Electronic article surveillance label with field modulated dielectric

1. A security tag, comprising: a marker comprising a field modulated dielectric material operatively responsive to radio frequencies and having a reflection coefficient, said field modulated dielectric material including a plurality of microspheres or a plurality of microcapsules, said marker to receive an interrogation signal to cause said marker to generate a reply signal, said marker to receive a modulation signal to change said reflection coefficient of said field modulated dielectric material in synchrony with said modulation signal to modulate said reply signal to form a modulated reply signal.

2. The security tag of claim 1 , wherein said microspheres are embedded within a polymer matrix, said microspheres to rotate within said polymer matrix in response to said modulation signal, with each microsphere having a first reflection coefficient on a first side and a second reflection coefficient on a second side.

3. The security tag of claim 2 , wherein said modulation signal creates a first electric field and second electric field, said first electric field to cause said microspheres to rotate in a first direction to display said first reflection coefficient on said first side, and said second electric field to cause said microspheres to rotate in a second direction to display said second reflection coefficient on said second side.

4. The security tag of claim 3 , wherein said reply signal is modulated to form said modulated reply signal in accordance with said rotation.

5. The security tag of claim 1 , each microcapsule further comprising: a positive electrode on a first side and a negative electrode on a second side; and, positively charged microparticles having a first reflection coefficient and negatively charged microparticles having a second reflection coefficient.

6. The security tag of claim 5 , wherein said modulation signal causes said marker to create a first electric field and a second electric field, said first electric field to cause said positively charged microparticles to migrate to said positive electrode and said negatively charged microparlicles to migrate to said negative electrode thereby displaying said first reflection coefficient on said first side and said second reflection coefficient on said second side, and said second electric field to cause said positively charged microparticles to migrate to said negative electrode and said negatively charged microparticles to migrate to said positive electrode thereby displaying said second reflection coefficient on said first side and said first reflection coefficient on said second side.

7. The security tag of claim 6 , wherein said reply signal is modulated to form said modulated reply signal in accordance with said migration.

8. The security tag of claim 1 , wherein said interrogation signal comprises one of a 2.45 Gigahertz microwave signal and 915 Megahertz microwave signal.

9. The security tag of claim 1 , wherein said modulation signal comprises an electrical field signal with a frequency between 1 Hertz to 100 Kilohertz.

10. The security tag of claim 1 , wherein said interrogation signal is an electromagnetic first signal within a first frequency range .DELTA.f1, and said modulation signal is a magnetic second signal within a second frequency range .DELTA.f2, where .DELTA.f1>>.DELTA.f2, and said modulated reply signal is an electromagnetic third signal composed by said first signal, an amplitude of which is modulated by said second signal.

11. The security tag of claim 1 , wherein said interrogation signal is an electromagnetic first signal within a first frequency range .DELTA.f1, and said modulation signal is a magnetic second signal within a second frequency range .DELTA.f2, where .DELTA.f1>>.DELTA.f2, and said modulated reply signal is an electromagnetic third signal composed by said first signal, a frequency of which is modulated by said second signal.

12. A system, comprising: a transmitter to transmit an interrogation signal within an interrogation zone; a generator to generate a modulation signal; a security tag to receive said interrogation signal and said modulation signal, said security tag comprising a marker comprising a field modulated dielectric material having a reflection coefficient, said field modulated dielectric material including a plurality of microspheres or a plurality of microcapsules, said marker to generate a reply signal in response to said interrogation signal, and to change said reflection coefficient of said field modulated dielectric material in synchrony with said modulation signal to modulate said reply signal to form a modulated reply signal; a receiver to receive said modulated reply signal; and a controller to detect said security tag within said interrogation zone and output a detect signal.

13. The system of claim 12 , further comprising an alarm system to couple to said controller, said alarm system to receive said detect signal and generate an alarm in response to said detect signal.

14. The system of claim 12 , wherein said microspheres are embedded within a polymer matrix, said microspheres to rotate within said polymer matrix in response to said modulation signal, wit each microsphere having a first reflection coefficient on a first side and a second reflection coefficient on a second side.

15. The system of claim 14 , wherein said modulation signal creates a first electric field and second electric field, said first electric field to cause said microspheres to rotate in a first direction to display said first reflection coefficient on said first side, and said second electric field to cause said microspheres to rotate in a second direction to display said second reflection coefficient on said second side.

16. The system of claim 15 , wherein said reply signal is modulated to form said modulated reply signal in accordance with said rotation.

17. The system of claim 12 , each microcapsule further comprising: a positive electrode on a first side and a negative electrode on a second side; and, positively charged microparticles having a first reflection coefficient and negatively charged microparticles having a second reflection coefficient.

18. The system of claim 17 , wherein said modulation signal causes said marker to create a first electric field and a second electric field, said first electric field to cause said positively charged microparticles to migrate to said positive electrode and said negatively charged microparticles to migrate to said negative electrode thereby displaying said first reflection coefficient on said first side and said second reflection coefficient on said second side, and said second electric field to cause said negatively charged microparticles to migrate to said negative electrode and said negatively charged microparticles to migrate to said positive electrode thereby displaying said second reflection coefficient on said first side and said first reflection coefficient on said second side.

19. The system of claim 18 , wherein said reply signal is modulated to form said modulated reply signal in accordance with said migration.

20. The system of claim 12 , wherein said interrogation signal comprises one of a 2.45 Gigahertz microwave signal and 915 Megahertz microwave signal.

21. The system of claim 12 , wherein said modulation signal comprises an electrical field signal with a frequency between 1 Hertz to 100 Kilohertz.

22. A method, comprising:

receiving an interrogation signal at a marker comprising a field modulated dielectric material operatively responsive to microwave energy and having a reflection coefficient, said field modulated dielectric material including a plurality of microspheres or a plurality of microcapsules;

generating a reply signal in response to said interrogation signal;

receiving a modulation signal at said marker; and

modulating said reply signal in response to said modulation signal by changing said reflection coefficient for said marker to form a modulated reply signal.

23. The method of claim 22 , wherein said modulation signal creates a first electric field and a second electric field, and said modulating comprises: rotating said microspheres within said field modulated dielectric material in a first direction to display a first reflection coefficient on a first side in response to said first electric field to form a first reflection coefficient; and rotating said microspheres in a second direction to display a second reflection coefficient on a second side in response to said second electric field to form a second reflection coefficient.

24. The method of claim 23 , wherein said first reflection coefficient and second reflection coefficient modulates said reply signal to form said modulated reply signal.

25. The method of claim 22 , wherein said modulation signal causes said marker to create a first electric field and a second electric field, and said modulating comprises: moving positively charged microparticles to a positive electrode of said microcapsule and said negatively charged microparticles to a negative electrode of said microcapsule to display a first reflection coefficient on a first side of said microcapsule and a second reflection coefficient on a second side of said microcapsule in response to said first electric field to form first reflection coefficient; and moving said positively charged microparticles to said negative electrode and said negatively charged microparticles to said positive electrode to display said second reflection coefficient on said first side and said first reflection coefficient on said second side in response to said second electric field to form a second reflection coefficient.

26. The method of claim 25 , wherein said first reflection coefficient and second reflection coefficient modulate said reply signal to form said modulated reply signal.