Antenna for reader/writer and reader/writer having the antenna

• US 20050162331A1
• Filed: 01/17/2003
• Published: 07/28/2005
• Est. Priority Date: 01/17/2002
• Status: Active Grant

• Current Assignee: Mitsubishi Materials Corporation
• Original Assignee: Mitsubishi Materials Corporation
• Inventors: Yahata, Seirou, Tsuchida, Takashi, Endo, Takanori
• Granted Patent: US 7,495,625 B2
• Time in Patent Office: Days
• US Class Current: 343/788
• CPC Class Codes: G06K 19/07771 the record carrier comprising means for minimising adverse effects on the data communication capability of the record carrier, e.g. minimising Eddy currents induced in a proximate metal or otherwise electromagnetically interfering object
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G06K 7/10346 the antenna being of the far field type, e.g. HF types or dipoles
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 1/52 Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure absorbing means H01Q17/00
• CPC Class Codes: H01Q 7/06 with core of ferromagnetic material H01Q7/02 takes precedence

Abstract

A soft magnetic member (5) which is formed by a composite of an organic object such as a metal grain powder, a flake, a ferrite grain powder, a ferrite, an amorphous film or a layered member of the amorphous film with 10 mm or lower thickness so as to satisfy a predetermined relationship with an antenna area, a circumference length, and a magnetic transmission ratio and a conductive member (7) which has approximately 10×10⁻⁸ Ωm or lower, more preferably 0.005 Ω or lower initial resistance are provided between the an antenna coil which is formed at least one loop and a metal surface (6) of the conductive member such as a metal casing. The magnetic flux which invades into the conductive object is blocked by the soft magnetic member (5) and the conductive member (7) so as to restrict the influence thereof. By doing this, it is possible to provide a reader/writer antenna for an RFID system in which it is possible to restrict a variance of a resonating frequency and an increase in a loss even if it is disposed so as to contact the conductive object such as a metal casing.

Claims

1. A reader/writer antenna which is used for an RFID system for non-contacting data communication wherein a plain soft magnetic member is disposed on a surface for disposing an object of the antenna coil which is formed by at least one turn.

3. A reader/writer antenna according to claim 1 or 2 wherein the soft magnetic member is formed so as to overlap a part of the antenna coil in an orthogonal view toward an antenna surface of the antenna coil;

and a magnetic flux which is generated by the antenna coil is formed asymmetrically with reference to a center axis of the antenna coil.

7. A reader/writer antenna according to any one of claims 1 to 6 wherein a thickness of a soft magnetic member or a thickness of a plain plate magnetic core is set to be approximately 10 mm or thinner.

8. A reader/writer antenna according to claim 1 wherein a thickness T for a soft magnetic member or magnetic core for the plain plate satisfies a relationship S/L>

t>

S/(L/μ

) under condition that S indicates an area for the antenna coil, L indicates a circumferential length of the antenna coil, and μ

indicates a magnetic transmittance ratio of the soft magnetic member.

9. A reader/writer antenna according to claim 1 wherein the soft magnetic member is a compound of either a metal power, a flake or a ferrite power which are formed by flattening a metal powder.

10. A reader/writer antenna according to claim 9 wherein the metal power is either one of a carbonyl iron powder, a reduced iron powder, an atomized power, or an amorphous powder.

11. A reader/writer antenna according to claim 9 wherein the metal power or the flake is a flake which is made by flattening a water-atomized iron base alloy or an iron base alloy power mechanically.

12. A reader/writer antenna according to claim 11 wherein the iron base alloy contains 6 w % to 15 w % of silicon.

13. A reader-writer antenna according to claim 11 wherein the iron base alloy contains at least approximately 1 w % of aluminum or lower, approximately 3 w % of nickel or copper lower, approximately 5 w % of chromium or lower, approximately 10 w % of cobalt or lower in addition to approximately 6 w % to 15 w % of silicon.

14. A reader/writer antenna according to claim 9 wherein the compound is an injection molded member, a compressed molded member, a rolled stripped member, or a member to which a painting member is applied.

16. A reader/writer antenna according to claim 1 wherein the soft magnetic member is an amorphous film or a layered member of the amorphous film.

17. A reader/writer antenna according to claim 1 wherein a non-magnetic conductive member of which initial resistance is approximately 10×

10<sup>−

8</sup> Ω

m or lower or a conductive member of which initial resistance is approximately 3×

10<sup>−

8</sup> Ω

m is disposed between the soft magnetic member and the object.

18. A reader/writer antenna according to claim 1 wherein a non-magnetic conductive member which has a 0.015 Ω

resistance which is more preferably 0.005 Ω

or lower with 1 cm length, 1 cm width is disposed between the soft magnetic member and the object.

19. A reader/writer antenna according to claim 1 wherein the object is a metal member or a member which contains a metal member.

20. A reader/writer wherein the reader/writer antenna according to any one of claims 1 to 19 is disposed so as to contact a casing which is formed by a non-magnetic member which has an initial resistance of approximately 10×

10 Ω

m or lower.

2. A reader/writer antenna which is used for an RFID system for non-contacting data communication wherein a plain soft magnetic member is disposed on a surface for disposing an object of the antenna coil which is formed by winding the plain soft magnetic member in a spiral manner.

21. A reader/writer antenna according to claim 2 wherein the casing is made of a conductive member which has 0.015 Ω

, more preferably 0.005 Ω

or lower resistance.

4. A reader/writer antenna which is used for an RFID system for non-contacting data communication wherein the antenna coil is formed such that a top surface and a back surface of the plain plate is wound around a magnetic core which is formed by a soft magnetic member.

6. A reader/writer antenna according to claim 4 or 5 wherein a soft magnetic plain plate is disposed on a surface for disposing an object for the antenna coil.

5. A reader/writer antenna which is used for an RFID system for non-contacting data communication wherein the antenna coil is formed such that a circumferential surface of a column is wound around a columnar magnetic core which is formed by a soft magnetic member.

15. The soft magnetic member is either one of an amorphous alloy, a permalloy, a magnetic steel, a silicon steel, a sendust alloy, a Fe—

AL alloy, or a soft magnetic ferrite.