In-line stress/strain detector

Claim 1

A detector to be buried in a particulate medium and operative to generate signals in response to stressing of said medium and to deliver the signals to a monitoring circuit, comprising: a. an elongated assembly comprising multiple successive signal-generating detector units connected by cable means to said monitoring circuit; and b. each detector unit comprising multiple sets of paired opposed plates of magnetic material, the opposed plates being spaced apart in the direction of the thickness dimension of the unit at their central portions and the sets of plates having contiguous edges aligned with each other along the length dimension of the detector unit which is great as compared with its width and which edges closely approach each other to form air gaps, magnet means extending longitudinally between the central portions of the paired plates and spaced from their lateral edges and said magnet means having opposed poles spaced in the direction of the thickness dimension and located contiguous to the respective plates, a winding surrounding the width and entire length of the magnet means and disposed in the space between the lateral edges of the plates and the magnet means, and said winding being coupled to the cable means, and resilient strip means interposed between a plate of each pair and said magnet means and yieldably maintaining the air gaps by keeping the plates mutually separated at their peripheries.