Modulation of the resonant frequency of a circuit using an energy field

• US 7,123,129 B1
• Filed: 03/18/2003
• Issued: 10/17/2006
• Est. Priority Date: 08/14/1995
• Status: Expired due to Fees

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Schrott, Alejandro Gabriel, Von Gutfeld, Robert Jacob, Gambino, Richard Joseph
• Primary Examiner(s): Holloway, III, Edwin C.
• Application Number:
  US10/391,515
• Time in Patent Office: 1,309 Days
• Field of Search: 340/10.1, 340/5.8, 340/505, 340/572.5, 340/10.3, 340/10.34, 340/5.61, 340/572.1, 340/572.6, 235/380, 235/492, 70/57.1, 70/571, 367/6, 342/42, 342/44, 342/51
• US Class Current: 340/10.1
• 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

Abstract

A transponder has a resonant RLC circuit with one or more electromagnetic energy storage components that vary in response to an externally applied modulating energy field. In addition to the externally modulating energy field, a base station transmits a carrier signal with a frequency essentially the same as the quiescent resonant frequency of the RLC circuit. As the component(s) vary, the resonant frequency of the RLC circuit changes, modulating the carrier signal with the external modulating energy field. Effects of the modulation are detected by the base station. Information (e.g., the presence of a tag) is obtained by receiving and demodulating the modulated signal at the base station. One or more or the circuit elements (e.g, different preferred embodiments of one or more capacitors, inductors, and resistors) can be varied (e.g. mechanically) to modulate the carrier signal. This allows the resonant circuit to modulate the carrier signal with multiple modulation frequencies to encode multiple bits of information on the carrier.

Claims

1. A transponder comprising a circuit having two or more circuit components that determine a response of the circuit, at least one of the circuit components varying in response to an external modulating energy field so that the circuit response changes, where the circuit components comprise one or more variable capacitors, and

where at least one of the capacitors is a plate capacitor having one or more first plates and a second plate, the first and second plates being separated by a gap having a gap size, and where at least the first plate has a movement in response to the external modulating energy field, the movement causing the capacitance of the capacitor to vary.

2. A transponder, as in claim 1, where one or more of the first plates is a constrained plate being constrained at zero or more points by a constraint and the constraints determine one or more mechanical resonance frequencies of the constrained plate.

3. A transponder, as in claim 2, where the movement is a non-resonance response to the external modulating energy field and the external modulating energy field has a frequency not equal to any of the mechanical resonance frequencies of the constrained plate.

4. A transponder, as in claim 1, where the movement of the first plate causes a change in the gap size between the first and second plate.

5. A transponder, as in claim 4, where the external modulating energy field has a modulating frequency and the movement is a vibration of the first plate at the modulating frequency.

6. A transponder, as in claim 5, where the change in the gap size is greatest when the modulating frequency is equal to any one of the mechanical resonance frequencies.

7. A transponder, as in claim 4, where the external modulation energy field is an acoustic field.

8. A transponder, as in claim 2, where the constrained plate is a cantilever having a first and second end and the first end is constrained by being fixably attached to a support and the second end is unconstrained to permit the movement, the movement being a vibration changing the gap size.

9. A ponder, as in claim 2, where the constrained plate is a bar having a first and second end and the first end and second end are constrained by being fixably attached to a support the bar further capable of a transverse mechanical motion at one or more of the mechanical resonance frequencies in a direction that changes the gap size.

10. A transponder, as in claim 2, where the constrained plate is constrained at zero points, therefore being an unconstrained plate capable of a transverse mechanical motion at one or more of the mechanical resonance frequencies in a direction that changes the size.

11. A transponder, as in claim 1, where the first plate is a bimorph, the bimorph having a first and second layer.

12. A transponder, as in claim 11, where the external modulating energy field includes any one of the following:

an acoustic field, an electromagnetic field varying at a modulating frequency, and an electromagnetic field varying at a modulating frequency with a DC magnetic bias.

13. A transponder, as in claim 11, where the first layer is made of a magnetostrictive material.

14. A transponder, as in claim 13, where the second layer is made of a coercive material left in a remanent state with a coercivity greater than an amplitude of the external modulating energy field.

15. A transponder, as in claim 14, where a change in gap size is greatest when a modulating frequency of the external modulating energy field is equal to a mechanical resonance frequency of the first plate.

16. A transponder, as in claim 13, where the external modulating energy field is an electromagnetic field and the change in the gap size is greatest where a modulating frequency of the modulating energy field is equal to one half of the frequency of one the mechanical resonance frequencies of the first plate.

