Wireless monitoring and identification using spatially inhomogeneous structures

• US 6,472,987 B1
• Filed: 07/14/2000
• Issued: 10/29/2002
• Est. Priority Date: 07/14/2000
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Gershenfeld, Neil, Fletcher, Richard
• Primary Examiner(s): TRIEU, VAN THANH
• Application Number:
  US09/617,249
• Time in Patent Office: 837 Days
• Field of Search: 340/572.6, 340/572.1, 340/551, 340/572.2, 340/572.4, 340/572.7, 428/694.TM, 148/304, 148/403, 148/442, 235/449, 235/493, 420/581
• US Class Current: 340/572.4
• CPC Class Codes: G06K 19/0672 with resonating marks
• CPC Class Codes: G08B 13/2408 using ferromagnetic tags
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip

Abstract

Tags encode information by means of spatial inhomogeneities that may be detected in the time domain; in effect, characteristics in space are transformed into time for sensing purposes. Such tags may be very inexpensively produced yet carry appreciable quantities of data. The inhomogeneities may be obtained by simple physical modifications to, or externally applied field biases operating on, materials that are very inexpensive to procure.

Claims

1. A method of sensing information, the method comprising the steps of:

a. providing-a magnetically responsive element having a length;

b. varying, along the length of the element, the responsiveness of the element to an applied field in a spatial pattern corresponding to the information, such that a propagation rate of a magnetic response along the length will vary in accordance with the spatial pattern;

c. subjecting the element to an applied field to induce the magnetic response therein; and

d. sensing changes in the response propagation rate to recover the spatially-encoded information.

2. The method of claim 1 wherein:

a. the element is amorphous and magnetically susceptible;

b. the applied field is a magnetic field; and

c. the response of the element to the field is sensed over time or as a function of phase to recover the spatially encoded information.

3. The method of claim 2 wherein the element is a thin, elongated, amorphous metal wire having a width smaller than a magnetic domain, such that application of the magnetic field causes a domain wall to propagate along the length of the element.

4. The method of claim 2 wherein the responsiveness is varied by application of bias fields operative within discrete spatial regions, the bias fields selectively retarding or enhancing magnetic induction through the element, sensing of the induction revealing the information.

5. The method of claim 4 wherein the bias fields are contained within a magnetic bias strip in proximity to the element.

6. The method of claim 2 wherein the element has a length and responsiveness is varied by introducing discrete physical modifications along the length of the element, the physical modifications selectively retarding or enhancing magnetic induction through the element, sensing of the induction revealing the information.

7. The method of claim 6 wherein magnetic induction in the element propagates as a domain wall, the physical modifications functioning as domain wall barriers.

8. A system for encoding and sensing information, the system comprising:

a. a field-responsive element having a length along which is varied the responsiveness of the element to an applied field, the variation conforming to a spatial pattern corresponding to the information, such that a propagation rate of a magnetic response along the length will vary in accordance with the spatial pattern; and

b. means for sensing a time-dependent response of the element to an applied field to recover the spatially encoded information.

9. The system of claim 8 wherein:

a. the element is elongated, amorphous, and magnetically susceptible;

b. the applied field is a magnetic field; and

c. the sensing means senses the response of the element to the field over time or as a function of phase to recover the spatially encoded information.

10. The system of claim 9 wherein the element is a thin amorphous metal wire having a width smaller than a magnetic domain, such that application of the magnetic field causes a domain wall to propagate along the length of the element.

11. The system of claim 9 further comprising means for applying a series of bias fields operative within discrete spatial regions of the magnetically susceptible element, the bias fields varying the responsiveness of the element by selectively retarding or enhancing magnetic induction through the element, the sensing means sensing the induction to reveal the information.

12. The system of claim 11 wherein the bias fields are contained within a magnetic bias strip in proximity to the element.

13. The system of claim 9 wherein the element comprises discrete physical modifications along the length thereof, the modifications varying the responsiveness of the element by selectively retarding or enhancing magnetic induction through the element, the sensing means sensing the induction to reveal the information.

14. The system of claim 13 wherein magnetic induction in the element propagates as a domain wall, the physical modifications functioning as domain wall barriers.