Other Exterior IDS Sensor Candidates. The following provides a
brief description of other candidate sensors that may be used in conditions
when the most commonly deployed sensors are not suited. See the sources
identified in par. 4.5.1 for more details.
Electric Field Fence Sensor. An electric field fence sensor
consists of an alternating current field generator which excites a field
wire, one or more sensing wires that couple to the field, and an amplifier
and signal processor to amplify and detect changes in signal amplitude
generated by intrusions. A human body distorts the coupling between the
field and the sensing wires thus generating a signal. This sensor can be
employed to follow terrain and is useful over hilly terrain. Supervisory
circuits have been designed to detect cutting, shortening, or breaking of
wires. Zone lengths are typically 330 feet (100 m).
Seismic-Magnetic Buried Line Sensor. This sensor consists of
a cable that is sensitive to both seismic and magnetic disturbances and a
processor to evaluate signals that are generated in the cable. Detection is
based on the fact that seismic disturbances will either move the cables in
the earth's magnetic field or strain the magnetic core. Either will generate
a voltage in the sensing coil. This sensor is useful in remote areas, but
may suffer false alarms from wind-induced ground motion and other localized
pressure sources such as moving vehicles and trains.
Seismic Buried Line Sensor. There are three types of seismic
sensors: piezoelectric sensors, balanced pressure systems, and geophone line
sensors. Each are activated by seismic energy generated by intruders and
each can follow irregular terrain and crooked sectors. Such sensors can be
used in combination with other sensors (such as microwave sensors) to
optimize detection capability while minimizing false alarms.
Magnetic Buried Line Sensor. This is a passive sensor that is
sensitive to disturbances in the local magnetic field caused by nearby
movement of ferromagnetic material. When an intruder with ferromagnetic
material crosses the loop, the electrical signal generated causes an alarm.
Electromechanical Fence Disturbance Sensor. When an attempt
is made to climb a fence, the fence moves. This motion can cause a switch
mechanism to open or close, generating an alarm. This is called an
electromechanical fence disturbance sensor. Electromechanical fence sensors
use a set of point transducers to detect fence motion. These point
transducers produce an analog signal, rather than a switch closure, and use
an electronic signal processor to extract alarm information from the signal.
sensor that operates on the principle of target motion generating a frequency
change or Doppler shift which is detected by the receiver. Such radars can
provide coverage over irregular terrain.