System and method for automatic tuning of a magnetic field generator

• US 20030234631A1
• Filed: 05/05/2003
• Published: 12/25/2003
• Est. Priority Date: 06/20/2002
• Status: Active Grant

• Current Assignee: Alfred E. Mann Foundation For Scientific Research
• Original Assignee: Alfred E. Mann Foundation For Scientific Research
• Inventors: Schulman, Joseph H., Gord, John, Cosendai, Gregoire, Arcos-Burgos, Maria-Isabel
• Granted Patent: US 7,015,769 B2
• Time in Patent Office: Days
• US Class Current: 318/677
• CPC Class Codes: A61N 1/025 Digital circuitry features of electrotherapy devices, e.g. memory, clocks, processors
• CPC Class Codes: A61N 1/37229 Shape or location of the implanted or external antenna
• CPC Class Codes: A61N 1/3787 from an external energy source
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 5/02 with variable tuning element having a number of predetermined settings and adjustable to a desired one of these settings
• CPC Class Codes: H03L 5/02 of power

Abstract

An automatic tuning system for a magnetic field generating tuned circuit includes a processor configured to maintain the resonant frequency of a tuned circuit equal to a reference frequency. The tuned circuit is driven by a power amplifier whose output provides an amplified signal at the reference frequency. The tuned circuit includes a magnetic field generating inductor and a bank of individually switchable capacitors controlled by the processor capable of adding and removing the respective capacitances to and from the tuned circuit. The inductor includes a Faraday shield to shield the tuned circuit from the influence of electric fields. A power sense circuit monitors the power delivered by the power amplifier to the tuned circuit and the processor sequentially switches the capacitors in a binary progression format to achieve maximum power delivery indicative of conforming the resonant frequency of the tuned circuit to the reference frequency. In an alternate embodiment of the invention, the inductor includes a plurality of taps that provide individually selectable inductance values available for use in the process of conforming the resonant frequency of the tuned circuit to the reference frequency. In further alternate embodiments, the variable capacitor is in the form of a motor driven variable capacitor and the tuning sequence relies on a phase locked loop using the phase of a reference frequency signal and the phase of the inductor current as control parameters.

Claims

1. An automatic tuning system for a magnetic field generator comprising:

a processor;

a power source;

a tuned circuit comprising a magnetic field generating inductor (L) and an adjustable capacitor (C), the values of the L and C establishing the tuned circuit resonant frequency,

a power amplifier coupled to the power source, said power amplifier having an output coupled to and adapted to drive the tuned circuit;

a reference frequency oscillator circuit coupled to the power amplifier so as to cause the power amplifier to generate an output signal at a reference frequency; and

a sense circuit coupled to the power amplifier and adapted to sense a signal indicative of the power delivered by the power amplifier to the tuned circuit and provide thereby a power level signal relating to such power delivered, whereby the power delivered by the power amplifier is a function of the resonant frequency of the tuned circuit, and wherein the processor monitors the power level signal and causes the adjustable capacitor to be adjusted to a capacitance value that maximizes the power delivered by the power amplifier.

2. The system of claim 1 wherein the sense circuit includes a resistor coupled between the power source and the power amplifier in a manner to provide a power level signal representative of the power delivered by the power amplifier.

3. The system of claim 1 wherein the adjustable capacitor comprises a capacitor bank comprising a plurality of capacitors, each capacitor selectively switchable to be in parallel circuit arrangement with selected others of the plurality of capacitors of the bank.

4. The system of claim 3 wherein each capacitor of the plurality has a corresponding capacitance value and progressing through the capacitor bank from the capacitor having the smallest capacitance value to the capacitor having the largest capacitance value, the capacitors are arranged so that their respective capacitance values, are in binary progression order.

5. The system of claim 3 further comprising a fixed capacitor in parallel circuit arrangement with said capacitor bank.

6. The system of claim 3 further comprising a variable trim capacitor in parallel circuit arrangement with said capacitor bank.

7. The system of claim 3 wherein the capacitor bank includes a plurality of switches, each switch being uniquely associated with a respective one of the capacitors of the capacitor bank, each switch having first and second states, such that in the first state the switch is adapted to add the respective capacitor in parallel circuit connection with selected other capacitors of the bank and in the second state the switch is adapted to remove the respective capacitor from parallel circuit arrangement with selected other capacitors of the bank.

8. The system of claim 7 wherein the processor, responsive to the value of the power level signal, controls the states of the switches so as to add and remove the respective capacitors from the bank in a preprogramed sequence, to thereby establish a capacitance value of the bank that maximizes the power delivered by the power amplifier to the tuned circuit.

