SYSTEM AND METHOD FOR MEASURING VARIABLE IMPEDANCE ELEMENTS IN A WIRELESS SENSOR

• US 20150123679A1
• Filed: 03/14/2013
• Published: 05/07/2015
• Est. Priority Date: 05/10/2012
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Access Business Group International LLC (Alticor Incorporated)
• Inventors: Kuyvenhoven, Neil W., Dean, Cody D., Baarman, David W., Moes, Benjamin C., Nguyen, Hai D., Norconk, Matthew J., Schwannecke, Joshua K., Taylor, Joshua B., Melton, Joseph S. Jr., Stoddard, Ronald L.
• Granted Patent: US 10,481,189 B2
• Time in Patent Office: Days
• US Class Current: 324/652
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
• CPC Class Codes: G01R 27/28 Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response in line transmission systems H04B3/46
• CPC Class Codes: G06K 19/0717 the sensor being capable of sensing environmental conditions such as temperature history or pressure
• CPC Class Codes: H04B 5/26 using coils

Abstract

A wireless remote sensor (110) that is powered by an inductive transmitter (112) and is configured to produce an oscillating wave that varies based on one or more sensed parameters. The oscillating wave is communicated to the inductive transmitter (112) by reflected impedance, where it can be detected to determine the sensed value(s). In another aspect, the present invention provides a wireless remote sensor with a Wheatstone bridge arrangement having an internal resonant circuit to produce an electromagnetic field indicative of the sensed value. In a third aspect, the present invention provides a wireless remote sensor with optical feedback from a reference circuit and a sensor circuit. In a fourth aspect, the present invention provides a wireless remote temperature sensor having coils printed on a material with a high coefficient of thermal expansion so that the size and/or shape of the coils varies as the temperature increases or decreases.

Claims

1. A wireless remote sensor for sensing a parameter comprising:

a receiver coil configured to wireless receive power from a wireless power transmitter; and

an oscillating circuit coupled to said receiver coil whereby oscillations of said oscillating circuit are communicated to the wireless power transmitter by reflected impedance, said oscillating circuit having a variable impedance element that varies with a value of the parameter to be sensed, wherein a duty cycle of said oscillations varies based on variations in said variable impedance element.

2. The remote sensor of claim 1 wherein said oscillating circuit includes a charge/discharge circuit configured to alternately charge and discharge said oscillating circuit, said oscillations corresponding with said charges and discharges.

3. The remote sensor of claim 2 wherein said charge/discharge circuit includes a charge subcircuit with a charge capacitor that is charged by power wirelessly received via said receiver coil.

4. The remote sensor of claim 3 wherein said charge/discharge circuit includes a trigger for transitioning said charge/discharge circuit between a charge state and a discharge state, said trigger being a diode having a reverse breakdown voltage selected to transition said charge/discharge circuit from said charge to said discharge when said charge capacitor reaches a threshold.

5. The remote sensor of claim 3 wherein said charge/discharge circuit includes a discharge subcircuit having a current latch configured to selectively discharge said charge capacitor.

6. The remote sensor of claim 5 wherein said charge subcircuit includes a charge resistor, said charge resistor being said variable impedance element.

7. The remote sensor of claim 5 further including a discharge resistor, said discharge resistor being said variable impedance element.

8. The remote sensor of claim 5 wherein said oscillating circuit includes first and second variable impedance elements, said first variable impedance element being a variable resistor in said charge subcircuit, said second variable impedance element being a variable resistor arranged to vary a duration of said discharge state.

9. The remote sensor of claim 3 further including a normalization circuit for normalizing a voltage provided to said charge subcircuit.

10. The remote sensor of claim 9 wherein said normalization circuit includes a voltage clamp.

11. The remote sensor of claim 3 wherein said charge/discharge circuit includes a trigger for transitioning said charge/discharge circuit between a charge state and a discharge state, said trigger being a comparator and a voltage divider selected to maintain a substantially uniform charge duration despite variations in voltage provided to said charge subcircuit.

12. The remote sensor of claim 11 wherein said comparator includes a first input coupled to an output of said voltage divider and a second input coupled to an output of said charge subcircuit.

13. The remote sensor of claim 12 wherein said charge/discharge circuit includes a discharge subcircuit having a current latch configured to selectively discharge said charge capacitor, an output of said comparator coupled to said current latch, whereby said comparator output engages said current latch.

14. The remote sensor of claim 5 wherein said discharge subcircuit include a modulating leg, said modulating leg having a modulating resistor, said modulating leg coupled to said current latch whereby said modulating leg is applied only when said current latch is on.

