Contact sensor for area surveillance - uses sensor wire connected to piezoelectric or electromagnetic transducer

摘要

The sensor comprises a thin wire (10) vertically supported on an oscillatory membrane (15), which closes a box (16) in which a piezoelectric element (17) is sealed in epoxy resin (18). When the wire is disturbed its oscillatory movement is transmitted by the membrane to the piezoelectric element which transmits corresponding electric signals along connection lines (14) to a receiver. A mechanical contact may replace the element. Alternatively, the wire may form part of an oscillator whose oscillation frequency is varied by contact of the wire with an external object, this being effected by a change in inductance or capacitance of which the wire forms part. The piezoelectric element and oscillator may be combined in a sensor to provide sensitivity to both noise and metal objects. The sensor is used for recognising certain characteristics of vehicles, e.g. tanks.