Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-10-10
2001-11-27
Mullen, Thomas (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C235S449000, C340S551000
Reexamination Certificate
active
06323770
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the exploitation of magnetic properties in a range of practical techniques, and utilizes a new technique of spatial magnetic interrogation in conjunction with a magnetic marker or identification tag. More particularly, but not exclusively, the invention relates to methods of determining the presence and/or the location of a magnetic marker or tag within an interrogation zone; to methods of identifying a magnetic tag (e.g. identifying a given tag in order to discriminate that tag from others); to systems for putting these methods into practice; to magnetic tags for use in such methods and systems; and to the storage of data in such tags, and the subsequent remote retrieval of data from such tags.
It should be understood that the terms “tag” and “marker” are used herein interchangeably; such devices may be used in many different applications and, depending on the magnetic qualities of the device, may serve to denote (a) the mere presence of the tag (and hence that of an article to which the tag is attached); or (b) the identity of the tag (and hence that of an article to which it is attached); or they may serve to define the precise position of the tag with respect to predetermined coordinates (and hence that of an article to which it is attached); or they may serve to provide access codes (e.g. for entry into secure premises; or for ticketing purposes, e.g. on public transport networks); or they may serve generally to discriminate one article or set of articles from other articles.
In addition, the terms “AC field” and “DC field” are used herein to denote magnetic fields whose characteristics are, respectively, those associated with an electrical conductor carrying an alternating current (AC) or a direct current (DC).
The tags, methods and systems of this invention have a wide variety of applications as indicated above. These include (but are not restricted to) inventory control, ticketing, automated shopping systems, monitoring work-in-progress, security tagging, access control, anti-counterfeiting, and location of objects (in particular the precise positioning of workpieces (e.g. probes in surgery)).
PRIOR ART
There are a number of passive data tag systems currently available. The most widely-used is based on optically-read printed patterns of lines, popularly known as barcodes. The tag element of such systems is very low-cost, being typically just ink and paper. The readers are also relatively low cost, typically employing scanning laser beams. For many major applications the only real drawback to barcodes is the need for line-of-sight between the reader and the tag.
For applications where line-of-sight is not possible, systems not employing optical transmission have been developed. The most popular employ magnetic induction for coupling between the tag and the interrogator electronics. These typically operate with alternating magnetic fields in the frequency range of 50 kHz to 1 MHz, and generally employ integrated electronic circuits (“chips”) to handle receive and transmit functions, and to provide data storage and manipulation. In order to avoid the need for a battery, power for the chip is obtained by rectification of the interrogating signal received by an antenna coil. In order to increase the power transferred, and to provide discrimination against unwanted signals and interference, the coil is usually resonated with a capacitor at the frequency of the interrogation signal carrier frequency. A typical product of this type is the TIRIS system manufactured by Texas Instruments Ltd.
Other multi-bit data tag systems have employed conventional h.f. radio technology, or technologies based on surface acoustic waves or magnetostriction phenomena.
FIELD OF THE INVENTION
The present invention involves, inter alia, the use of a new type of passive data tag system which employs small amounts of very high-permeability magnetic material, and a scanned magnetic field for interrogation. Since the magnetic material can be in the form of a thin foil, wire or film, it can be bonded directly to a substrate, e.g. paper or a plastics material, to form self-supporting tags.
Alternatively, the magnetic material may be incorporated into the structure of an article with which the tag is to be associated; thus a tag may be formed in situ with the article in question by applying the magnetic material to the surface of the article, or by embedding the magnetic material within the body of the article.
The invention exploits magnetic fields which contain a “magnetic null”—this term is used herein to mean a point, line, plane or volume in space at or within which the component of the magnetic field in a given linear direction is zero. The volume in space over which this condition is met can be very small—and this gives rise to certain embodiments of the invention in which precise position is determined. Typically the magnetic null will be extant over a relatively small linear range. It should be understood that, where there is a magnetic null, it is possible (and is often the case) that the magnetic field component in a direction orthogonal to the given linear direction will be substantial. In some embodiments of this invention, such a substantial orthogonal field is desirable.
One way of creating the magnetic null is to employ opposing magnetic field sources. These may be current-carrying coils of wire, or permanent magnets (these being well suited to small-scale systems), or combinations of coil(s) and permanent magnet(s). It is also possible to exploit the magnetic nulls which exist in specific directions when a single coil or permanent magnet is used.
For large scale applications, the magnetic field sources are preferably coils carrying direct current.
The invention also utilizes the relative movement between a magnetic marker and an applied magnetic field in order to effect passage over the marker of the magnetic null. This can be achieved by moving the marker with respect to the applied magnetic field, or by holding the marker in a fixed position while the magnetic field is scanned over it. Generally, the invention exploits the difference between the magnetic behavior of the marker in (i) a zero field (at the magnetic null), and (ii) in a high, generally saturating, magnetic field.
TAGS OF THIS INVENTION
According to one aspect of the present invention, there is provided a magnetic marker or tag which is characterized by carrying a plurality of discrete magnetically active regions in a linear array. The discrete magnetically active regions may be supported on a substrate, e.g. paper or a plastics material, or they may be self-supporting. Alternatively, the magnetic elements may be incorporated directly into or onto articles during, manufacture of the articles themselves. This is appropriate, for example. when the articles are goods, e.g,. retail goods, which carry the tags for inventory purposes; or when the articles are tickets or security passes.
A tag as defined above can also be formed from a continuous strip of high permeability material, discrete regions of which have their magnetic properties permanently or temporarily modified. It will be appreciated that such a process can begin with a high permeability strip selected regions of which are then treated so as to modify their magnetic properties, generally by removing or reducing their magnetic permeability; or with a strip of high permeability magnetic material accompanied by a magnetizable strip positioned close to the high permeability magnetic material, e.g. overlying it or adjacent to it, selected regions of which are magnetized. In relatively simple embodiments, each magnetically active region has the same magnetic characteristics; in more complex embodiments, each magnetically active region can possess a different magnetic characteristic, thus making it possible to assemble a large number of tags, each with unique magnetic properties and hence with a unique magnetic identity and signature (when processed by a suitable reader device).
Because the invention utilizes relative mo
Flying Null Limited
Mullen Thomas
Oppenheimer Wolff & Donnelly LLP
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