Metal compensated radio frequency identification reader

• US 6,307,517 B1
• Filed: 06/13/2000
• Issued: 10/23/2001
• Est. Priority Date: 06/13/2000
• Status: Expired due to Fees

• Current Assignee: Farpointe Data Incorporated (dormakaba Holding AG)
• Original Assignee: Applied Wireless Identifications Group Incorporated (AWID)
• Inventors: Lee, Donny V.
• Primary Examiner(s): PHAN, THO GIA
• Application Number:
  US09/592,715
• Time in Patent Office: 497 Days
• Field of Search: 343/702, 343/741, 343/742, 343/788, 343/866, 343/867, 343/872, 343/895, 235/381, 235/487, 340/572.1, 340/572.2, 340/572.6, 340/825.54, 340/825.69
• US Class Current: 343/741
• 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 13/2408 using ferromagnetic tags
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• 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

Abstract

The present invention features an improved radio frequency identification (RFID) reader which operates with a low power consumption and which may tolerate a wide fluctuation in input voltages. The RFID reader is housed so that the influence of its physical surroundings, especially metallic objects, on system performance is minimized. A pre-compensation metal plate is used to stabilize the self-resonant frequency of the reader, even in the presence of large metal masses. The pre-compensation plate may be formed from aluminum or another non-ferrous material or, for long-range RFID readers, from ferrite or another similar, high magnetically permeable material. In addition, the RFID reader features improved sensitivity so that the effective operating distance is maximized. Also, the operating frequency is dynamically controlled in discrete steps of 10 Hz or less so that the effects of component parameter drift, temperature change, or other external factors are minimized. The RFID reader also automatically adapts itself to the requirements of an external access control system to which it is attached.

Claims

1. A reader for use in radio frequency identification (RFID) applications, comprising:

a) a housing for mounting an RFID device on an external mounting surface;

b) an antenna disposed within said housing;

c) RF generation means for generating an RF signal at a predetermined frequency disposed in said housing, said RF generation means being operatively connected to said antenna for cooperatively generating an RF field external to said housing;

d) digital signal processing means disposed in said housing for interpreting variations in said RF field caused by a transponder external to said housing interacting with said RF field; and

e) a pre-compensation plate disposed in said housing proximate said antenna for substantially eliminating changes to said RF field caused by influences of metal at or near said external surface.

2. The reader for use in RFID applications as recited in claim 1, wherein said antenna comprises an antenna coil.

3. The reader for use in RFID applications as recited in claim 2, wherein said antenna coil comprises an air core coil.

4. The reader for use in RFID applications as recited in claim 2, wherein said antenna coil forms a portion of a resonant circuit, said resonant circuit further comprising a capacitor.

5. The reader for use in RFID applications as recited in claim 4, wherein said antenna coil has an inductance having a nominal, predetermined value and said capacitor has a nominal, predetermined capacitance and both inductance and capacitance values are controlled to within 1% of their respective nominal values.

6. The reader for use in RFID applications as recited in claim 4, wherein said RF generation means and said digital signal processing means are disposed upon a printed wiring circuit card disposed in said housing substantially parallel to said antenna coil and at a predetermined distance therefrom.

7. The reader for use in RFID applications as recited in claim 6, wherein said predetermined distance is maintained by a spacer inserted between said antenna coil and said printed wiring circuit card.

8. The reader for use in RFID applications as recited in claim 7, further comprising:

potting material within said housing and substantially completely surrounding said printed wiring circuit card and said antenna coil and wherein said spacer prevents said potting material from contacting said antenna coil.

9. The reader for use in RFID applications as recited in claim 6, wherein said RF generation means and said digital signal processing means are supplied at least one supply voltage from a voltage source external to said housing.

10. The reader for use in RFID applications as recited in claim 9, wherein said at least one supply voltage is a DC voltage.

11. The reader for use in RFID applications as recited in claim 10, wherein said at least one DC voltage is in the range of approximately 3.5 to 12 volts DC.

12. The reader for use in RFID applications as recited in claim 1, wherein said pre-compensation plate comprises at least one material from the group of non-ferrous metal, ferrous metal, aluminum and ferrite material.

13. The reader for use in RFID applications as recited in claim 12, further comprising:

a ferrite plate external to said housing for placement between said housing and said mounting surface.

14. A radio frequency identification (RFID) system, comprising:

a) an RFID reader generating an electromagnetic field at a predetermined frequency; and

b) an RFID transponder adapted to interact with said electromagnetic field and containing an ID code associated therewith;

wherein said RFID transponder causes a disruption of said electromagnetic field whereby said ID code is transmitted to said RFID reader as a data stream comprising;

an imbedded data length preamble and at least two data bit groups each having a parity bit associated therewith.

15. The radio frequency identification (RFID) system as recited in claim 14, wherein each of said data bit groups comprises three data bits.

16. The radio frequency identification (RFID) system as recited in claim 14, wherein said data stream is dynamically alterable to a length of between approximately 26 and 52 data bits.

17. The radio frequency identification (RFID) system as recited in claim 14, wherein said RFID system is adapted to interface with an access control system external thereto and said RFID comprises automatic configuration means to sense at least a data polarity requirement of said access control system and to configure an output of said RFID system to conform to said requirement.

18. The radio frequency identification (RFID) system as recited in claim 14, wherein said predetermined frequency is dynamically alterable in response to at least one condition from the group:

changing a parameter of a component within said RFID, changing temperature, changing an external metallic mass.

19. The radio frequency identification (RFID) system as recited in claim 18, wherein said predetermined frequency is dynamically alterable in discrete steps.

20. The radio frequency identification (RFID) system as recited in claim 19, wherein said discrete steps are less than approximately 10 Hz.

21. The radio frequency identification (RFID) system as recited in claim 20, wherein each of said data bit groups comprises three data bits.

22. The radio frequency identification (RFID) system as recited in claim 20, wherein said data stream is dynamically alterable to a length of between approximately 26 and 52 data bits.

23. The radio frequency identification (RFID) system as recited in claim 20, wherein said RFID system is adapted to interface with an access control system external thereto and said RFID comprises automatic configuration means to sense at least a data polarity requirement of said access control system and to configure an output of said RFID system to conform to said requirement.