Pressure sensitive intrusion sensing line

Claim 1

An intrusion sensing line to be buried below the surface of a medium and operative to deliver electrical signals in response to pressure changes in the medium resulting from intrusive stresses applied thereto, comprising: (a) multiple sealed metal transducer shells respectively spaced apart along said sensing line and joined together by multiple lengths of flexible metal tubing, the lengths having ends which extend into and terminate within the shells, the tubing and shells being sealed together by metal-to-metal bonding, and each transducer shell having one flat face comprising a diaphragm which is flexible in response to said pressure changes; (b) a transducer unit inside each shell comprising a thin insulating board having one side overlying and bonded to said diaphragm face and having a flat piezoceramic transducer member bonded to its other side, the member comprising a piezoceramic disc with first and second electrodes bonded to its faces, the insulating board and transducer member and electrodes being operative to flex with said diaphragm face of the shell; and (c) two insulated wires extending through the lengths of tubing and the shells comprising the sensing line, and the wires being coupled respectively with the first and second electrodes in each shell.