Coded surveillance system having magnetomechanical marker

• US 4,510,490 A
• Filed: 06/03/1982
• Issued: 04/09/1985
• Est. Priority Date: 04/29/1982
• Status: Expired due to Term

• Current Assignee: Identitech Corporation
• Original Assignee: Allied Corp. (Honeywell International Inc.)
• Inventors: Anderson, Philip M. III, Kearney, James E., Bretts, Gerald R.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US06/384,814
• Time in Patent Office: 1,041 Days
• Field of Search: 340/572, 340/552, 340/561, 340/567, 340/568, 340/551, 343/6.8 R, 343/6.5 R, 343/6.5 SS, 343/6.8 LC, 324/201, 324/260
• US Class Current: 340/572.1
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G06K 19/0672 with resonating marks
• CPC Class Codes: G06K 7/086 sensing passive circuit, e.g. resonant circuit transponders
• CPC Class Codes: G08B 13/24 by interference with electromagnetic field distribution
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver
• CPC Class Codes: H01F 1/153 Amorphous metallic alloys, e.g. glassy metals making ferrous amorphous alloys C22C33/003
• CPC Class Codes: Y10S 428/928 Magnetic property

Abstract

A magnetic article surveillance system marker is adapted, when armed, to resonate at preselected frequencies provided by an incident magnetic field applied within an interrogation zone. The marker is a plurality of elongated ductile strips of magnetostrictive ferromagnetic material each of the strips being disposed adjacent to a ferromagnetic element which, upon being magnetized, magnetically biases the strips and arms them to resonate at the preselected frequencies. A substantial change in effective magnetic permeability of the marker at the preselected frequencies provides the marker with signal identity.

Claims

1. For use in a magnetic article surveillance system, a marker adapted to (i) mechanically resonate at preselected frequencies provided by an incident magnetic field applied within an interrogation zone, and (ii) undergo a substantial change in effective magnetic permeability at each of said preselected frequencies that provides said marker with signal identity, said marker comprising a plurality of strips of magnetostrictive ferromagnetic material, each of said strips being adapted to be magnetically biased and thereby armed to resonate at a single, different one of said preselected frequencies, and having a magnetomechanical coupling factor, k, greater than 0, where k=√

(1-f_r² /f_a²), f_r and f_a being the resonant and antiresonant frequencies, respectively.

2. A marker as recited in claim 1, wherein said material is at least 50 percent amorphous.

3. A marker as recited in claim 2, wherein said material has a composition consisting essentially of the formula M_a N_b O_c X_d Y_e Z_f, where M is at least one of iron and cobalt, N is nickel, O is at least one of chromium and molybdenum, X is at least one of boron and phosphorous, Y is silicon, Z is carbon, "a"-"f" are in atom percent, "a" ranges from about 35-85, "b" ranges from about 0-45, "c" ranges from about 0-7, "d" ranges from about 5-22, "e" ranges from about 0-15 and "f" ranges from about 0-2, and the sum of d+e+f ranges from about 15-25.

4. A marker as recited in claim 1, wherein said material is at least 80 percent amorphous.

5. A marker as recited in claim 1, wherein each of said strips is sandwiched between the faces of two pieces of fabric, each of said pieces of fabric having planar dimensions greater than the corresponding aggregate dimensions of said strips, said pieces of fabric being joined together at the edges thereof to form fabric sandwiched strips.

6. A marker as recited in claim 5, wherein said fabric sandwich strips are disposed within an airtight casing of polymeric film.

7. A marker as recited in claim 1, wherein said incident magnetic field is swept to provide said frequencies.

8. A marker as recited in claim 1, wherein each of said frequencies is provided in the form of a pulse.

9. A marker as recited in claim 8, wherein each of said pulses has a width equal to 1/(2f_r), where f_r is the resonant frequency of said strip.

10. A marker as recited in claim 1, wherein said change in effective magnetic permeability is of the order of 1200%.

11. A marker as recited in claim 1, wherein said strip is magnetically biased by a magnetic bias field ranging from about 0.1 to 20 Oe.

12. A marker as recited in claim 11, wherein said magnetic bias field has a magnitude which yields a maximum k.

13. A marker as recited in claim 1, wherein said strips are annealed in a saturating magnetic field applied thereto in a direction perpendicular to the length thereof.

