MAGNETIC FIELD MEASUREMENT METHOD AND MAGNETIC FIELD MEASUREMENT DEVICE

• US 20160131723A1
• Filed: 10/30/2015
• Published: 05/12/2016
• Est. Priority Date: 11/12/2014
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: NAGASAKA, Kimio
• Granted Patent: US 9,964,604 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/243 specially adapted for magnetocardiographic [MCG] signals
• CPC Class Codes: A61B 5/245 specially adapted for magnetoencephalographic [MEG] signals
• CPC Class Codes: G01R 33/0206 Three-component magnetometers
• CPC Class Codes: G01R 33/0322 using the Faraday or Voigt effect
• CPC Class Codes: G01R 33/26 using optical pumping

Abstract

A light source unit irradiates a gas cell disposed in a measurement region with linearly polarized light in which the direction of travel is a z-axis direction and the vibration direction of an electric field is a y-axis direction. A polarimeter detects optical characteristics of light passing through the gas cell. A magnetic field generator applies an artificial magnetic field, capable of varying an x-axis component, a y-axis component, and a z-axis component, to the measurement region. A calculation control unit generates a plurality of artificial magnetic fields, calculates a magnetization value or a value corresponding to the magnetization value on the basis of the detection results of the polarimeter, and calculates an original magnetic field present in the measurement region, using an artificial magnetic field when the magnetization value or the value corresponding to the magnetization value satisfies a condition for external value.

Claims

1. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement device, the magnetic field measurement device including (i) a light source unit that emits linearly polarized light in which a first direction, a second direction and a third direction are orthogonal to each other, (ii) a medium, disposed in the measurement region, which changes optical characteristics of the linearly polarized light in accordance with a magnetic field, and that is irradiated along the third direction with the linearly polarized light of which a vibration direction of an electric field is the second direction, (iii) an optical detector that detects the optical characteristics, and (iv) a magnetic field generator that applies an artificial magnetic field to the measurement region, the method comprising:

generating a plurality of artificial magnetic fields, obtained by changing an artificial magnetic field component in the third direction, in the magnetic field generator;

calculating a magnetization value that is a component of a magnetization vector of the medium in the first direction or a value corresponding to the magnetization value based on detection results of the optical detector; and

calculating an original magnetic field present in the measurement region, using an artificial magnetic field of the plurality of artificial magnetic fields when the magnetization value or the value corresponding to the magnetization value satisfies a specified condition.

10. The magnetic field measurement method according to claim 1, further comprising:

generating a magnetic field of a difference in the original magnetic field with respect to a target magnetic field, in the magnetic field generator;

disposing a measuring object in the measurement region; and

measuring a magnetic field that is radiated by the measuring object, using the detection results of the optical detector while the magnetic field of the difference is generated.

2. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement device, the magnetic field measurement device including (i) a light source unit that emits linearly polarized light in which a first direction, a second direction and a third direction are orthogonal to each other, (ii) a medium, disposed in the measurement region, which changes optical characteristics of the linearly polarized light in accordance with a magnetic field, and that is irradiated along the third direction with the linearly polarized light of which a vibration direction of an electric field is the second direction, (iii) an optical detector that detects the optical characteristics, and (iv) a magnetic field generator that applies an artificial magnetic field to the measurement region, the method comprising:

generating a plurality of artificial magnetic fields, obtained by changing an artificial magnetic field component in the third direction and one artificial magnetic field component in the first direction and the second direction, in the magnetic field generator, in a state where the other artificial magnetic field component in the first direction and the second direction is set to a fixed value;

calculating a magnetization value that is a component of a magnetization vector of the medium in the first direction or a value corresponding to the magnetization value based on detection results of the optical detector; and

calculating an original magnetic field present in the measurement region, using an artificial magnetic field of the plurality of artificial magnetic fields when the magnetization value or the value corresponding to the magnetization value satisfies a condition for external value.

3. The magnetic field measurement method according to claim 2, wherein the calculating of the original magnetic field includes calculating using:

a first magnetic field that is an artificial magnetic field when the magnetization value or value corresponding to the magnetization value satisfies a maximum value condition; and

a second magnetic field that is an artificial magnetic field when the magnetization value or value corresponding to the magnetization value satisfies a minimum value condition.

4. The magnetic field measurement method according to claim 2, wherein the one artificial magnetic field component is an artificial magnetic field component in the second direction, and the other artificial magnetic field component is an artificial magnetic field component in the first direction, and

the calculating of the original magnetic field includes calculating using the following Expressions (1) to (3):

5. The magnetic field measurement method according to claim 3, wherein the one artificial magnetic field component is an artificial magnetic field component in the first direction, and the other artificial magnetic field component is an artificial magnetic field component in the second direction, and

the calculating of the original magnetic field includes calculating using the following Expressions (4) to (6):

6. The magnetic field measurement method according to claim 2, wherein the fixed value is zero.

11. The magnetic field measurement method according to claim 2, further comprising:

generating a magnetic field of a difference in the original magnetic field with respect to a target magnetic field, in the magnetic field generator;

disposing a measuring object in the measurement region; and

measuring a magnetic field which is radiated by the measuring object, using the detection results of the optical detector while the magnetic field of the difference is generated.

