Efficient object identification system

• US 4,364,043 A
• Filed: 09/08/1981
• Issued: 12/14/1982
• Est. Priority Date: 05/30/1979
• Status: Expired due to Fees

• Current Assignee: AWA Ltd., The University of Adelaide
• Original Assignee: University of Adelaide
• Inventors: Eshraghian, Kamran, Cole, Peter H., Roy, Ashim K.
• Primary Examiner(s): Yusko, Donald J.
• Application Number:
  US06/299,887
• Time in Patent Office: 462 Days
• Field of Search: 340/825.54, 340/825.55, 340/38 L, 343/6.5 SS, 343/6.8 R
• US Class Current: 340/10.34
• CPC Class Codes: B61L 25/043 using inductive tags
• 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: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G07C 9/28 the pass enabling tracking or indicating presence
• CPC Class Codes: G08G 1/017 identifying vehicles G08G1/015, G08G1/054 take precedence
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A system for the remote identification of objects using near-field electromagnetic coupling between an interrogator a transponder and a receiver in which a reply carrier at a subharmonic of the interrogation frequency is obtained by regulating, with minimum energy loss and synchronously with the interrogator signal, the energy exchange process between the transponder coupling element and a complementary storage element, and further varying, also with minimum energy loss and synchronously with the resultant oscillation waveform, the said energy exchange process so that the reply carrier becomes modulated with an information bearing code, the modulation rate being not constrained by the transponder tuned circuit bandwidth.

Claims

1. An identification system for objects comprising

(A) a transmitter and receiver together forming an interrogator and including an transmitting near-field coupling element and a receiving near-field coupling element,

(B) a transponder having at least one near-field coupling element connected to receive at a first frequency a signal from the said transmitting near-field coupling element and to transmit at a second frequency a reply to the said receiving near-field coupling element,

(C) means within the transponder to form at least one resonant circuit containing the transponder coupling element and associated complementary energy storage element,

(D) means within the transponder for the generation of a reply code, characterised in that there are

(E) control and switching means within the transponder for regulating with minimum energy loss the pattern of energy exchange between the transponder coupling element and the associated complementary energy storage element whereby at least subharmonics of the interrogation frequency are generated as a reply signal within the transponder coupling element, and means for further varying also with minimum energy loss the pattern of energy exchange between the transponder coupling element and its complementary energy storage element so that an information bearing reply is generated in the said reply signal.

14. An object identification system according to claim 1 in which a plurality of near-field coupling elements are used in the transponder and in which energy is exchanged in a cyclic fashion between the said coupling element and a set of reactive energy storage elements via a switching array so that a subharmonic of the interrogation signal is generated within at least one of the said transponder coupling elements.

15. An object identification system as in claim 14 wherein an information bearing code is imposed upon the reply signal either simultaneously or in time sequence.

16. An object identification system according to claim 15 wherein the said code is an amplitude modulated code, the rate of information transfer being not limited by the bandwidth of the transponder resonant circuit.

17. An object identification system as in claim 15 wherein the said code is a phase modulated code, the rate of information transfer being not limited by the bandwidth of the transponder resonant circuit.

18. An object identification system as in claim 15 wherein the said code is imposed upon the reply signal by means of the simultaneous generation of a plurality of reply frequencies.

19. An object identification system as in claim 15 wherein the said code is imposed upon the reply signal by means of the successive generation of a sequence of reply frequencies.

20. An object identification system as in claim 14 wherein part of the energy received at the said first frequency in the said transponder is rectified and stored to assist in actuating the said control and switching means.

2. A system for identification of objects comprising a transmitting means having at least one near-field coupling element for generation of an interrogation signal at a first frequency, and a remote transponder comprising

electromagnetic coupling means containing at least one near-field coupling element for reception of the interrogation signal and establishing a reply signal field at a second frequency

reactive energy storage means to provide resonance with the coupling element and enhancement of the power transfer across the electromagnetic path

switching means placed between the coupling element and tuning elements to regulate the flow of stored energy between those elements so that the resulting oscillation contains a subharmonic of the first frequency, thereby providing a reply signal carrier at the said second frequency

control means connected to operate said switching means at times which preserve stored energy in the reactive elements and which maintain synchronism with the interrogation signal

and coding means synchronised with the oscillation in the said coupling and tuning elements and connected to the said control means to vary the pattern of energy exchanges between the said elements so that the said reply carrier becomes modulated with an information bearing code at rates unrelated to transponder tuned circuit bandwidth without reduction in reply signal level

and receiving means containing at least one near-field coupling element and means for demodulating said reply signal.

3. A system for the remote identification of objects by means of transmitting by near-field electromagnetic coupling an interrogation signal to a transponder, in which the exchange of energy between a near-field coupling element and a tuning element is regulated by switching means placed between these elements and in which the coupling element current and voltage waveforms contain simultaneously components at the interrogation frequency and a subharmonic thereof, the subharmonic frequency providing a reply carrier signal, the switching means operating at instances of time at which loss of stored energy in the resonant circuit comprising said coupling and tuning elements is minimised and which maintain phase coherence between the interrogation signal and the resulting coupling element waveform, and in which a code generator synchronised with the waveform of oscillation in the near-field coupling element is used to further vary the pattern of energy exchange between the coupling and tuning elements to modulate the said subharmonic reply carrier with an information bearing signal.

4. An object identification system as in claim 3 in which the said second frequency is a multiple of a subharmonic of the said first frequency but is not an integer multiple of the said first frequency.

5. An object identification system as in claim 4 wherein the said transponder contains means for detection of instants of time at which alteration of the interconnections between the reactive energy storage elements may be effected with minimum energy loss, and means to effect switching at the detected instants of time.

6. An object identification system as in claim 5 wherein to provide preservation of stored energy the said alteration of interconnection between reactive energy storage elements is effected at zeros of inductor current.

7. An object identification system as in claim 6 wherein the energy exchange process between the transponder near-field coupling element and its complementary energy storage element is regulated by a switch connected in series with the said complementary energy storage element.

8. An object identification system as in claim 5 wherein to provide preservation of stored energy the said alteration of interconnection between reactive energy storage elements is effected at zeros of capacitor voltage.

9. An object identification system as in claim 8 wherein the energy exchange process between the transponder near-field coupling element and its complementary energy storage element is regulated by a switch connected in parallel with the said complementary energy storage element.

10. An object identification system as in claim 5 wherein the said transponder contains means for detection of instants of time at which oscillations which are suspended may be resumed in synchronism with the interrogation signal.

11. An object identification system as in claim 10 wherein the said detection is provided by means of a phase-locked-loop synchronised at selected intervals to the coupling element waveform.

12. An object identification system as in claim 10 wherein the said detection is provided by an electronic circuit which samples during the suspended oscillation the interrogation signal.

13. An object identification system as in claim 10 wherein the said detection is provided by means of an auxiliary oscillation of a period related to that of the interrogation signal.