AU738834B2 - Device for reading magnetic tags - Google Patents

Description

S&F Ref: 398004D2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S

I.

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Flying Null Limited Harston Mill, Harston Cambridgeshire CB2 United Kingdom Andrew Nicholas Dames Spruson Ferguson St Martins Tower 31 Market Street Sydney NSW 2000 Device for Reading Magnetic Tags The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c -1- DEVICE FOR READING MAGNETIC TAGS This application is divided out of Application No.

AU 52806/96(hereinafter termed "the parent application").

The parent application relates to the exploitation of magnetic properties in a range of practical techniques, and utilises a new technique of spatial magnetic interrogation in conjunction with a magnetic marker or identification tag. More particularly,_ it 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 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 the mere presence of the tag (and hence that of an article to which the tag is attached); or 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 co-ordinates (and hence that of an article to which it is attached); or they may serve to provide access codes 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 -2articles.

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 the invention disclosed in the parent application 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, 15 anti-counterfeiting, and location of objects (in particular the precise positioning of workpieces [e.g.

probes in surgery]). Full details of the magnetic interrogation technique on which these various practical applications are based are found in the 20 parent application (AU 52806/96) and in International ~Patent Application No. PCT/GB97/00823 (published as WO 96/31790 and hereinafter referred to as "the PCT application") from which it is derived.

The parent application describes and claims a method of interrogating a magnetic element having non- S" ilinear magnetic properties, which is characterised by the steps of: applying a magnetic field to an interrogation zone where the magnetic element is, or is expected to be, located, said magnetic filed being: (i) generated by magnetic field generating means positioned independently of said magnetic element; and (ii) such that a magnetic null as herein defined is generated within said interrogation zone, the magnetic null being contiguous with regions where the applied magnetic field is sufficient to saturate the, or a part of the, -3magnetic element; causing relative movement between said magnetic field and said magnetic element such that at least a portion of the magnetic element becomes magnetically saturated and then enters the magnetic null; and detecting the magnetic response of the magnetic element during said relative movement.

The present invention is concerned with a tag reader which comprises a plurality of permanent magnets disposed in a circular array around a gap, the poles of said permanent magnets being disposed so that each of the magnets has its pole of one polarity (for example North) positioned on the inside of the circular array, and its pole of the opposite polarity (for example South) positioned on the outside of the circular array; and a coil disposed coaxially with said circular array adjacent to said permanent magnets. The permanent magnets are preferably polymer-bonded ferrite magnets.

20 A tag reader as defined above may be incorporated into a position sensor which detects the position of an article carrying or including a magnetic tag. It may, for example, detect the tag as it passes through a magnetic null located in the centre of the device.

A device in accordance with this invention is expected to be of use in some of the interrogation methods described and claimed in the parent application.

The invention will now be illustrated with reference to the accompanying drawing, which illustrates a loop reader head which utilises a plurality of permanent magnets disposed in an annular array with a coil to generate the desired field pattern. As illustrated, ten polymer-bonded ferrite -4magnets are disposed in an annular array with like poles facing inwards. A common transmit/receive coil LI sits within the annulus of magnets in the manner indicated. The tag is read as it passes through the null plane in the centre of the loop of magnets.

o S 00 *oe *oe

Claims (4)

1. A tag reader which comprises a plurality of permanent magnets disposed in a circular array around a gap, the poles of said permanent magnets being disposed so that each of the magnets has its pole of one polarity (for example North) positioned on the inside of the circular array, and its pole of the opposite polarity (for example South) positioned on the outside of the circular array; and a coil disposed coaxially with said circular array adjacent to said permanent magnets.

2. A reader as claimed in claim 1, wherein said permanent magnets are polymer-bonded ferrite magnets.

3. A position sensor which includes a reader as claimed in claim 1 or 2.

4. A tag reader substantially as hereinbefore described. Dated 18 February, 2000 Flying Null Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON