RF transponder system with parallel resonant interrogation series resonant response

• US 5,608,417 A
• Filed: 05/16/1996
• Issued: 03/04/1997
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Assa Abloy AB
• Original Assignee: Palomar Technologies Incorporated
• Inventors: de Vall, Franklin B.
• Primary Examiner(s): Le, Hoanganh T.
• Application Number:
  US08/650,007
• Time in Patent Office: 292 Days
• Field of Search: 343/895, 343/866, 343/867, 343/741, 343/742, 343/749, 340/572
• US Class Current: 343/895
• 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 19/07779 the inductive antenna being a coil
• CPC Class Codes: G06K 19/07783 the coil being planar
• CPC Class Codes: G06K 19/07784 the inductive antenna consisting of a plurality of coils stacked on top of one another
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: H01Q 1/36 Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewithH01Q1/08, H01Q1/14 take precedence
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

A transponder system employs a transponder antenna with a distributed inductance and capacitance that exhibit parallel and series resonant frequencies. Transmissions to the transponder circuit are made at one or more parallel resonant frequencies to maximize the excitation of the transponder circuit, while return signals transmitted back from the transponder are modulated at one or more series resonant frequencies to maximize the signal current. The transponder antenna is implemented as a pair of aligned coils on opposite sides of a thin dielectric substrate, with the coils connected together through the substrate at one point and the substrate thickness not more than about 25 microns to obtain a significant mutual inductance between the coils.

Claims

1. A transponder communications system, comprising:

A) a transponder that includes;

a) means for providing a distributed inductance and capacitance with parallel and series resonance at different respective parallel and series resonant frequencies;

b) an active return signal generator circuit coupled to said inductance and capacitance means, wherein said return signal generator circuit generates and applies to said inductance and capacitance means a return information signal having one of said series resonant frequencies, and

c) a power circuit coupled to said inductance and capacitance means and tuned to respond to an actuation signal received by said inductance and capacitance means, said power circuit having one of said parallel resonant frequencies and supplying an energizing signal to said return signal generator circuit; and

B) an exciter/reader that includes;

a) a transmitter for transmitting said actuation signal to said transponder at one of said parallel resonant frequencies, and

b) a receiver for receiving said information signal transmitted from said transponder at said series resonant frequency.

2. The transponder communications system of claim 1, wherein said transmitter and receiver are combined in a transceiver with a common antenna for transmitting signals to and receiving signals from said transponder.

3. The transponder communications system of claim 1, wherein said inductance and capacitance means comprises a dielectric substrate with a pair of mutually connected coils with respective inductances on opposite faces of the substrate, said mutually connected coils having a common winding direction and positioned in substantial registration with each other to produce a substantial mutual inductance that makes the total antenna inductance greater than the sum of the coils'"'"' individual inductances.

4. The transponder communications system of claim 3, wherein said dielectric substrate is not more than about 25 microns thick between said mutually connected coils.

5. The transponder communications system of claim 3, wherein said mutually Connected coils generally describe spirals which have respective inner and outer ends and have only one site of mutual connection, said mutual connection being provided by a first electrical connector that extends through the substrate and connects the coils at one end.

6. The transponder communications system of claim 5, wherein said transponder is disposed on the same substrate face as one of said coils and is connected to the opposite end of said one coil, with the opposite end of the other coil connected to the circuit by a second electrical connector that extends through the substrate.

7. The transponder communications system of claim 1, wherein said antenna coil is characterized by multiple parallel resonant frequencies, and said transmitter transmits actuating signals to said transponder at at least two of said parallel resonant frequencies.

8. The transponder communications system of claim 7, said return signal generator circuit comprising a writable identification code circuit that responds to energization at one of said parallel resonant frequencies with an identification code transmitted from said coil at said series resonant frequency, wherein said transmitter transmits a transponder energization signal at said one parallel resonant frequency, and a code write signal at another parallel resonant frequency.

9. The transponder communications system of claim 1, wherein said antenna coil is characterized by multiple series resonant frequencies, and said return signal generator circuit generates and applies to said antenna coil different information signals at different respective series resonant frequencies.

10. A radio frequency (RF) antenna structure, comprising:

a dielectric substrate,

a pair of mutually connected antenna coils on opposite sides of said substrate, said coils having a common winding direction, said coils being positioned in substantial registration with each other and said coils characterized by parallel and series resonance at different respective parallel and series resonant frequencies, and

an active circuit on said substrate that responds to energization from said coils at one of said parallel resonant frequencies by energizing said coils to transmit an information signal at one of said series resonant frequencies,

said substrate having a thickness between said coils of not more than about 25 microns, thereby enabling a substantial mutual inductance between said coils that makes the total antenna coil inductance greater than the sum of each coils'"'"' individual inductance.

11. The RF antenna structure of claim 10, wherein said mutually connected coils generally describe spirals which have respective inner and outer ends and have only one site of mutual connection, said mutual connection being provided by a first electrical connector that extends through the substrate and connects the coils at one end.

12. The RF antenna structure of claim 10, wherein said coils are arranged on said substrate to exhibit multiple parallel resonant frequencies and multiple series resonant frequencies.

13. A radio frequency (RF) antenna structure, comprising:

a dielectric substrate,

a pair of mutually connected antenna coils on opposite sides of said substrate which are oriented on the substrate to produce a mutual inductance between the coils that is greater than the sum of their individual inductances, said coils being characterized by parallel and series resonance at different respective parallel and series resonant frequencies and generally describing spirals which have respective inner and outer ends and have only one site of mutual connection, said mutual connection being provided by an electrical connector that extends through the substrate and connects the coils'"'"' inner ends, and

an active circuit on said substrate that responds to energization from said coils at one of said parallel resonant frequencies by energizing said coils to transmit an information signal at one of said series resonant frequencies.

14. The RF antenna structure of claim 13, wherein said coils are arranged on said substrate with a distributed inductance and capacitance characterized by parallel and series resonance at different respective parallel and series resonant frequencies.

15. The RF antenna structure of claim 14, wherein said coils are arranged on said substrate to exhibit multiple parallel resonant frequencies and multiple series resonant frequencies.

16. A radio frequency (RF) transponder, comprising:

a dielectric substrate,

means formed on said substrate for providing a distributed inductance and capacitance characterized by parallel and series resonance at different respective parallel and series resonance frequencies,

an active signal generator coupled to said inductance and capacitance means and positioned on said substrate, wherein said active signal generator generates and applies to said inductance and capacitance means an information signal at one of said series resonant frequencies, and

a power circuit on said substrate for supplying an energizing signal to said active signal generator when said inductance and capacitance means receives an actuation signal generated by a remotely-located exciter/reader at one of said parallel resonant frequencies.

17. The RF transponder of claim 16 wherein said inductance and capacitance means comprises a pair of mutually connected coils with respective inductances on opposite faces of the dielectric substrate, said mutually connected coils having a common winding direction and positioned in substantial registration with each other to produce a substantial mutual inductance that makes the total antenna inductance greater than the sum of the coils'"'"' individual inductances.

18. The RF transponder of claim 17, wherein said dielectric substrate is not more than about 25 microns thick between said mutually connected coils.

19. The RF transponder of claim 16, wherein said inductance and capacitance means is characterized by multiple series resonant frequencies, and said active signal generator generates and applies to said inductance and capacitance means different information signals at different respective series resonant frequencies.