triboelectric properties of the
cable, in response to a disturbance, can provide a larger voltage
response over prior art cables.