Magnetic field response measurement acquisition system

• US 20050007239A1
• Filed: 04/30/2004
• Published: 01/13/2005
• Est. Priority Date: 04/30/2003
• Status: Active Grant

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: U.S.A. as represented by the Administrator of the National Aeronautics and Space Administration
• Inventors: Taylor, Bryant D., Woodard, Stanley E., Fox, Robert L., Shams, Qamar A., Bryant, Robert G., Fox, Melanie L.
• Granted Patent: US 7,086,593 B2
• Time in Patent Office: Days
• US Class Current: 340/10.200
• CPC Class Codes: B60C 11/243 Tread wear sensors, e.g. electronic sensors
• CPC Class Codes: B60C 23/0449 Passive transducers, e.g. using surface acoustic waves, backscatter technology or pressure sensitive resonators near field passive transducers B60C23/0428
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: G01F 23/26 by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
• CPC Class Codes: G01F 23/263 by measuring variations in capacitance of capacitors
• CPC Class Codes: G01F 23/268 mounting arrangements of probes
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01L 19/086 for remote indication
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00

Abstract

Magnetic field response sensors designed as passive inductor-capacitor circuits produce magnetic field responses whose harmonic frequencies correspond to states of physical properties for which the sensors measure. Power to the sensing element is acquired using Faraday induction. A radio frequency antenna produces the time varying magnetic field used for powering the sensor, as well as receiving the magnetic field response of the sensor. An interrogation architecture for discerning changes in sensor'"'"'s response frequency, resistance and amplitude is integral to the method thus enabling a variety of measurements. Multiple sensors can be interrogated using this method, thus eliminating the need to have a data acquisition channel dedicated to each sensor. The method does not require the sensors to be in proximity to any form of acquisition hardware. A vast array of sensors can be used as interchangeable parts in an overall sensing system.

Claims

1. A magnetic field response measurement acquisition system, comprising:

one or more inductively powered magnetic field response sensors;

antenna means for transmitting radio frequency energy to and receiving radio frequency energy from said one or more sensors;

an interrogation means for regulating said radio frequency transmission and reception, and for analyzing the signals received from said one or more sensors, wherein said processor means can interrogate multiple sensors concurrently using a single acquisition channel, does not require that said signals from said one or more sensors be transmitted as modulated signals on a radio frequency carrier, and can acquire more than one measurement from each said sensor.

2. The acquisition system of claim 1, wherein said antenna means is a single switching antenna.

3. The acquisition system of claim 1, wherein said antenna means is separate transmission and receiving antennae.

4. The acquisition system of claim 1, wherein said interrogation means is portable.

5. The acquisition system of claim 1, wherein said interrogation means is handheld.

6. The acquisition system of claim 1, wherein said one or more sensors are selected from the group consisting of inductor-capacitor circuits powered by Faraday induction and inductor-capacitor-resistor circuits powered by Faraday induction.

7. The acquisition system of claim 6, wherein the responses of said sensors change corresponding with a change in the physical states that said sensors measure.

8. The acquisition system of claim 7, wherein the attributes of said responses are one or more attributes selected from the group consisting of frequency, amplitude and bandwidth.

9. The acquisition system of claim 1, wherein said system has the ability to acquire measurements resulting from changes in capacitor geometric, capacitor dielectric, inductor geometric, inductor permeability, and resistance.

10. The acquisition system of claim 1, wherein said antenna means are one or more broadband antennas.

11. The acquisition system of claim 1 having more than one sensor, wherein the range of measurement frequencies of said sensors are within the range of said antenna means but do not overlap.

12. The acquisition system of claim 8, wherein said individual ranges of resonant frequencies correspond to the physical property values to be measured.

13. The acquisition system of claim 1, wherein said one or more sensors are embedded in material that is transmissive to radio frequency energy.

14. The acquisition system of claim 1, wherein said antenna means is a metallic foil.

The acquisition system of claim 1, wherein said antenna means is a thin film deposited on a dielectric membrane.

15. The acquisition system of claim 1, wherein said one or more sensors are fabricated using metal deposition.

16. The acquisition system of claim 6, wherein one or more sensors has a capacitor embedded in a conducting material and an inductor placed away from the surface of the conductive material.

