Impedance matching coil assembly for an inductively coupled transponder

• US 5,084,699 A
• Filed: 08/30/1989
• Issued: 01/28/1992
• Est. Priority Date: 05/26/1989
• Status: Expired due to Term

• Current Assignee: Algernon Promotions Inc
• Original Assignee: Trovan Ltd
• Inventors: DeMichele, Glenn A.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Weissman, Peter
• Application Number:
  US07/400,600
• Time in Patent Office: 881 Days
• Field of Search: 340/825.54, 340/825.31, 340/825.34, 340/870.31, 340/870.32, 340/870.34, 340/870.35, 340/572, 340/825.72, 340/825.3, 343/867, 343/742, 324/207.18, 324/207.22, 324/207.26, 336/182, 336/183, 336/184, 336/125, 336/126
• US Class Current: 340/10.34
• CPC Class Codes: B61L 25/04 Indicating or recording train identities
• CPC Class Codes: B61L 25/043 using inductive tags
• 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 7/10178 including auxiliary means for focusing, repeating or boosting the electromagnetic interrogation field comparable booster antennas integrated on the record carrier itself G06K19/07794
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil

Abstract

A coil assembly for use in an inductively powered transponder including a primary coil and a secondary coil wrapped around the same coil forming ferrite rod. The primary coil'"'"'s leads are left floating while the secondary coil'"'"'s leads are connected to the integrated identification circuit of the transponder. There are approximately three times as many turns to the primary coil as there are turns to the secondary coil. The primary coil is configured to self resonate at the operating frequency of the identification circuit when brought within range of an interrogator'"'"'s magnetic field, thereby creating a voltage across the primary coil having a high source impedance. The secondary coil is configured to resonate at the same operating frequency, but to convert the high source impedance level of the primary coil to a low source impedance level, which is more suitable for powering the identification circuit and which substantially matches the impedance level of the secondary coil to the impedance level of the interrogator field, thereby maximizing the quantity of energy which can be transferred between the interrogator and the transponder.

Claims

1. A transponder coil assembly for disposition in a transmitted electromagnetic field and operative to transfer power derived from the electromagnetic field to an associated integrated circuit device in electrical communication with the coil assembly, comprising:

a magnetic core;

first coil means including a first length of wire wound about said core and having a first predetermined number of turns, the ends of said first length of wire being open-circuited such that said first coil means and its interturn capacitance form a resonant circuit operative to convert energy within said field into inductive power at a first impedance level; and

second coil means including a second length of wire wound around said core and inductively coupled to said first coil means, said second coil means being operative to convert said inductive power into an electrical power signal at a second impedance level and to output said power signal to an integrated circuit device connected across the ends of said second length of wire.

2. A transponder coil assembly as recited in claim 1, wherein said second number of turns is substantially fewer in number than said first number of turns.

3. A transponder coil assembly as recited in claim 2, wherein the square of the ratio of said first number of turns to said second number of turns is proportional to the ratio of said first impedance level to said second impedance level.

4. A transponder coil assembly as recited in claim 3, wherein said first impedance level is at least six times greater than said second impedance level, whereby the voltage of said inductive power is stepped down and the current of said inductive power is stepped up when said inductive power is converted to said power signal.

5. A transponder coil assembly as recited in claim 1, wherein said field is transmitted to said coil assembly at a first frequency, and wherein said first coil means is operative to self-resonate at said first frequency so as to maximize the quantity of energy derived from said field and converted by said first coil means into said inductive power.

6. In a transponder having an integrated identification circuit device in electrical communication with a coil assembly that is wrapped about a magnetic core and is operative to be inductively coupled to a transmitter by an electromagnetic field, and is further operative to transfer power derived from the field to the circuit device, an improved coil assembly comprising:

first coil means including a first length of conductive wire disposed in winding relation around said core and having its ends open circuited, said first coil means being operative to inductively couple with said electromagnetic field and convert the energy within said electromagnetic field into an induction power field having a first impedance level; and

second coil means including a second length of conductive wire disposed in winding relation around said core and having its ends coupled to said circuit device, said second coil means being operative to receive said power field, to convert the energy in said power field into an electrical power signal having a second impedance level, and to output said power signal to said circuit device through its coupled ends, whereby the power transferred to said circuit device is at said second impedance level.

