Metal compensated radio frequency identification reader
DCFirst Claim
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.
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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.
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Citations
23 Claims
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1. A reader for use in radio frequency identification (RFID) applications, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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.
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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.
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10. The reader for use in RFID applications as recited in claim 9, wherein said at least one supply voltage is a DC voltage.
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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.
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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.
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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.
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14. A radio frequency identification (RFID) system, comprising:
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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.- View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification