Impedance matching network and multidimensional electromagnetic field coil for a transponder interrogator

• US 20050024198A1
• Filed: 09/01/2004
• Published: 02/03/2005
• Est. Priority Date: 07/20/1999
• Status: Active Grant

• Current Assignee: William H. Ward Jr
• Original Assignee: William H. Ward Jr
• Inventors: Ward, William H. Jr.
• Granted Patent: US 7,145,451 B2
• Time in Patent Office: Days
• US Class Current: 340/505
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil

Abstract

An improved interrogator for an inductively coupled identification system is disclosed. The interrogator provides a multidimensional electromagnetic field through a plurality of coils aligned relative to each other. The coils provide a rotating magnetic field having approximately constant amplitude regardless of orientation with respect to the transponder. An additional coil may be utilized to precess the multidimensional electromagnetic field. The interrogator may further provide an impedance matching network that includes a series drive capacitor to match the impedance of a capacitor in parallel with a coil to a driver load impedance.

Claims

1-22. -22. (Cancelled).

23. A radio frequency identification system interrogator, comprising:

a first antenna adapted to generate a first magnetic field component having a first phase;

a second antenna adapted to generate a second magnetic field component having a second phase;

a driver circuit coupled to the first and second antennas to provide at least one signal to cause the generation of first and second magnetic field components;

whereby said first and second magnetic fields generated by said first antenna and said second antenna interact to form a time varying composite magnetic field.

24. The interrogator of claim 23, further comprising a detector for detecting a transponder signal modulated on said time varying composite magnetic field.

25. The interrogator of claim 24, further comprising a processor for processing the transponder signal.

26. A radio frequency identification system, comprising:

an interrogator having,

a first coil inductor adapted to generate a first magnetic field component having a first phase;

a second coil inductor adapted to generate a second magnetic field component having a second phase, said first coil inductor and said second coil inductor mounted substantially perpendicular to each other and the first phase and the second phase are in quadrature;

means for exciting said first and second magnetic fields at a first frequency for generating a rotating composite magnetic field which rotates;

a passive detector for receiving the electromagnetic signal from said interrogator and transmitting a modulated electromagnetic signal to the interrogator at a second frequency, higher than said first frequency.

30. The interrogator of claim 26, wherein said driver further comprises:

an oscillator adapted to generate a first signal at twice a carrier frequency; and

a phase splitter coupled to said oscillator and adapted to split said first signal into an in-phase component to drive said first coil and a quadrature phase component to drive said second coil at said carrier frequency.

27. An interrogator for an identification system, comprising:

a first coil;

a second coil;

a driver coupled to and driving said first coil and said second coil by providing a phase differentiated time varying signal to each of said first and second coils to cause said coils to generate a rotating magnetic field;

a detector for detecting a transponder signal modulated on said rotating magnetic field; and

a processor for processing said transponder signal.

28. The interrogator of claim 27, wherein said driver further comprises:

an oscillator adapted to generate a first signal at twice a carrier frequency; and

a phase splitter coupled to said oscillator and adapted to split said first signal into an in-phase component to drive said first coil and a quadrature phase component to drive said second coil at said carrier frequency.

29. The interrogator of claim 27, wherein said processor further comprises:

at least one potentiometer coupled to said detector and adapted to nullify interference on said transponder signal;

an amplifier coupled to said at least one potentiometer and adapted to amplify said transponder signal;

a filter coupled to said amplifier and adapted to filter said transponder signal;

a demodulator coupled to said filter and adapted to demodulate said transponder signal;

at least one decoder coupled to said demodulator and adapted to decode said transponder signal; and

a signal processor coupled to said at least one decoder and adapted to process said transponder signal.

31. An interrogator for an inductively-coupled identification system, comprising:

a plurality of coils positioned relative to one another each energized with a different time varying drive signal adapted so as to generate a composite rotating magnetic field having an approximately constant amplitude in all orientations relative to a transponder.

32. The interrogator of claim 31, wherein said plurality of coils includes a first coil adapted to generate a first magnetic field component having a first phase and a second coil adapted to generate a second magnetic field component having a second phase.

33. The interrogator of claim 32, wherein said first and second coils are positioned substantially perpendicular to each other.

34. The interrogator of claim 33, wherein the first phase and the second phase are in quadrature.

35. The interrogator of claim 32, wherein the first phase magnetic field component and the second phase magnetic field component are in quadrature.

36. The interrogator of claim 32, further comprising a pickup coil positioned perpendicular to both of said first and second coils.

37. The interrogator of claim 31, further comprising a detector which detects a transponder signal modulated on the composite rotating magnetic field.

38. The interrogator of claim 37, further comprising a processor which processes the transponder signal.

39. The interrogator of claim 31, further comprising a series drive capacitor for each of said coils and through which said coils are driven, and a parallel tank capacitor for each said coil, wherein said series drive capacitor and said parallel tank capacitor provide an impedance matching network.

40. The interrogator of claim 31, further comprising a precession coil which generates a magnetic field component to precess said composite rotating magnetic field.

41. The interrogator of claim 40, wherein said precession coil is aligned relative to said plurality of coils and driven with a signal offset in frequency from at least one signal driving said plurality of coils.

42. The interrogator of claim 31, wherein said composite rotating magnetic field does not make a complete rotation and changes direction sufficiently to capture transponders with unfavorable orientations.

43. The interrogator of claim 31, further comprising impedance matching means for matching the impedance of said coils to a drive circuit of the interrogator.

44. The interrogator of claim 43, wherein said impedance matching means includes at least one of series and tank capacitors connected to said coils.

45. The interrogator of claim 31, wherein said coils are disposed perpendicular to one another.

46. The interrogator of claim 45, wherein a transponder in the plane of the axes of said coils senses an alternating magnetic field of full amplitude regardless of the angle of a transponder coil of the transponder with respect to said coils of the interrogator.

47. The interrogator of claim 31, further comprising an impedance matching network, said network including a capacitor in parallel with one of said coils and a series drive capacitor which matches the impedance of the capacitor to a driven load impedance.