JP2016109667A - Magnetic field measurement method and magnetic field measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make magnetic field measurement in multiple directions possible in an optical pump type magnetometry, although probe light is monodirectional.SOLUTION: In a magnetic field measurement device 1, a light source 18 irradiates a gas cell 12 with a linear polarized light serving as both a pump light and a probe light in the direction of axis Z, a magnetic field generator 8 applies, to the gas cell 12, a magnetic field Athat is the time function f(t) of an amplitude Aassuming n fixed values f(i=1, and so on, n) and a magnetic field Athat is the time function g(t) of an amplitude Aassuming m fixed values g(j=1, and so on, m), in each of directions of axes X and Y. An arithmetic control unit 30 calculates the magnetic field C (C, C, C) of a measurement area using the X, Y-axis components A, Aof an artificial magnetic field A and a spin polarization degree Mthat is equivalent to the measured value Wof a magnetometric sensor 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic field measurement method and a magnetic field measurement apparatus using light.

  A magnetic field measurement device using light can measure a minute magnetic field generated from a living body such as a magnetic field from the heart (magnetomagnetic field) and a magnetic field from the brain (magnetomagnetic field). The application of is expected. In such a magnetic field measurement apparatus, pump light and probe light are irradiated to a gas cell in which a gas (gas) such as an alkali metal is sealed. The atoms enclosed in the gas cell are excited by pump light and spin-polarized, and the polarization plane of the probe light transmitted through the gas cell is rotated according to the magnetic field by the magneto-optic effect. The magnetic field is measured by measuring the rotation angle of the polarization plane of the probe light before and after transmission through the gas cell (for example, Patent Document 1).

JP 2013-108833 A

  In the conventional general optical pumping type magnetic field measuring apparatus, the detection axis of the magnetic field is one direction, and when the direction of the detection axis is different from the direction of the magnetic field, the projection component to the detection axis of the magnetic field is measured. However, the magnetic field actually distributed in the space is a three-dimensional vector, and it is desirable to measure a magnetic field in a triaxial direction such as XYZ orthogonal three axes in order to measure the magnetic field more precisely. Since the detection axis is a direction corresponding to the irradiation direction of the probe light, when the detection axis is simply increased by increasing the irradiation direction of the probe light, it is necessary to make the respective irradiation directions accurately orthogonal. When the irradiation direction is inclined with respect to the assumed direction, the detection axis is inclined accordingly, and as a result, an error occurs in the measured value of the magnetic field, which is a three-dimensional vector.

  The present invention has been made in view of the above circumstances, and the object thereof is to enable measurement of magnetic fields in a plurality of directions while the probe light is in one direction in the optical pump type magnetic field measurement. Alternatively, magnetic measurement is performed with high accuracy.

  Application Example 1 In a first invention for solving the above-described problem, a first direction, a second direction, and a third direction are orthogonal to each other, a light source that emits light, and the light in the third direction. A medium that passes along and changes an optical characteristic according to a magnetic field of a measurement region, a photodetector that detects the optical characteristic, and a first magnetic field generator that applies a magnetic field in the first direction to the measurement region; Is a magnetic field measurement method for measuring a magnetic field in the measurement region, and the first magnetic field generator has a first level side first level as a magnetic field in the first direction. A constant magnetic field of the first direction side, a constant magnetic field of the second level, and a constant magnetic field of the first direction side third level, the detection result of the photodetector, and the first direction Calculating a magnetic field in the measurement region using a magnetic field. .

  According to the magnetic field measurement method of this application example, the magnetic field vector in the measurement region can be calculated by irradiating light in only one direction such as the third direction (Z direction). That is, the first direction (X direction) component, the second direction (Y direction) component, and the third direction (Z direction) component of the magnetic field in the measurement region can be calculated by light irradiation in only one direction. . Specifically, as a magnetic field in a first direction (X direction) orthogonal to the third direction (Z direction), which is the light emission direction, with respect to a medium that changes the optical characteristics of light according to the magnetic field in the measurement region. Apply three levels of constant magnetic field. And the magnetic field of a measurement area | region is calculated using the detection result of the optical characteristic of light, and the magnetic field of a 1st direction (X direction).

  Application Example 2 As a second invention, in the magnetic field measurement method according to the first invention, the calculation of the magnetic field in the measurement region includes a magnetization value indicating a component in the first direction of the magnetization vector of the medium. Is calculated based on the detection result of the photodetector, and the first magnetization value when the first direction side first level constant magnetic field is generated, and the first direction side The 2-1 magnetization value when a two-level constant magnetic field is generated, the 3-1 magnetization value when the first direction side third-level constant magnetic field is generated, and the first You may comprise the magnetic field measuring method which is calculating the magnetic field of the said measurement area | region using the magnetic field of one direction.

  According to the magnetic field measurement method of this application example, the magnetization value indicating the component in the first direction (X direction) of the magnetization vector of the medium is calculated based on the detection result of the optical characteristic of the medium, and the first direction (X direction) ) Magnetic field vectors (first direction of the magnetic field (first direction of the magnetic field)) using the three magnetization values when the three levels of constant magnetic fields are generated and the magnetic field in the first direction (X direction). X direction) component, second direction (Y direction) component, and third direction (Z direction) component).

ただし、前記計測領域の磁場はＣ＝（Ｃ_x，Ｃ_y，Ｃ_z）であり、ｘ，ｙ，ｚはそれぞれ前記第１方向、前記第２方向、前記第３方向の空間座標であり、Ｍ_xiは前記第１方向側第ｉ水準の一定磁場が発生されているときの磁化値であり、ａ，ｃは定数であり、Ａ₁₀ｆ_iは前記第１方向側第ｉ水準の一定磁場である。 Application Example 3 As a third invention, in the magnetic field measurement method of the second invention, the calculation of the magnetic field in the measurement region is the first direction side i-th level which is the magnetic field in the first direction. A magnetic field measurement method, which is to apply the following formula 1 to each combination of a constant magnetic field (i = 1, 2, 3) and a magnetization value when the magnetic field in the first direction is generated: It may be configured.

However, the magnetic field of the measurement region is C = (C _x , C _y , C _z ), and x, y, z are spatial coordinates in the first direction, the second direction, and the third direction, respectively. M _xi is the magnetization value when a constant magnetic field of the i level the first direction is generated, a, c are constants, a ₁₀ f _i is constant magnetic field of the i level the first direction It is.

According to the magnetic field measurement method of this application example, each value for each combination of the three levels of the constant magnetic field that is the magnetic field in the first direction (X direction) and the magnetization value when the constant magnetic field is generated. By solving the simultaneous equations consisting of three equations substituting into Equation 1, the magnetic field (C _x , C _y , C _z ) in the measurement region of the medium, which is a three-dimensional vector, can be calculated.

  Application Example 4 As a fourth invention, any one of the first to third magnetic field measurement methods, wherein the first direction side first level constant magnetic field and the first direction side second level constant magnetic field are provided. In addition, a magnetic field measurement method may be configured in which at least one of the first direction side third level constant magnetic fields is a zero magnetic field.

  Application Example 5 In the fifth aspect of the invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source that emits light, the light passes along the third direction, and a measurement region A magnetic field measurement apparatus comprising: a medium that changes an optical characteristic according to a magnetic field of the light; a photodetector that detects the optical characteristic; and a second magnetic field generator that applies a magnetic field in the second direction to the measurement region. Is a magnetic field measurement method for measuring a magnetic field in the measurement region, wherein the second magnetic field generator has a first level constant magnetic field as the second direction magnetic field, The measurement is performed using the direction-side second level constant magnetic field and the second direction-side third level constant magnetic field, the detection result of the photodetector, and the second direction magnetic field. Calculating a magnetic field in the region.

  According to the magnetic field measurement method of this application example, the magnetic field vector in the measurement region can be calculated by irradiating light in only one direction such as the third direction (Z direction). That is, the first direction (X direction) component, the second direction (Y direction) component, and the third direction (Z direction) component of the magnetic field in the measurement region can be calculated by light irradiation in only one direction. . Specifically, as a magnetic field in the second direction (Y direction) orthogonal to the third direction (Z direction), which is the light emission direction, with respect to the medium that changes the optical characteristics of light according to the magnetic field in the measurement region. Apply three levels of constant magnetic field. And the magnetic field of a measurement area | region is calculated using the detection result of the optical characteristic of light, and the magnetic field of a 2nd direction (Y direction).

  Application Example 6 As a sixth invention, in the magnetic field measurement method according to the fifth invention, the calculation of the magnetic field in the measurement region includes a magnetization value indicating a component in the first direction of the magnetization vector of the medium. Is calculated based on the detection result of the photodetector, the first direction magnetization value when the first direction constant magnetic field is generated in the second direction side, and the second direction side The first-second magnetization value when a two-level constant magnetic field is generated, the first-third magnetization value when the second-direction-side third-level constant magnetic field is generated, and the first You may comprise the magnetic field measuring method which is calculating the magnetic field of the said measurement area | region using the magnetic field of 2 directions.

  According to the magnetic field measurement method of this application example, the magnetization value indicating the component in the first direction (X direction) of the magnetization vector of the medium is calculated based on the detection result of the optical characteristic of the medium, and the second direction (Y direction) ) Magnetic field vectors (first direction of the magnetic field (first direction of the magnetic field)) using the three magnetization values when the three levels of constant magnetic fields are generated and the magnetic field in the second direction (Y direction). X direction) component, second direction (Y direction) component, and third direction (Z direction) component).

ただし、前記計測領域の磁場はＣ＝（Ｃ_x，Ｃ_y，Ｃ_z）であり、ｘ，ｙ，ｚはそれぞれ前記第１方向、前記第２方向、前記第３方向の空間座標であり、Ｍ_xjは前記第２方向側第ｊ水準の一定磁場が発生されているときの磁化値であり、ａ，ｃは定数であり、Ａ₂₀ｇ_jは前記第２方向側第ｊ水準の一定磁場である。 Application Example 7 As a seventh invention, in the magnetic field measurement method of the sixth invention, the calculation of the magnetic field in the measurement region is the second direction side j-th level which is the magnetic field in the second direction. A magnetic field measurement method, which is to apply the following Equation 2 to each combination of a constant magnetic field (j = 1, 2, 3) and a magnetization value when the magnetic field in the second direction is generated It may be configured.

However, the magnetic field of the measurement region is C = (C _x , C _y , C _z ), and x, y, z are spatial coordinates in the first direction, the second direction, and the third direction, respectively. M _xj is a magnetization value when the second direction side j level constant magnetic field is generated, a and c are constants, and A ₂₀ g _j is the second direction side j level constant magnetic field. It is.

According to the magnetic field measurement method of this application example, each value for each combination of the three levels of the constant magnetic field that is the magnetic field in the second direction (Y direction) and the magnetization value when the constant magnetic field is generated. By solving a simultaneous equation consisting of three equations obtained by substituting into the equation 2, the magnetic field (C _x , C _y , C _z ) in the measurement region of the medium, which is a three-dimensional vector, can be calculated.

  Application Example 8 As the eighth invention, any one of the fifth to seventh magnetic field measurement methods, wherein the second direction side first level constant magnetic field and the second direction side second level constant magnetic field are provided. In addition, a magnetic field measurement method may be configured in which at least one of the second direction side third level constant magnetic fields is a zero magnetic field.

  Application Example 9 In a ninth invention, a first direction, a second direction, and a third direction are orthogonal to each other, a light source that emits light, the light passes along the third direction, and a measurement region A medium that changes the optical characteristics in accordance with the magnetic field, a photodetector that detects the optical characteristics, a first magnetic field generator that applies the magnetic field in the first direction to the measurement region, and a magnetic field in the second direction Is a magnetic field measurement method for measuring a magnetic field in the measurement region, wherein the first magnetic field generator includes the first magnetic field generator. Generating a first level constant magnetic field in the first direction side and a second level constant magnetic field in the first direction side as the direction magnetic field, and causing the second magnetic field generator to As the magnetic field, the second direction side first level constant magnetic field and the second direction side second level Generating a constant magnetic field; and calculating a magnetic field in the measurement region using the detection result of the photodetector, the magnetic field in the first direction, and the magnetic field in the second direction. This is a measurement method.

  According to the magnetic field measurement method of this application example, the magnetic field vector in the measurement region can be calculated by irradiating light in only one direction such as the third direction (Z direction). Specifically, as a magnetic field in a first direction (X direction) orthogonal to the third direction (Z direction), which is the light emission direction, with respect to a medium that changes the optical characteristics of light according to the magnetic field in the measurement region. Two levels of constant magnetic fields are applied, and two levels of constant magnetic fields are applied as magnetic fields in the third direction (Z direction) and the second direction (Y direction) orthogonal to the first direction (X direction). And the magnetic field of a measurement area | region is calculated using the detection result of the optical characteristic of light, the magnetic field of a 1st direction (X direction), and the magnetic field of a 2nd direction (Y direction).

