SMALL GAMMA SHIELDED SHORTED PATCH RFID TAG

• US 20090096613A1
• Filed: 10/14/2008
• Published: 04/16/2009
• Est. Priority Date: 10/12/2007
• Status: Active Grant

• Current Assignee: Assa Abloy AB
• Original Assignee: Solstice Medical, LLC
• Inventors: Westrick, Michael D.
• Granted Patent: US 7,916,033 B2
• Time in Patent Office: Days
• US Class Current: 340/572.7
• CPC Class Codes: G06K 19/07735 the record carrier comprising means for protecting against electrostatic discharge
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole

Abstract

An RFID tag includes a substrate made of a material with a high dielectric constant of greater than approximately 4 and having a first side and a second side. A patch antenna is mounted to the first side of the substrate. A metallic ground plane is mounted to the second side of the substrate, and includes a feed through hole. A metallic backplane is coupled with the ground plane, on a side of the ground plane opposite the substrate. The backplane and/or the ground plane includes a recess. An RFID circuit is positioned within the recess. A shorting wall includes a plurality of through holes extending through the substrate and interconnecting the antenna with the ground plane. The plurality of through holes are generally linearly arranged relative to each other along an edge of the ground plane. An electrically conductive via extends through the substrate and the feed through hole of the ground plane. The via has a diameter which is slightly less than the feed through hole. The via interconnects the antenna with the RFID circuit. The via is at a distance from the shorting wall whereby an impedance of the RFID circuit approximately matches an impedance of the antenna.

Claims

1. A radio frequency identification (RFID) tag, comprising:

a substrate comprised of a material with a high dielectric constant of greater than approximately 4 and having a first side and a second side,

a patch antenna mounted to said first side of said substrate;

a metallic ground plane mounted to said second side of said substrate, said ground plane including a feed through hole;

a metallic backplane coupled with said ground plane, on a side of said ground plane opposite said substrate, at least one of said backplane and said ground plane including a recess;

an RFID circuit positioned within said recess;

a shorting wall including a plurality of through holes extending through said substrate and interconnecting said antenna with said ground plane, said plurality of through holes being generally linearly arranged relative to each other along an edge of said ground plane; and

an electrically conductive via extending through said substrate and said feed through hole of said ground plane, said via having a diameter which is slightly less than said feed through hole, said via interconnecting said antenna with RFID circuit, said via being at a distance from said shorting wall whereby an impedance of said RFID circuit approximately matches an impedance of said antenna.

2. The RFID tag of claim 1, wherein said ground plane and said backplane substantially surround and form a gamma radiation shield for said RFID circuit within said recess.

3. The RFID tag of claim 1, including an overmolded housing at least partially surrounding and hermetically sealing said RFID tag, said housing being comprised of a material which has a low dielectric constant of less than 5.

4. The RFID tag of claim 3, wherein said housing is autoclavable.

5. The RFID tag of claim 4, wherein said housing is formed from one of a plastic, silicone and epoxy material.

6. The RFID tag of claim 3, wherein said housing is formed from one of polyphenylsulfone, polysulfone, polythemide, and insert silicone rubber.

7. The RFID tag of claim 1, wherein said substrate is comprised of one of a ceramic filled polytetraflouroethylene (PTFE) and a metal oxide ceramic.

8. The RFID tag of claim 1, including an insulated electrical terminal mounted to said second side of said substrate, said RFID circuit being coupled with said electrical terminal.

9. The RFID tag of claim 1, wherein said backplane extends past said substrate so as to be self resonating.

10. The RFID tag of claim 9, wherein said backplane includes a pair of mounting holes in an area outside said ground plane.

11. The RFID tag of claim 9, wherein said housing seals against said backplane.

12. The RFID tag of claim 1, wherein said backplane is a stamped metal backplane including said recess.

13. The RFID tag of claim 1, wherein said backplane includes said recess.