17. A transponder, as in claim 2, where the external modulating energy field is a time varying magnetic field and the each of the first plates and each of the second plates have an area of overlap, the first and second plates consisting of soft magnetic material, the first plates being cantilevers with a first and a second end, the first end being constrained and the second end being free to move, the second end of the first plate being attracted to the second end of the second plate with a time varying force due to the presence of the time varying magnetic field, the time varying force causing a mechanical vibration of the plates, the capacitance of the capacitor formed by these two plates changing due to a change in the gap size caused by the mechanical vibration.

18. A transponder, as in claim 2, where the energy field is a time varying magnetic field and the first plate is in the presence of a non-uniform magnetic bias field, the first plate comprising any one of the following:

a magnetostrictive material and a soft magnetic material.

19. A transponder, as in claim 18, where the magnetic bias field is supplied by any one of the following:

an externally applied spatially non-uniform magnetic field and the second plate being made from a high coercivity material left in a remanent state.

20. A transponder, as in claim 1, where at least a portion of the first plate is capable of slidably moving with respect to the second plate to change the gap size.

21. A transponder, as in claim 1, where, in response to the external modulating energy field, at least a portion of the first plate and a portion of the second plate are capable of slidably moving with respect to one another to change the gap size.

22. A transponder, as in claim 20, where the first plate is made of a magnetostrictive material and is caused to slidably move when excited by the external modulating energy field, the external modulating energy field being a magnetic field varying at a modulating frequency.

23. A transponder, as in claim 22, where the first plate is attached to an elastic link that provides a restoring force allowing the first plate to mechanically resonate at one or more mechanical resonance frequencies in response to the modulating magnetic field.

24. A transponder, as in claim 1, where the first plate and the second plate are configured to have an area of overlap, and the movement of the first plate causes a change in the overlap area in manner to vary the capacitance of the capacitor.

25. A transponder, as in claim 24, where the first plate is made of a magnetostrictive material and slides in response to the external modulating energy field, the external modulating energy field being an electromagnetic field.

28. A transponder, as in claim 24, where two or more of the first plates slide in a plane parallel to the second plate, each of the first plate sliding directions being non-parallel with one another.

26. A transponder, as in 24, where the first plate is constrained by an elastic link that provides a restoring force giving rise to one or more mechanical resonant frequencies of the first plate.

27. A transponder, as in claim 26, where the overlap change is the greatest under any one of the following conditions:

a. a modulating frequency of the external modulating energy field is equal to one half of one of the mechanical resonant frequencies, and

b. the external modulating energy field has an AC part and a DC part, the DC part is greater than a peak amplitude of the AC part and the modulating frequency is equal to one of the mechanical resonant frequencies.

29. A transponder comprising a resonant circuit having two or more electromagnetic energy storage components that determine a circuit resonance frequency of the resonant circuit, at least one of the electromagnetic storage components varying in response to an external modulating energy field so that the circuit resonance frequency changes,

where one or more of the electromagnetic storage components is a variable inductor comprising:

(a) a coil; and

(b) a flux changing element, the flux changing element varying the inductance of the variable inductor by changing a flux of the variable inductor non-linearly with respect to a change of current flowing in the variable inductor.

30. A transponder, as in claim 29, where the flux changing element is a ferromagnetic sheet that is driven in and out of a non-linear range of a hysteresis curve of the ferromagnetic sheet by the external modulating energy field.

31. A transponder, as in claim 29, where the flux changing element is one or more moving plates in proximity to the coil, where said plates are constrained at zero or more points by a constraint and the constraints determine one or more mechanical resonant frequencies of the constrained plates, the plates being moved by the external modulating energy field.

32. A transponder, as in claim 29, where the flux changing element is one or more mutual inductances coupled to the coil by the flux.

33. A transponder, as in claim 32, where the coupling is varied by a ferromagnetic sheet that is driven in and out of a non-linear range of a hysteresis curve of the ferromagnetic sheet by the external modulating energy field.

34. A transponder, as in claim 32, where the coupling is varied by one or more moving plates in proximity to the coil, where said moving plates are constrained at zero or more points and the constraints determine one or more mechanical resonant frequencies of the constrained plates, the plates being moved by the external modulating energy field.