  Application Example 10 As a tenth aspect of the invention, in the magnetic field measurement method according to the ninth aspect of the invention, calculating the magnetic field in the measurement region is a magnetization value indicating a component in the first direction of the magnetization vector of the medium. 1) when a constant magnetic field of the first level side first level and a constant magnetic field of the second direction side first level are generated. 1-1, the first magnetization value of the first direction side, and the first magnetization value of the second direction when the second direction side second level constant magnetic field is generated. , The first direction side second level constant magnetic field, the 2-1 magnetization value when the second direction side first level constant magnetic field is generated, and the first direction side second level. And the 2-2 magnetization when the second direction side second level constant magnetic field is generated. A magnetic field in the measurement region by using three or more magnetization values, 2) the magnetic field in the first direction, and 3) the magnetic field in the second direction. A measurement method may be configured.

  According to the magnetic field measurement method of this application example, the magnetization value indicating the component in the first direction (X direction) of the magnetization vector of the medium is calculated based on the detection result of the optical characteristic of the medium, and the first direction (X direction) 3) or more of the four magnetization values when the two levels of the constant magnetic field and the two levels of the constant magnetic field in the second direction (Y direction) are respectively generated. The magnetic field in the measurement region is calculated using the magnetization value, the magnetic field in the first direction (X direction), and the magnetic field in the second direction (Y direction).

ただし、前記計測領域の磁場はＣ＝（Ｃ_x，Ｃ_y，Ｃ_z）であり、ｘ，ｙ，ｚはそれぞれ前記第１方向、前記第２方向、前記第３方向の空間座標であり、Ｍ_xijが前記第１方向側第ｉ水準の一定磁場と前記第２方向側第ｊ水準の一定磁場とが発生されているときの磁化値であり、ａ，ｃは定数であり、Ａ₁₀ｆ_iが前記第１方向側第ｉ水準の一定磁場であり、Ａ₂₀ｇ_jが前記第２方向側第ｊ水準の一定磁場である。 Application Example 11 As the eleventh invention, in the magnetic field measurement method according to the tenth invention, the calculation of the magnetic field in the measurement region is the first direction side i-th level which is the magnetic field in the first direction. A constant magnetic field of (i = 1, 2), a constant magnetic field of the second direction side j level (j = 1, 2) which is a magnetic field in the second direction, a magnetic field in the first direction and the second The magnetic field measurement method may be configured to calculate the magnetic field in the measurement region based on the fact that each combination of the magnetization value when the magnetic field in the direction is generated satisfies the following mathematical formula 3. .

However, the magnetic field of the measurement region is C = (C _x , C _y , C _z ), and x, y, z are spatial coordinates in the first direction, the second direction, and the third direction, respectively. M _xij is a magnetization value when the first direction side i-level constant magnetic field and the second direction side j-level constant magnetic field are generated, a and c are constants, and A ₁₀ f _i is a constant magnetic field at the i-level in the first direction side, and A ₂₀ g _j is a constant magnetic field at the j-level in the second direction side.

According to the magnetic field measurement method of this application example, the X-side i-level constant magnetic field that is the magnetic field in the first direction (X direction) and the Y-side j-level constant that is the magnetic field in the second direction (Y direction). For each combination of the magnetic field and the magnetization value when the magnetic field in the first direction (X direction) and the magnetic field in the second direction (Y direction) are generated, By solving the simultaneous equations, the magnetic field (C _x , C _y , C _z ) in the measurement region of the medium, which is a three-dimensional vector, can be calculated.

  Application Example 12 As a twelfth invention, there is provided a magnetic field measurement method according to any one of the ninth to eleventh inventions, wherein the first direction side first level constant magnetic field and the first direction side second. One of the constant magnetic fields of the level is a zero magnetic field, and one of the constant magnetic fields of the second direction side first level and the constant magnetic field of the second direction side second level is a zero magnetic field. It may be configured.

  Application Example 13 In a thirteenth aspect of the invention, the first direction, the second direction, and the third direction are orthogonal to each other, a light source that emits light, the light passes along the third direction, and a measurement region A medium that changes the optical characteristics in accordance with the magnetic field, a photodetector that detects the optical characteristics, a first magnetic field generator that applies the magnetic field in the first direction to the measurement region, and a magnetic field in the second direction For measuring a magnetic field in the measurement region, comprising: a second magnetic field generator that applies a magnetic field to the medium; and a third magnetic field generator that applies a magnetic field in the third direction to the medium. A magnetic field measurement method, wherein the first magnetic field generator is caused to generate a first magnetic field in a first direction as a magnetic field in the first direction, a detection result of the photodetector, and First calculating the magnetic field of the measurement region as an original magnetic field using the magnetic field in the first direction The second step of arranging the measurement object in the measurement region, the difference magnetic field between the target magnetic field and the original magnetic field to be formed in the measurement region, the first magnetic field generator and the second magnetic field A third step for generating the magnetic field generator and the third magnetic field generator, and using the detection result of the photodetector during a period when the third step is performed and the second step is completed, And a fourth step of measuring the magnetic field generated by the measurement object.

  According to the magnetic field measurement method of this application example, the magnetic field generated by the measurement object can be measured in a state where the measurement region is a predetermined target magnetic field. For example, if the target magnetic field is set to a zero magnetic field so as to cancel out the original magnetic field leaking into the measurement region from the outside, the magnetic field generated by the measurement object can be accurately measured.

  Application Example 14 In the fourteenth aspect of the invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source that emits light, the light passes along the third direction, and a measurement region A medium that changes an optical characteristic in accordance with a magnetic field, a photodetector that detects the optical characteristic, a first magnetic field generator that applies a magnetic field in the first direction to the medium, and a magnetic field in the second direction. A magnetic field measuring device comprising: a second magnetic field generator that applies to the medium; and a third magnetic field generator that applies a magnetic field in the third direction to the medium. In the measurement method, the first magnetic field generator is configured to generate a first magnetic field in a first direction as a magnetic field in the first direction, a detection result of the photodetector, and the first A first step of calculating a magnetic field in the measurement region as an original magnetic field using a magnetic field in one direction; A second step of placing a measurement object in the measurement region, and a first direction component of a magnetic field that is a difference between a target magnetic field and a source magnetic field that is a magnetic field that is desired to be formed in the measurement region. A constant magnetic field added to a constant level magnetic field is generated in the first magnetic field generator, a magnetic field of a second direction component of the differential magnetic field is generated in the second magnetic field generator, and a third magnetic field of the differential magnetic field is generated. A third step of causing the third magnetic field generator to generate a magnetic field having a directional component; and a detection result of the photodetector and a first direction during a period when the third step is performed and the second step is completed. And a fourth step of measuring the magnetic field generated by the measurement object using a constant fourth level magnetic field.

  According to the magnetic field measurement method of this application example, the magnetic field generated by the measurement object can be measured in a state where the measurement region is a predetermined target magnetic field. For example, if the target magnetic field is set to zero in order to cancel out the original magnetic field leaking into the measurement region from the outside, the magnetic field generated by the measurement object can be accurately measured as a vector quantity.

  Application Example 15 According to a fifteenth aspect, the first direction, the second direction, and the third direction are orthogonal to each other, a light source that emits light, the light passes along the third direction, and a measurement region A medium that changes an optical characteristic in accordance with a magnetic field, a photodetector that detects the optical characteristic, a first magnetic field generator that applies a magnetic field in the first direction to the measurement region, and the first magnetic field generator In addition, as the first direction magnetic field, the first direction side first level constant magnetic field, the first direction side second level constant magnetic field, and the first direction side third level constant magnetic field are generated. And a calculation control unit that executes calculation of the magnetic field in the measurement region using the detection result of the photodetector and the magnetic field in the first direction. .

  According to the magnetic field measurement apparatus of this application example, the magnetic field vector of the measurement region can be calculated by irradiating light in only one direction such as the third direction (Z direction). That is, the first direction (X direction) component, the second direction (Y direction) component, and the third direction (Z direction) component of the magnetic field in the measurement region can be calculated by light irradiation in only one direction. . Specifically, as a magnetic field in a first direction (X direction) orthogonal to the third direction (Z direction), which is the light emission direction, with respect to a medium that changes the optical characteristics of light according to the magnetic field in the measurement region. Apply three levels of constant magnetic field. And the magnetic field of a measurement area | region is calculated using the detection result of the optical characteristic of light, and the magnetic field of a 1st direction (X direction).

  Application Example 16 According to a sixteenth aspect, the first direction, the second direction, and the third direction are orthogonal to each other, a light source that emits light, the light passes along the third direction, and a measurement region A medium that changes an optical characteristic in accordance with a magnetic field, a photodetector that detects the optical characteristic, a second magnetic field generator that applies a magnetic field in the second direction to the measurement region, and the second magnetic field generator In addition, the second direction side first level constant magnetic field, the second direction side second level constant magnetic field, and the second direction side third level constant magnetic field are generated as the second direction magnetic field. And a calculation control unit that executes calculation of the magnetic field in the measurement region using the detection result of the photodetector and the magnetic field in the second direction. .

  According to the magnetic field measurement apparatus of this application example, the magnetic field vector of the measurement region can be calculated by irradiating light in only one direction such as the third direction (Z direction). That is, the first direction (X direction) component, the second direction (Y direction) component, and the third direction (Z direction) component of the magnetic field in the measurement region can be calculated by light irradiation in only one direction. . Specifically, as a magnetic field in the second direction (Y direction) orthogonal to the third direction (Z direction), which is the light emission direction, with respect to the medium that changes the optical characteristics of light according to the magnetic field in the measurement region. Apply three levels of constant magnetic field. And the magnetic field of a measurement area | region is calculated using the detection result of the optical characteristic of light, and the magnetic field of a 2nd direction (Y direction).

  Application Example 17 In a seventeenth aspect, the first direction, the second direction, and the third direction are orthogonal to each other, the light source that emits light, the light passes along the third direction, and the measurement region A medium that changes the optical characteristics in accordance with the magnetic field, a photodetector that detects the optical characteristics, a first magnetic field generator that applies the magnetic field in the first direction to the measurement region, and a magnetic field in the second direction Is applied to the measurement region, and the first magnetic field generator has a first magnetic field in the first direction as a magnetic field in the first direction, and a first magnetic field in the first direction. Generating a constant magnetic field of two levels, and causing the second magnetic field generator to generate a magnetic field in the second direction as a magnetic field in the second direction, the first level constant magnetic field, and the second direction side second level. Generating a constant magnetic field, and a detection result of the photodetector, a magnetic field in the first direction, and , Using a magnetic field of the second direction, a magnetic field measurement apparatus comprising: a calculation control unit, the to perform, and calculating the magnetic field of the measuring region.

  According to the magnetic field measurement apparatus of this application example, the magnetic field vector in the measurement region can be calculated by irradiating light in only one direction such as the third direction (Z direction). Specifically, as a magnetic field in a first direction (X direction) orthogonal to the third direction (Z direction), which is the light emission direction, with respect to a medium that changes the optical characteristics of light according to the magnetic field in the measurement region. Two levels of constant magnetic fields are applied, and two levels of constant magnetic fields are applied as magnetic fields in the third direction (Z direction) and the second direction (Y direction) orthogonal to the first direction (X direction). And the magnetic field of a measurement area | region is calculated using the detection result of the optical characteristic of light, the magnetic field of a 1st direction (X direction), and the magnetic field of a 2nd direction (Y direction).

The schematic side view which shows an example of a structure of the magnetic field measuring apparatus which concerns on this embodiment. It is a schematic diagram explaining the structure of the magnetic field generator which concerns on this embodiment, and the figure seen from the Y direction specifically. It is a schematic diagram explaining the structure of the magnetic field generator which concerns on this embodiment, and the figure seen from the X direction specifically. It is a schematic diagram explaining the structure of the magnetic field generator which concerns on this embodiment, and the figure seen from the Z direction specifically. It is a schematic diagram explaining the structure of the magnetic sensor which concerns on this embodiment, and the top view seen from the Z direction specifically ,. It is a schematic diagram explaining the structure of the magnetic sensor which concerns on this embodiment, and the side view seen from the Y direction specifically ,. The function block diagram of the calculation control part which concerns on this embodiment. The figure explaining the alignment when there is no magnetic field. The figure explaining the change of the alignment by a magnetic field. The figure explaining the change of the polarization plane of a linearly polarized light by permeate | transmitting a gas cell. The figure explaining the change of the polarization plane of a linearly polarized light by permeate | transmitting a gas cell. The figure which shows the relationship between alignment azimuth angle (theta) and the detection result of probe light. The figure which shows the relationship between alignment azimuth angle (theta) and the detection result of probe light. The figure which shows the relationship between alignment azimuth angle (theta) and the detection result of probe light. The figure which shows the relationship between alignment azimuth angle (theta) and the detection result of probe light. The figure which shows the relationship between alignment azimuth angle (theta) and the detection result of probe light.

Hereinafter, embodiments will be described with reference to the drawings.
In addition, in order to make each member in each drawing into a size that can be recognized on each drawing, the members are illustrated with different scales.

