JP6521248B2 - Magnetic field measuring method and magnetic field measuring apparatus - Google Patents

Description

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

  A magnetic field measurement apparatus using light can measure a very small magnetic field generated from a living body such as a magnetic field from the heart (cardiac magnetism) or a magnetic field from the brain (brain magnetism). 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 the pump light to be 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-optical 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 measurement apparatus, the detection axis of the magnetic field is one direction, and when the detection axis and the direction of the magnetic field are different, the projection component of the magnetic field to the detection axis is measured. However, the magnetic field actually distributed in space is a three-dimensional vector, and when it is intended to measure the magnetic field more precisely, it is desirable to measure magnetic fields in three axial directions such as XYZ orthogonal three axes. 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 precisely orthogonalize the respective irradiation directions. When the irradiation direction is tilted with respect to the assumed direction, the detection axis is inclined accordingly, and as a result, an error occurs in the measurement value of the magnetic field which is a three-dimensional vector.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to measure magnetic fields in a plurality of directions while probe light is in one direction in optical pump type magnetic field measurement. Or to perform magnetic measurement with high accuracy.

  Application Example 1 In the first invention for solving the above problems, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light is in the third direction. Medium which passes along and changes the optical characteristic according to the magnetic field of the measurement area, a photodetector which detects the optical characteristic, and a first magnetic field generator which applies the magnetic field in the first direction to the measurement area A magnetic field measurement apparatus for measuring the magnetic field in the measurement area, wherein the first magnetic field generator uses the first direction side first level as the magnetic field in the first direction. Generating a constant magnetic field of the first direction, a constant magnetic field of the second direction, and a constant magnetic field of the third direction of the first direction, a detection result of the light detector, and And calculating a magnetic field of the measurement area using a magnetic field. .

  According to the magnetic field measurement method 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 of the magnetic field of the measurement area, the second direction (Y direction) component, and the third direction (Z direction) component can be calculated by irradiating light in only one direction. . Specifically, as the magnetic field in the first direction (X direction) orthogonal to the third direction (Z direction) which is the light emission direction, with respect to the medium in which the optical characteristics of light are changed according to the magnetic field in the measurement region. Three levels of constant magnetic field are applied. Then, the magnetic field in the measurement area is calculated using the detection result of the optical characteristic of the light and the magnetic field in the first direction (X direction).

  According to a second aspect of the invention, in the magnetic field measurement method according to the first aspect of the invention, calculating the magnetic field in the measurement area is a magnetization value indicating a component of the magnetization vector of the medium in the first direction. Calculation based on the detection result of the light detector, and a 1-1 magnetization value when the first direction side first level constant magnetic field is generated, and the first direction side first The 2-1st magnetization value when two levels of constant magnetic fields are generated, the 3-1st magnetization value when the first direction side third level constant magnetic fields are generated, and The magnetic field measurement method may be configured to calculate the magnetic field of the measurement area using the magnetic field in 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 characteristics of the medium, and the first direction (X direction The magnetic field vector in the measurement region (first direction of the magnetic field (the first direction of the magnetic field) using the three magnetization values when each of the three levels of constant magnetic fields is generated as the magnetic field of) and the magnetic field in the first direction (X direction) The X direction component, the second direction (Y direction) component, and the third direction (Z direction) component are calculated.

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。 According to a third aspect of the present invention, in the magnetic field measurement method according to the second aspect of the present invention, calculating the magnetic field in the measurement region is performed on the first direction side i that is the magnetic field in the first direction. A magnetic field measurement method is to apply Equation 1 below 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. You may configure.

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

According to the magnetic field measurement method of this application example, each value is obtained for each combination of three levels of constant magnetic fields that are magnetic fields in the first direction (X direction) and the magnetization value when this constant magnetic field is generated. The magnetic field (C _x , C _y , C _z ) of the measurement area of the medium, which is a three-dimensional vector, can be calculated by solving a simultaneous equation consisting of three expressions in which

  According to a fourth aspect of the present invention, in the magnetic field measurement method according to any one of the first to third aspects, the first direction-side first level constant magnetic field, and the first direction-side second level constant magnetic field. The magnetic field measurement method may be configured such that at least one of the constant magnetic fields on the first direction side third level is a zero magnetic field.

