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WO2007030862A1 - Dispositif d'attenuation d'une antenne d'un interrogateur - Google Patents

Dispositif d'attenuation d'une antenne d'un interrogateur Download PDF

Info

Publication number
WO2007030862A1
WO2007030862A1 PCT/AU2006/001319 AU2006001319W WO2007030862A1 WO 2007030862 A1 WO2007030862 A1 WO 2007030862A1 AU 2006001319 W AU2006001319 W AU 2006001319W WO 2007030862 A1 WO2007030862 A1 WO 2007030862A1
Authority
WO
WIPO (PCT)
Prior art keywords
coil
conductive loop
interrogator
loop
magnetic
Prior art date
Application number
PCT/AU2006/001319
Other languages
English (en)
Inventor
Graham Alexander Munro Murdoch
Stuart Colin Littlechild
Original Assignee
Magellan Technology Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2005904989A external-priority patent/AU2005904989A0/en
Application filed by Magellan Technology Pty Ltd filed Critical Magellan Technology Pty Ltd
Publication of WO2007030862A1 publication Critical patent/WO2007030862A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
    • H01Q7/04—Screened antennas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
    • H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
    • H01Q1/2216—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in interrogator/reader equipment

Definitions

  • the present invention relates to the field of radio frequency identification (RFID).
  • RFID radio frequency identification
  • the invention relates to an interrogator antenna for interrogating an RFID transponder
  • the invention has been developed primarily for interrogating multiple passive transponders which are attached to objects to be identified by those respective transponders and will be described hereinafter with reference to that application.
  • a typical application is the identification of RFID transponders or other FRID devices, such as those embedded in plastic tokens or cards that are stacked on each other.
  • interrogators use antenna coils to generate an oscillating magnetic field which interrogates or excites an RFID transponder.
  • These interrogator antennae have generally been open frame coils. Where strong magnetic fields are required (roughly greater than 1A/m) and the coils are larger than about 0.3m x. 0.3m these coils tend to emit high levels of stray magnetic fields which can contravene occupational health and safety (OH&S) regulations and/or electromagnetic emission (EM) regulations.
  • O&S occupational health and safety
  • EM electromagnetic emission
  • the housing is preferentially made of a high conductivity metal such as copper or aluminium. Although poorer conductivity metals have also been used they are less desirable due to their higher losses and the greater wall thickness required to adequately screen the fields. Leakage of the fields out of the entrance and exit ports must also be suppressed and special suppression structures are available.
  • TRP Tunnel Reader Programmer
  • TRP has excellent shielding properties
  • a major drawback is that it is only suitable for applications where the RFID transponders are moved in and out of the TRP, usually on a conveyor or similar.
  • TRP are inherently unsuitable for applications requiring the interrogator to operate on a flat surface such as a table or wall.
  • flat planar antenna coils are required however these coils can suffer from high stray field emissions levels. Due to the reciprocal nature of the magnetic field they are also susceptible to interference from external sources. Since the radiation of stray fields and the reception of external interference are reciprocal reducing either one inherently reduces the other.
  • Figure 1 illustrates a number of prior art methods employed.
  • the stray fields can be reduced by winding the coil as a figure of eight so that the magnetic field generated by each half of the coil is oppositely directed to the other half. In this way the fields from each half of the coil cancel at a distance.
  • the method of using counter wound coils to generate self cancelling fields at a distance can be extended to three (or more) coils provided the magnetic moment of the coils are designed to cancel each other.
  • An object of the present invention is to provide an improved shield for an antenna associated with an interrogator.
  • a further object of the present invention is to alleviate at least one disadvantage associated with the prior art.
  • the present invention provides, in an inventive aspect, an interrogator for and/or method of interrogating an RFID transponder, the interrogator comprising at least one coil for generating a magnetic interrogating field, and a conductive loop that is placed in proximity to at least one coil in at least one plane, the coil being positioned substantially within the conductive loop and the conductive loop being an electrical short circuit.
  • the present invention provides, in another inventive aspect, in an interrogator for interrogating an RFID transponder, the interrogator having at least one coil for generating a magnetic interrogating field, a conductive loop being formed of a relatively low reluctance material and being configured as an electrical short circuit and being adapted to be placed substantially around at least one of the at least one coil and in at least one plane.
  • the present invention provides, in a further inventive aspect, a method of attenuating a magnetic field emanating from an interrogator adapted to interrogate an RFID transponder, the method comprising the steps of generating a magnetic interrogating field with a coil; and providing a low impedance conductive loop proximate the coil, the loop being formed in a manner having an electrical short circuit.
  • the present invention provides, in yet another inventive aspect, an interrogator for interrogating an RFID transponder, the interrogator comprising at least one coil for generating a magnetic interrogating field, and a conductive loop that totally surrounds the coil, where the coil is positioned inside the conductive loop.