15. The remote sensor of claim 14 wherein said modulating leg is coupled to said current latch by a transistor, said modulating resistor having a value selected to cause said transistor to operate as an amplifier dependent at least in part on a variable impedance element.

16. A wireless remote sensor system for sensing a parameter comprising:

a wireless power supply for supplying wireless power;

a wireless remote sensor including;

a receiver coil for wirelessly receiving power from a wireless power supply;

a Wheatstone bridge arrangement coupled to said receiver coil and having a resistor network with a variable impedance element and an internal resonant circuit, said variable impedance element having an impedance that varies with a value of the parameter, said internal resonant circuit producing an electromagnetic field having a least one characteristic that varies with variations in said variable impedance element; and

a sense coil for receiving said electromagnetic field produced by said internal resonant circuit, said sense coil coupled to a sensor capable of sensing at least one characteristic of said electromagnetic field that varies with variations in said variable impedance element.

17. The wireless remote sensor system of claim 16 wherein said variable impedance element includes a variable resistor.

18. The wireless remote sensor system of claim 16 wherein said variable impedance element is a thermistor.

19. The wireless remote sensor system of claim 17 wherein said internal resonant circuit includes an internal coil and an internal capacitance.

20. The wireless remote sensor system of claim 16 wherein said Wheatstone bridge arrangement includes two variable resistors selected and arranged to amplify variations in said electromagnetic field resulting from variations in the parameter.

21. The wireless remote sensor system of claim 16 wherein said Wheatstone bridge arrangement includes four variable resistors selected and arranged to amplify variations in said electromagnetic field resulting from variations in the parameter.

22. The wireless remote sensor system of claim 19 wherein said internal capacitance is a variable capacitance that varies with a parameter to be sensed.

23. The wireless remote sensor system of claim 22 wherein said internal resonant circuit include a variable resistor that varies with a parameter to be sensed.

24. The wireless remote sensor system of claim 16 wherein said internal resonant circuit includes an internal coil, said internal coil including a first portion and a second portion, said first portion being counter-wound with respect to said second portion, said sense coil including a first portion and a second portion, said first portion of said sense coil being counter-wound with respect to said second portion of said sense coil.

25. The wireless remote sensor system of claim 24 wherein wireless power supply includes a transmitter coil, said sense coil being disposed within said transmitter coil;

and

wherein said internal coil is disposed within said receiver coil.

26. A wireless remote sensor system for sensing a parameter comprising:

an inductive transmitter with a transmitter coil;

a wireless remote sensor having a reference circuit and sensor circuit, said reference circuit including a receiver coil and a reference signal generator for generating a reference signal, said reference signal varying with at least one of circuit drift over time and variations in coupling between said transmitter coil and said receiver coil, said sensor circuit including a receiver coil, a variable impedance element that varies with the parameter and a sensor signal generator for generating a sensor signal, said sensor signal varying with variations in said variable impedance element and variations in at least one of circuit drift over time and coupling between said transmitter coil and said receiver coil of said sensor circuit; and

a signal receiver configured to receive said reference signal and said sensor signal, said signal receiver being configured to determine variations in said variable impedance element as a function of said reference signal and said sensor signal.

27. The system of claim 26 wherein said reference signal generator is a reference LED, said signal receiver including a first optical sensor configured to sense an intensity of said reference LED.

28. The system of claim 27 wherein said sensor signal generator is a sensor LED, said signal receiver including a second optical sensor configured to sense an intensity of said sensor LED.

29. The system of claim 28 wherein said variable impedance element is a variable resistor.

30. The system of claim 29 wherein said variable impedance element is a thermistor.

31. The system of claim 28 wherein said reference receiver coil and said sensor receiver coil are wrapped about a generally common axis and extend through a generally common plane.

32. The system of claim 31 wherein said reference receiver coil is a spiral wound coil and said sensor receiver coil is a spiral wound coil wound with winding substantially parallel to those of said reference receiver coil.

33. The system of claim 32 wherein said reference receiver coil defines an internal space;

and

wherein said reference LED and said sensor LED are disposed in said internal space.

34. The system of claim 33 wherein said transmitter coil defines an internal space;

and

wherein said first optical sensor and said second optical sensor are disposed in said internal space of said transmitter coil.