  In the fifth aspect of the present invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light passes along the third direction, and a measurement region A magnetic field measurement apparatus comprising: a medium that changes optical characteristics according to the magnetic field of the magnetic field, a photodetector that detects the optical characteristics, and a second magnetic field generator that applies a magnetic field in the second direction to the measurement region A magnetic field measurement method for measuring a magnetic field in the measurement area, wherein the second magnetic field generator uses the second direction side constant first magnetic field as the magnetic field in the second direction, the second magnetic field generator. Generating the constant magnetic field on the direction second level and the constant magnetic field on the second direction side; and using the detection result of the light detector and the magnetic field in the second direction. Calculating the magnetic field of the region.

  According to the magnetic field measurement method 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 of the magnetic field of the measurement area, the second direction (Y direction) component, and the third direction (Z direction) component can be calculated by irradiating light in only one direction. . Specifically, as a magnetic field in a second direction (Y direction) orthogonal to a third direction (Z direction) which is an emission direction of light with respect to a medium in which optical characteristics of light are changed according to the magnetic field in the measurement region. Three levels of constant magnetic field are applied. Then, the magnetic field of the measurement area is calculated using the detection result of the optical characteristic of the light and the magnetic field in the second direction (Y direction).

  According to a sixth aspect of the present invention, in the magnetic field measurement method according to the fifth aspect of the present invention, calculating the magnetic field in the measurement area is a magnetization value indicating a component of the magnetization vector of the medium in the first direction. Calculation based on the detection result of the light detector, and a 1-1 magnetization value when the first direction constant magnetic field is generated on the second direction side; The first and second magnetization values when two levels of constant magnetic fields are generated, the first to third magnetization values when the second direction side third level constant magnetic fields are generated, and A magnetic field measurement method may be configured to calculate a magnetic field in the measurement area using a magnetic field in two directions.

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

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。 The seventh aspect of the present invention is the magnetic field measurement method according to the sixth aspect of the present invention, wherein calculating the magnetic field in the measurement region is performed on the second direction side jth level which is the magnetic field in the second direction. A magnetic field measurement method is to apply Equation 2 below to each of a combination of a constant magnetic field (j = 1, 2, 3) and a magnetization value when the magnetic field in the second direction is generated. You may configure.

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

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

  According to an eighth aspect of the present invention, in the magnetic field measurement method according to any one of the fifth to seventh aspects, the constant magnetic field at the first level on the second direction, and the constant magnetic field at the second level on the second direction. The magnetic field measurement method may be configured such that at least one of the constant magnetic fields on the second direction side third level is a zero magnetic field.

  In the ninth aspect of the present invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light passes along the third direction, and a measurement region A medium for changing the optical characteristics according to the magnetic field of the light source, a photodetector for detecting the optical characteristics, a first magnetic field generator for applying the magnetic field in the first direction to the measurement area, and a magnetic field in the second direction And a second magnetic field generator for applying the second magnetic field generator to the measurement area is a magnetic field measurement method for measuring the magnetic field of the measurement area, the first magnetic field generator comprising: Generating the first direction-side first level constant magnetic field and the first direction-side second level constant magnetic field as the first direction magnetic field, and the second magnetic field generator in the second direction As the magnetic field, a constant magnetic field of the second direction side first level, and a second direction side second level Generating a constant magnetic field, and calculating the magnetic field of the measurement area using the detection result of the light detector, the magnetic field in the first direction, and the magnetic field in the second direction. It is a measurement method.

  According to the magnetic field measurement method 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). Specifically, as the magnetic field in the first direction (X direction) orthogonal to the third direction (Z direction) which is the light emission direction, with respect to the medium in which the optical characteristics of light are changed 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 a second direction (Y direction) orthogonal to the third direction (Z direction) and the first direction (X direction). Then, the magnetic field of the measurement area is calculated using the detection result of the optical characteristic of light, the magnetic field in the first direction (X direction), and the magnetic field in the second direction (Y direction).