[Configuration of magnetic field measurement device]
First, a configuration example of the magnetic field measurement apparatus according to this embodiment will be described. FIG. 1 is a schematic side view showing an example of the configuration of the magnetic field measurement apparatus according to the present embodiment. FIG. 2 is a diagram illustrating the configuration of the magnetic field generator according to the present embodiment, and specifically, is a diagram viewed from the Y direction. FIG. 3 is a diagram illustrating the configuration of the magnetic field generator according to the present embodiment, and specifically, is a diagram viewed from the X direction. FIG. 4 is a diagram illustrating the configuration of the magnetic field generator according to the present embodiment, and specifically, is a diagram viewed from the Z direction. FIG. 5 is a schematic diagram for explaining the configuration of the magnetic sensor according to the present embodiment, specifically, a plan view seen from the Y direction. FIG. 6 is a schematic diagram illustrating the configuration of the magnetic sensor according to the present embodiment, and specifically, is a side view seen from the Y direction. FIG. 7 is a functional configuration diagram of the arithmetic control unit according to the present embodiment.

  A magnetic field measurement apparatus 1 shown in FIG. 1 is a measurement apparatus that measures a magnetic field generated by a measurement object as a vector quantity. An apparatus that measures a part of information (for example, one component, size, presence / absence, etc.) of a magnetic field generated by a measurement object is referred to as a magnetic measurement apparatus. In this embodiment, the measurement object is a human body (subject), and the magnetic field generated by the measurement object is a magnetocardiogram (a magnetic field generated from electrophysiological activity of the heart) or a cerebral magnetism. Here, the case where the magnetic field measurement apparatus 1 is a measurement apparatus that measures the magnetocardiogram as a vector quantity will be described as an example.

  The magnetic field measurement device 1 is a device that measures a magnetic field using an optical pumping method, and is a so-called one-beam method that uses both pump light and probe light. Note that the configuration is not limited to the one-beam type, and a so-called two-beam type configuration in which a light source for irradiating pump light and a light source for irradiating probe light may be separated. As shown in FIG. 1, the magnetic field measurement device 1 includes a base 3, a table 4, a magnetic shield device 6, a magnetic field generator 8, a magnetic sensor 10, and an arithmetic control unit 30 (see FIG. 7). ing.

  In the magnetic sensor 10 shown in FIG. 6, a direction (irradiation direction) in which laser light (also referred to as irradiation light) 18a emitted from the light source 18 passes through the gas cell 12 is defined as a third direction (Z direction in the present embodiment). The vibration direction of the linearly polarized light component of the irradiation light is the second direction (Y direction in this embodiment). A direction orthogonal to the second direction (Y direction) and the third direction (Z direction) is defined as a first direction (X direction in the present embodiment). The first direction (X direction), the second direction (Y direction), and the third direction (Z direction) are the axial directions of the Cartesian coordinate system, and are hereinafter referred to as the X axis direction, the Y axis direction, and the Z axis direction, respectively. To do.

  In FIG. 1, the Z-axis direction is a vertical direction, which is the height direction of the magnetic field measuring apparatus 1 (up and down direction in FIG. 1). The X-axis direction and the Y-axis direction are horizontal directions, and are the directions in which the base 3 and the upper surface of the table 4 extend. The height direction (left-right direction in FIG. 1) of the subject 9 in the lying state is assumed to be along the X-axis direction. Therefore, the direction crossing the height direction of the subject 9 (the direction from the back to the front in FIG. 1) is the Y-axis direction.

  The base 3 is disposed on the bottom surface inside the magnetic shield device 6 (main body portion 6a), and extends to the outside of the main body portion 6a along the X-axis direction, which is the direction in which the subject 9 can move. The table 4 includes a first table 4a, a second table 4b, and a third table 4c. On the base 3, the 1st table 4a which moves along an X-axis direction by the linear motion mechanism 3a is installed. On the 1st table 4a, the 2nd table 4b which raises / lowers along a Z-axis direction with the raising / lowering apparatus which is not shown in figure is installed. On the 2nd table 4b, the 3rd table 4c which moves on a rail along a Y-axis direction by the linear motion mechanism which is not shown in figure is installed.

  The magnetic shield device 6 includes a rectangular tube-shaped main body 6a having an opening 6b. The inside of the main body 6a is hollow, and the cross-sectional shape of a surface (a plane perpendicular to the X-axis direction in the YZ cross-section) configured in the Y-axis direction and the Z-axis direction is approximately rectangular. When the magnetocardiogram is measured, the subject 9 is accommodated in the body portion 6a while lying on the table 4. The main body 6a extends in the X-axis direction and functions as a passive magnetic shield by itself.

  The base 3 protrudes in the + X direction from the opening 6b of the main body 6a. As for the size of the magnetic shield device 6, for example, the length in the X-axis direction is about 200 cm, and one side of the opening 6b is about 90 cm. Then, the subject 9 lying on the table 4 can move in and out of the magnetic shield device 6 along the X-axis direction along the base 3 together with the table 4 from the opening 6b.

  The main body 6a of the magnetic shield device 6 is formed of a ferromagnetic material having a relative magnetic permeability of, for example, several thousand or more, or a high conductivity conductor. As the ferromagnetic material, permalloy, ferrite, iron, chromium, or cobalt-based amorphous material can be used. As the high conductivity conductor, for example, aluminum or the like having a magnetic field reduction effect by an eddy current effect can be used. It is also possible to form the main body 6a by alternately laminating ferromagnetic materials and high conductivity conductors.

  A magnetic field generator 8 is installed inside the main body 6a. The magnetic field generator 8 is composed of a triaxial Helmholtz coil, and can generate a predetermined magnetic field in the X axis, Y axis, and Z axis directions with respect to the measurement region 5. That is, the magnetic field generator 8 includes at least a first magnetic field generator 8X that generates a magnetic field in the X-axis direction and a second magnetic field generator 8Y that generates a magnetic field in the Y-axis direction. It is preferable to include a third magnetic field generator 8Z that generates a magnetic field.

  In the present embodiment, the magnetic field generator 8 includes a first magnetic field generator (a pair of Helmholtz coils facing each other along the X-axis direction) 8X and a second magnetic field generator (a pair of Helmholtz coils facing along the Y-axis direction). Coil) 8Y and a third magnetic field generator (a pair of Helmholtz coils facing each other along the Z-axis direction) 8Z. A measurement region 5 is a region in the main body 6 a of the magnetic shield device 6 where the magnetic field measurement device 1 measures the magnetocardiogram. The chest 9 a and the magnetic sensor 10, which are measurement positions in the subject 9, are arranged in the measurement region 5.

  As shown in FIGS. 2, 3, and 4, the diameters of the Helmholtz coil 8 </ b> X, the Helmholtz coil 8 </ b> Y, and the Helmholtz coil 8 </ b> Z included in the magnetic field generator 8 are larger than the diameter of the measurement region 5. That is, the measurement region 5 is included in a region surrounded by the first magnetic field generator 8X, the second magnetic field generator 8Y, and the third magnetic field generator 8Z. It is preferable that the centers of the Helmholtz coils 8X, 8Y, and 8Z, the center of the measurement region 5, and the center of the magnetic sensor 10 substantially coincide. In this way, a magnetic field that is a three-dimensional vector can be accurately measured in the measurement region 5.

  Moreover, it is preferable that the distance between a pair of opposing Helmholtz coils is larger than the diameter of other Helmholtz coils. For example, as shown in FIGS. 2, 3, and 4, it is preferable that the distance between a pair of opposing Helmholtz coils 8X is larger than the diameters of the Helmholtz coil 8Y and the Helmholtz coil 8Z. In this way, a parallel and uniform magnetic field can be generated along the Y axis (or Z axis) by the pair of Helmholtz coils 8Y (or 8Z). Similarly, the distance between the pair of Helmholtz coils 8Y (or 8Z) is preferably larger than the diameter of the other Helmholtz coils.

  2, 3, and 4, a distance between a pair of Helmholtz coils 8 </ b> X (for example, in the case of FIG. 2, a distance along the X axis between the left Helmholtz coil 8 </ b> X and the right Helmholtz coil 8 </ b> X). It is assumed that the diameter is smaller than the diameters of the other Helmholtz coil 8Y and Helmholtz coil 8Z. In this case, the Helmholtz coil 8X enters inside a cylindrical region having the pair of Helmholtz coils 8Y (or 8Z) as the bottom surface. Then, the magnetic field formed by the pair of Helmholtz coils 8Y (or 8Z) is distorted, and it is difficult to generate a parallel and uniform magnetic field along the Y axis (or Z axis) in the vicinity of the measurement region 5. Become.

  On the other hand, when the distance between the pair of Helmholtz coils 8X is larger than the diameters of the other Helmholtz coils 8Y and 8Z, the cylindrical region having the bottom surfaces of the pair of Helmholtz coils 8Y (or 8Z). The Helmholtz coil 8X is disposed outside. Then, the Helmholtz coil 8X suppresses the distortion of the magnetic field formed by the pair of Helmholtz coils 8Y (or 8Z), and generates a parallel and uniform magnetic field along the Y axis (or Z axis) in the vicinity of the measurement region 5. It becomes possible.

  As described above, it is preferable that the pair of Helmholtz coils 8Y and the pair of Helmholtz coils 8Z are arranged outside the columnar region having the pair of Helmholtz coils 8X as bottom surfaces. Then, a pair of Helmholtz coils 8Z and a pair of Helmholtz coils 8X are arranged outside the cylindrical region with the pair of Helmholtz coils 8Y as the bottom surface, and outside the cylindrical region with the pair of Helmholtz coils 8Z as the bottom surface. A pair of Helmholtz coils 8X and a pair of Helmholtz coils 8Y are preferably arranged.

  In this embodiment, the Helmholtz coil is described as having a circular shape, but the Helmholtz coil is not limited to a circular shape, and may be a polygon such as a quadrangle. When the shape of the Helmholtz coil is a polygon, another Helmholtz coil perpendicular to the height direction of the prism is disposed outside the prismatic region having the pair of Helmholtz coils as the bottom surface.

  The magnetic sensor 10 is fixed to the ceiling of the main body 6a via a support member 7. The magnetic sensor 10 measures the strength component of the magnetic field in the Z-axis direction of the measurement region 5. The magnetic sensor 10 measures a magnetic field using an optical pumping method. When measuring the magnetocardiogram of the subject 9, the first table 4 a and the third table 4 c are moved so that the chest 9 a that is the measurement position in the subject 9 is opposed to the magnetic sensor 10, and the chest 9 a The second table 4b is raised so as to approach the magnetic sensor 10.

  In the measurement of a weak magnetic field using the optical pumping type magnetic sensor 10, the magnetic field (original magnetic field) flowing in from the outside due to the environment such as geomagnetism and urban noise existing in the measurement region 5 in which the gas cell 12 is disposed is canceled. Is preferred. This is because the presence of the original magnetic field is affected by the influence, which causes a decrease in sensitivity to the magnetic field generated by the measurement object (subject 9) and a decrease in measurement accuracy. In the present embodiment, the magnetic shield device 6 suppresses the inflow of the magnetic field from the outside to the measurement region 5. And the measurement area | region 5 vicinity can be kept at the low magnetic field near a zero magnetic field with the magnetic field generator 8 arrange | positioned inside the main-body part 6a.

  As shown in FIG. 5, the magnetic sensor 10 includes a light source 18, a gas cell 12, and photodetectors 14 and 15. The light source 18 outputs a laser beam 18a having a wavelength corresponding to the absorption line of cesium. Although the wavelength of the laser beam 18a is not particularly limited, in this embodiment, for example, the wavelength is set to a wavelength of 894 nm corresponding to the D1 line. The light source 18 is a tunable laser, and the laser light 18a output from the light source 18 is continuous light having a constant light amount.

  In the present embodiment, the light source 18 is installed in the calculation control unit 30. Laser light 18 a emitted from the light source 18 is supplied to the main body of the magnetic sensor 10 through the optical fiber 19. The main body of the magnetic sensor 10 and the optical fiber 19 are connected via an optical connector 20. The laser beam 18 a supplied via the optical connector 20 travels in the −Y direction and enters the polarizing plate 21. The laser beam 18a that has passed through the polarizing plate 21 is linearly polarized light. Then, the laser beam 18 a sequentially enters the first half mirror 22, the second half mirror 23, the third half mirror 24, and the first reflection mirror 25.

  The first half mirror 22, the second half mirror 23, and the third half mirror 24 reflect a part of the laser beam 18a to travel in the + X direction, pass a part of the laser beam 18a, and travel in the -Y direction. Let The first reflecting mirror 25 reflects all the incident laser light 18a in the + X direction. The laser beam 18a is divided into four optical paths by the first half mirror 22, the second half mirror 23, the third half mirror 24, and the first reflection mirror 25. The reflectivity of each mirror is set so that the light intensity of the laser beam 18a in each optical path becomes the same light intensity.

  Next, as shown in FIG. 6, the laser beam 18 a is sequentially incident on the fourth half mirror 26, the fifth half mirror 27, the sixth half mirror 28, and the second reflection mirror 29. The fourth half mirror 26, the fifth half mirror 27, and the sixth half mirror 28 reflect a part of the laser light 18a to travel in the + Z direction, pass a part of the laser light 18a, and travel in the + X direction. . The second reflecting mirror 29 reflects all the incident laser light 18a in the + Z direction.

