Piezoelectric stress/strain intrusion detectors

Claim 1

A detector suitable for use in an array to be buried below the surface of the earth and connected by coaxial cable means to circuitry to detect intrusions which apply downward pressures to said surface above the array, comprising: a. a metallic cup having an enclosing side wall portion open at one end and closed at the other end by a diaphragm portion, the side wall portions having one or more cable-receiving openings therethrough; b. cap means closing said open end of the cup; c. piezoelectric transducer disc means having oppositely poled electrodes and one of the electrodes of said disc means being conductively bonded to the diaphragm portion inside the cup for deformation of the disc means therewith when the diaphragm portion is flexed by said pressures; d. said cable means passing into the cup via a side wall opening, and the cable means having an outer conductor conductively coupled to the cup and having an inner conductor coupled to the other of said oppositely poled electrodes inside the cup; e. strain relief means comprising a hollow ferrule extending through each opening and fixed in the side wall of the cup and leading thereinto, and the cable means passing through a ferrule and fixed thereto; and f. sealing means for sealing the cup and the portions of the cable means entering said ferrules against entry of moisture.