Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1992-06-05
1995-10-03
Peng, John K.
Communications: electrical
Condition responsive indicating system
Specific condition
340572, G08B 1324
Patent
active
054555639
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the modification of the magnetic properties of materials, and in particular in respect to the performance of high-permeability magnetic materials used in anti-pilferage or article location systems.
Certain types of markers used in anti-pilferage systems or article location systems rely for their detection and recognition on the magnetic response of a component or components of the marker to an applied varying magnetic field. Desirable magnetic properties include high but well-defined magnetic permeability, low hysteresis, and well-defined response non-linearities such as are found at the approach to magnetic saturation. It is known that the physical dimensions and shapes of the magnetic components are important in determining their response and performance in the systems. The present invention is concerned with the modification and in particular the improvement of the performance of these components by surface modulations added during manufacture within the component, perhaps in conditions where it is not possible of desirable to change the main shape or dimensions of the component.
SUMMARY OF THE INVENTION
Examples of these components include strips, sheets or thin films of high-permeability amorphous, crystalline or mixed-phase magnetic material, such as strips of melt-spun amorphous magnetic alloy or thin films of magnetic alloy deposited upon a substrate.
According to one aspect of the present invention, there is provided a method of modifying the magnetic properties of a thin film of a magnetically active material, which comprises forming surface modulations on said material in order to partition the material into regions which display at least some degree of mutual magnetic independence.
According to a second aspect of the present invention, there is provided a marker or tag for use in an anti-pilferage or article location system, which marker includes a thin film of a magnetically active material supported on a substrate, characterised in that said magnetically active material has formed on it surface modulations which partition said material into regions which display at least some degree of mutual magnetic independence.
Generally, the magnetically active material will be a high-permeability, low-coercivity material and will be supported on a substrate.
The surface modulations are advantageously formed by a technique involving the removal of material from the film; the technique may involve the application of a blade or sharpened point to the surface of said material, or removal of material by chemical means. Preferred techniques include cutting, scribing, perforation and scratching. Advantageously, less than 25% of the magnetically active material is removed. In most embodiments, less than 5% of the magnetically active material is removed, and in the currently preferred embodiments between 0.1% and 1% is removed.
Alternatively, the surface modulations may be formed by a technique which does not remove material from the thin film, for example by a technique which is such as to cause localised plastic deformation of the magnetically active material. Examples of suitable techniques are stamping, cracking or folding the thin film. The surface modulations may also be formed by means of impregnation or localised heating. This can be achieved by means of focused electromagnetic radiation, laser radiation, ion beams, beams of neutral particles, jets of solid particles or jets of liquids.
In other embodiments, the surface modulations are formed by means of localised application of further quantities of the same magnetically active material or of a different magnetically active material.
The surface modulations are preferably such as to change the effective magnetic permeability of the material with little effect on its total saturation magnetisation. They also advantageously reduce the coercive force for high-frequency excitation of the magnetically active material.
In summary, techniques of use in the present invention include cutting (fully or par
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Chambers Stephen H.
Davies Dafydd G.
Esselte Meto International Produktions GmbH
Mullen Jr. Thomas J.
Peng John K.
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