Device for punctual measurement of a radiofrequency magnetic field with constant amplitude and frequency

• US 7,573,263 B2
• Filed: 08/31/2006
• Issued: 08/11/2009
• Est. Priority Date: 09/19/2000
• Status: Expired due to Term

• Current Assignee: ThinkLogix, LLC (Ascend Innovation Management, LLC)
• Original Assignee: Fahrenheit Thermoscope LLC (Intellectual Ventures LLC)
• Inventors: Geoffroy, Philippe, Bouvier, Jacky
• Primary Examiner(s): Assouad; Patrick J
• Assistant Examiner(s): Schindler; David M.
• Application Number:
  US11/514,289
• Publication Number:
  US 20070126423A1
• Time in Patent Office: 1,076 Days
• Field of Search: 235/436, 235/438, 235/439, 235/449, 235/450, 235/440, 324/244, 324/260, 324/261, 324/262, 324/247, 324/256, 324/258, 340/572.1, 340/10.1, 455/41.1, 455/41.2
• US Class Current: 324/260
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/0095 Testing the sensing arrangement, e.g. testing if a magnetic card reader, bar code reader, RFID interrogator or smart card reader functions properly testing of electrical circuits G01R31/28

Abstract

The invention concerns a device for measuring a radiofrequency magnetic field, characterised in that it comprises on a common support: a coil forming a primary reception antenna; a voltage-controlled oscillator, monitored so that its output frequency depends on the amplitude of the magnetic field received on the coil forming primary antenna; an absorption modulation load connected to the oscillator output; a secondary antenna sensitive to the magnetic field influenced by the absorption modulation resulting from the power supply load by the voltage-controlled oscillator, and means for operating the available signal on the secondary antenna.

Claims

1. A method of using a device for determining a value of a magnetic field, the method comprising:

said device rectifying an alternating voltage output from at least one coil in an alternating magnetic field;

said device controlling a voltage controlled oscillator using the rectified voltage;

said device outputting a signal from the voltage controlled oscillator, wherein the signal has a frequency that depends on an amplitude of the magnetic field at the at least one coil;

said device chopping current in a modulation resistance connected between the rectified voltage and a switching device that receives the signal from the voltage controlled oscillator, wherein current through a modulation resistance is chopped at the frequency of the signal from the voltage controlled oscillator which results in modulating current in the at least one coil; and

said device determining a value of the magnetic field by demodulating an output voltage of an antenna coupled to the at least one coil, wherein the output voltage alternates at a frequency of the magnetic field and is modulated in amplitude at the frequency of the signal from the voltage controlled oscillator;

wherein said at least one coil, the voltage controlled oscillator, the modulation resistance and the antenna are carried by said device.

2. The method of claim 1, wherein said coupling of the antenna to the at least one coil is an electromagnetic coupling, wherein the device includes a support made of a non-magnetic material, wherein the support carries said at least one coil, the voltage controlled oscillator, the modulation resistance and the antenna.

3. A device comprising:

a support, wherein the support carries;

a first coil configured to generate a first current in response to receiving a magnetic field;

a voltage controlled oscillator (VCO) configured to receive an input voltage that is dependent on an amplitude of the first current and to generate a first output voltage having a first frequency that is dependent upon the input voltage;

a first load controllable by the first output voltage;

an antenna coupled to the first coil such that an amplitude modulation of the first current in the first coil induces an amplitude modulation of a second output voltage of the antenna; and

circuitry configured to operate on the second output voltage in order to output an indication of an intensity of the magnetic field.

4. The device of claim 3 further comprising:

a rectifier configured to rectify the first current from the first coil in order to generate a rectified voltage that is dependent on the amplitude of the first current, wherein the VCO and the first load are coupled to receive the rectified voltage, wherein said input voltage of the VCO is a fraction of the rectified voltage.

5. The device of claim 4, wherein the first load includes a resistance and a transistor coupled in series, wherein the transistor is coupled to the VCO so that the first output voltage controls flow of second current through the first load.

6. The device of claim 4, wherein the first load is a current generator.

7. The device of claim 4, wherein the support is made of a non-magnetic material.

8. The device of claim 4, wherein the device is a card.

9. The device of claim 4, wherein the first coil, the VCO and the first load are included on a chip.

10. The device of claim 4, wherein the magnetic field is emitted by a second coil.

11. The device of claim 10, wherein the second coil is part of a contact-free card reader.

12. The device of claim 4, wherein the antenna surrounds the first coil, the VCO and the first load.

13. The device of claim 12, wherein the antenna comprises two or more turns of an electrical conductor wound collectively around the first coil, the VCO, and the first load.

14. The device of claim 4, wherein the circuitry includes a display unit for displaying said indication of the intensity of the magnetic field.

15. The device of claim 4, wherein the circuitry is configured to demodulate a first signal from the second output voltage, wherein the first signal alternates at the first frequency, wherein the circuitry is configured to operate on the first signal to estimate the first frequency and to compute said intensity of the magnetic field from the estimate of the first frequency.