17. The acquisition system of claim 2, wherein said interrogation means comprises the following steps:

(a) at the lower limit of a predetermined range, transmitting a radio frequency harmonic for a predetermined length of time from said antenna;

(b) switching said transmission mode of said antenna off;

(c) turning the receiving mode of said antenna on;

(d) rectifying the received response from said sensor to determine its amplitude;

(e) storing the amplitude, A_i(t), and the frequency, ω

_i(t), of the response;

(f) switching the receiving mode off and the transmission mode on;

(g) shifting the transmitted radio frequency harmonic by a predetermined amount;

(h) transmitting the harmonic for a predetermined length of time;

(i) switching the transmission mode off;

(j) switching the receiving mode on;

(k) rectifying the received response from said sensor to determine its amplitude;

(l) storing said current amplitude, A_i, and said frequency, ω

_i;

(m) comparing said amplitude, A_i, to the two previously recorded amplitudes, A_i-1 and A_i-2;

(n) if said previous amplitude, A_i-1, is greater than said amplitude, A_i, and the previous amplitude, A_i-1, is greater than the amplitude prior to it, A_i-2, storing said amplitude, A_i-1, as the amplitude inflection and the corresponding frequency, ω

_i-1, for the current frequency sweep;

(o) comparing said amplitudes obtained in step (n) with the amplitudes of the next subsequent sweep;

(p) repeating steps (f) through (l) if an amplitude inflection has not been reached; and

(q) once amplitude inflection has been reached, continuing the sweep to said next sensor.

25. The acquisition system of claim 3, wherein said interrogation means comprises the following steps:

(a) at the lower limit of a predetermined range, transmitting a radio frequency harmonic for a predetermined length of time from said antenna;

(b) turning said transmission antenna;

(c) turning said receiving antenna on;

(d) rectifying the received response from said sensor to determine its amplitude;

(e) storing the amplitude, A_i(t), and the frequency, ω

_i(t), of the response;

(f) turning said receiving antenna off and transmission antenna on;

(g) shifting the transmitted radio frequency harmonic by a predetermined amount;

(h) transmitting the harmonic for a predetermined length of time;

(i) turning said transmission antenna off;

(j) turning said receiving antenna on;

(k) rectifying the received response from said sensor to determine its amplitude;

.

(l) storing said current amplitude, A_i, and said frequency, ω

_i;

(m)comparing said amplitude, A_i, to the two previously recorded amplitudes, A_i-1 and A_i-2;

(n) if said previous amplitude, A_i-1, is greater than said amplitude, A_i, and the previous amplitude, A_i-1, is greater than the amplitude prior to it, A_i-2, storing said amplitude, A_i-1, as the amplitude inflection and the corresponding frequency, ω

_i-1, for the current frequency sweep;

(o) comparing said amplitudes obtained in step (n) with the amplitudes of the next subsequent sweep;

(p) repeating steps (f) through (1) if an amplitude inflection has not been reached; and

(q) once amplitude inflection has been reached, continuing the sweep to said next sensor.

33. The acquisition system of claim 1, wherein said interrogation means comprises:

an one antenna for transmitting and receiving a varying magnetic field;

a microcontroller that places said antenna into transmission mode and submits a binary code to a frequency synthesizer, said frequency synthesizer concerting said code into a square wave with the frequency of the wave dependent on said binary code;

a high-speed amplifier that amplifies said square wave;

a low pass filter that attenuates all frequencies that are higher than a prescribed frequency for application to said antenna for a prescribed number of cycles;

applying said low pass filter signal to said antenna for a prescribed number of cycles;

a radio frequency receiving/transmission switch for switching said antenna to receiving mode;

a high speed amplifier that amplifies the signal from said sensor after it is received from said antenna;

a diode peak detector that rectifies said amplified signal and creates a DC value proportional to signal amplitude;

an op amp that amplifies said DC voltage from said peak detector;

an analog to digital converter that converts said signal from said op amp to a digital signal; and

said microcontroller storing the amplitude of digital signal and the transmission frequency.

39. The acquisition system of claim 1, wherein one or more said sensors is metamorphic.

40. The acquisition system of claim 1, wherein one or more said sensors is multifunctional.

41. The acquisition system of claim 1, wherein at least one said sensor is mounted to a conductive surface, further wherein said sensor has an inductor that has a fixed separation from said conductive surface.

42. The acquisition system of claim 1, wherein at least one said sensor is measuring response of a conductive cavity, further wherein the inductor of said sensor is mounted external to said cavity at a fixed distance from said cavity wall, the capacitor of said sensor is mounted internal to said cavity, and said antenna is mounted external to said cavity.