  According to a tenth aspect of the present invention, in the magnetic field measurement method according to the ninth aspect of the present invention, calculating the magnetic field in the measurement region is a magnetization value indicating a component of the magnetization vector of the medium in the first direction. Calculating based on the detection result of the light detector, and 1) when the first direction-side first level constant magnetic field and the second direction-side first level constant magnetic field are generated The first 1-1 magnetization value, the first direction-side first level constant magnetic field, and the second direction-side second level constant magnetic field is generated. A constant magnetic field of the first direction side second level, and a 2-1st magnetization value when the second direction side first level constant magnetic field is generated, and the first direction second level The second magnetic field when the constant magnetic field of the second direction and the constant magnetic field of the second direction side second level are generated The magnetic field of the measurement area is calculated using three or more magnetization values of 2) a magnetic field in the first direction, and 3) a magnetic field in the second direction. The 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 characteristics of the medium, and the first direction (X direction And two or more of the four magnetization values when two levels of constant magnetic fields are generated, respectively, and two levels of constant magnetic fields, which are magnetic fields in the second direction (Y direction). The magnetic field in the measurement area 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。 According to an eleventh aspect of the present invention, in the magnetic field measurement method according to the tenth aspect of the present invention, calculating the magnetic field in the measurement area is performed on the first direction side level i that 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 of the second direction, a magnetic field of the first direction and the second The magnetic field measurement method may be configured to calculate the magnetic field of the measurement area based on the fact that the combination of the magnetization value when the magnetic field in the direction is generated and the following each satisfy the following formula 3 .

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

According to the magnetic field measurement method of this application example, the constant magnetic field at the i-th level on the X side, which is the magnetic field in the first direction (X direction), and the j-th level on the y side, the magnetic field in the second direction (Y direction) For each of the combinations of the magnetic field, the magnetic field when the magnetic field in the first direction (X direction) and the magnetic field in the second direction (Y direction) are generated, four values are substituted in Equation 3 for each value. The magnetic field (C _x , C _y , C _z ) of the measurement area of the medium, which is a three-dimensional vector, can be calculated by solving the following simultaneous equations.

  According to a twelfth aspect of the present invention, in the magnetic field measurement method according to any one of the ninth to eleventh aspects, the first direction-side fixed magnetic field of the first direction, and the first direction-side second The magnetic field measuring method, wherein one of the constant magnetic fields of the level is a zero magnetic field, and the one of the constant magnetic field of the second direction side first level and the one of the constant magnetic field of the second direction side second level is a zero magnetic field You may configure.

  In the thirteenth aspect of the present invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light passes along the third direction, and a measurement region A medium for changing the optical characteristics according to the magnetic field of the light source, a photodetector for detecting the optical characteristics, a first magnetic field generator for applying the magnetic field in the first direction to the measurement area, and a magnetic field in the second direction For measuring the magnetic field of the measurement area, the magnetic field measuring apparatus comprising: a second magnetic field generator applying the magnetic field to the medium; and a third magnetic field generator applying the magnetic field in the third direction to the medium A method of measuring a magnetic field, wherein the first magnetic field generator generates, as a magnetic field in the first direction, a constant magnetic field on a first direction side first level, a detection result of the light detector, and Calculating a magnetic field of the measurement area as an original magnetic field using a magnetic field in a first direction; And a second step of arranging the measurement object in the measurement area, and a magnetic field of a difference between the target magnetic field, which is a magnetic field desired to be formed in the measurement area, and the original magnetic field. The third step to be generated in the magnetic field generator and the third magnetic field generator, and the third step are performed, and the detection result of the light detector is used during the period when the second step is completed. And a fourth step of measuring a magnetic field generated by the object to be measured.

  According to the magnetic field measurement method of the application example, it is possible to measure the magnetic field generated by the measurement object in a state where the measurement region is a predetermined target magnetic field. For example, in order to offset the original magnetic field leaking into the measurement area from the outside, if the target magnetic field is made a zero magnetic field, the magnetic field generated by the measurement object can be accurately measured.

  In the fourteenth aspect of the present invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light passes along the third direction, and a measurement region A medium for changing the optical characteristics according to the magnetic field of the light source, a photodetector for detecting the optical characteristics, a first magnetic field generator for applying the magnetic field in the first direction to the medium, and a magnetic field in the second direction A magnetic field measuring apparatus comprising a second magnetic field generator applied to the medium and a third magnetic field generator applying a magnetic field in the third direction to the medium, a magnetic field for measuring the magnetic field in the measurement area A measurement method, wherein the first magnetic field generator generates a first magnetic field on the first direction side as a magnetic field in the first direction; a detection result of the light detector; Calculating a magnetic field of the measurement area as an original magnetic field using a magnetic field in one direction; A second step of disposing a measurement target in the measurement area, and a component in a first direction of a magnetic field of a difference between the target magnetic field, which is a magnetic field to be formed in the measurement area, and the original magnetic field. A constant magnetic field applied to a constant constant magnetic field is generated in the first magnetic field generator, a magnetic field of a component in a second direction of the difference magnetic field is generated in the second magnetic field generator, and a third of the difference magnetic fields is generated. Of generating a magnetic field of a component of a direction in the third magnetic field generator, and a detection result of the light detector and a first direction during a period in which the third step is performed and the second step is completed And a fourth step of measuring a magnetic field generated by the measurement object using a constant magnetic field at a side fourth level.

