MAGNETIC NOISE REJECTION APPARATUS AND MAGNETIC FIELD MEASUREMENT APPARATUS

• US 20170219661A1
• Filed: 12/22/2016
• Published: 08/03/2017
• Est. Priority Date: 01/29/2016
• Status: Active Grant

• Current Assignee: Advantest Corporation
• Original Assignee: Advantest Corporation
• Inventors: Ogata, Yuji, Hata, Yoshiyuki, Hayakawa, Toshiaki, Tanaka, Takeshi
• Granted Patent: US 10,444,298 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 33/0029 Treating the measured signals, e.g. removing offset or noise
• CPC Class Codes: G01R 33/0041 using feed-back or modulation techniques

Abstract

There is provided a magnetic noise rejection apparatus which includes: a plurality of cancellation coils arranged near a target object; a plurality of magnetic sensors disposed inside the respective cancellation coils; an adder circuit configured to take a sum of outputs of the plurality of magnetic sensors; and a feedback control circuit configured to supply the cancellation coils with such a common feedback drive current that the sum of the outputs of the magnetic sensors is equal to a sum of outputs of the magnetic sensors under a zero magnetic field.

Claims

1. A magnetic noise rejection apparatus comprising:

a plurality of cancellation coils arranged near a target object;

a plurality of magnetic sensors disposed inside the respective cancellation coils;

an adder circuit configured to take a sum of outputs of the plurality of magnetic sensors; and

a feedback control circuit configured to supply the cancellation coils with such a common feedback drive current that the sum of the outputs of the magnetic sensors is equal to a sum of outputs of the magnetic sensors under a zero magnetic field.

2. The magnetic noise rejection apparatus according to claim 1, wherein

the plurality of small magnetic coils are connected in series and driven by a current from a common drive circuit.

3. The magnetic noise rejection apparatus according to claim 1, wherein

the plurality of magnetic sensors operate by electric power supplied from a common power source.

4. The magnetic noise rejection apparatus according to claim 1, wherein

compensation magnets are provided to the respective magnetic sensors, the compensation magnets being configured to compensate for offsets of the respective magnetic sensors.

5. The magnetic noise rejection apparatus according to claim 4, wherein

each of the compensation magnets includes a coil and an adjustment circuit configured to adjust a drive current to be supplied to the coil, and all of the adjustment circuits operate by a drive current from a common power source.

6. The magnetic noise rejection apparatus according to claim 4, wherein

each of the compensation magnets includes a permanent magnet with a magnetic force adjusted according to a characteristic of each magnetic sensor.

7. The magnetic noise rejection apparatus according to claim 1, further comprising:

a second feedback control circuit configured to remove a variance of a DC magnetic field component of the corresponding magnetic coil based on the output of each magnetic sensor.

8. The magnetic noise rejection apparatus according to claim 1, further comprising:

DC magnetic field compensation coils provided to the respective small magnetic coils; and

an individual feedback control circuit configured to output a drive current to each of the DC magnetic field compensation coils based on a result of comparison between an output value of the corresponding magnetic sensor and a predetermined reference value, and to correct a variance of DC magnetic field components between the magnetic sensors.

9. A magnetic field measurement apparatus comprising:

a plurality of cancellation coils arranged near a target object;

a plurality of magnetic sensors disposed inside the respective cancellation coils;

an adder circuit configured to take a sum of outputs of the plurality of magnetic sensors;

a feedback control circuit configured to supply the cancellation coils with such a common feedback drive current that the sum of the outputs of the magnetic sensors is equal to a sum of outputs of the magnetic sensors under a zero magnetic field; and

a measurement circuit configured to detect a magnetic field generated from an inside of the target object based on output values of the individual magnetic sensors.

10. A magnetic field measurement apparatus comprising:

a plurality of cancellation coils arranged near a target object;

a plurality of magnetic sensors disposed inside the respective cancellation coils;

an adder circuit configured to output a total value of outputs of the magnetic sensors;

a feedback control circuit configured to supply the cancellation coils with such a common feedback drive current that the total value of the outputs of the magnetic sensors is equal to a total value of outputs of the magnetic sensors under a zero magnetic field; and

a measurement circuit configured to detect a magnetic field generated from a location away from the target object based on the feedback drive current of the feedback control circuit.