Emi, LLC

Thorn Emi Plc

David J Sansom

Robert A Woolley

Simon N Willcock

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.

E.A.S. tag having a control component with selectively magnetizeable

A permanently structured magnetic recording tape includes a pattern of first and second regions of acicular iron oxide particles, the first `A` regions being orientated at 22.5.degree. (clockwise) to the tapes axis and the second `B` regions being orientated at 67.5.degree. (clockwise) to the tape axis. A permanent magnet applies a developing field at 45.degree. (anti-clockwise) to the tape axis such that, at the transition in orientation direction, the normal components of remanence in `A` and `B` regions are in opposite directions, thereby increasing pole strength at the transitions compared with longitudinal development, and enhancing the output signal at the magnetoresistive read-out transducer. A second magnetoresistive transducer senses fluctuations in magnetic polarity at the tape edge to verify whether the medium is genuine.

Magnetic recording

A sensing element suitable for sensing two components h.sub.x and h.sub.y of an external magnetic field in an orthogonal co-ordinate system comprises a reverse C-shape first electrical conductor vacuum deposited onto an electrical insulating substrate. A layer of photoresist applied to a region insulates the conductor from a magnetoresistive element which has two connectors linked thereto. Further application of photoresist insulates the element from a second vacuum deposited electrical conductor. Wires locate with respective conductors where gold deposition in the vicinity of the wire ends achieves electrical continuity. A control circuit applies current, within a periodic cycle, in alternate directions through the first conductor while a current is applied in a single direction through the second conductor. In the following cycle the current direction through the second conductor is reversed. Values of the element electrical resistivity for the four combination of current (and hence magnetic field) directions allow solution of a simultaneous equation to yield h.sub.x and h.sub.y.

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Chertsey, United Kingdom

David J Sansom