  • the present invention provides, in another inventive aspect, a method for interrogating an RFID transponder, the method comprising the steps of generating a magnetic interrogating field with a coil; and providing a low impedance conductive loop at the periphery of the coil for confining the generated magnetic field within the conductive loop.
  • the attenuation device of the present invention may be a shield.
  • an interrogator constructed in accordance with the preferred embodiments of the invention serve to confine the coils magnetic fieid within a conductive loop that surrounds the coii(s) reducing the fringing fields.
  • the field produced by an interrogator's coil induces eddy currents in the conductive loop.
  • These eddy currents produce their own field which in effect subtracts from the interrogator coil's field such that the total net field passing through the conductive loop is (nearly) zero and hence the fifed outside the conductive loop must also be (nearly) zero.
  • the present invention has been found to result in a number of advantages, such as: • The confined field will only read transponders ciose to the interrogator coil
  • Figure 1 illustrates an example of prior art methods of reducing stray magnetic fields
  • Figures 2(a) and 2(b) illustrate a three dimensional sketch and schematic cross sectional view of a coil and the generated magnetic field
  • Figures 3(a) to 3(b) illustrate a three dimensional sketch and schematic cross sectional view of the invention
  • Figure 4 illustrates a three dimensional sketch of the invention where there is more than one coil
  • Figure 5 iilustrates, in cross section, the magnetic fields associated with Figure 4 when only one coil is generating a magnetic field
  • Figure 6 illustrates an electrical model for .the coii and conductive loop combination
  • Figure 7 illustrates a set of equations that that represents how the conductive loop operates
  • Figure 8 illustrates two coils in close proximity, where the conductive loops serve to reduce the coupling between the coils;
  • Figure 9 illustrates the conductive loop being grounded to screen against electric fields.
  • the magnetic field can be calculated by vector addition of the magnetic field from each loop portion. Close to the coil to a distance less than or about the linear dimension of the coii, the field is dominated by the closet loop portion of the coil. At greater distances the fields from the other portion(s) of the coil add to the field and eventually at a distance of about 10 times the linear dimension of the coil, the fields will substantially cancel (effectively). This is provided that the total magnetic moment of the coils loops is zero. Clearly close to and adjacent the coil, the field is strong and transponders may be interrogated unintentionally.
  • Figures 2(a) and 2(b) show a three dimensional sketch and schematic cross sectional view of a coil and the generated magnetic field. As it can be seen, the magnetic field extends well beyond the coil boundaries.
  • Figures 3(a) and 3(b) shows a three dimensional sketch and schematic cross sectional view of an embodiment according to an aspect of the present invention where a conductive loop has been placed around the coil
  • the loop should have a very low resistance at the operating frequency.
  • the resistance should be less than 1 ohm and more preferably less than 100 milliohms and even more preferably 10 milliohms or less and be relatively coplanar with the coil, although proximity to the coil is acceptable.
  • the loop is made of aluminium or copper since these materials have a low resistance, however other suitable conductive and relatively low resistance materials may be used.
  • the loop effectively operates as a shorted loop through which the net magnetic flux is substantially zero because it is a short circuited loop.
  • Figure 4 illustrates a three dimensional sketch of the invention where there is more than one coil and Figure 5 illustrates, in cross section, the magnetic fields associated with Figure 4 when only one coil is generating a magnetic.
  • Figure 4 three coils are shown, although obviously, the present invention is applicable to any number of coils, and/or in any orientation. It is also applicable to more complex coil shapes such as the shapes shown in Figure 1. When one of these coils is active, the flux passing through the coil must equal the flux passing between the coi! and the loop as shown in Figure 5.
  • the three coil arrangement shown in Figure 4 has been found to be advantageous for reading transponders over a large area such as a table top, for example a gaming table.
  • Grounding the loop can also serve to screen the coil from external electric interference in the same manner as a faraday screen, as illustrated in figure 9.
  • Figure 6 shows an electrical model for the coil and conductive loop combination.
  • the coil is L1 driven by current H .
  • the conductive loop inductance and resistance are L2 and r2 respectively.
  • L2 is m.
  • Current 11 induces a voltage V2 in L2 and causes current I2 to fiow in L2.
  • Figure 7 illustrates a set of equations that represent the operation of the conductive loop.
  • Figure 8 shows two coils in close proximity where the conductive loops serve to reduce the coupling between the coils. Since the leakage field is small, the coils can be brought into . close proximity without compromising their performance. Also for the multi coil combination shown in Figures 4 and 5, a relatively small leakage current means that the return flux from each coil is substantially confined to be inside the conductive loop and hence transponders may be interrogated when substantially placed inside or proximate the conductive loop.
  • Figure 9 shows how the conductive loop may be grounded to screen against external eiectric fields.