  The fourth half mirror 26, the fifth half mirror 27, the sixth half mirror 28, and the second reflection mirror 29 divide the laser light 18a in one optical path into four optical paths. The reflectivity of each mirror is set so that the light intensity of the laser beam 18a in each optical path becomes the same light intensity. Therefore, the laser beam 18a is separated into 16 optical paths. The reflectivity of each mirror is set so that the light intensity of the laser beam 18a in each optical path is the same.

  On the + Z direction side of the fourth half mirror 26, the fifth half mirror 27, the sixth half mirror 28, and the second reflection mirror 29, 16 gas cells 12 in 4 rows and 4 columns are installed in each optical path of the laser light 18a. Has been. Then, the laser light 18 a reflected by the fourth half mirror 26, the fifth half mirror 27, the sixth half mirror 28, and the second reflection mirror 29 passes through the gas cell 12.

  The gas cell 12 is a box having a gap inside, and in this gap, an alkali metal gas is sealed as a medium that changes the optical characteristics of light according to the magnetic field in the measurement region 5 (see FIG. 1). . The alkali metal is not particularly limited, and potassium, rubidium or cesium can be used. In this embodiment, for example, cesium is used as an alkali metal.

  A polarized light separator 13 is installed on the + Z direction side of each gas cell 12. The polarization separator 13 is an element that separates the incident laser beam 18a into two polarized component laser beams 18a orthogonal to each other. As the polarization separator 13, for example, a Wollaston prism or a polarization beam splitter can be used.

  A photodetector 14 is installed on the + Z direction side of the polarization separator 13, and a photodetector 15 is installed on the + X direction side of the polarization separator 13. The laser beam 18 a that has passed through the polarization separator 13 enters the photodetector 14, and the laser beam 18 a that is reflected by the polarization separator 13 enters the photodetector 15. The photodetector 14 and the photodetector 15 output a signal corresponding to the amount of received light of the incident laser beam 18 a to the arithmetic control unit 30.

  It is desirable that the photodetectors 14 and 15 be made of a non-magnetic material because the photodetectors 14 and 15 may affect the measurement when a magnetic field is generated. The magnetic sensor 10 has heaters 16 installed on both sides in the X-axis direction and both sides in the Y-axis direction. The heater 16 preferably has a structure that does not generate a magnetic field. For example, a heater that heats steam or hot air through a flow path can be used. Instead of the heater, the gas cell 12 may be dielectrically heated by a high frequency voltage.

  The magnetic sensor 10 is disposed on the + Z direction side of the subject 9 (see FIG. 1). A magnetic field vector B (including a target magnetic field vector generated by the measurement target) detected by the magnetic sensor 10 in the measurement region 5 enters the magnetic sensor 10 from the −Z direction side. The magnetic field vector B passes through the fourth half mirror 26 to the second reflection mirror 29, passes through the gas cell 12, passes through the polarization separator 13, and exits from the magnetic sensor 10.

  The magnetic sensor 10 is a sensor called an optical pumping type magnetic sensor or an optical pumping atomic magnetic sensor. The cesium in the gas cell 12 is heated and is in a gas state. Then, by irradiating the cesium gas with the laser beam 18a that has been linearly polarized, the cesium atoms are excited and the direction of the magnetic moment is aligned. When the magnetic field vector B passes through the gas cell 12 in this state, the magnetic moment of the cesium atom precesses due to the magnetic field of the magnetic field vector B. This precession is called Larmor precession.

  The magnitude of the Larmor precession has a positive correlation with the strength of the magnetic field vector B. The Larmor precession rotates the deflection surface of the laser beam 18a. The magnitude of the Larmor precession and the amount of change in the rotation angle of the deflection surface of the laser beam 18a have a positive correlation. Therefore, the intensity of the magnetic field vector B and the amount of change in the rotation angle of the deflection surface of the laser beam 18a have a positive correlation. The sensitivity of the magnetic sensor 10 is high in the Z-axis direction of the magnetic field vector B, and low in the direction orthogonal to the Z-axis direction.

  The polarization separator 13 separates the laser beam 18a transmitted through the gas cell 12 into two-component linearly polarized light in the axial directions (α axis and β axis shown in FIG. 11) orthogonal to each other. One separated linearly polarized light is guided to the photodetector 14, and the other linearly polarized light is guided to the photodetector 15. The photodetector 14 and the photodetector 15 receive the linearly polarized light components of the two orthogonal components, generate a signal corresponding to the received light amount, and output the signal to the arithmetic control unit 30. By detecting the intensity of each linearly polarized light, the rotation angle of the deflection surface of the laser beam 18a can be detected. The intensity of the magnetic field vector B can be detected from the change in the rotation angle of the deflection surface of the laser beam 18a.

  An element including the gas cell 12, the polarization separator 13, the photodetector 14, and the photodetector 15 is referred to as a sensor element 11. In the present embodiment, 16 sensor elements 11 in 4 rows and 4 columns are arranged in the magnetic sensor 10. The number and arrangement of the sensor elements 11 in the magnetic sensor 10 are not particularly limited. The sensor elements 11 may be 3 rows or less or 5 rows or more. Similarly, the sensor elements 11 may have 3 rows or less or 5 rows or more. As the number of sensor elements 11 increases, the spatial resolution can be increased.

  As illustrated in FIG. 7, the arithmetic control unit 30 includes an operation unit 31, a display unit 32, a communication unit 33, a processing unit 40, and a storage unit 50. The operation unit 31 is an input device such as a button switch, a touch panel, a keyboard, or various sensors, and outputs an operation signal corresponding to the performed operation to the processing unit 40. By the operation unit 31, various instructions such as a magnetic field measurement start instruction are input.

  The display unit 32 is a display device such as an LCD (Liquid Crystal Display) and performs various displays based on display signals from the processing unit 40. Measurement results and the like are displayed on the display unit 32. The communication unit 33 is a communication device such as a wireless communication device, a modem, a cable communication cable jack or a control circuit, and is connected to a given communication line to realize communication with the outside.

  The processing unit 40 includes, for example, a microprocessor such as a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit), an electronic component such as an ASIC (Application Specific Integrated Circuit) and an IC (Integrated Circuit) memory. Realized. The processing unit 40 controls the operation of the arithmetic control unit 30 by executing various arithmetic processes based on a predetermined program and data, an operation signal from the operation unit 31, a measurement signal from the magnetic sensor 10, and the like.

  The processing unit 40 includes an irradiation control unit 41, a magnetic field generation control unit 42, an original magnetic field calculation unit 43, a bias magnetic field determination unit 44, and a target magnetic field calculation unit 45. The processing unit 40 executes a magnetic measurement process (see the flowchart shown in FIG. 13) according to the magnetic field measurement program 51 stored in the storage unit 50.

In the magnetic measurement processing according to the present embodiment, for example, before measurement of a magnetic field generated by a measurement object such as a human heart or brain, as an initial setting, the original measurement region 5 in a state where the measurement object is not placed is used. The magnetic field _Cx is calculated. Then, in a state in which a bias magnetic field that cancels the original field C _x is generated in the magnetic field generator 8, the measurement of the magnetic field measurement object is generated. That is, the measurement of the magnetic field generated by the measurement object (subject 9) is performed in a state where the external magnetic field (original magnetic field) flowing into the measurement region 5 is reduced.

  The irradiation control unit 41 controls irradiation of irradiation light by the light source 18 of the magnetic sensor 10. Specifically, the irradiation control unit 41 controls the light intensity of the irradiation light, the direction of the linearly polarized light plane included in the irradiation light, and the like in addition to the start and end of irradiation of the irradiation light by the light source 18.

The magnetic field generation control unit 42 controls the magnetic field generator 8 (8X, 8Y, 8Z) to generate a predetermined magnetic field in each of the X, Y, and Z axis directions. Specifically, the magnetic field generation control unit 42, the initial setting, a predetermined artificial magnetic field _{A (A x, A y,} A z) and a magnetic field generator 8 (8X, 8Y, 8Z) is generated on. As will be described in detail later, the artificial magnetic field A is an alternating magnetic field f (ωt) in which the first direction (X direction) component and the second direction (Y direction) component have the same amplitude and period but different phases. , A magnetic field vector whose third direction (Z direction) component is zero (A _z = 0). The artificial magnetic field A (A _x , A _y , A _z ) is stored in the storage unit 50 as artificial magnetic field data 52.

Further, the magnetic field generation control unit 42 at the time of measurement, the bias magnetic field B _b (B _bx , B _by , B _bz ) determined by the bias magnetic field determination unit 44 and the artificial magnetic field A (A _x , A _y , A _z ). And the combined magnetic field (B _b + A) is generated in the magnetic field generator 8 (8X, 8Y, 8Z).

The X-axis direction component A _x of the artificial magnetic field A is sequentially supplied to the magnetic field generator 8X by an X-side first level constant magnetic field, an X-side second level constant magnetic field, and an X-side third level constant magnetic field. It may be generated. Similarly, the magnetic field generator 8Y, as Y-axis direction component A _y of the artificial magnetic field A, Y side first level constant magnetic field, Y-side constant magnetic field of the second level, and, the Y-side constant magnetic field of the third level It may be generated sequentially. Further, the magnetic field generator 8X sequentially generates an X-side first level constant magnetic field and an X-side second level constant magnetic field as the X-axis direction component A _x of the artificial magnetic field A, and the magnetic field generator 8Y The Y-side first level constant magnetic field and the Y-side second level constant magnetic field may be sequentially generated as the Y-axis direction component A _y of the artificial magnetic field A.

Original magnetic field calculator 43, the magnetic field generator 8 (8X, 8Y, 8Z) artificial magnetic field vector _{A (A x, A y,} A z) in a state in which generating a, the signal output from the magnetic sensor 10 Based on this, the original magnetic field vector C (C _x , C _y , C _z ) is calculated. Specifically, a magnetic sensor measurement value (square difference W ₋ ) obtained based on a signal output from the magnetic sensor 10 is a spin polarization degree M _x, and an X-axis direction component of the artificial magnetic field vector A at a certain time t. a _x value a _x (t), and, the value of the Y-axis direction component a _y a _y (t), a combination of a spin polarization M _x (t), the spin polarization M _x differs 3 Get more than one combination.

Then, by defining a simultaneous equation consisting of three or more equations obtained by substituting each of the acquired combinations into Equation 17 to be described later, and executing a predetermined arithmetic operation process for solving the simultaneous equations, the original magnetic field vector C (C _x , C _y , C _z ) is calculated. The calculated original magnetic field C (C _x , C _y , C _z ) is stored in the storage unit 50 as the original magnetic field data 53.

The bias magnetic field determination unit 44 determines a bias magnetic field B _b (B _bx , B _by , B _bz ) that cancels the original magnetic field vector C (C _x , C _y , C _z ) calculated by the original magnetic field calculation unit 43. To do. The determined bias magnetic field B _b (B _bx , B _by , B _bz ) is stored in the storage unit 50 as the bias magnetic field data 54.

The target magnetic field calculation unit 45 generates the measurement target based on a signal output from the magnetic sensor 10 in a state where the measurement target is arranged and the magnetic field generator 8 generates the bias magnetic field B _b. The target magnetic field vector B (B _x , B _y , B _z ) is calculated. Specifically, the measured value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 is the spin polarization M _x, and the X-axis direction component A _x of the artificial magnetic field vector A at a certain time t. value a _x (t), and, the value of the Y-axis direction component a _y a _y (t), a combination of a spin polarization M _x (t), is three or more different spin polarization M _x Get the combination.

Then, by defining a simultaneous equation consisting of three or more equations obtained by substituting each of the acquired combinations into Equation 17, and executing a predetermined arithmetic operation process for solving the simultaneous equations, the original magnetic field vector C ( C _x , C _y , C _z ) is calculated as a target magnetic field B (B _x , B _y , B _z ) generated by the measurement object. The calculated target magnetic field vector B (B _x , B _y , B _z ) is stored in the storage unit 50 as measured magnetic field data 55. The magnetic sensor measurement value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 is stored in the storage unit 50 as magnetic sensor measurement data 56.

  The storage unit 50 includes a storage device such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a hard disk. The storage unit 50 stores a program, data, and the like for the processing unit 40 to integrally control the calculation control unit 30, and is used as a work area of the processing unit 40. Operation data from the operation unit 31 is temporarily stored. In the present embodiment, the storage unit 50 stores a magnetic field measurement program 51, artificial magnetic field data 52, original magnetic field data 53, bias magnetic field data 54, measured magnetic field data 55, and magnetic sensor measurement data 56. Is done.

[principle]
The measurement principle of the magnetic field in the magnetic field measuring apparatus 1 will be described. FIG. 8 is a diagram for explaining alignment when there is no magnetic field. FIG. 9 is a diagram for explaining a change in alignment due to a magnetic field. 10 and 11 are diagrams for explaining the change of the polarization plane of linearly polarized light due to transmission through the gas cell. FIG. 12 is a diagram illustrating the relationship between the alignment azimuth angle θ and the probe light detection result.

  In the following description, a time-series description is given to make the principle easy to understand, but in reality, (A) optical pumping and (C) probing occur simultaneously in the one-beam system of this embodiment. obtain.