16. The device according to claim 4, wherein the rectified voltage supplies power to the VCO.

17. The device of claim 3, wherein said coupling of the antenna to the first coil is an electromagnetic coupling, wherein the support is made of a non-magnetic material.

18. A device, comprising:

a support, wherein the support carries;

a first coil configured to generate a first current in response to receiving a magnetic field;

a rectifier coupled to the first coil, wherein the rectifier is configured to receive the first current and generate a rectified voltage that is dependent upon an amplitude of the first current;

a voltage controlled oscillator (VCO) configured to receive an input voltage that is a fraction of the rectified voltage and further configured to generate a first output voltage having a first frequency that is dependent upon the input voltage;

a first load coupled to receive the first output voltage, wherein the first load is configured to vary with said first output voltage;

an antenna coupled to said first coil such that an amplitude modulation of the first current in the first coil induces an amplitude modulation of a second output voltage of the antenna; and

circuitry configured to output an indication of a strength of the magnetic field based on the second output voltage.

19. The device of claim 18, wherein the circuitry includes a display unit for displaying the indication of the strength of the magnetic field.

20. The device of claim 18 wherein the magnetic field is emitted by a second coil.

21. The device of claim 18, wherein the antenna surrounds the first coil, the rectifier, the VCO and the first load.

22. The device of claim 18, wherein said coupling of the antenna to said first coil is an electromagnetic coupling, wherein the support is made of a non-magnetic material.

23. A system comprising:

an induction coil configured to emit an alternating magnetic field; and

a device comprising;

a first coil configured to generate a first current in response to receiving the alternating magnetic field;

a voltage controlled oscillator (VCO) configured to receive an input voltage that is dependent upon an amplitude of the first current and to generate a first output voltage having a first frequency that is dependent upon the input voltage;

a first load controllable by said first output voltage;

an antenna coupled to the first coil such that an amplitude modulation of the first current in the first coil induces a corresponding amplitude modulation of a second output voltage of the antenna; and

circuitry configured to operate on the second output voltage in order to output an indication of an intensity of the alternating magnetic field.

24. The system of claim 23, wherein the antenna surrounds the first coil, the VCO and the first load.

25. The system of claim 23, wherein said coupling of the antenna to the first coil is an electromagnetic coupling, wherein the device includes a support made of a non-magnetic material, wherein the support carries the first coil, the voltage controlled oscillator, the first load, the antenna and said circuitry.

26. A device comprising:

a card, wherein the card carries;

at least one coil;

a voltage controlled oscillator configured to produce an oscillating signal having an output frequency that depends on an amplitude of a magnetic field at the at least one coil;

an absorption modulation load, wherein current through the absorption modulation load is chopped at the output frequency of the voltage controlled oscillator which results in modulating current in the at least one coil;

an antenna coupled to the at least one coil, wherein the antenna is configured to provides an output signal that alternates at a frequency of the magnetic field and is modulated in amplitude at the output frequency of the voltage controlled oscillator; and

circuitry configured to operate on the output signal in order to output an indication of a strength of the magnetic field.

27. The device of claim 26, wherein said coupling of the antenna to said at least one coil is an electromagnetic coupling, wherein the card is made of a non-magnetic material.

28. A device comprising:

a support, wherein the support carries;

at least one coil;

a voltage controlled oscillator configured to generate a first output voltage whose frequency depends on an amplitude of a magnetic field at the at least one coil;

a current generator configured to generate a current that depends on the first output voltage;

an antenna coupled to the at least one coil, wherein the antenna is configured to provide a second output voltage alternating at a frequency of the magnetic field and modulated in amplitude at the output frequency of the voltage controlled oscillator; and

circuitry configured to operate on the second output voltage in order to output an indication of a strength of the magnetic field.

29. The device of claim 28, wherein the magnetic field is emitted by a second coil that is part of a contact-free card reader.

30. The device of claim 28, wherein said at least one coil, the voltage controlled oscillator and the current generator are included on a chip that is surrounded by the antenna.

31. The device of claim 28, wherein said coupling of the antenna to said at least one coil is an electromagnetic coupling, wherein the support is made of a non-magnetic material.

32. A device comprising:

a support, wherein the support carries;

a first coil configured to generate a first current in response to receiving a magnetic field;

a voltage controlled oscillator (VCO) configured to receive an input voltage that is dependent on an amplitude of the first current and to generate a first output voltage having a first frequency that is dependent upon the input voltage;

a means for varying a load depending on the first output voltage;

an antenna coupled to the first coil such that an amplitude modulation of the first current in the first coil induces an amplitude modulation of a second output voltage of the antenna; and

circuitry configured to operate on the second output voltage in order to output an indication of an intensity of the magnetic field.

33. The device of claim 32 further comprising a means for rectifying the first current in order to generate a rectified signal, wherein the rectified signal determines the input voltage, wherein the rectified signal is supplied to said means for varying a load.

34. The device of claim 32, wherein said coupling of the antenna to the first coil is an electromagnetic coupling, wherein the support is made of a non-magnetic material.