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

• US 20030184288A1
• Filed: 04/04/2003
• Published: 10/02/2003
• Est. Priority Date: 09/19/2000
• Status: Active Grant

• Current Assignee: ThinkLogix, LLC (Ascend Innovation Management, LLC)
• Original Assignee: Fahrenheit Thermoscope LLC (Intellectual Ventures LLC)
• Inventors: Bouvier, Jacky, Geoffroy, Philippe
• Granted Patent: US 7,429,859 B2
• Time in Patent Office: Days
• 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 (10): 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 (22) sensitive to the magnetic field influenced by the absorption modulation resulting from the power supply load by the voltage-controlled oscillator, and means (30) for operating the available signal on the secondary antenna (22).

Claims

1. Device for measuring a radiofrequency magnetic field, characterised by the fact that it comprises the following, on a common support (10):

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 the primary antenna;

an absorption modulation load connected to the oscillator output;

a secondary antenna (22) sensitive to the magnetic field influenced by the absorption modulation resulting from the power supply to the load by the voltage controlled oscillator, and

means (30) for using the available signal on the secondary antenna (22).

2. Device according to claim 1, characterised by the fact that the support (10) consists of a card made of nonmagnetic material.

3. Device according to either of claims 1 or 2, characterised by the fact that it comprises a chip integrated on the support, including the primary antenna, the voltage controlled oscillator and the absorption modulation load.

4. Device according to one of claims 1 to 3, characterised by the fact that it also comprises a display unit (36).

5. Device according to one of claims 1 to 4, characterised by the fact that the absorption modulation load is formed from a resistance.

6. Device according to one of claims 1 to 4, characterised by the fact that the absorption modulation load comprises a current generator.

7. Device according to one of claims 1 to 6, characterised by the fact that the secondary antenna is composed of a few turns of an electrical conductor wound tightly around the assembly formed by the primary coil, the voltage controlled oscillator and the absorption modulation load.

8. Device according to one of claims 1 to 7, characterised by the fact that the operating means comprise a demodulator (31) connected to the output from the secondary antenna (22).

9. Device according to claim 8, characterised by the fact that it comprises a filter (32) at the output from the demodulator.

10. Device according to one of claims 1 to 9, characterised by the fact that the operating means comprise a high gain amplifier (33) to trigger a comparator system (34) outputting a logical level frequency output signal.

11. Device according to one of claims 1 to 10, characterised by the fact that the operating means comprise a microcontroller programmed to calculate information representative of the value of the magnetic field starting from the available information at the output from the secondary antenna (22).

12. Device according to one of claims 1 to 11, characterised by the fact that the coil (AP) forming primary antenna is input to a rectifier (R) that supplies a DC voltage (VDD) that supplies power to the voltage controlled oscillator (VCO), controls it and supplies the modulation load (MA) connected in series with a switching transistor (T) controlled through the output from the voltage controlled oscillator (VCO).