(A) Optical pumping The gas of alkali metal atoms sealed in the gas cell 12 is pump light adjusted to a wavelength corresponding to the transition of the state of the ultrafine structure quantum number F to F ′ (= F−1) of the D1 line. (In this embodiment, irradiation with light passing through the gas cell 12) irradiates a group in which substantially the same number of atoms whose spins are substantially antiparallel (reverse) (spin polarized) are mixed. This state is called alignment. Note that the spin polarization of one atom relaxes with time, but since the pump light is CW (continuous wave) light, the formation and relaxation of spin polarization are repeated simultaneously and continuously. As a result, a steady spin polarization is formed as a whole group of atoms.

  When the measurement region 5 is a zero magnetic field, the alignment is represented by a probability distribution of the magnetic moment of atoms. When the pump light is linearly polarized as in the present embodiment, the shape is the vibration direction of the electric field of the linearly polarized light of the pump light (in the present embodiment, the Y-axis direction) as shown in FIG. The shape of the region R connecting the two ellipses extending along).

(B) Action of magnetic field When a certain magnetic field exists in the measurement region 5, the alkali metal atoms start precessing around the direction of the magnetic field vector (the magnetic field received by the gas cell 12) as the rotation axis. Then, as shown in FIG. 9, the direction of alignment (the direction along the major axis of the ellipse) is obtained by adding the optical pumping action by the pump light and the relaxation action caused by gas atoms colliding with the inner wall of the gas cell 12. ) Changes so as to rotate around the origin O.

  The alignment direction is in a steady state with an arrangement rotated by an angle (θ) corresponding to the strength of the magnetic field with respect to the Y axis. Here, the alignment direction is θp, and the orthogonal direction is θs. Further, an angle θ formed by the alignment direction θp with respect to the Y-axis direction that is the vibration direction of the electric field of the pump light is defined as an alignment azimuth angle θ. The alignment azimuth angle θ increases mainly according to the magnetic field strength in the Z-axis direction.

(C) Probing Consider a situation where probe light having a linearly polarized component that vibrates in the Y-axis direction with an electric field vector E ₀ (light that passes through the gas cell 12 in this embodiment) passes through the atomic group in this state. That is, as shown in FIG. 10, the linearly polarized light whose probe beam electric field oscillates along the Y-axis direction passes through the gas cell 12 in the + Z direction. In FIG. 10, the origin O corresponds to the position of an atomic group (gas atoms sealed in the gas cell 12), and this atomic group is optically pumped, so that the alignment distributed in the region along the Y-axis direction is achieved. Has occurred. In the Z-axis direction, the −Z direction side indicates linearly polarized light before transmitting through the atomic group, and the + Z direction indicates linearly polarized light (transmitted light) transmitted through the atomic group.

When linearly polarized light is transmitted through the atomic group, the polarization plane of the linearly polarized light is rotated due to linear dichroism, and its electric field vector changes to E ₁ . The linear dichroism is a property in which the transmittance of linearly polarized light differs between a direction θp along the alignment (see FIG. 9) and a direction θs perpendicular to the alignment (see FIG. 9). Specifically, since the component in the direction θs perpendicular to the alignment is absorbed more than the direction θp along the alignment, the polarization plane of the probe light rotates so as to approach the direction θp along the alignment.

FIG. 11 is a diagram showing the state of rotation of the polarization plane before and after the linearly polarized light passes through the atomic group on the XY plane perpendicular to the Z-axis direction that is the irradiation direction of the probe light. In the present embodiment, the probe light incident on the gas cell 12 is linearly polarized light of an electric field vector E ₀ whose electric field vibration direction is the Y-axis direction. Alignment, the component in the direction θp of the probe light transmitted by the transmittance t _p, the components of the direction θs is transmitted with transmittance t _s. Since by linear dichroism is t _p> t _s, the plane of polarization of the probe light transmitted through the gas cell 12 is rotated so as to approach the direction theta] p. Thus, the light passing through the gas cell 12 has an electric field vector E ₁ .

Specifically, a component along the alignment of the electric field vector E ₀ is expressed as E _0P, and a component along the direction perpendicular to the alignment of the electric field vector E ₀ and the traveling direction of the linearly polarized light is expressed as E _0s . Further, a component along the alignment of the electric field vector E ₁ is expressed as E _1P, and a component along a direction perpendicular to the alignment of the electric field vector E ₁ and the traveling direction of the linearly polarized light is expressed as E _1s . In this case, there is a relationship between E _1P = t _p E _0P and E _1s = t _s E _0s .

Assuming that the angle formed by the direction along the alignment and the vibration direction of the electric field of the probe light (hereinafter referred to as “alignment azimuth angle”) is θ, the direction θp and the direction θs of the electric field vector E ₁ are Each component is calculated by the following Equation 4.

As described above, the probe light that has passed through the gas cell 12 is, by the polarization separator 13, the α axis that forms +45 degrees with respect to the Y axis direction, which is the irradiation direction of the probe light, and −45 degrees with respect to the Y axis direction. Are separated into two polarization components with the β axis. The α-axis direction component E _α and the β-axis direction component E _β of the linearly polarized light of the electric field vector E ₁ transmitted through the gas cell 12 are calculated by Equation 5.

The photodetectors 14 and 15 measure the light intensity of each of the two polarization components of the α axis and the β axis, and output a signal corresponding to the amount of received light to the arithmetic control unit 30. The arithmetic control unit 30 processes the signals from the photodetectors 14 and 15, and calculates the sum of squares W ₊ and the square difference W ₋ of the components in the axial directions of the α axis and the β axis according to the following formulas 6 and 7. calculate. E _α represents the light intensity of the component in the α-axis direction, and E _β represents the light intensity of the component in the β-axis direction.

In FIG. 12, the α-axis and β-axis direction components E _α and E _β of the linearly polarized light of the electric field vector E ₁ with respect to the alignment azimuth angle θ, and their square values E _α ² and E _β ^2, and the α-axis and β A square sum W ₊ and a square difference W ₋ of the components in the respective axial directions of the axes are shown. The alignment azimuth angle θ = 0 means that the measurement region 5 is in a zero magnetic field (see FIG. 8). However, the transmittance t _p = 1 of the component in the direction θp and the transmittance t _s = 0.8 of the component in the direction θs.

12, squared difference W _- Focusing on the value, the square difference W _- vibrates a cycle of 180 degrees with respect to the alignment azimuth theta. Since the square difference W ₋ changes substantially linearly with respect to the alignment azimuth angle θ when the alignment azimuth angle θ is in the range of −45 degrees to +45 degrees, high sensitivity can be obtained. Further, since the center of the linear change is 0 degree and the range of the linear change is wider than others (such as the sum of squares W ₊ ), it is suitable for measuring the magnetic field generated in the measurement region 5. Since the biomagnetic field such as the magnetocardiogram and the magnetoencephalogram is weak and the alignment azimuth angle θ is small, the rotation angle of the polarization plane can be observed with high sensitivity by using the square difference W ₋ .

  However, as described above, if an unnecessary magnetic field different from the magnetic field to be measured exists in the measurement region 5, the sensitivity is affected by the influence and the measurement accuracy is lowered. Usually, in order to measure a magnetic field to be measured such as a magnetocardiogram or a magnetoencephalogram, the magnetic shield device 6 is used in an environment in which entry of the magnetic field from the outside to the measurement region 5 is suppressed (in a state where the external magnetic field is small). However, depending on the magnetic shield device 6, it is difficult to sufficiently reduce the external magnetic field so as not to affect the measurement. In other words, intrusion of an external magnetic field cannot often be completely shielded by the magnetic shield device 6. A magnetic shield that can completely shield magnetism is a large-scale device, is expensive, and is expensive to install and operate.

  Therefore, in the present embodiment, after using the magnetic shield device 6, an external magnetic field (referred to as the original magnetic field C) leaking into the magnetic shield device 6 is measured and reduced by the magnetic field generator 8. Then, the magnetic field to be measured is measured. However, in the first place, when the external magnetic field is low or the external magnetic field is stable, the present embodiment can be configured without using even the magnetic shield device 6.

According to FIG 12, in a range alignment azimuth θ of +45 °, the square difference W _- is spin polarization _{(M x, M y, M} z) in the X-axis direction component M _x (hereinafter, Is approximately proportional to the spin polarization M _x ). This spin polarization M _x corresponds to the magnetization value that is the X-axis direction component of the magnetization vector that combines the magnetic moments of the atoms. For this reason, hereinafter, the square difference W ₋ is treated as the spin polarization degree M _x . In the present embodiment, focusing on the spin polarization M _x, the value of the spin polarization M _x is the component B _x of a magnetic field vector B to be applied to the gas cell 12, B _y, depending on how B _z Let us derive a relational expression that represents whether or not it changes.

Time evolution of alignment caused by optical pumping spin polarization _{(M x, M y, M} z) is approximated by Bloch equations (Bloch Equations) shown in Equation 8 to Equation 10 below. γ _F represents a gyromagnetic ratio determined by the type of medium gas (alkali metal atom gas) in the gas cell 12. Also, gamma ₀ is spin polarization _{(M x, M y, M} z) represents the rate of relaxation, gamma _p represents an optical pumping speed. M _p is the maximum magnetization when the spins of the alkali metal atom group are all aligned in one direction.

Pumping light and probe light, because it is irradiated to the gas cell 12 with regularly constant power, spin polarization _{(M x, M y, M} z) stationary solution of the left-hand side of Equation 8 to Equation 10 above Each can be solved with zero. The solution is obtained by Equations 11 to 13.

  In Equations 11 to 13, a and c are constants and are given by Equation 14 below.

(D) Measurement of magnetic field By the magnetic field generator 8 (8X, 8Y, 8Z), the artificial magnetic field A (A _x , A _y , A _z ) is respectively applied to the gas cell 12 in the X, Y, Z axis directions. Consider the case of generating / applying. In this case, the magnetic field vector B (B _x , B _y , B _z ) detected by the magnetic sensor 10 is an artificial magnetic field vector A (A _x , A _y , A _z ) generated by the magnetic field generator 8 as shown in Equation 15. _z ) and the original magnetic field vector C ( _Cx , _Cy , _Cz ). The original magnetic field C is a magnetic field that exists in the measurement region 5 when the artificial magnetic field A is zero.

Here, the Z-axis direction component A _z of the artificial magnetic field vector A is set to zero (A _z = 0). Further, let the X-axis direction component A _x of the artificial magnetic field vector A be a function A ₁₀ f (t) having an amplitude A ₁₀ and the Y-axis direction component A _{y be} a function A ₂₀ g (t) having an amplitude A ₂₀ . Therefore, the magnetic field vector B (B _x , B _y , B _z ) detected by the magnetic sensor 10 in the measurement region 5 is expressed by the following mathematical formula 16. The amplitude A ₁₀ and the amplitude A ₂₀ are coefficients having a magnetic field dimension, and the function f (t) and the function g (t) are non-dimensional functions.

Substituting Equation 16 into the spin polarization degree M _x in Equation 11 yields Equation 17.

Note that if A ₁₀ = A ₂₀ = A ₀ , control and calculation are facilitated, and these mathematical expressions become the following mathematical expression 18.

By substituting Equation 18 into the spin polarization M _x of Equation 11, Equation 19 is obtained.

Then, using Equation 19, three values of each component (C _x , C _y , C _z ) of the unknown original magnetic field vector C are calculated as follows. That is, the measurement using the magnetic field measurement apparatus 1 is performed, and the X-axis direction component A _x (t) and the Y-axis direction component A _y (t) of the artificial magnetic field A by the magnetic field generator 8 at a certain time t , The spin polarization degree M _x (t) (that is, the output value W ₋ of the magnetic sensor 10), and three or more combinations having different spin polarization degrees M _x (t) are acquired.

For each combination, a simultaneous equation consisting of three equations obtained by substituting the artificial magnetic fields A _x (t), A _y (t) and the spin polarization M _x (t) into Equation 19 Generate. By solving the simultaneous equations, each component (C _x , C _y , C _z ) of the unknown original magnetic field vector C can be calculated.

In Equation 19, the constants a and c may be unknown. In other words, it is assumed that Formula 19 includes five unknowns, that is, each component (C _x , C _y , C _z ) of the original magnetic field vector C and constants a and c. In this case, measurement using the magnetic field measurement apparatus 1 is performed, and a combination of the artificial magnetic fields A _x (t) and A _y (t) at a certain time t and the spin polarization M _x (t), Five combinations having different degrees of polarization M _x (t) are acquired. Then, simultaneous equations composed of five equations obtained by substituting each value into Equation 19 for each combination are generated. By solving this simultaneous equation, each component (C _x , C _y , C _z ) of the unknown original magnetic field vector C and the constants a, c can be calculated.

Furthermore, obtaining the artificial magnetic field _{A x (t), A y} (t), a combination of a spin polarization M _x (t), the spin polarization M _x (t) is different from six or more combinations However, the fitting of Equation 19 may be applied. Specifically, the spin polarization M _x calculated using Equation 19, so that the deviation between the M _x is a measured value of the magnetic sensor 10 is minimized, each component of which is unknown original magnetic field vector C ( _Cx , _Cy , _Cz ) and constants a and c are calculated.