14. A marker as recited in claim 13, wherein said strips are annealed at a temperature ranging from about 300°

to 450°

C. for an annealing time ranging from about 7 to 120 min.

15. A marker as recited in claim 1, wherein said marker further comprises at least one ferromagnetic element disposed adjacent to said strips and adapted to magnetically bias said strips and arm them to resonate at said preselected frequencies.

16. A marker as recited in claim 15 wherein said ferromagnetic element has coercivity higher than that of any of the magnetostrictive material of the strips.

17. A marker as recited in claim 15, wherein said ferromagnetic element is adapted to further magnetically bias said strips to decrease resonances and thereby dearm the marker.

18. A marker as recited in claim 15, wherein said material is at least 50 percent amorphous.

19. A marker as recited in claim 18, wherein said ferromagnetic element has coercivity higher than said amorphous material.

20. A marker as recited in claim 15, wherein said material is at least 80 percent amorphous.

21. A marker as recited in claim 20, wherein each of said strips is comprised of amorphous material and said ferromagnetic element comprises a crystalline region of the amorphous material of each strip.

22. A marker as recited in claim 16, wherein said ferromagnetic element comprises a plurality of pieces of high magnetic coercivity material, each of said strips having a different one of said pieces disposed adjacent thereto.

32. A marker as recited in claim 6, wherein said casing is seated with air contained therein to form a pillow-like shape.

23. An article surveillance system responsive to the presence of at least one of a plurality of markers within an interrogation zone, comprising:

a. means for defining an interrogation zone;

b. generating means for generating a magnetic field having a frequency band within said interrogation zone said generating means including an interrogating coil;

c. a plurality of markers associated with an article appointed for passage through said interrogation zone, each of said markers being adapted to undergo a substantial change in its effective magnetic permeability at a different preselected frequency within said frequency band that provides each of said markers with signal identity, and comprising a strip of magnetostrictive, ferromagnetic material adapted to be magnetically biased and thereby armed to mechanically resonate at a single frequency within the frequency band of said magnetic field, said strip having a magnetomechanical coupling factor, k, greater than 0, where k=√

(1-f_r² /f_a²), f_r and f_a being the resonant and anti-resonant frequencies, respectively; and

d. detecting means for detecting said mechanical resonances of said markers within said interrogation zone at each different preselected frequency.

24. An article surveillance system as recited in claim 23, wherein said generating means includes frequency sweeping means adapted to sweep through each different preselected frequency of said markers.

25. An article surveillance system as recited in claim 23, wherein said generating means includes energizing means adapted to provide said interrogating coil with a burst of sine wave frequencies that includes each said different preselected frequency.

26. An article surveillance system as recited in claim 23, wherein said generating means includes energizing means adapted to provide said interrogating coil with pulses, wherein the width of each pulse is equal to 1/(2f_r) where f_r is the preselected frequency.

27. An article surveillance system as recited in claim 23, wherein said generating means includes energizing means adapted to provide said interrogating coil with a burst of noise.

28. An article surveillance system as recited in claim 23, wherein said generating means includes energizing means adapted to provide said interrogating coil with a burst of sweeping sine wave frequency.

29. An article surveillance system as recited in claim 23 wherein said generating means includes energizing means for providing said interrogating coil with an energizing signal, said detecting means includes receiving means for distinguishing a resonant frequency for each of said markers detected by said receiving coil from other frequencies induced therein and said system further includes synchronizing means associated with said energizing means and said receiving means for sequentially activating and deactivating each of said energizing means and said receiving means.

30. An article surveillance system as recited in claim 29, wherein said synchronizing means is adapted to prevent activation of said energizing means for substantially the entire period of time that said receiving means is activated.

31. An article surveillance system as recited in claim 30, wherein said synchronizing means is adapted to prevent activation of said receiving means for substantially the entire period of time that said energizing means is activated.

33. An article surveillance system as recited in claim 29, wherein each of said markers comprises a plurality of strips of magnetostrictive, ferromagnetic material and said receiving means is adapted to distinguish all resonant frequencies for each of said markers detected by said receiving coil from other frequencies induced therein.