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

1. A device, comprising:

a support, wherein the support carries:

at least one coil;

a voltage controlled oscillator 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; and

an antenna coupled to the at least one coil, wherein the antenna provides an output voltage alternating at a frequency of the magnetic field and modulated in amplitude at the output frequency of the voltage controlled oscillator.

2. The device according to claim 1 , wherein the coil, the voltage controlled oscillator, and the absorption modulation load are located on a chip.

3. The device according to claim 1 , further comprising circuitry for determining a value of the magnetic field from an output voltage of the antenna.

4. The device according to claim 1 , wherein the absorption modulation load includes a resistance.

5. The device according to claim 1 , wherein the antenna comprises two or more turns of an electrical conductor wound collectively around the coil, the voltage controlled oscillator, and the absorption modulation load.

6. The device according to claim 3 , wherein the circuitry comprises a demodulator connected to the output from the antenna.

7. The device according to claim 6 , comprising a filter at the output from the demodulator.

8. The device according to claim 3 , wherein the circuitry comprises a high gain amplifier adapted to trigger a comparator system outputting a logical level frequency output signal.

9. The device according to claim 3 , wherein the circuitry comprises a microcontroller programmed to calculate a value of the magnetic field based on processed output from the antenna.

10. The device according to claim 1 , wherein the coil inputs to a rectifier that outputs a DC voltage that:

supplies power to and controls the voltage controlled oscillator; and

supplies power to the modulation load which is connected in series with a switching transistor controlled through the output from the voltage controlled oscillator.

11. The device according to claim 1 , wherein the support is made of non-magnetic material.

12. The device of claim 3 , further comprising a display unit for displaying the value of the magnetic field.

13. The device of claim 1 , wherein the device measures a radiofrequency magnetic field having constant amplitude and frequency.

14. The device of claim 13 , wherein the magnetic field has a strength of about 10 −3 Tesla.

15. 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.

16. The method of claim 15 , wherein said determining further comprises filtering the demodulated output voltage.

17. The method of claim 16 , wherein said determining further comprises amplifying the filtered, demodulated output voltage with a high gain amplifier.

18. The method of claim 17 , wherein said determining further comprises calculating the value for the magnetic field based on the amplified, filtered, demodulated output voltage.

19. The method of claim 15 , further comprising displaying the determined value of the magnetic field.

20. A device comprising:

a sensor comprising:

a coil;

a voltage controlled oscillator having an output frequency that depends on an amplitude of a magnetic field at the coil; and

an absorption modulation load, wherein current through the absorption modulation load is generated by a voltage induced in the coil by the magnetic field, and wherein the current is chopped at the output frequency of the voltage controlled oscillator; and

an antenna, wherein the antenna comprises a plurality of turns of an electrical conductor wound around the sensor.

21. The device of claim 20 , wherein the antenna provides an output voltage alternating at a frequency of the magnetic field and modulated in amplitude at the output frequency of the voltage controlled oscillator.

22. A device made by a method comprising:

populating a chip with at least a coil, a voltage controlled oscillator, and an absorption modulation load, wherein the voltage controlled oscillator has an output frequency that depends on an amplitude of a magnetic field at the coil, and current through the absorption modulation load is generated by a voltage induced in the coil by the magnetic field, and wherein the current is chopped at the output frequency of the voltage controlled oscillator; and

forming an antenna by winding a plurality of turns of an electrical conductor around the chip.

23. The device of claim 22 , wherein the method further comprises populating a support with at least the antenna wound around the chip and circuitry for determining a value of the magnetic field from a voltage induced in the antenna.

24. The device of claim 23 , wherein the method further comprises implementing a display on the support to display the value of the magnetic field.

25. A device, comprising:

at least one coil;

a voltage controlled oscillator 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; and

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

wherein the magnetic field is emitted by a second coil.

26. A device, comprising:

at least one coil;

a voltage controlled oscillator 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; and

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

wherein the antenna surrounds the at least one coil, the voltage controlled oscillator and the absorption modulation load.