Further, the amplitudes A ₀ of the time functions f (t) and g (t), which are the artificial magnetic fields A _x and A _y , are compared with the X-axis direction component C _x and the Y-axis direction component _Cy of the original magnetic field C. If it is sufficiently small (approximately 1/10 or less. A ₀ <(C _x / 10), A ₀ <(C _y / 10)), Equation 19 is simplified to Equation 20 and further facilitates measurement. .

In this way, using Equations 19 and 20, the artificial magnetic field A (A _x , A _y , A _z ) by the magnetic field generator 8 and the spin polarization M _x (that is, the square difference W ₋ ) at that time From this, the original magnetic field vector C (C _x , C _y , C _z ) can be calculated.

(E) Artificial magnetic field A
The artificial magnetic field A (A _x , A _y , A _z ) is determined as follows. That is, the time function f (t) of the X-axis direction component A _x of the artificial magnetic field A takes n different levels, i.e., fixed values f _i (i = 1,..., N). The time function g (t) of the Y-axis direction component A _y takes a fixed value g _j (j = 1,..., M) which is m different levels. At the same time, a total of n × m measurement periods τk (k = i,..., N × m) corresponding to all combinations of the fixed values f _i and g _j of the time functions g (t) and f (t), respectively. ) Are defined so that time functions f (t) and g (t) exist.

In the present embodiment, as described above, the artificial magnetic fields A _x (t) and A _y (t) at a certain time t are used to calculate the components (C _x , C _y , C _z ) of the original magnetic field vector C. And the spin polarization degree M _x (t), and it is necessary to obtain three or more combinations having different spin polarization degrees M _x (t). That is, it is necessary to determine the fixed values f _i and g _j that the time functions f (t) and g (t) take so that there are three or more measurement periods τk (k ≧ 3).

Then, the spin polarization degree M _x in the measurement period τk corresponding to the combination of the fixed values f _i and g _i of the time functions f (t) and g (t) of the artificial magnetic fields A _x and A _y is expressed by Equations 19 and 19, respectively. From each of 20, the following formulas 21 and 22 are obtained. Here, the spin polarization M _x (t) when f (t) = f _i and g (t) = g _j is represented by M _xij .

Since there are three unknowns C _x , C _y , and C _z , three or more M _xij are measured. Therefore, when changing both the X side and the Y side, n is an integer of 2 or more, m is an integer of 2 or more, and a total of 4 or more M _xij is measured. When changing only the X side, n is an integer of 3 or more, and 3 or more M _xij are measured. When changing only the Y side, m is an integer of 3 or more, and 3 or more M _xij are measured.

When the coefficients a and c are both unknown numbers, the number of unknowns is five, so three or more M _xij are measured. Therefore, when changing both the X side and the Y side, one of n or m is an integer of 2 or more, the other of n or m is an integer of 3 or more, and a total of 6 or more M _xij is measured. . When changing only the X side, n is an integer of 5 or more and 5 or more M _xij are measured. When only the Y side is changed, m is an integer of 5 or more, and 5 or more M _xij are measured.

As in the previous case, if A ₁₀ = A ₂₀ = A ₀ , control and calculation are facilitated, and Equations 21 and 22 become Equations 23 and 24, respectively.

[Process flow]
13 and 14 are flowcharts for explaining the flow of magnetic field measurement processing according to the present embodiment. This process is a process realized by each part of the processing unit 40 shown in FIG. 7 executing the magnetic field measurement program 51. Further, a case where the measurement object is a human body (subject 9) and the magnetocardiogram (magnetic field generated from electrophysiological activity of the heart) and the magnetoencephalogram are measured will be described as an example.

As shown in FIG. 13, first, the irradiation control unit 41 causes the light source 18 to start irradiation with irradiation light including a linearly polarized light component that also serves as pump light and probe light (step S01). Next, the original magnetic field C is measured. Specifically, the magnetic field generation control unit 42 sends the artificial magnetic field A (A _x = A ₀ f _i , A _y = A ₀ g _j , 0) corresponding to the target combination (i, j) to the magnetic field generator 8. ) Is generated (step S02). Then, a measured value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 in this state is acquired (step S03).

The processes in steps S02 and S03 are the number i (i = 1 to n) of the fixed value f of the time function f (t) that is the X-axis direction component A _x of the artificial magnetic field and the Y-axis direction component A _y . It is repeatedly executed for each combination with the number j (j = 1 to m) of the fixed value g of the time function g (t) (step S04). That is, when all the combinations of (i, j) have not been completed (step S04: NO), the processes of step S02 and step S03 are performed on the combination of (i, j) for which processing has not been executed. Executed.

When the processing of step S02 and step S03 is completed for all combinations of (i, j) (step S04: YES), the original magnetic field calculation unit 43 and the measured values (square difference) obtained from the artificial magnetic fields A _x and A _y. Using the combination with W ₋ ), the original magnetic field vector C (C _x , C _y , C _z ) is calculated (step S05). Subsequently, the bias magnetic field determination unit 44 determines a bias magnetic field B _b that cancels the calculated original magnetic field C (step S06).

Next, as shown in FIG. 14, the measurement object is placed close to the magnetic sensor 10 (step S07). And the magnetic field B which this measuring object generate | occur | produces is measured. Specifically, the magnetic field generation control unit 42 includes an artificial magnetic field A (A _x = A ₀ f _i , A _y = A ₀ g _j , 0) corresponding to the target combination (i, j) and a bias magnetic field B. A combined magnetic field with _b is generated in the magnetic field generator 8 (step S08). In this state, a measured value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 is acquired (step S09).

The processes in steps S08 and S09 are the number i (i = 1 to n) of the fixed value f of the time function f (t), which is the X-axis direction component A _x of the artificial magnetic field, and the Y-axis direction component A _y . It is repeatedly executed for each combination with the number j (j = 1 to m) of the fixed value g of the time function g (t) (step S10). That is, when all the combinations of (i, j) are not completed (step S10: NO), the processes of steps S08 and S09 are performed on the combination of (i, j) for which processing is not executed. Executed.

When the processing of step S08 and step S09 is completed for all combinations of (i, j) (step S10: YES), the target magnetic field calculation unit 45 and the artificial magnetic fields A _x , A _y and the acquired measured value (square difference) A magnetic field B (B _x , B _y , B _z ) generated by the measurement object is calculated using a combination with W ₋ ) (step S11). Thereafter, the irradiation control unit 41 ends the irradiation of irradiation light by the light source 18 (step S12). When the above processing is performed, the processing unit 40 ends the magnetic measurement processing.

As specific examples of the magnetic field measuring apparatus 1 configured as described above, three examples specifically showing the artificial magnetic field A (A _x , A _y , A _z ) will be described below.

[First embodiment]
The first embodiment is an embodiment in which the time function f (t) having the X-axis direction component A _x of the artificial magnetic field A takes _two fixed values f ₁ and f ₂ (corresponding to Application Example 9). In the first embodiment, at least one of the two fixed values f ₁ and f ₂ is zero, and the time function g (t) with the Y-axis direction component A _y is two fixed values g ₁ and g _2. And at least one of the two fixed values g ₁ and g ₂ is zero.

FIG. 15 is a graph showing an example of the artificial magnetic fields A _x and A _y and the spin polarization M _{x in} the first embodiment. In the figure, a graph of the artificial magnetic fields A _x , A _y and the spin polarization degree M _x is shown in order from the top with the horizontal axis as the common time t.

The time function f (t) takes f ₁ = 0, f ₂ = 1 as a fixed value f _i , and the time function g (t) takes g ₁ = 0, g ₂ = 1 as a fixed value g _j. ,I take the. Therefore, the X-axis direction component A _x of the artificial magnetic field A is “A ₀ f ₁ = 0”, which is a constant magnetic field of the X side first level, and “A ₀ f ₂ =, which is a constant magnetic field of the X side second level. A ₀ ”is taken. The Y-axis direction component A _y is expressed as “A ₀ g ₁ = 0”, which is a constant magnetic field of the Y side first level, and “A ₀ g ₂ = A ₀ ”, which is a constant magnetic field of the Y side second level. Take binary.

There are four measurement periods τ1 to τ4 corresponding to all combinations of the fixed values f ₁ and f ₂ of the time function f (t) and the fixed values g ₁ and g ₂ of the time function g (t). . The spin polarizations M _{x1 to} M _x4 in the measurement periods τ1 to τ4 are different from each other. That is, the X-side i-th level (i = 1, 2), which is the X-axis direction component A _x of the artificial magnetic field A necessary for calculating the original magnetic field vector C (C _x , C _y , C _z ) using Expression 19. ), A Y-direction j-th level (j = 1, 2) constant magnetic field that is a Y-axis direction component A _y , and a spin polarization M _x that is a magnetization value, Three or more combinations having different M _x can be acquired.

Specifically, in the first measurement period τ1 in which i = j = 1, the time function f (τ1) = f ₁ = 0 and g (τ1) = g ₁ = 0. That is, an X-side first level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A, and a Y-side first level constant magnetic field is generated as the Y-axis direction component A _y . Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes Equation 25 below.

Then, Expression 23 of the spin polarization degree M _x that is the 1-1st magnetization value becomes the following Expression 26.

In the second measurement period τ2 where i = 2 and j = 1, the time function f (τ2) = f ₂ = 1 and g (τ2) = g ₁ = 0. That is, an X-side second level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A, and a Y-side first level constant magnetic field is generated as the Y-axis direction component A _y . Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 27.

Then, Expression 23 of the spin polarization degree M _x that is the 2-1st magnetization value becomes the following Expression 28.

In the third measurement period τ3 in which i = 1 and J = 2, the time function f (τ3) = f ₁ = 0 and g (τ3) = g ₂ = 1. That is, an X-side first level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A, and a Y-side second level constant magnetic field is generated as the Y-axis direction component A _y . Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 29.

Then, Equation 23 of the spin polarization degree M _x that is the first to second magnetization values becomes the following Equation 30.

In the fourth measurement period τ4 where i = j = 2, the time function f (τ4) = f ₂ = 1 and g (τ4) = g ₂ = 1. That is, an X-side second level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A, and a Y-side second level constant magnetic field is generated as the Y-axis direction component A _y . Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 31.

Then, Equation 23 of the spin polarization degree M _x which is the 2-2 magnetization value becomes the following Equation 32.

The first equation is obtained by substituting the magnetization value (M _x1 ) obtained from the magnetic field measurement apparatus 1 in the first measurement period τ1 into the left side of Equation 26. The second equation is obtained by substituting the magnetization value (M _x2 ) obtained from the magnetic field measurement apparatus 1 in the second measurement period τ2 into the left side of Equation 28. The third equation is obtained by substituting the magnetization value (M _x3 ) obtained from the magnetic field measurement apparatus 1 in the third measurement period τ3 into the left side of Equation 30. The fourth equation is obtained by substituting the magnetization value (M _x4 ) obtained from the magnetic field measurement apparatus 1 in the fourth measurement period τ4 into the left side of Equation 32. Then, these four equations are combined to calculate an original magnetic field vector C (C _x , C _y , C _z ) that is an unknown number.

[Second Embodiment]
In the second embodiment, the time function f (t) with the X-axis direction component A _x of the artificial magnetic field A takes three fixed values f ₁ , f ₂ , and f ₃ . In the second embodiment, at least one of the three fixed values f ₁ , f ₂ , f ₃ is zero, and the time function g (t) as the Y-axis direction component A _y has three fixed values g _1. , G ₂ , g ₃ , and at least one of the three fixed values g ₁ , g ₂ , g ₃ is zero.

FIG. 16 is a graph showing an example of the artificial magnetic fields A _x and A _y and the spin polarization M _x in the second embodiment. This figure shows a graph of the artificial magnetic fields A _x and A _y and the spin polarization M _{x with} the horizontal axis as time t. Further, in order to make it easy to understand the change of the spin polarization degree M _x , the lower graph shows a part of the upper graph enlarged in the vertical axis direction.

The time function f (t) takes f ₁ = 0, f ₂ = 1, f ₃ = −1 as a fixed value f _i , and the time function g (t) has a fixed value g _j and g ₁ = Take 0, g ₂ = 1, g ₃ = -1. Therefore, the artificial magnetic fields A _x and A _y both take ternary values (0, A ₀ , −A ₀ ). Then, fixed value f ₁ ~f ₃ of time function f (t), and, there is a fixed value g ₁ corresponds to all combinations of to g ₃ 9 single measurement period τ1~τ9 time function g (t) .

Spin polarization M _x1 ~M _x9 in the measurement period τ1~τ9 respectively, it is different. That is, it is a combination of the artificial magnetic fields A _x , A _y and the spin polarization degree M _x necessary for calculating the original magnetic field vector C (C _x , C _y , C _z ) using Equation 19, can be extreme M _x acquires three or more different combinations.

Specifically, in the first measurement period τ1 in which i = j = 1, the time function f (τ1) = f ₁ = 0 and g (τ1) = g ₁ = 0. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 33.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 34.

In the second measurement period τ2 where i = 2 and j = 1, the time function f (τ2) = f ₂ = 1 and g (τ2) = g ₁ = 0. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 35.

