Radio frequency transponder with improved read distance

• US 6,281,794 B1
• Filed: 05/25/1999
• Issued: 08/28/2001
• Est. Priority Date: 01/02/1998
• Status: Expired due to Term

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Duan, Dah-Weih, Heinrich, Harley Kent
• Primary Examiner(s): Lee, Benjamin C.
• Application Number:
  US09/318,590
• Time in Patent Office: 826 Days
• Field of Search: 340/572.1, 340/10.1, 340/10.4, 343/860, 343/711, 343/700.MS, 342/44, 342/42, 455/215, 333/32
• US Class Current: 340/572.1
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• 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 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G08B 13/2414 using inductive tags
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2431 Tag circuit details
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: G08B 13/2462 Asset location systems combined with EAS inventory, tracking, logistic G06Q10/00; entrance control systems G07C9/00
• CPC Class Codes: H01L 24/02 Bonding areas on insulating substrates, e.g. chip carriers, H01L23/49816, H01L23/49838, H01L23/5389; Manufacturing methods related thereto
• CPC Class Codes: H01L 2924/01005 Boron [B]
• CPC Class Codes: H01L 2924/01014 Silicon [Si]
• CPC Class Codes: H01L 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/01033 Arsenic [As]
• CPC Class Codes: H01L 2924/01075 Rhenium [Re]
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01088 Radium [Ra]
• CPC Class Codes: H01L 2924/10329 Gallium arsenide [GaAs]
• CPC Class Codes: H01L 2924/14 Integrated circuits
• CPC Class Codes: H01L 2924/19042 being an inductor
• CPC Class Codes: H01L 2924/30105 : Capacitance
• CPC Class Codes: H01L 2924/30107 : Inductance
• CPC Class Codes: H01L 2924/3011 : Impedance
• CPC Class Codes: H01Q 1/2225 : used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 13/02 : Waveguide horns
• CPC Class Codes: H01Q 15/16 : curved in two dimensions, e.g. paraboloidal
• CPC Class Codes: H01Q 19/106 : using two or more intersecting plane surfaces, e.g. corner reflector antennas
• CPC Class Codes: H01Q 19/132 : Horn reflector antennas; Off-set feeding
• CPC Class Codes: H01Q 21/065 : Patch antenna array
• CPC Class Codes: H01Q 9/0414 : in a stacked or folded configuration
• CPC Class Codes: H01Q 9/0428 : radiating a circular polarised wave

Abstract

A radio frequency identification transponder (RFID tag) in accordance with the principles of the present invention includes a tag antenna and RFID circuitry having respective input impedances Za and ZL. In accordance with the principles of the invention, the read distance of the RFID tag is maximized by connecting an inductor in series between the antenna and the RFID tag circuitry. The inductor having an impedance ZL that maximizes the expression [(Ra)(Ga)]^½|(ZL|/|Za+Zind+ZL|, where | | indicates the absolute value of the enclosed expression.

Claims

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

a tag antenna having impedance Z_a,

radio frequency identification (RFID) circuitry responsive to electromagnetic signals received at the tag antenna, the circuitry having an input impedance Z_L, and

an inductor having an impedance Z_ind connected in series between the antenna and the RFID circuitry, the value of the inductor chosen to maximize the expression [(R_a)(G_a)]^½

|(Z_L)|/|(Z_a+Z_ind+Z_L)|, where | | indicates the absolute value of the enclosed expression.

2. The RFID tag of claim 1 wherein the imaginary part of the inductor impedance is equal in magnitude to the difference between the absolute value of the imaginary part of the antenna impedance and the absolute value of the imaginary part of the RFID circuitry impedance.

3. The RFID tag of claim 2 wherein the load resistance is minimized.

4. The RFID tag of claim 1 wherein the RFID circuitry is incorporated on a single integrated circuit.

5. The RFID tag of claim 4 wherein the inductor is incorporated on the integrated circuit.

6. The RFID tag of claim 5 wherein the inductor is formed using an integrated circuit excavation technique.

7. An RFID system comprising:

a base station,

a radio frequency identification transponder (RFID tag) including;

a tag antenna having an impedance Z_a,

radio frequency identification (RFID) circuitry responsive to electromagnetic signals received at the tag antenna, the circuitry having an input impedance Z_L, and

an inductor having an impedance Z_ind connected in series between the antenna and the RFID circuitry the value of the inductor chosen to maximize the expression [(R_a)(G_a)]^½

|(Z_L)|/|(Z_a+Z_ind+Z_L)|, where [ ] indicates the absolute value of the enclosed expression.

8. The system of claim 7 wherein the imaginary part of the inductor impedance is equal in magnitude to the difference between the absolute value of the imaginary part of the antenna impedance and the absolute value of the imaginary part of the RFID circuitry impedance.

9. The system of claim 8 wherein the load impedance is minimized.

10. The system of claim 7 wherein the RFID circuitry is incorporated on a single integrated circuit.

11. The system of claim 10 wherein the inductor is incorporated on the integrated circuit.

12. The system of claim 11 wherein the inductor is formed using an integrated circuit excavation technique.

13. A method of maximizing an RFID tag read range, the tag including an antenna having an impedance Z_a and RFID tag circuitry, or a load, having an input impedance Z_L, comprising the steps of:

determining the impedance Z_L of the load,

determining the impedance of the antenna Z_a,

determining the value of an inductor which, when connected in series between the antenna and the RFID tag circuitry, maximizes the expression [(R_a)(G_a)]^½

|(Z_L)|/|(Z_a+Z_ind+Z_L)|, where [ ] indicates the absolute value of the enclosed expression, and

connecting such an inductor in series between the antenna and the RFID tag circuitry.

14. The method of claim 13 wherein the inductor is selected such that the imaginary part of its impedance is equal in magnitude to the difference between the absolute value of the imaginary part of the antenna impedance and the absolute value of the imaginary part of the RFID tag circuitry impedance.

15. The method of claim 14 wherein the RFID circuitry is formed on a single integrated circuit.

16. The method of claim 15 wherein the inductor is incorporated on the integrated circuit.

17. The method of claim 16 wherein the inductor is formed using an integrated circuit excavation technique.