Abstract: A coil (6) forming part of a tuned circuit (8) is wound around a gapped magnetic core (2). As a magnetic stripe (14) is passed under core (2), variations to the amplitude and frequency of the circuit (8) occur dependent upon the magnetic data on the strip (14). Selected data are manipulated to derive several values (32, 36, 38, and 40) for combination via AND-gate (47). Only if the combination value is above a threshold value is an indication given that the stripe (14) is genuine and not an attempted copy.

Abstract: A tag for use with an electromagnetic identification system includes a magnetic control component 1, having alternating regions 10, 20 of, respectively, high and medium coercivity material, and an element 30 of magnetically soft material. The element 30 may be polarized so as to deactivate the tag by, for example, selectively demagnetizing the regions 20 of medium coercivity, such as by exposing the tag to an alternating magnetic field having an initial field strength which is intermediate between the coercivity of the regions 10, 20, which may be formed as a striped coating or from a number of discrete magnetic components.