9. The system of claim 8 wherein a switch comprises a relay having said first and second states, such that in the first state the respective capacitor is switched to be in parallel circuit arrangement with selected other capacitors of the bank and in the second state the respective capacitor is switched so as to be removed from parallel circuit arrangement with selected other capacitors of the bank.

10. The system of claim 8 wherein the preprogramed sequence comprises binary capacitor switching.

11. The system of claim 7 wherein a switch comprises a semiconductor device in series circuit arrangement with a respective capacitor such that in a first state the semiconductor device is conductive and causes such respective capacitor to be placed in parallel circuit arrangement with selected other capacitors of the bank and in the second state the semiconductor device is non-conductive and causes such respective capacitor to be removed from parallel circuit arrangement with selected other capacitors of the bank.

12. The system of claim 1 wherein the magnetic field generating inductor includes a secondary coil adapted to provide a field strength signal having a magnitude corresponding to the strength of the generated magnetic field, wherein the processor causes the adjustable capacitor to be adjusted to a value that maximizes the field strength signal.

13. The system of claim 1 wherein the maximum power is delivered by the power amplifier to the tuned circuit when the adjustable capacitor is adjusted to a value such that the resonant frequency of the tuned circuit equals the reference frequency.

14. The system of claim 13 wherein the reference frequency is about 2 MHZ.

15. The system of claim 4 wherein said plurality of capacitors comprises eight capacitors.

16. The system of claim 4 wherein the smallest value of capacitance is one picofarad.

17. The system of claim 4 wherein the value of inductance is about 12 uH.

18. The system of claim 1, wherein the inductor comprises a plurality of concentrically wound turns of a single conductor, the conductor being embedded within a flexible, solid, nontoxic material.

19. The system of claim 18, wherein the concentric turns of the conductor lie in a plane.

20. The system of claim 19, wherein the inductor has an essentially “

horse race track”

shape defining an inner perimeter and an outer perimeter and wherein the inductor further includes an electric shield comprising a plurality of projections extending essentially orthogonally from a base, the projections sized such that they extend completely around the inductor between the inner perimeter and the outer perimeter and ending in proximity to the base when the base is positioned to be in contact with the outer perimeter of the inductor.

21. The system of claim 20 wherein the inductor has first and second surfaces and inner and outer side walls therebetween and wherein the projections are spaced apart and adjacent to each other and the base is positioned in contact with and along the outer side wall of the inductor.

22. The system of claim 20 wherein the inductor has first and second surfaces and inner and outer side walls therebetween and wherein the projections are spaced apart and adjacent to each other and the base is positioned in contact with and along the inner side wall of the inductor.

23. The system of claim 20 wherein the shield comprises at least two shields, each shield comprising a plurality of spaced apart projections extending orthogonally from a base, the inductor having first and second surfaces and inner and outer side walls therebetween, wherein one shield is located such that the base thereof is positioned along and in proximity to the outer perimeter of the first surface of the inductor, the projections being sized to extend from the base to the inner perimeter of the inductor, and another shield being located such that the base thereof is positioned along and in proximity to the outer perimeter of the second surface of the inductor, the projections being sized to extend from the base to the inner perimeter of the inductor.

24. The system of claim 23 wherein the inductor has first and second surfaces and inner and outer side walls therebetween and wherein the base of one shield is positioned to be in contact with and along the outer side wall of the inductor, and wherein the base of the other shield is positioned to be in contact with and along the inner side wall of the inductor, such that the projections of one shield extend along the first surface and the projections of the other shield extend along the second surface.

25. The system of claim 20 or claim 21 or claim 22 or claim 23 or claim 24 wherein the shield is formed of a metallic plated shielding tape comprising polyester fabric plated with copper.

26. The system of claim 20 further comprising a spacer disposed between the electric shield and the inductor, the spacer comprising a material having a dielectric constant selected from the group consisting of air and a vacuum.

27. The system of claim 1, wherein the adjustable capacitor comprises a motor driven adjustable capacitor, wherein the processor causes the motor to adjust the adjustable capacitor to a capacitance value that maximizes the power delivered by the power amplifier.

28. The system of claim 27, wherein the motor is a stepper motor and wherein the processor causes the motor to index the adjustable capacitor through a range of discrete capacitance values to a capacitance value that maximizes the power delivered by power amplifier.