7. An improved coil assembly as recited in claim 6, wherein said first length of wire includes a first number of turns disposed in winding relation around said core, and said second length of wire includes a second number of turns substantially fewer in number than said first number of turns and disposed in winding relation around said core, and further wherein the square of the ratio of said first number of turns to said second number of turns is proportional to the ratio of said first impedance level to said second impedance level.

8. An improved coil assembly as recited in claim 7, wherein at least a six to one ratio exists between said first impedance level and said second impedance level.

9. An improved coil assembly as recited in claim 7, wherein said field is transmitted to said coil assembly at a first frequency, and wherein said first coil means is operative to self-resonate at said first frequency so as to maximize the quantity of energy derived from said field and converted by said first coil means into said power field.

10. An improved coil assembly as recited in claim 6, wherein said electromagnetic field is transmitted to said coil assembly at a first frequency, and wherein said first coil means is operative to self-resonate at said first frequency so as to maximize the quantity of energy derived from said electromagnetic field and converted by said first coil means into said power field.

11. A method for matching the impedance coupling between a transponder and an electromagnetic field generated proximate the transponder, the transponder including an integrated identification circuit device in electrical communication with a coil assembly having a central core and primary and secondary coils each disposed in winding relation around the core, the coil assembly being operative to transfer power derived from the electromagnetic field to the circuit device, comprising the steps of:

receiving said electromagnetic field with a first length of conductive wire having open-circuited ends and forming said primary coil;

converting the energy in said electromagnetic field into an induction power field having a first impedance level;

receiving said power field with a second length of conductive wire forming said secondary coil and having its ends coupled to said circuit device;

converting said power field into an electrical power signal having a second impedance level which substantially matches the impedance level of said electromagnetic field; and

transferring said power signal to said circuit device, whereby the quantity of energy transferred from said electromagnetic field to said circuit device is maximized by matching said second impedance level with said first impedance level.

12. A method for matching the impedance coupling between a transponder and an electromagnetic field generated proximate the transponder as recited in claim 11, wherein said field is transmitted to said transponder at a first frequency, and wherein said step of converting the energy in said field includes the step of tuning said first coil to self-resonate at said first frequency.

13. An electronic identification system for transmitting a high intensity electromagnetic field within the proximity of a transponder coil assembly inductively coupled to the high intensity field, the transponder coil assembly being operative to transfer power derived from the high intensity field to an integrated circuit device in electrical communication with the coil assembly and to retransmit a low intensity electromagnetic field which is detected by the identification system, comprising:

a transmission and detection apparatus for transmitting said high intensity field and detecting the presence of said low intensity field emanating from said transponder coil assembly despite the presence of said high intensity field; and

a transponder coil assembly, including;

a core;

first transponder coil means including a first length of wire disposed in winding relation around said core and with its ends open-circuited, and operative to receive said high intensity field and to convert the energy within said high intensity field into an induction power field having a first impedance level; and

second transponder coil means disposed in winding relation around said core and operative to receive said power field, to convert the energy is said power field into an electrical power signal having a second impedance level, and to output said power signal to said integrated circuit device, whereby the power transferred to said circuit device is at said second impedance level and is sufficient to induce said circuit device to produce an identification signal for retransmission by said transponder coil assembly to said transmission and detection apparatus.

