Registers – Records – Magnetic
Reexamination Certificate
1998-10-09
2002-04-16
Frech, Karl D. (Department: 2876)
Registers
Records
Magnetic
C235S488000, C235S449000, C235S462010
Reexamination Certificate
active
06371379
ABSTRACT:
This invention relates to magnetic tags or markers, to systems for storing data in such tags and for subsequently retrieving the data remotely, and to methods utilising such tags and systems.
Such tags and systems have a wide variety of applications. These include inventory control, ticketing, automated shopping systems, monitoring work-in-progress, security tagging and access control, anti-counterfeiting and item verification.
1. 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.
2. The Invention
The present invention relates to a new type of passive data tag system which employs small amounts of very high-permeability magnetic material, and an alternating 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 paper or plastic to form self-supporting tags.
More particularly, according to one aspect of the present invention there is provided a magnetic marker or tag, which comprises (a) a first magnetic material characterised by high permeability, low coercivity and a non-linear B-H characteristic; and (b) a second magnetic material which is capable of being permanently magnetised, characterised in that said second magnetic material is magnetised with a non-uniform field pattern.
Appropriate manufacturing techniques for the new label are well-known in conventional label manufacture, and in particular in the manufacture of 1-bit labels for retail security applications. Alternatively, the magnetic elements could be incorporated directed into the items to be tagged during manufacture.
In such a tag, the field pattern in the second material may vary in amplitude and/or direction and/or polarity. The second magnetic material is advantageously formed of discrete, magnetised sections of a magnetic bias material, e.g. a plastics material substrate coated with a ferromagnetic layer or film, e.g. of ferrite. The desired magnetic field pattern may be written onto a strip or tape of magnetic bias material. Thus it is possible to use audio or video recording tape as the bias material.
The magnetic field pattern may vary across the width of said strip or tape as well as along its length.
Preferably, the first magnetic material has an extrinsic relative permeability greater than 10
3
and a coercivity not more than 10 A/m. In one embodiment, the first magnetic material takes the form of an elongate strip or wire; in another, it is in the form of a thin film. When a strip form of first magnetic material is used, it preferably has dimensions in the ranges: width—from 0.1 mm to 10 mm, more preferably from 0.5 mm to 5 mm; and thickness from 5 &mgr;m to 500 &mgr;m, more preferably from 10 &mgr;m to 100 &mgr;m. When in thin film form, the first magnetic material is advantageously in the form of one or more patches each having an area in the range 1 mm
2
to 500 mm
2
, preferably from 10 mm
2
to 100 mm
2
. Such patches may each have a thickness in the range from 0.1 &mgr;m to 10 &mgr;m.
If desired, the said first and second magnetic layers may be supported by a substrate formed of paper or a plastics material. Such a support, however, may not be required. The tag will generally be adapted to be secured to an article to serve as an identifying tag for that article. It may, for example, be used as an antipilferage or anti-counterfeiting tag. It may alternatively be used as a verification tag. In this context, it may for example be used to confirm that an article has been assigned to its proper position during a sorting or distribution process.
According to another aspect, the present invention provides a data storage and retrieval system which comprises a plurality of magnetic markers or tags as claimed in claim 1 and a detection system comprising (i) first means for generating an alternating magnetic field; (ii) second means for detecting harmonics generated by the interaction between the first magnetic material of the tag and the alternating magnetic field produced in use by said first means; and (iii) third means for correlating the detection of harmonics by said second means with the alternating magnetic field generated by said first means.
In such a data storage and retrieval system, the third means is preferably arranged to determine the amplitude and phase of the harmonics generated by the interaction of the first magnetic material of the tag and the alternating magnetic field, the harmonics of interest normally being selected from harmonics in the range of 2nd to 100th. The third means may be arranged to determine the characteristics of the harmonics produced by the marker and to compare the detected characteristics with information in a data bank, this information serving to correlate the detected characteristics with known characteristics relating to items on an inventory.
In one embodiment, the third means is arranged to determine the number of harmonic bursts detected per cycle of the generated alternating magnetic field. Alternatively, the third means may be arranged to determine the point or points within each cycle of the alternating magnetic field at which harmonic bursts are detected.
In preferred embodiments, the detection system is arranged to determine the characteristics of harmonic bursts produced by the tag or marker and to compare the detected characteristics with information in a data bank, this information serving to correlate the detected characteristics with known characteristics relating to items on an inventory. The characteristics selected for analysis may include the shape of the envelope of said harmonic bursts.
The means for generating an alternating magnetic field is advantageously arranged so that, in use, it generates a first, high frequency alternating magnetic field and a second,. low frequency alternating magnetic field. For example, the high frequency alternating magnetic field may be at a frequency in the range of from 250 Hz to 20 kHz, advantageously in the range from 3 kHz to 10 kHz; and the low frequency alternating magnetic field may be at a frequency in the range of from 1 Hz to 250 Hz, advantageously in the range of from 5 Hz to 50 Hz.
Currently preferred interrogation systems are adapted to generate a high frequency alternating magnetic field at a frequency in the range of from 1 kHz to 10 kHz, e.g. from 4 kHz to 8 kHz, and a low frequency alternating magnetic field at a frequency in the range of from 8 Hz to 50 Hz, e.g. from 10 Hz to 20 Hz.
The system will typically operate with a high frequency alternating magnetic field in the range 1 kHz-10 kHz, together with a low
Crossfield Michael David
Dames Andrew Nicholas
Flying Null Limited
Frech Karl D.
Oppenheimer Wolff & Donnelly LLP
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