29. In an automatic tuning system for a magnetic field generator comprising, a tuned circuit comprising a magnetic field generating inductor (L) and an adjustable capacitor (C), the values of the L and C establishing a tuned circuit resonant frequency, a power amplifier having an output coupled to and adapted to drive the tuned circuit, the power amplifier providing, at said output, an amplified signal at a preselected reference frequency, the method of tuning the tuned circuit comprising the steps of:

(1) adjusting the adjustable capacitor to a predetermined initial capacitance value;

(2) measuring the power delivered by the power amplifier to the tuned circuit;

(3) incrementally changing the capacitance value of the adjustable capacitor;

(4) repeating steps 2 and 3 for all possible capacitance values of the adjustable capacitor; and

(5) readjusting the adjustable capacitor to have the capacitance value that maximizes the power (max a power point) delivered to the tuned circuit.

30. The method of claim 29 wherein the adjustable capacitor comprises a capacitor bank comprising a plurality of capacitors, each capacitor selectively switchable to be in parallel circuit arrangement with selected other capacitors of the plurality of capacitors of the bank, wherein each capacitor of the plurality has a corresponding capacitance value and progressing through the capacitor bank from the capacitor having the smallest capacitance value to the capacitor having the largest capacitance value, the capacitors are arranged so that their respective capacitance values, are in binary progression order format, wherein the step of incrementally changing the capacitance value of the adjustable capacitor further comprises selectively switching the capacitors of the bank, to be in a parallel circuit arrangement with other selected capacitors of the bank, in binary progression order.

31. The method of claim 30 further including the step of storing each measured value of the power delivered by the power amplifier in association with an indicia of the corresponding capacitance value that yields such measured power.

32. The method of claim 31 further comprising periodically measuring the power delivered by the power amplifier and reinitiating the tuning of the tuned circuit if the delivered power so measured is less than a predetermined percentage of the max power point.

33. The method of claim 32 further comprising selecting about 80% as the predetermined percentage.

34. The method of claim 32 whereupon reinitiating the tuning of the tuned circuit comprises adjusting the adjustable capacitor to a capacitance value corresponding to a fixed number of stored measured values of delivered power prior to that which yielded the max power point and then selectively switching the capacitors of the bank to a capacitance value that corresponds to the fixed number of stored measured values of delivered power beyond that which yielded the max power point.

35. The method of claim 34 comprising selecting the capacitance value of the adjustable capacitor to that which yields the max power point.

36. The method of claim 35 further comprising performing steps (1) to (5) upon the failure to adjust the adjustable capacitor to a capacitance value that yields the max power point.

37. The method of claim 36 further comprising issuing an error message upon the failure to adjust the adjustable capacitor to a capacitance value that yields the max power point.

38. The method of claim 35 comprising selecting the capacitance value of the adjustable capacitor to that which yields delivered power that is within a preselected percentage of the max power point.

39. The method of claim 38 comprising selecting about 20% as the preselected percentage.

40. The method of claim 29 comprising selecting about 2 MHZ as the preselected reference frequency.

41. The method of claim 30 comprising selecting 8 capacitors as the plurality of capacitors.

42. The method of claim 30 comprising selecting about 1 pF as the smallest capacitance value.

43. The method of claim 30 comprising selecting about 12 uH as the inductor value.

44. The method of claim 34 comprising selecting 32 as the fixed number of stored measured values.

45. An automatic tuning system for a magnetic field generator comprising:

a processor;

a power source;

a tuned circuit comprising an adjustable magnetic field generating inductor (L) and an adjustable capacitor (C), the adjusted values of the L and C establishing the tuned circuit resonant frequency,

a power amplifier coupled to the power source, said power amplifier having an output coupled to and adapted to drive the tuned circuit;

a reference frequency oscillator circuit coupled to the power amplifier so as to cause the power amplifier to generate an output signal at a reference frequency; and

a sense circuit coupled to the power amplifier and adapted to sense a signal indicative of the power delivered by the power amplifier to the tuned circuit and provide thereby a power level signal relating to such power delivered, whereby the power delivered by the power amplifier is a function of the resonant frequency of the tuned circuit, and wherein the processor monitors the power level signal and causes the adjustable capacitor and the adjustable inductor to be adjusted to respective capacitance and inductance values that maximizes the power delivered by the power amplifier.

46. The system of claim 45 wherein the adjustable inductor includes a plurality of taps, each tap relating to a different respective inductance value for said inductor, the system further comprising a controllable switch adapted to switch between each inductor tap to thereby controllably alter the resonant frequency of the tuned circuit.

47. The system of claim 46 wherein the controllable switch switches between different ones of the plurality of taps under the control of the processor.