Then, Expression 23 of the spin polarization degree M _x becomes the following Expression 36.

In the third measurement period τ3 where i = 3 and j = 1, the time function f (τ3) = f ₃ = −1 and g (τ3) = g ₁ = 0. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 37.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 38.

In the fourth measurement period τ4 where i = 1 and j = 2, the time function f (τ4) = f ₁ = 0 and g (τ4) = g ₂ = 1. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 39.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 40.

In the fifth measurement period τ5 in which i = j = 2, the time function f (τ5) = f ₂ = 1 and g (τ5) = g ₂ = 1. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 41.

Then, Expression 23 of the spin polarization degree M _x becomes the following Expression 42.

In the sixth measurement period τ6 where i = 3 and j = 2, the time function f (τ6) = f ₃ = −1 and g (τ6) = g ₂ = 1. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 43.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 44.

In the seventh measurement period τ7 where i = 1 and j = 3, the time function f (τ7) = f ₁ = 0 and g (τ7) = g ₃ = −1. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 45.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 46.

In the eighth measurement period τ8 where i = 2 and j = 3, the time function f (τ8) = f ₂ = 1 and g (τ8) = g ₃ = −1. Therefore, Expression 16 of the magnetic field B applied to the gas cell 12 becomes Expression 47 below.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 48.

In the ninth measurement period τ9 where i = j = 3, the time function f (τ9) = f ₃ = −1 and g (τ9) = g ₃ = −1. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 becomes the following Equation 49.

Then, Equation 23 of the spin polarization degree M _x becomes the following Equation 50.

The first equation is obtained by substituting the magnetization value (M _x1 ) obtained from the magnetic field measurement apparatus 1 in the first measurement period τ1 into the left side of Equation 34. The second equation is obtained by substituting the magnetization value (M _x2 ) obtained from the magnetic field measurement apparatus 1 in the second measurement period τ2 into the left side of Equation 36. The third equation is obtained by substituting the magnetization value (M _x3 ) obtained from the magnetic field measurement apparatus 1 in the third measurement period τ3 into the left side of Equation 38.

The fourth equation is obtained by substituting the magnetization value (M _x4 ) obtained from the magnetic field measurement apparatus 1 in the fourth measurement period τ ₄ into the left side of the equation 40. The fifth equation is obtained by substituting the magnetization value (M _x5 ) obtained from the magnetic field measurement apparatus 1 in the fifth measurement period τ5 into the left side of the equation 42. The sixth equation is obtained by substituting the magnetization value (M _x6 ) obtained from the magnetic field measuring apparatus 1 in the sixth period τ6 into the left side of the equation 44.

The seventh equation is obtained by substituting the magnetization value (M _x7 ) obtained from the magnetic field measurement apparatus 1 in the seventh measurement period τ7 into the left side of the equation 46. The eighth equation is obtained by substituting the magnetization value (M _x8 ) obtained from the magnetic field measuring apparatus 1 in the eighth measurement period τ8 into the left side of the equation 48. The ninth equation is obtained by substituting the magnetization value (M _x9 ) obtained from the magnetic field measurement apparatus 1 in the ninth measurement period τ9 into the left side of the equation 50. Then, these nine equations are combined to calculate the original magnetic field vector C (C _x , C _y , C _z ), which is an unknown number.

[Third embodiment]
The third embodiment is an embodiment that generates and applies only the uniaxial component (X-axis component) as the artificial magnetic field A (corresponding to Application Example 2). In other words, this corresponds to the case where g (t) = 0 in Expression 17 of the spin polarization M _x . Further, the time function f (t) as the X-axis direction component A _{x of} the artificial magnetic field A takes three fixed values f ₁ , f ₂ , f ₃ , and these three fixed values f ₁ , f ₂ , f ₃ Of these, one is zero.

That is, for example, X-axis direction component A _x of the artificial magnetic field A is constant magnetic field of the X-side first level "A ₀ f _i = 0" as an X-side constant magnetic field of the second level, "A ₀ f _“2 = A ₀ ” and “A ₀ f ₃ = −A ₀ ”, which is a constant magnetic field of the third level on the X side. Accordingly, Equations 21 and 22 of the spin polarization degree M _x become the following Equations 51 and 52, respectively.

In this case, a fixed value f ₁ ~f ₃ 3 single measurement period corresponding to each τ1~τ3 artificial magnetic field A is present. For example, the time function f (t) is assumed to take f ₁ = 0, f ₂ = 1, and f ₃ = −1 as fixed values f _i . Then, these three measurement periods τ1 to τ3 are the same as the measurement periods τ1 to τ3 in Example 2 described above.

That is, in the first measurement period τ1 where i = 1 and j = 1 (g ₁ = 0), the X-side first level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A. . The magnetic field B applied to the gas cell 12 is expressed by Equation 33, and the spin polarization degree M _{x that} is the 1-1st magnetization value is expressed by Equation 34.

Further, in the second measurement period τ2 in which i = 2 and j = 1 (g ₁ = 0), the X-side second level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A. . The magnetic field B applied to the gas cell 12 is expressed by Equation 35, and the spin polarization degree M _{x that} is the 2-1st magnetization value is expressed by Equation 36.

In the third measurement period τ3 in which i = 3 and j = 1 (g ₁ = 0), the X-side third level constant magnetic field is generated as the X-axis direction component A _x of the artificial magnetic field A. Then, the magnetic field B applied to the gas cell 12 is Equation 37, the spin polarization M _x is a magnetization value of 3-1 is formula 38.

Thus, spin polarization M _x in the measurement period τ1~τ3 respectively, are different. Therefore, it is a combination of the artificial magnetic fields A _x , A _y and the spin polarization degree M _x necessary for calculating the original magnetic field vector C (C _x , C _y , C _z ) using Expression 17, can be extreme M _x acquires three or more different combinations.

[Fourth embodiment]
The fourth embodiment is an embodiment in which only the uniaxial component (Y-axis component) is generated and applied as the artificial magnetic field A (corresponding to Application Example 6). In other words, this corresponds to the case where f (t) = 0 in Formula 17 of the spin polarization degree M _x . Further, the time function g (t) as the Y-axis direction component A _{y of} the artificial magnetic field A takes three fixed values g ₁ , g ₂ , g ₃ , and these three fixed values g ₁ , g ₂ , g ₃ Of these, one is zero.

That is, for example, Y-axis direction component A _y of the artificial magnetic field A is constant magnetic field in the Y-side first level "A ₀ g _i = 0" and a Y-side constant magnetic field of the second level, "A ₀ g _“2 = A ₀ ” and “A ₀ g ₃ = −A ₀ ”, which is a constant magnetic field of the third level on the Y side. Accordingly, Equations 21 and 22 of the spin polarization degree M _x become the following Equations 53 and 54, respectively.

In this case, a fixed value g ₁ to g ₃ 3 single measurement period corresponding to each τ1~τ3 artificial magnetic field A is present. For example, the time function g (t) is assumed to take g ₁ = 0, g ₂ = 1, and g ₃ = −1 as the fixed value g _j . Then, these three measurement periods τ1 to τ3 are the same as the measurement periods τ1 to τ3 in Example 2 described above.

That is, in the first measurement period τ1 in which i = 1 (f ₁ = 0) and j = 1, a Y-side first level constant magnetic field is generated as the Y-axis direction component A _y of the artificial magnetic field A. . The magnetic field B applied to the gas cell 12 is expressed by Equation 33, and the spin polarization degree M _{x that} is the 1-1st magnetization value is expressed by Equation 34.

Further, in the second measurement period τ2 in which i = 1 (f ₁ = 0) and j = 2, a Y-side second level constant magnetic field is generated as the Y-axis direction component A _y of the artificial magnetic field A. . The magnetic field B applied to the gas cell 12 is given by Equation 39, and the spin polarization degree M _{x that} is the 1-2nd magnetization value is given by Equation 40.

Further, in the third measurement period τ3 where i = 1 (f ₁ = 0) and j = 3, a Y-side third level constant magnetic field is generated as the Y-axis direction component A _y of the artificial magnetic field A. . Then, the magnetic field B applied to the gas cell 12 is Equation 45, the spin polarization M _x is a magnetization value of 1-3 is formula 46.

Thus, spin polarization M _x in the measurement period τ1~τ3 respectively, are different. Therefore, it is a combination of the artificial magnetic fields A _x , A _y and the spin polarization degree M _x necessary for calculating the original magnetic field vector C (C _x , C _y , C _z ) using Expression 17, can be extreme M _x acquires three or more different combinations.

[Fifth embodiment]
The fifth embodiment is an embodiment in which a predetermined magnetic field is created in the measurement region 5 instead of setting the measurement region 5 in a state where the measurement object is not placed to a zero magnetic field as in the above-described embodiment. . A magnetic field to be created in the measurement region 5 in a state where no measurement object is placed is referred to as a target magnetic field. If the target magnetic field is not a zero magnetic field but a predetermined magnetic field, the measured value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 in step S03 shown in FIG. After acquiring a combination with the values of the magnetic fields A _x and A _y , the following processing is performed.

As a first step, the magnetic field in the measurement region 5 is calculated as the original magnetic field C by using a combination of the acquired measurement value (square difference W ₋ ) and the artificial magnetic fields A _x and A _y (corresponding to step S05). . Subsequently, as a second step, a measurement object (subject 9) is placed in the measurement region 5 (corresponding to step S07). In the fifth embodiment, in order to make the target magnetic field not a zero magnetic field but a predetermined magnetic field, a bias magnetic field B _b that cancels the calculated original magnetic field C is applied to the measurement region 5 (steps S06 and S08). ) Is not performed.

  Subsequently, as a third step, the first magnetic field generator 8X, the second magnetic field generator 8Y, and the third magnetic field generation are performed using a difference magnetic field between the target magnetic field and the original magnetic field C, which is a predetermined magnetic field to be formed in the measurement region 5. Generated in the device 8Z (corresponding to step S08). As a result, the artificial magnetic field A and the original magnetic field C applied by the magnetic field generator 8 (8X, 8Y, 8Z) are combined, and a predetermined magnetic field can be created as the target magnetic field in the measurement region 5. Note that the order of the second step and the third step may be switched.

And as a 4th process, it is measured using the measured value (square difference W < _- >) obtained based on the signal output from the magnetic sensor 10 in the period when the 3rd process is performed and the 2nd process is complete | finished. The magnetic field B generated by the object is measured (corresponding to step S11). Thereby, in the state which made the measurement area | region 5 the predetermined target magnetic field, the magnetic field B which the measuring object generate | occur | produced can be measured.

  Also in the first to fourth embodiments described above, a target magnetic field that is a difference between the target magnetic field and the original magnetic field C, which is a predetermined magnetic field to be formed in the measurement region 5, is generated in the measurement region 5. A predetermined magnetic field can be created. In the fifth embodiment, if the target magnetic field is set to zero to cancel out the original magnetic field C leaking into the measurement region 5 from the outside, the magnetic field B generated by the measurement object (strictly speaking, the magnetic field Z-direction component) can be accurately measured.

[Sixth embodiment]
6th Example is an Example in the case of making the magnetic field of a predetermined three-dimensional vector as a target magnetic field in the measurement area | region 5 with respect to 5th Example. In the sixth embodiment, the first step and the second step are the same as in the fifth embodiment.

As a third step, the X-direction component of the difference magnetic field between the target magnetic field C (C _x , C _y , C _z ), which is a predetermined magnetic field formed in the measurement region 5, is constant at the X-side first level. A constant magnetic field added to the magnetic field is generated in the first magnetic field generator 8X, the magnetic field of the Y direction component of the differential magnetic field is generated in the second magnetic field generator 8Y, and the magnetic field of the Z direction component of the differential magnetic field is generated first. It is generated by the three magnetic field generator 8Z (corresponding to step S08). Thereby, the artificial magnetic field A (A _x , A _y , A _z ) applied by the magnetic field generator 8 (8X, 8Y, 8Z) and the original magnetic field C (C _x , C _y , C _z ) are synthesized, A magnetic field of a predetermined three-dimensional vector can be created as a target magnetic field in the measurement region 5. Note that the order of the second step and the third step may be switched.

And as a 4th process, the measured value (square difference W < _- >) and 3rd alternating magnetic field which are obtained based on the signal output from the magnetic sensor 10 in the period when the 3rd process is performed and the 2nd process is complete | finished And the fourth alternating magnetic field are used to measure the magnetic field B (B _x , B _y , B _z ) generated by the measurement object (corresponding to step S11). Thereby, the magnetic field B generated by the measurement object can be measured in a state where the measurement region 5 is a target magnetic field of a predetermined three-dimensional vector.

Also for the first to fourth embodiments described above, the X of the magnetic field of the difference between the target magnetic field C (C _x , C _y , C _z ) that is a predetermined magnetic field to be formed in the measurement region 5 and the original magnetic field C (C _x , C _y , C _z ). A predetermined magnetic field can be created as a target magnetic field in the measurement region 5 by generating a magnetic field having components in the Y, Z directions. In the sixth embodiment, if the target magnetic field is zero to cancel out the original magnetic field C (C _x , C _y , C _z ) leaking into the measurement region 5 from the outside, a measurement object is generated. The magnetic field B to be measured can be accurately measured as a vector quantity.