Landscapes

  • Near-Field Transmission Systems (AREA)

Abstract

L'invention concerne un interrogateur destiné à interroger un transpondeur RFID, l'interrogateur comportant au moins une bobine qui génère un champ d'interrogation magnétique et une boucle conductrice, la bobine étant placée dans la boucle conductrice. De préférence, la boucle conductrice est à base d'aluminium ou de cuivre et fournit une boucle conductrice à impédance relativement faible à la périphérie de la bobine pour confiner le champ magnétique produit à l'intérieur de la boucle conductrice. De préférence, la bobine et la boucle conductrice sont coplanaires. Il peut y avoir plusieurs bobines placées de manière coplanaire avec et dans la boucle conductrice.
PCT/AU2006/001319 2005-09-12 2006-09-08 Dispositif d'attenuation d'une antenne d'un interrogateur WO2007030862A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2005904989A AU2005904989A0 (en) 2005-09-12 An Attenuation Device for an Antenna of an Interrogator
AU2005904989 2005-09-12

Publications (1)

Publication Number Publication Date
WO2007030862A1 true WO2007030862A1 (fr) 2007-03-22

Family

ID=37864546

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU2006/001319 WO2007030862A1 (fr) 2005-09-12 2006-09-08 Dispositif d'attenuation d'une antenne d'un interrogateur

Country Status (1)

Country Link
WO (1) WO2007030862A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009132019A3 (fr) * 2008-04-21 2009-12-30 Mu-Gahat Holdings, Inc. Mise en forme de champ h au moyen d’une boucle de court-circuit
US8395525B2 (en) 2008-02-25 2013-03-12 Magnet Consulting, Inc. Extending the read range of passive RFID tags
GB2495689A (en) * 2009-10-16 2013-04-24 Igt Reno Nev Delimiting betting zones in RFID enabled casino tables
US8432283B2 (en) 2008-01-11 2013-04-30 Magnet Consulting, Inc. Enhancing the efficiency of energy transfer to/from passive ID circuits using ferrite cores

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989007347A1 (fr) * 1988-02-04 1989-08-10 Uniscan Ltd. Concentrateur de champs magnetiques
WO1999049337A1 (fr) * 1998-03-23 1999-09-30 Magellan Technology Pty Limited Interrogateur pour interroger un repondeur rfid

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989007347A1 (fr) * 1988-02-04 1989-08-10 Uniscan Ltd. Concentrateur de champs magnetiques
WO1999049337A1 (fr) * 1998-03-23 1999-09-30 Magellan Technology Pty Limited Interrogateur pour interroger un repondeur rfid

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8432283B2 (en) 2008-01-11 2013-04-30 Magnet Consulting, Inc. Enhancing the efficiency of energy transfer to/from passive ID circuits using ferrite cores
US8988224B2 (en) 2008-01-11 2015-03-24 Magnet Consulting, Inc. Enhancing the efficiency of energy transfer to/from passive ID circuits using ferrite cores
US8395525B2 (en) 2008-02-25 2013-03-12 Magnet Consulting, Inc. Extending the read range of passive RFID tags
WO2009132019A3 (fr) * 2008-04-21 2009-12-30 Mu-Gahat Holdings, Inc. Mise en forme de champ h au moyen d’une boucle de court-circuit
US8395507B2 (en) 2008-04-21 2013-03-12 Magnet Consulting, Inc. H-field shaping using a shorting loop
US8981940B2 (en) 2008-04-21 2015-03-17 Magnet Consulting, Inc. H-field shaping using a shorting loop
GB2495689A (en) * 2009-10-16 2013-04-24 Igt Reno Nev Delimiting betting zones in RFID enabled casino tables
US8690678B2 (en) 2009-10-16 2014-04-08 Igt Shape control of magentic fields for table games
GB2495689B (en) * 2009-10-16 2014-05-07 Igt Reno Nev Shape control of magentic fields for table games

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