14. An electronic identification system as recited in claim 13, wherein said transmission and detection apparatus includes:

a support means;

means for generating a first electrical signal for use in creating said high intensity field;

a transmitter coil affixed to said support means for receiving said first electrical signal and transmitting said high intensity field, said transmitter coil including one or more conductive windings circumscribing a substantially polygonal volume of space having a central axis, said transmitter coil being adapted to generate a magnetic flux field within said volume;

first and second receiver coils disposed within said volume of space at significantly separated points and adapted to have linking relationships with portions of said flux field, said first and second receiver coils being electrically connected to each other in a differential circuit relationship such that the magnitude of electrical signals induced in said first and second receiver coils by electromagnetic energy transmitted by said transmitter coil are substantially equal and opposite to each other, whereby electromagnetic energy generated by said coil assembly and passing through at least one of said first and second receiver coils will induce an electrical signal of greater magnitude in one receiver coil than will be induced in the other receiver coil and cause a current to flow in said differential circuit which corresponds to the energy generated by said coil assembly; and

means responsive to said current flowing in said differential circuit and operative to indicate a measure of the energy generated by said external source, whereby said integrated circuit device in communication with said coil assembly is remotely detected and identified.

15. An electronic identification system as recited in claim 14, wherein said portions of said flux field varies in intensity at said significantly separated points, and wherein said first and second receiver coils electrically compensate for variations in the intensity of said flux field.

16. An electronic identification system as recited in claim 14, wherein said first and second receiver coils are substantially identical in shape and have linking relationships with substantially identical portions of said flux field.

17. An electronic identification system as recited in claim 14, wherein said first and second receiver coils and said transmitter coil are substantially co-planar.

18. An electronic identification system as recited in claim 14, wherein said first and second receiver coils are disposed within said volume of space at substantially diametrically opposed points.

19. An electronic identification system as recited in claim 14, wherein said first and second receiver coils are each more sensitive to said low-intensity field than said transmitter coil.

20. An electronic identification system as recited in claim 14, wherein said first receiver coil includes one or more conductive windings circumscribing a first substantially polygonal volume of space having a first central axis, and wherein said second receiver coil includes one or more conductive windings circumscribing a second substantially polygonal volume of space having a second central axis.

21. An electronic identification system as recited in claim 20, wherein first central axis and said second central axes are substantially parallel to said central axis of said transmitter coil.

22. An electronic identification system as recited in claim 21, wherein said first central axis and second central axis are equidistant from said central axis of said transmitter coil.

23. An electronic identification system as recited in claim 20, wherein said first central axis and said second central axis are substantially co-axial.

24. An electronic identification system as recited in claim 20, wherein said first and second polygonal volumes of space are each smaller than said polygonal volume of space of said transmitter coil.

25. An electronic identification system as recited in claim 13, wherein said second transponder coil means includes a second length of wire having a second predetermined number of turns disposed in winding relation around said core, and further wherein the ends of said second length of wire are connected to said integrated circuit device.

26. An electronic identification system as recited in claim 25, wherein the square of the ratio of said first number of turns to said second number of turns is proportional to the ratio of said first impedance level to said second impedance level.

27. An electronic identification system as recited in claim 26, wherein said first impedance level is at least six times greater than said second impedance level, whereby the voltage of said power field is stepped down and the current of said power field is stepped up when said power field is converted to said power signal.

28. An electronic identification system as recited in claim 13, wherein said high intensity field is transmitted to said transponder coil assembly at a first frequency level, and wherein said first transponder coil means is operative to self-resonate at said first frequency level so as to maximize the quantity of energy derived from said high intensity field and converted by said first transponder coil means into said power field.

29. A transponder device for receiving transmitted electromagnetic energy and transmitting a responsive signal, comprising:

a nonconductive substrate forming a support member for various components of said transponder device;

means forming a transponder circuit affixed to said substrate;

a magnetic core affixed to said substrate;

first coil means disposed in winding relation about said core and including a first number of turns, the ends of said first coil means being open-circuited; and

second coil means disposed in winding relation about said core and being electrically connected to said transponder circuit, said second coil means including a second number of turns substantially fewer in number than said first number of turns, said first and second coil means being inductively coupled together and operative to collect said transmitted electromagnetic energy and provide electric power to said transponder circuit.

30. A transponder device as described in claim 29 wherein said first coil means is operative to self-resonate at the frequency of said transmitted electromagnetic energy.

31. A transponder device as described in claim 29 wherein the impedance level of said first coil means is at least six times greater than the impedance level of said second coil means.

32. A transponder device as described in claim 29 wherein said first number of turns is approximately 3800 turns and said second number of turns is approximately 500 turns.