35. A transponder comprising a resonant circuit having resonant circuit components comprising two or more electromagnetic energy storage components that determine a circuit resonance frequency of the resonant circuit, at least one of the resonant circuit components varying in response to an external modulating energy field so that a characteristic of the resonant circuit changes, where one or more of the resonant circuit components is a variable impedance, the variable impedance being a material exhibiting magneto-impedance changed by the external modulating energy field, the external modulating energy field being an electromagnetic field.

36. A transponder, as in claim 35, where the variable impedance is made of a magnetoresistive material including any of the following:

permalloy, Sb, Bi, non-magnetic/magnetic layered compounds such as copper-permalloy, manganese oxides.

37. A transponder, as in claim 35, where the material is a soft magnetic wire comprising the alloy FeCoSiB.

38. A transponder comprising:

a resonant circuit having two or more electromagnetic energy storage components that determine a circuit resonance frequency of the resonant circuit;

an external modulating energy field, having one or more modulating waveforms;

one or more of the electromagnetic energy storage components being a varying component, the varying component being varied in response to one or more of the modulating waveforms of the external modulating energy field, the varying component causing the circuit resonance frequency to change; and

an electromagnetic carrier field with a carrier frequency, the carrier frequency being modulated in response to change in the circuit resonance frequency to encode information on the carrier frequency.

39. A transponder, as in claim 38, where the information is a binary code having one or more bits, each bit having a bit value, and each bit value is capable of indicating the presence and absence of change in the circuit resonance frequency.

40. A system for obtaining information from a transponder, comprising:

a base station that transmits an electromagnetic carrier field with a carrier frequency and an external modulating energy field, the external modulating energy field having one or more modulating waveforms;

a transponder having a resonant circuit with two or more electromagnetic energy storage components that determine a circuit resonance frequency of the resonant circuit, one or more of the electromagnetic energy storage components being a varying component, each of the varying components being varied by one or more of the modulating waveforms, the varying component causing the circuit resonance frequency to change thereby modulating the carrier field to encode information on the carrier field; and

a receiver for receiving the modulated carrier field and detecting the information on the carrier field.

41. A system, as in claim 40, where the carrier field is modulated with amplitude modulation.

42. A system, as in claim 40, where the carrier field is modulated with frequency modulation.

43. A system, as in claim 40, where the transponder is a tag on an object and the information describes the object.

44. A system, as in claim 40, where the information is a binary code having one or more bits, each bit having a bit value, and each bit value is capable of indicating the presence and absence of one of the modulating waveforms.

45. A system, as in claim 40, where the external modulating energy field includes any one of the following:

an acoustic field, an electromagnetic field, and an electromagnetic field with a magnetic DC bias.

46. A method of creating a modulated carrier field comprising the steps of:

transmitting an electromagnetic carrier field and an external modulating energy field, the electromagnetic carrier field having a carrier frequency and the external modulating energy field having one or more modulating waveforms; and

modulating the carrier field with a transponder, the transponder having a resonant circuit with two or more electromagnetic energy storage components that determine a circuit resonance frequency of the resonant circuit, one or more of the electromagnetic energy storage components being a varying component, each of the varying components being varied by one or more of the modulating waveforms, the varying component causing the circuit resonance frequency to change thereby modulating the carrier field.

47. A method, as in claim 46, where the the electromagnetic carrier field and the external modulating energy field are transmitted by a base station.

48. A method, as in claim 46, where the modulating waveforms cause modulation of the carrier field which represents information.

49. A method, as in claim 48, where the modulated carrier field is received by a receiver that demodulates the modulated carrier field to obtain the information.

50. A transponder comprising:

a resonant circuit having resonant circuit components comprising two or more electromagnetic energy storage components that determine a circuit resonance frequency of the resonant circuit;

an electromagnetic carrier field with a carrier frequency and having an absorbed part, the absorbed part being an amount of energy of the carrier field being absorbed by the resonant circuit, the absorbed part being greatest at the circuit resonance frequency; and

at least one of the resonant circuit components being directly responsive to an energy field impinging directly thereon to change the energy of the carrier field absorbed by the resonant circuit;

where the carrier field further comprises a reflected part and a transmitted part, the reflected part being a reflected amount of energy of the carrier field being reflected from the resonant circuit and the transmitted part being a transmitted amount of energy of the carrier field that passes through the resonant circuit, where all of the energy of carrier field equals the sum of the absorb part, the reflected part, and the transmitted part, and where the at least one of the resonant circuit components changes the circuit resonance frequency to modulate the absorbed part, reflected pant, and transmitted part.