43. The acquisition system of claim 1, wherein multiple sensors measure response of a conductive cavity, further wherein said inductors of said sensors are mounted external to said cavity at a fixed distance from said cavity wall, and said antenna is mounted internal to said cavity.

44. The acquisition system of claim 1, wherein at least one sensor measures material phase transition.

45. The acquisition system of claim 1, wherein at least one sensor measures one or more attributes selected from the group consisting of strain, fluid-level, proximity, displacement, shear, torsion, pressure, angular orientation, dielectric level, fluid level, solid particle level, material phase transition, moisture exposure, chemical exposure, stoichemetric changes, wear, bond separation, identification of conductive materials, relative place orientation, and displacement rate.

46. The acquisition system of claim 1, wherein at least one said sensor comprises one or more interdigital electrodes positioned such that said electrodes are parallel to a surface of wear.

47. The acquisition system of claim 1, wherein at least one said sensor comprises one or more interdigital electroplates.

49. The acquisition system of claim 1, wherein at least one said sensor comprises two parallel electroplates for displacement measurements.

50. The acquisition system of claim 1, wherein at least one said sensor comprises a dielectric affixed to a stationary electroplate for displacement measurements.

51. The acquisition system of claim 1, wherein at least one said sensor comprises n pairs of parallel electroplates separated by a dielectric medium, for fluid level measurement.

52. The acquisition system of claim 1, wherein at least one said sensor comprises two parallel electroplates separated by a dielectric medium, for fluid level measurement.

18. The acquisition system of claim 18, wherein the sweep rate for each said sensor is dependent on the rate of change of the physical state being measured.

19. The acquisition system of claim 18, wherein said sensors have one or more different resolutions.

20. The acquisition system of claim 18, wherein the resolution of one or more sensors is not fixed.

21. The acquisition system of claim 18, wherein dynamic measurements are obtained by comparing variation in one ore more responses selected from the group consisting of frequencies, of a current sweep with those of prior sweeps.

22. The acquisition system of claim 18, wherein a change in position of a sensor is obtained from comparison of amplitude variations of successive sweeps.

23. The acquisition system of claim 18, wherein said interrogation means determines amplitude, frequency and bandwidth variation with time.

24. The acquisition system of claim 18, wherein said first sweep determines all resonant frequencies and corresponding amplitudes.

35. The acquisition system of claim 18, wherein data is stored for the entire range, followed by peak amplitudes being determined for each said sensor, further wherein said peak amplitudes and corresponding frequencies are stored for comparisons to subsequent sweeps.

37. The acquisition system of claim 18, further comprising a data file corresponding to each said sensor, comprising said sensor type, response variation, frequency partition and measurement band for each said partition sweep after said resonant is identified on said initial sweep and further comprising a table that correlates response variation to a physical state, said data files for each said sensor concatenated to form an aggregate file.

26. The acquisition system of claim 26, wherein the sweep rate for each said sensor is dependent on the rate of change of the physical state being measured.

27. The acquisition system of claim 26, wherein said sensors have one or more different resolutions.

28. The acquisition system of claim 26, wherein the resolution of one or more sensors is not fixed.

29. The acquisition system of claim 26, wherein dynamic measurements are obtained by comparing variation in one ore more responses selected from the group consisting of frequencies, of a current sweep with those of prior sweeps.

30. The acquisition system of claim 26, wherein a change in position of a sensor is obtained from comparison of amplitude variations of successive sweeps.

31. The acquisition system of claim 26, wherein said interrogation means determines amplitude, frequency and bandwidth variation with time.

32. The acquisition system of claim 26, wherein said first sweep determines all resonant frequencies and corresponding amplitudes.

36. The acquisition system of claim 26, wherein data is stored for the entire range, followed by peak amplitudes being determined for each said sensor, further wherein said peak amplitudes and corresponding frequencies are stored for comparisons to subsequent sweeps.

38. The acquisition system of claim 26, further comprising a data file corresponding to each said sensor, comprising said sensor type, response variation, frequency partition and measurement band for each said partition sweep after said resonant is identified on said initial sweep and further comprising a table that correlates response variation to a physical state, said data files for each said sensor concatenated to form an aggregate file.

34. The acquisition system of claim 34, comprising separate transmission and receiving antennae.

48. The acquisition system of claim 48, wherein said sensor further comprises an element positioned between said electroplates, said elements selected from the group consisting of temperature sensitive dielectric, thermomagnetic, and phase transition dielectric.