Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1994-09-06
1996-11-19
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340551, G08B 13187
Patent
active
055766935
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and a device for remote sensing of objects. Within trade and industry the interest in non-optical and non-contact sensing of objects have increased lately. In stores and superstores it is interesting to read price labels and similar elements, and within the industry it is desirable to read identification labels in industrial materials flows. A plurality of non-optical and non-contact principles of identification of labels are used at present. Most common is perhaps antitheft labels in shops.
In a commonly used embodiment in trading, labels are used which are provided with a resonant circuit comprising a capacitive and an inductive element. Said resonant circuit can be forced to resonance by applying an electromagnetic signal having a defined energy content at the resonant frequency to said label in an interrogation zone normally provided at the exit of the shop. A detection device detecting signals from said resonant circuit at the resonant frequency produces an alarm if a label provided with an "activated" resonant circuit enters into said interrogation zone. A practical embodiment of a resonant circuit intended for this purpose is disclosed in U.S. Pat. No. 4,578,654. A complete system includes also a device for "deactivating" said label which is done on payment of the merchandise on which the label is attached to.
A problem of all previously known labels used for the purpose of limiting pilferage is a lack of ability of individually identifying each label when a plurality of labels is present simultaneously in said interrogation zone. For the purpose mentioned the problem is not relevant because an alarm should be delivered independently if one or a plurality of labels having an "activated" resonant circuit enters into said interrogation zone and is detected.
SUMMARY OF INVENTION
The method according to the present invention is based on the fact that certain magnetic and mechanical properties of elements shaped as tapes, wires or strips of amorphous materials are changed when the elements are exposed to a magnetic field, a so called bias field. The position/direction of an element is for instance related to the magnetic field in the longitudinal or axial direction of the amorphous element, and the mechanical resonant frequency of the element is a measure of the position/direction of the element. Corresponding conditions apply for a component comprising an amorphous element which is magnetically coupled to an inductive element in turn included in an electrical resonant circuit. When the magnetic field is changed the magnetic properties of the amorphous element are changed, and by that the inductance of said inductive element is changed. Then also the resonant frequency of the electrical resonant circuit is changed.
Also materials other than amorphous materials can be used according to the invention. The essential property of the material is that the characteristics thereof, for instance magnetic or elastic properties, are effected by magnetic fields. The influence must have such an extent that the change of properties is measurable by remote detecting, i.e. without establishment of a physical contact with said elements. It is also possible to use other materials, the electric or magnetic properties thereof being changed by an external magnetic field. An example is a material that is magnetoresistive, that is the electrical conductivity thereof being changed depending on a magnetic field, and a magnetooptical material, that is a material the light conducting ability thereof is changed depending on an applied magnetic field. For materials of said latter type a phenomenon referred to as the FARADY EFFECT is utilized, that is that the plane of oscillation of polarized light is pivoted, the pivoting angle being proportional to the magnetic field strength, or the phenomenon referred to as the KERR EFFECT, according to which a similar effect appears in some materials under influence of an electrical field.
The resonant frequency of an amorphous e
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Persson Leif
Tyren Carl
RSO Corporation N.V.
Swann Glen
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