48. The system of claim 47 wherein the controllable switch comprises a plurality of relay controlled switches, each relay of said plurality controlling a respective one of the controlled switches, each relay being actuated under the control of said processor.

49. The system of claim 48 wherein the controllable switch comprises a plurality of semiconductor device switches, each semiconductor device switch of said plurality being coupled to a respective one of the plurality of taps, each semiconductor device switch being actuated under the control of said processor.

50. An automatic tuning system for a magnetic field generator comprising:

tuned circuit means comprising inductor means and capacitor means, the values of the inductor means and capacitor means establishing the resonant frequency of the tuned circuit means,

power means for delivering power to the tuned circuit means at a reference frequency; and

means for adjusting the resonant frequency of the tuned circuit means for maximizing the power transferred from the power means to the tuned circuit means, whereby the power delivered by the power means is a function of the resonant frequency of the tuned circuit, wherein the delivered power is maximized when the resonant frequency of the tuned circuit means equals the reference frequency.

51. The system of claim 50 wherein the adjusting means adjusts the value of the capacitor means for adjusting the resonant frequency of the tuned circuit means to equal the reference frequency.

52. The system of claim 50 wherein the adjusting means adjusts the value of the inductor means for adjusting the frequency of the tuned circuit means to equal the reference frequency.

53. The system of claim 50 further comprising monitoring means for monitoring the power delivered by the power means wherein the adjusting means adjusts the resonant frequency of the tuned circuit means for obtaining the maximized value of delivered power (max power).

54. The system of claim 53 wherein the adjusting means further readjusts the resonant frequency of the tuned circuit means for re-maximizing the delivered power when the monitored delivered power falls below a preselected value.

55. The system of claim 54 wherein the preselected value comprises 80% of the max power.

56. In an automatic tuning system for a magnetic field generator comprising, a tuned circuit comprising a magnetic field generating inductor (L) and an adjustable capacitor (C), the values of the L and C establishing the tuned circuit resonant frequency, a power amplifier having an output coupled to and adapted to drive the tuned circuit, the power amplifier providing, at said output, a tuned circuit drive signal at a preselected reference frequency, a method of tuning the tuned circuit comprising the steps of:

(1) commencing the tuning of the tuned circuit with the adjustable capacitor at an initial capacitance value;

(2) measuring the power delivered by the power amplifier to the tuned circuit;

(3) changing the capacitance value of the adjustable capacitor;

(4) repeating steps 2 and 3 through a range of capacitance values of the adjustable capacitor; and

(5) adjusting the adjustable capacitor to have the capacitance value that provided the maximum value of the delivered power measured in step (2).

57. An automatic tuning system for a magnetic field generator comprising:

a processor;

a power source;

a tuned circuit comprising a magnetic field generating inductor (L) and an adjustable capacitor (C), the values of the L and C establishing the resonant frequency of the tuned circuit;

a power amplifier coupled to the power source, said power amplifier having an output coupled to and adapted to drive the tuned circuit;

a reference frequency oscillator circuit providing a reference frequency signal, said oscillator circuit coupled to the power amplifier so as to cause the power amplifier to generate an output signal at the reference frequency; and

a sense circuit coupled to the reference frequency oscillator circuit and adapted to sense a first parameter related to the reference frequency signal, the sense circuit further coupled to the inductor and adapted to sense a second parameter related to the inductor and provide an error signal as a function of the first and second parameters, wherein the power delivered by the power amplifier to the tuned circuit is a function of the resonant frequency of the tuned circuit, and wherein the processor monitors the error signal and causes the adjustable capacitor to be adjusted to a capacitance value that optimizes the error signal to thereby optimize the power delivered by the power amplifier.

58. The tuning system of claim 57 wherein the reference frequency signal is a voltage signal and the first parameter is the phase angle of such voltage signal and wherein the second parameter is the phase angle of the current flowing in the inductor, wherein the sense circuit provides the error signal being the difference of the phase angle between the first and second parameters.

59. The tuning system of claim 58 wherein the processor causes the adjustable capacitor to be adjusted so as to obtain a minimum value of the error signal such minimum value being defined as the optimal value thereof.

60. The tuning system of claim 59 wherein the processor periodically re-tunes the tuned circuit when the value of the error signal lies outside a range of values defined by a preselected amount from the optimal value.

61. The tuning system of claim 60 wherein the preselected amount is ±

30 degrees, and when the error signal lies outside such range of values, the processor causes the adjustable capacitor to be adjusted to a capacitance value that causes the error signal to be within the preselected range of values.