7. A magnetic field measurement method of measuring a magnetic field of a measurement region in a magnetic field measurement device, the magnetic field measurement device including (i) a light source unit that emits linearly polarized light in which a first direction, a second direction and a third direction are orthogonal to each other, (ii) a medium, disposed in the measurement region, which changes optical characteristics of the linearly polarized light in accordance with a magnetic field, and that is irradiated along the third direction with the linearly polarized light of which a vibration direction of an electric field is the second direction, (iii) an optical detector that detects the optical characteristics, and (iv) a magnetic field generator that applies an artificial magnetic field to the measurement region, the method comprising:

generating artificial magnetic fields of a plurality of combinations obtained by changing artificial magnetic field components in the first direction to the third direction, the artificial magnetic fields obtained by periodically changing the artificial magnetic field component in the third direction, in the magnetic field generator;

calculating a magnetization value that is a component of a magnetization vector of the medium in the first direction or a value corresponding to the magnetization value based on detection results of the optical detector; and

calculating an original magnetic field present in the measurement region, using an artificial magnetic field of the artificial magnetic fields when a ratio of a temporal change of the magnetization value or value corresponding to the magnetization value to a temporal change of the artificial magnetic field component in the third direction satisfies a condition for external value.

8. The magnetic field measurement method according to claim 7, wherein the calculation of the original magnetic field is based on the magnetic field of the measurement region when the condition for external value is a zero magnetic field.

9. The magnetic field measurement method according to claim 7, wherein the artificial magnetic field component in the third direction includes a change at a period equal to or less than a cut-off angular frequency.

12. The magnetic field measurement method according to claim 7, further comprising:

generating a magnetic field of a difference in the original magnetic field with respect to a target magnetic field, in the magnetic field generator;

disposing a measuring object in the measurement region; and

measuring a magnetic field which is radiated by the measuring object, using the detection results of the optical detector while the magnetic field of the difference is generated.

13. A magnetic field measurement device comprising:

a light source unit that emits linearly polarized light in which a first direction, a second direction and a third direction are orthogonal to each other;

a medium, disposed in a measurement region, which changes optical characteristics in accordance with a magnetic field, which is irradiated from the third direction with the linearly polarized light of which a vibration direction of an electric field is the second direction, and which transmits the irradiation linearly polarized light;

an optical detector that detects the optical characteristics;

a magnetic field generator that applies an artificial magnetic field, capable of varying each component in the first direction, the second direction, and the third direction, to the measurement region; and

a calculation control processor unit that generates a plurality of artificial magnetic fields, obtained by changing an artificial magnetic field component in the third direction and one artificial magnetic field component in the first direction and the second direction, in the magnetic field generator, in a state where the other artificial magnetic field component in the first direction and the second direction is set to a fixed value, calculating a magnetization value that is a component of a magnetization vector of the medium in the first direction or a value corresponding to the magnetization value on the basis of detection results of the optical detector, and calculating an original magnetic field present in the measurement region, using the artificial magnetic field of the magnetic field generator when the magnetization value or value corresponding to the magnetization value satisfies a condition for external value.

14. A magnetic field measurement device comprising:

a light source unit that emits linearly polarized light in which a first direction, a second direction and a third direction are orthogonal to each other;

a medium, disposed in a measurement region, which changes optical characteristics in accordance with a magnetic field, which is irradiated from the third direction with the linearly polarized light of which a vibration direction of an electric field is the second direction, and which transmits the irradiation linearly polarized light;

an optical detector that detects the optical characteristics;

a magnetic field generator that applies an artificial magnetic field, capable of varying each component in the first direction, the second direction, and the third direction, to the measurement region; and

a calculation control processor unit that generates artificial magnetic fields of a plurality of combinations obtained by changing artificial magnetic field components in the first direction to the third direction, the artificial magnetic fields obtained by periodically changing the artificial magnetic field component in the third direction, in the magnetic field generator, calculating a magnetization value which is a component of a magnetization vector of the medium in the first direction or a value corresponding to the magnetization value on the basis of detection results of the optical detector, and calculating an original magnetic field present in the measurement region, using an artificial magnetic field when a ratio of a temporal change of the magnetization value or value corresponding to the magnetization value to a temporal change of the artificial magnetic field component in the third direction satisfies a condition for external value.

15. A magnetic field measurement device comprising:

a light source unit that emits linearly polarized light propagating in a first direction and vibrating along a second direction, as irradiation light, the first direction being orthogonal to the second direction;

a gas cell having gaseous atoms sealed therein, wherein the light source unit emits the linearly polarized light as a laser beam having a frequency corresponding to a transition of a hyperfine structure level of the gaseous atoms, wherein the gas cell is disposed in a measurement region;

an optical detector that receives polarization components of the irradiation light generated by a polarization splitter and generates signals based on an amount of light received;

a magnetic field generator that applies artificial magnetic fields to the measurement region; and

a calculation control processor unit that receives the signals from the optical detector and that performs magnetic field measurement in the measurement region and magnetic field forming for forming a target magnetic field in the measurement region to calculate an original magnetic field present in the measurement region using the artificial magnetic fields.

16. The magnetic field measurement device according to claim 15, wherein the calculation control processor unit sets the magnetic field of the measurement region to be in a state of the target magnetic field, wherein the target magnetic field is a zero magnetic field.

17. The magnetic field measurement device according to claim 15, wherein the calculation control processor unit calculates the magnetic field present in the measurement region, using the value of the artificial magnetic field, when a calculated difference of measured components satisfies one or more specified conditions.

18. The magnetic field measurement device according to claim 15, wherein the irradiation light is pump light that causes the gaseous atoms in the gas cell to become spin-polarized such that one-beam-type magnetic sensing is used to measure a magnetic field within the measurement region using nonlinear magneto-optical rotation (NMOR).

19. The magnetic field measurement device according to claim 15, wherein the calculation control processor unit includes an artificial magnetic field control processor unit that sequentially generates a plurality of combinations of the artificial magnetic fields in the measurement region through the magnetic field generator.

20. The magnetic field measurement device according to claim 15, further comprising an amplitude detection unit that extracts amplitude information obtained as measurement results in the measurement region and wherein the calculation control processor unit calculates the original magnetic field using the artificial magnetic fields when the amplitude of a square difference becomes maximum as determined from the amplitude information.