[Function and effect]
Thus, according to the magnetic field measurement apparatus 1 of the present embodiment, irradiation light (probe light) in one direction (Z-axis direction) is applied to the gas cell 12 in which a gas (gas) such as an alkali metal atom is sealed. By irradiation, the magnetic field vector (C _x , C _y , C _z ) of the measurement region 5 can be calculated.

Specifically, the amplitude takes n fixed values f _i (i = 1,..., N) in the X and Y axis directions orthogonal to the irradiation direction (Z axis direction) of the irradiation light (probe light). field a _x is a time function f of a ₀ (t), and, m-number of fixed values g _j a (j = 1, ··, m ) times a function of the amplitude a ₀ take g (t) field a _{Apply y} . A combination of the artificial magnetic fields A _x and A _y and the spin polarization M _x corresponding to the measured value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10, and the spin polarization Acquire three or more combinations with different M _x . Then, the magnetic field C (C _x , C _y , C _z ) is calculated from Equation 17 using these combinations, the spin polarization M _x, and the artificial magnetic fields A _x , A _y .

[Modification]
It should be noted that embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can of course be changed as appropriate without departing from the spirit of the present invention.

(A) Bias magnetic field B _b
In the above-described embodiment, the magnetic field generator 8 generates the bias magnetic field B _b that cancels the original magnetic field C, and measures the magnetic field B (B _x , B _y , B _z ) generated by the measurement object. but the may perform the measurement without generating a bias magnetic field B _b. Specifically, first, similarly to the above-described embodiment, the original magnetic field _Cx is measured in advance without any measurement object. Thereafter, the measurement object is brought close to the magnetic sensor 10 to measure the magnetic field generated by the measurement object. At that time, only the artificial magnetic field A is generated in the magnetic field generator 8. In this case, the magnetic field applied to the measurement region 5 is a combined magnetic field of the original magnetic field C, the magnetic field B of the measurement object, and the artificial magnetic field A by the magnetic field generator 8. Therefore, the magnetic field B generated by the measurement object is obtained by subtracting the original magnetic field C _x measured in advance from the magnetic field C _x calculated using Expression 17 at this time.

(B) Measurement object In the above-described embodiment, the measurement object is a human body, and the magnetic field from the heart (magnetomagnetic field) or the magnetic field from the brain (magnetomagnetic field) is measured. Other than this may be used. And depending on the measurement object, the magnetic sensor 10 is brought close to the measurement object instead of bringing the measurement object close to the magnetic sensor 10 as in the above-described embodiment, and the magnetic field generated by the measurement object is generated. It is also possible to measure.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic field measuring apparatus, 5 ... Measurement area, 8 ... Magnetic field generator, 8X ... 1st magnetic field generator (Helmholtz coil), 8Y ... 2nd magnetic field generator (Helmholtz coil), 8Z ... 3rd magnetic field generator (Helmholtz) Coil), 9 ... subject (measuring object), 10 ... magnetic sensor, 12 ... gas cell (medium), 14, 15 ... photodetector, 18 ... light source, 30 ... calculation control unit.

Claims (17)

The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A first magnetic field generator for applying a magnetic field in the first direction to the measurement region;
Is a magnetic field measurement method for measuring the magnetic field in the measurement region,
In the first magnetic field generator, as the first direction magnetic field, the first direction side first level constant magnetic field, the first direction side second level constant magnetic field, and the first direction side third level. Generating a constant magnetic field of
Calculating the magnetic field of the measurement region using the detection result of the photodetector and the magnetic field in the first direction;
Magnetic field measurement method including Calculating the magnetic field in the measurement region includes calculating a magnetization value indicating a component in the first direction of the magnetization vector of the medium based on a detection result of the photodetector, A 1-1 magnetization value when a constant magnetic field of 1 level is generated, a 2-1 magnetization value when a constant magnetic field of the second direction side second level is generated, and the first Calculating the magnetic field of the measurement region using the 3-1 magnetization value when the constant magnetic field of the third level on the one direction side is generated and the magnetic field in the first direction;
The magnetic field measurement method according to claim 1. The calculation of the magnetic field in the measurement region includes generation of a constant magnetic field in the first direction side i-level (i = 1, 2, 3) that is the magnetic field in the first direction and a magnetic field in the first direction. The following formula 1 is applied to each of the combinations of the magnetization values when
The magnetic field measurement method according to claim 2.

However, the magnetic field of the measurement region is C = (C _x , C _y , C _z ), and x, y, and z are spatial coordinates in the first direction, the second direction, and the third direction, respectively. M _xi is the magnetization value when a constant magnetic field of the i level the first direction is generated, a, c are constants, a ₁₀ f _i is constant magnetic field of the i level the first direction It is. At least one of the first direction side first level constant magnetic field, the first direction side second level constant magnetic field, and the first direction side third level constant magnetic field is a zero magnetic field,
The magnetic field measurement method according to any one of claims 1 to 3. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A second magnetic field generator for applying a magnetic field in the second direction to the measurement region;
Is a magnetic field measurement method for measuring the magnetic field in the measurement region,
In the second magnetic field generator, the second direction side first level constant magnetic field, the second direction side second level constant magnetic field, and the second direction side third level as the second direction magnetic field. Generating a constant magnetic field of
Calculating the magnetic field of the measurement region using the detection result of the photodetector and the magnetic field in the second direction;
Magnetic field measurement method including Calculating the magnetic field of the measurement region includes calculating a magnetization value indicating a component in the first direction of the magnetization vector of the medium based on a detection result of the photodetector, The 1-1 magnetization value when a constant magnetic field of 1 level is generated, the 1-2 magnetization value when a constant magnetic field of the second direction side second level is generated, and the first Calculating the magnetic field in the measurement region using the first to third magnetization values when the third direction constant magnetic field is generated in the two directions and the magnetic field in the second direction;
The magnetic field measurement method according to claim 5. The calculation of the magnetic field in the measurement region includes the generation of a constant magnetic field of the second direction side j level (j = 1, 2, 3) that is the magnetic field of the second direction and a magnetic field of the second direction. The following equation 2 is applied to each of the combinations of the magnetization values when
The magnetic field measurement method according to claim 6.

However, the magnetic field of the measurement region is C = (C _x , C _y , C _z ), and x, y, z are spatial coordinates in the first direction, the second direction, and the third direction, respectively. M _xj is a magnetization value when the second direction side j level constant magnetic field is generated, a and c are constants, and A ₂₀ g _j is the second direction side j level constant magnetic field. It is. At least one of the second direction side first level constant magnetic field, the second direction side second level constant magnetic field, and the second direction side third level constant magnetic field is a zero magnetic field,
The magnetic field measurement method according to any one of claims 5 to 7. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A first magnetic field generator for applying a magnetic field in the first direction to the measurement region;
A second magnetic field generator for applying a magnetic field in the second direction to the measurement region;
Is a magnetic field measurement method for measuring the magnetic field in the measurement region,
Causing the first magnetic field generator to generate, as the first direction magnetic field, the first direction side first level constant magnetic field and the first direction side second level constant magnetic field;
Causing the second magnetic field generator to generate the second direction side first level constant magnetic field and the second direction side second level constant magnetic field as the second direction magnetic field;
Calculating the magnetic field of the measurement region using the detection result of the photodetector, the magnetic field in the first direction, and the magnetic field in the second direction;
Magnetic field measurement method including Calculating the magnetic field of the measurement region includes calculating a magnetization value indicating a component in the first direction of the magnetization vector of the medium based on a detection result of the photodetector;
1) The first direction-side first level constant magnetic field and the second direction-side first level constant magnetic field when the first-direction magnetization value is generated; Level constant magnetic field, and the second direction side second level constant magnetic field when being generated, the first-second magnetization value, the first direction side second level constant magnetic field, and the first direction magnetic field The 2-1 magnetization value when the two-direction first level constant magnetic field is generated, the first direction side second level constant magnetic field, and the second direction side second level constant magnetic field. 2-2 of the magnetization value when three are generated, and three or more magnetization values thereof,
2) the magnetic field in the first direction;
3) the magnetic field in the second direction;
Is to calculate the magnetic field of the measurement region,
The magnetic field measurement method according to claim 9. The calculation of the magnetic field in the measurement region includes the constant magnetic field of the first direction side i-level (i = 1, 2) that is the magnetic field in the first direction and the second magnetic field in the second direction. Each combination of a constant magnetic field at the j-th level (j = 1, 2) on the direction side and a magnetization value when the magnetic field in the first direction and the magnetic field in the second direction are generated is expressed by Equation 3 below. Calculating the magnetic field of the measurement region based on satisfying,
The magnetic field measurement method according to claim 10.

However, the magnetic field of the measurement region is C = (C _x , C _y , C _z ), and x, y, z are spatial coordinates in the first direction, the second direction, and the third direction, respectively. M _xij is a magnetization value when the first direction side i-level constant magnetic field and the second direction side j-level constant magnetic field are generated, a and c are constants, and A ₁₀ f _i is a constant magnetic field at the i-level in the first direction side, and A ₂₀ g _j is a constant magnetic field at the j-level in the second direction side. One of the first direction side first level constant magnetic field and the first direction side second level constant magnetic field is a zero magnetic field, the second direction side first level constant magnetic field, and the first direction side magnetic field One of the two-direction second level constant magnetic fields is a zero magnetic field,
The magnetic field measurement method according to any one of claims 9 to 11. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A first magnetic field generator for applying a magnetic field in the first direction to the medium;
A second magnetic field generator for applying a magnetic field in the second direction to the medium;
A magnetic field measurement apparatus comprising: a third magnetic field generator that applies a magnetic field in the third direction to the medium; and a magnetic field measurement method for measuring a magnetic field in the measurement region,
Causing the first magnetic field generator to generate a first level constant magnetic field as a magnetic field in the first direction;
A first step of calculating the magnetic field of the measurement region as an original magnetic field using the detection result of the photodetector and the magnetic field in the first direction;
A second step of placing a measurement object in the measurement region;
A third step of causing the first magnetic field generator, the second magnetic field generator, and the third magnetic field generator to generate a difference magnetic field between the target magnetic field and the original magnetic field, which are magnetic fields to be formed in the measurement region, ,
A fourth step of measuring a magnetic field generated by the measurement object using a detection result of the photodetector during a period when the third step is performed and the second step is completed. Method. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A first magnetic field generator for applying a magnetic field in the first direction to the medium;
A second magnetic field generator for applying a magnetic field in the second direction to the medium;
A magnetic field measurement apparatus comprising: a third magnetic field generator that applies a magnetic field in the third direction to the medium; and a magnetic field measurement method for measuring a magnetic field in the measurement region,
Causing the first magnetic field generator to generate a first level constant magnetic field as a magnetic field in the first direction;
A first step of calculating the magnetic field of the measurement region as an original magnetic field using the detection result of the photodetector and the magnetic field in the first direction;
A second step of placing a measurement object in the measurement region;
The first magnetic field is generated by adding a component in the first direction of the difference between the target magnetic field and the original magnetic field to be formed in the measurement region to the first level constant magnetic field on the first direction side. And generating a magnetic field of the second direction component of the difference magnetic field in the second magnetic field generator and generating a magnetic field of the third direction component of the differential magnetic field in the third magnetic field generator. The third step;
The magnetic field generated by the measurement object is obtained by using the detection result of the photodetector and the constant magnetic field of the fourth level in the first direction during the period in which the third process is performed and the second process is completed. A magnetic field measurement method comprising: a fourth step of measuring. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A first magnetic field generator for applying a magnetic field in the first direction to the measurement region;
In the first magnetic field generator, as the first direction magnetic field, the first direction side first level constant magnetic field, the first direction side second level constant magnetic field, and the first direction side third level. Generating a constant magnetic field, and calculating the magnetic field of the measurement region using the detection result of the photodetector and the magnetic field in the first direction,
Magnetic field measuring device equipped with. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A second magnetic field generator for applying a magnetic field in the second direction to the measurement region;
In the second magnetic field generator, the second direction side first level constant magnetic field, the second direction side second level constant magnetic field, and the second direction side third level as the second direction magnetic field. Generating a constant magnetic field, and calculating the magnetic field of the measurement region using the detection result of the photodetector and the magnetic field in the second direction;
Magnetic field measuring device equipped with. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source that emits light;
A medium through which the light passes along the third direction and changes an optical characteristic according to a magnetic field in a measurement region;
A photodetector for detecting the optical property;
A first magnetic field generator for applying a magnetic field in the first direction to the measurement region;
A second magnetic field generator for applying a magnetic field in the second direction to the measurement region;
Causing the first magnetic field generator to generate, as the first direction magnetic field, the first direction side first level constant magnetic field and the first direction side second level constant magnetic field;
Causing the second magnetic field generator to generate the second direction side first level constant magnetic field and the second direction side second level constant magnetic field as the second direction magnetic field;
A calculation control unit that executes the detection result of the photodetector, the magnetic field in the first direction, and the magnetic field in the second direction using the magnetic field in the second direction;
Magnetic field measuring device equipped with.

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