Electrically active resonant structures for wireless monitoring and control

• US 6,025,725 A
• Filed: 12/04/1997
• Issued: 02/15/2000
• Est. Priority Date: 12/05/1996
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Gershenfeld, Neil, Fletcher, Richard
• Primary Examiner(s): Do, Diep N.
• Application Number:
  US08/984,929
• Time in Patent Office: 803 Days
• Field of Search: 324/649, 324/652, 324/653, 324/655, 324/234, 324/236, 324/239, 361/268, 361/270, 363/20, 363/200, 363/207, 363/232, 331/65, 331/66, 340/572.5, 340/551, 29/25.42
• US Class Current: 324/652
• CPC Class Codes: H01F 17/0006 Printed inductances printed coils for dynamo-electric machines H02K3/26; printed circuits H05K

Abstract

A planar electromagnetic resonator utilizes an electromagnetically active material located between the capacitive or inductive elements of the resonator. A microscopic electrical property of this material is altered by an external condition, and that alteration, in turn, affects the behavior of the resonator in a consistent and predictable manner.

Claims

1. A device for remote sensing comprising an inductor and a capacitor connected to form an electrical circuit having a resonant frequency, the capacitor comprising a pair of conductors separated by a dielectric, the device comprising a material having an intrinsic electrical property altered by an external condition, alteration of the electrical property remotely detectably varying at least one characteristic of the circuit selected from resonant frequency, harmonic spectra and Q factor.

2. The device of claim 1 wherein the external condition is at least one of (a) applied force, (b) temperature, (c) humidity, and (d) light.

3. The device of claim 1 wherein the material having an intrinsic electrical property is also the dielectric.

4. The device of claim 3 wherein the intrinsic electrical property is charge leakage.

5. The device of claim 3 wherein the material is polyvinylidene difluoride in sheet form.

6. The device of claim 3 wherein the material is a piezoelectric ceramic.

7. The device of claim 3 wherein the material is a photoconductive polymer.

8. The device of claim 3 wherein the material is magnetostrictive.

9. The device of claim 3 wherein the material is ferroelectric.

10. The device of claim 1 wherein the material having an intrinsic electrical property is also the inductor.

11. The device of claim 10 wherein the intrinsic electrical property is magnetic permeability.

12. The device of claim 1 wherein the inductor comprises at least two pancake spirals of conductive material each disposed on an insulative sheet, the spirals having outermost loops electrically connected to one another, the spirals being disposed opposite one another to also serve as plates forming the capacitor, and the dielectric material being located between the spirals.

13. The device of claim 12 wherein the spirals are located on the same insulative sheet in spaced-apart relation to one another, the spirals being disposed opposite one another by folding of the sheet.

14. The device of claim 12 wherein the spirals each comprise an inner terminus, the inner terminus of at least one of the spirals comprising a solid area of conductive material.

15. The device of claim 3 wherein the dielectric material is sealed between the conductors.

16. The device of claim 3 wherein at least a portion of the dielectric material is at least partially exposed.

17. A method of sensing an external condition, the method comprising:

a. providing a device for remote sensing comprising an inductor and a capacitor connected to form an electrical circuit having a resonant frequency, the capacitor comprising a pair of conductors separated by a dielectric, the device comprising a material having an intrinsic electrical property altered by an external condition, alteration of the electrical property remotely detectably varying at least one characteristic of the circuit selected from resonant frequency, harmonic spectra and Q factor;

b. exposing the device to the external condition;

c. wirelessly measuring the characteristic; and

d. based on the measured characteristic, determining the external condition.

18. The method of claim 17 wherein the measurement is a time-domain measurement.

19. The method of claim 17 wherein the measurement is a frequency-domain measurement.

20. The method of claim 17 wherein the external condition is at least one of (a) applied force, (b) temperature, (c) humidity, (d) light.

21. The method of claim 17 wherein the wireless measurement step comprises applying a signal to the device and measuring power reflected from the package.

22. The method of claim 17 wherein the wireless measurement step comprises applying a signal to the device from a transmit antenna and measuring power received by a receive antenna.

23. The method of claim 17 wherein the wireless measurement step comprises applying a signal pulse to the device and, after the pulse, measuring ringdown from the device.

24. The method of claim 17 wherein the wireless measurement step comprises applying a signal to the device and measuring a resulting harmonic spectrum.

25. The method of claim 17 further comprising the step of providing first and second device each comprising a pair of conductors separated by a dielectric, each device comprising a material having an intrinsic electrical property altered by an external condition, alteration of the electrical property remotely detectably varying at least one characteristic of the circuit selected from resonant frequency, harmonic spectra and Q factor, the variation differing between the devices, and further comprising the steps of:

a. simultaneously wirelessly measuring at least one characteristic of the first and second circuits selected from resonant frequency, harmonic spectra and Q factor; and

b. based on the measured characteristic, determining the external condition relative to the first and second circuits.

26. The method of claim 17 wherein the characteristic is resonant frequency.

27. The method of claim 17 wherein the characteristic is Q factor.

28. The method of claim 17 wherein the characteristic is harmonic spectra.

29. A method of determining location comprising the steps of:

a. providing a plurality of devices, each device comprising

a coil and a capacitor forming a circuit having a resonant frequency;

b. electrically exciting the devices to produce interacting electrical signals;

c. sensing the signals as a function of time; and

d. based thereon, determining a location of at least one of the devices.

30. The method of claim 29 wherein the sensing step comprises measuring nonlinear time-domain signals and signal interactions.

31. The method of claim 29 wherein the sensing step comprising measuring energy at a plurality of frequencies as a function of time.