Marking strip for object detection monitored zone - has high permeability strip and narrower high coercivity strip

摘要

A marking element for detecting objects in a monitored zone is esp. for prevention of shop-lifting. An alternating magnetic field induces h.f. harmonic oscillations in the element which contains strips of high permeability and high coercivity materials. It is economical to make, contains little magnetic material, and is not easily deactivated. The high coercivity material strip is narrower than the high permeability strip by a factor between 0.1 and 0.75. The cross-section of the high coercivity material strip is chosen to ensure that its magnetic moment when magnetised by the field is not sufficient to saturate the strip of high permeability material. The element produces an identifiable signal when the high coercivity strip is magnetised. The total width of the strip is only a few millimetres.