Spatial magnetic interrogation
First Claim
1. A method of determining the position of a magnetic element, or the relative positions of two or more magnetic elements on a tag, the magnetic element(s) having non-linear magnetic properties and a preferential axis of magnetisation, the method comprising the steps of:
- (a) applying a magnetic field to an interrogation zone where the magnetic element(s) is or are located, or is or are expected to be located, said magnetic field being;
(i) generated by magnetic field generating means positioned independently of said magnetic element(s);
(ii) such that there exists within said interrogation zone a first region at which the component of the magnetic field resolved in a first direction is zero, and where in regions contiguous with said first region the component of the magnetic field resolved in said first direction is sufficient to saturate the, or a part of the, magnetic element(s); and
(iii) such that said first direction is or can be aligned with the preferential axis of magnetisation of the or each magnetic element;
(b) causing relative movement between said magnetic field and said magnetic element(s) in the direction of the preferential axis of magnetisation of the magnetic element(s) such that at least a portion of the magnetic element, or of each of the magnetic elements in turn, become magnetically saturated and then enters said first region;
(c) detecting the magnetic response of the or each magnetic element during said relative movement; and
(d) determining the position of the magnetic element, or the relative positions of the magnetic elements, from the time(s) of occurrence of the or each magnetic response.
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Accused Products
Abstract
Magnetic tags or markers are disclosed, together with a variety of techniques by means of which such tags may be interrogated. In one aspect, the magnetic marker or tag which is characterized by carrying a plurality of discrete magnetically active regions in a linear array. In another aspect, the invention provides a method of interrogating a magnetic tag or marker within a predetermined interrogation zone, the tag comprising a high permeability magnetic material, for example to read data stored magnetically in the tag or to use the response of the tag to detect its presence and/or to determine its position within the interrogation zone, characterized in that the interrogation process includes the step of subjecting the tag sequentially to: (1) a magnetic field sufficient in field strength to sacurate the high permeability magnetic material, and (2) a magnetic null as herein defined. Applications of such techniques are describer, inter alia, in relation to (a) identifying articles to which tags are attached; (b) accurate determination of position, as in the location of surgical probes; and (c) totalisation of purchases, where cash item carries a tag coded with data representing its nature and its price.
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Citations
21 Claims
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1. A method of determining the position of a magnetic element, or the relative positions of two or more magnetic elements on a tag, the magnetic element(s) having non-linear magnetic properties and a preferential axis of magnetisation, the method comprising the steps of:
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(a) applying a magnetic field to an interrogation zone where the magnetic element(s) is or are located, or is or are expected to be located, said magnetic field being; (i) generated by magnetic field generating means positioned independently of said magnetic element(s); (ii) such that there exists within said interrogation zone a first region at which the component of the magnetic field resolved in a first direction is zero, and where in regions contiguous with said first region the component of the magnetic field resolved in said first direction is sufficient to saturate the, or a part of the, magnetic element(s); and (iii) such that said first direction is or can be aligned with the preferential axis of magnetisation of the or each magnetic element; (b) causing relative movement between said magnetic field and said magnetic element(s) in the direction of the preferential axis of magnetisation of the magnetic element(s) such that at least a portion of the magnetic element, or of each of the magnetic elements in turn, become magnetically saturated and then enters said first region; (c) detecting the magnetic response of the or each magnetic element during said relative movement; and (d) determining the position of the magnetic element, or the relative positions of the magnetic elements, from the time(s) of occurrence of the or each magnetic response. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of determining the location of an object, which comprises the steps of:
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(a) securing to the object at least one magnetic element in the form of a small piece of a magnetic material having non-linear magnetic properties and a preferential axis of magnetisation, (b) applying a magnetic field to an interrogation zone where the magnetic element(s) is or are located, or is or are expected to be located, said magnetic field being; (i) generated by magnetic field generating means positioned independently of said magnetic element(s); (ii) such that there exists within said interrogation zone a first region at which the component of the magnetic field resolved in a first direction is zero, and wherein in regions contiguous with said first region the component of the magnetic field resolve din said first direction is sufficient to saturate the, or part of the, magnetic element(s); and (iii) such that said first direction is or can be aligned with the preferential axis of magnetisation of the or each magnetic element; (c) causing relative movement between said magnetic field and said magnetic element(s) in the direction of the preferential axis of magnetisation of the magnetic element(s) such that at least a portion of said magnetic element(s) becomes magnetically saturated and then enters said first region; (d) detecting the response of the magnetic element(s); and (e) calculating the position of the object from a consideration of said magnetic response and from the known parameters relating to said applied field and to the properties of the said magnetic material. - View Dependent Claims (18, 19, 20)
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21. A method of totalising data from an assembly of individual articles, each carrying a magnetic tag having a particular spatial arrangement of magnetic zones, said spatial arrangement being chosen such that the lengths and spacings between the zones represent a particular code sequence unique to that article and others sharing the same data value, characterised in that the assembly of articles is caused to move through a interrogation zone where the assembly is subjected to a series of steps comprising:
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(i) applying to each article a small piece of magnetic material; (ii) applying to the interrogation zone a magnetic field in which there exists a first region, where the component of the magnetic field resolved in a first direction is zero, and a region contiguous with said first region, in which the component of the magnetic field resolved in said first direction is sufficient to saturate the, or part of the, magnetic zones; (iii) for each article, (a) causing relative movement between said article and said magnetic field such that each of the said magnetic zones of the tag are traversed by the magnetic field or vide versa; (b) observing the magnetic interaction between said applied magnetic field and said magnetic zones; (c) determining the relative positions of the magnetic zones from the relative times of occurrence of the or each magnetic interaction; and (d) deducing the unique article identity and hence its data value, from the determined positions of the said magnetic zones by reference to the spatial arrangement chosen to encode the tag; and (iv) summing the data values of the individual articles.
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Specification