35. A wireless remote temperature sensor comprising:

a resonant circuit having a receiver coil and a capacitance, said receiver coil configured to receive power from an inductive transmitter; and

a substrate selected to vary in size in response to a change in temperature, said receiver coil supported by said substrate such that said substrate causes variation in a size or shape of said receiver coil when said substrate undergoes said change in temperature, said variation being sufficient to materially affect a reflected impedance of said receiver coil in the inductive transmitter.

36. The sensor of claim 35 wherein said substrate has a coefficient of thermal expansion selected to undergo expansion and contraction over said range of temperatures to be sensed, said receiver coil supported by said substrate such that said expansion and contraction of said substrate causes variations in said size or said shape of said receiver coil, said variations being sufficient to materially affect a reflected impedance of said receiver coil in the inductive transmitter.

37. The sensor of claim 36 wherein said receiver coil is a printed ink coil.

38. The sensor of claim 37 wherein said receiver coil is printed directly on said substrate.

39. The sensor of claim 36 wherein said receiver coil includes a plurality of undulations configured to permit said receiver coil to vary in shape with expansion and contraction of said substrate.

40. The sensor of claim 36 further including a re-resonator coil, said re-resonator coil supported by said substrate such that said expansion and contraction of said substrate causes variations in a size or shape of said re-resonator coil, said variations being sufficient to materially affect a reflected impedance of said re-resonator coil in the inductive transmitter.

41. The sensor of claim 40 wherein said re-resonator coil is a printed ink coil, said re-resonator coil disposed about said receiver coil.

42. A wireless remote sensor for sensing a parameter comprising:

a receiver coil configured to wireless receive power from a wireless power transmitter;

a voltage controlled oscillator operatively coupled to said receiver coil to receive power from said receiver coil; and

a variable impedance element coupled to said voltage controlled oscillator, whereby output oscillations of said voltage controlled oscillator are dependent on a value of said variable impedance element, said variable impedance element varying with a value of the parameter to be sensed, wherein a duty cycle of said output oscillations varies based on variations in said variable impedance element.

43. The remote sensor of claim 42 further including an antenna, said output oscillations of said voltage controlled oscillator being applied to said antenna, whereby said output oscillations may be communicated to a base sensor.

44. The remote sensor of claim 42 further including a signal coil, said output oscillations of said voltage controlled oscillator being applied to said signal coil, whereby said output oscillations may be communicated to a base sensor.

45. The remote sensor of claim 42 further including a load, said output oscillations of said voltage controlled oscillator being applied to a modulating subcircuit for modulating said load to said receiver coil, whereby said output oscillations may be communicated to a base sensor through said receiver coil by reflected impedance.

46. The remote sensor of claim 45 wherein said modulating subcircuit includes a MOSFET, said output oscillations being applied to a gate of said MOSFET.

47. The remote sensor of claim 46 wherein said MOSFET is coupled to a voltage offset circuit having a second variable impedance element, whereby a duty cycle of said load is dependent on a value of said second variable impedance element.

48. A wireless remote sensor system for sensing a parameter comprising:

an inductive transmitter with a transmitter coil;

a wireless remote sensor having;

a receiver coil configured to wireless receive power from a wireless power transmitter;

a voltage controlled oscillator operatively coupled to said receiver coil to receive power from said receiver coil; and

a variable impedance element coupled to said voltage controlled oscillator such that output oscillations of said voltage controlled oscillator are dependent on a value of said variable impedance element, said variable impedance element varying with a value of the parameter to be sensed, wherein a duty cycle of said output oscillations varies based on variations in said variable impedance element; and

a signal receiver configured to wirelessly receive a signal generated from said output oscillations, said signal receiver being configured to determine variations in said variable impedance element as a function of said received signal.

49. The wireless remote sensor system of claim 48 wherein said wireless remote sensor includes a transmitter antenna, said output oscillations of said voltage controlled oscillator being applied to said transmitter antenna for wireless transmission to said signal receiver.

50. The wireless remote sensor system of claim 49 wherein said signal receiver includes a receiver antenna configured to receive signals transmitted by said transmitter antenna.

51. The wireless remote sensor system of claim 48 wherein said wireless remote sensor includes a signal coil separate from said receiver coil, said output oscillations of said voltage controlled oscillator being applied to said signal transmit coil for wireless transmission to said signal receiver.

52. The wireless remote sensor system of claim 51 wherein said signal receiver includes a signal receive coil separate from said transmitter coil configured to receive signals transmitted by said signal transmit coil.

53. The wireless remote sensor system of claim 52 wherein said signal transmit coil and said signal receive coil are counterwound in a FIG. 8 configuration.