Responder target for theft detection apparatus

Abstract

A responder target for a magnetic detection system includes a signal element of high permeability low coercivity magnetic material such as permalloy or amorphous metal, and a control element of ferric oxide powder having the formula Fe.sub.3 O.sub.4 dispersed in a polymer binder. The ferric oxide powder having a coercivity H.sub.c in the range of 50-150 Oe and a particle size of 20-100 .mu.m, dispersed 20-35% by weight in the polymer binder. The ferric oxide powder in the binder is coated on a substrate to form a control element strip, laminated to the signal element, and chopped into lengths to form the responder target. Alternatively, the signal element strip is laminated to a support layer, and the ferric oxide is coated by extrusion over the signal element.

Dependencies are inferred from the claim text.