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

  In the fifteenth invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source that emits light, and the light passes along the third direction, and a measurement region A medium that changes optical characteristics according to the magnetic field of the light source, a photodetector that detects the optical characteristics, a first magnetic field generator that applies a magnetic field in the first direction to the measurement region, and the first magnetic field generator And generating, as the magnetic field in the first direction, a constant magnetic field of the first direction side first level, a constant magnetic field of the first direction side second level, and a constant magnetic field of the first direction side third level And a calculation control unit that calculates the magnetic field of the measurement area using the detection result of the light detector 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 area 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 of the magnetic field of the measurement area, the second direction (Y direction) component, and the third direction (Z direction) component can be calculated by irradiating light in only one direction. . Specifically, as the magnetic field in the first direction (X direction) orthogonal to the third direction (Z direction) which is the light emission direction, with respect to the medium for changing the optical characteristics of light according to the magnetic field in the measurement region. Three levels of constant magnetic field are applied. Then, the magnetic field in the measurement area is calculated using the detection result of the optical characteristic of the light and the magnetic field in the first direction (X direction).

  In the sixteenth invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light passes along the third direction, and a measurement region A medium that changes optical characteristics according to the magnetic field of the light source, a photodetector that detects the optical characteristics, a second magnetic field generator that applies a magnetic field in the second direction to the measurement region, and the second magnetic field generator And generating the second direction side first level constant magnetic field, the second direction side second level constant magnetic field, and the second direction third level constant magnetic field as the magnetic field in the second direction. And a calculation control unit that calculates the magnetic field of the measurement area using the detection result of the light detector 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 area 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 of the magnetic field of the measurement area, the second direction (Y direction) component, and the third direction (Z direction) component can be calculated by irradiating light in only one direction. . Specifically, as a magnetic field in a second direction (Y direction) orthogonal to a third direction (Z direction) which is an emission direction of light with respect to a medium in which optical characteristics of light are changed according to the magnetic field in the measurement region. Three levels of constant magnetic field are applied. Then, the magnetic field of the measurement area is calculated using the detection result of the optical characteristic of the light and the magnetic field in the second direction (Y direction).

  In the seventeenth invention, the first direction, the second direction, and the third direction are orthogonal to each other, and a light source for emitting light, and the light passes along the third direction, and a measurement region A medium for changing the optical characteristics according to the magnetic field of the light source, a photodetector for detecting the optical characteristics, a first magnetic field generator for applying the magnetic field in the first direction to the measurement area, and a magnetic field in the second direction A second magnetic field generator for applying the voltage to the measurement area, the first magnetic field generator, a magnetic field in the first direction, a constant magnetic field in the first direction, and a first magnetic field, and Generating a constant magnetic field of two levels, and, as the magnetic field of the second direction, generating a constant magnetic field of the second direction on the second direction side, and a second magnetic field on the second direction side. Generating a constant magnetic field, and the detection result of the light detector, the 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 the application example, the magnetic field vector of the measurement area can be calculated by irradiating light in only one direction such as the third direction (Z direction). Specifically, as the magnetic field in the first direction (X direction) orthogonal to the third direction (Z direction) which is the light emission direction, with respect to the medium in which the optical characteristics of light are changed 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 a second direction (Y direction) orthogonal to the third direction (Z direction) and the first direction (X direction). Then, the magnetic field of the measurement area is calculated using the detection result of the optical characteristic of light, the magnetic field in the first direction (X direction), and the magnetic field in the second direction (Y direction).

BRIEF DESCRIPTION OF THE DRAWINGS The schematic side view which shows an example of a structure of the magnetic field measurement 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, specifically, the figure seen from the Z direction. It is a schematic diagram explaining the structure of the magnetic sensor which concerns on this embodiment, and, specifically, the top view seen from Z direction. It is a schematic diagram explaining the structure of the magnetic sensor which concerns on this embodiment, and, specifically, the side view seen from the Y direction. FIG. 2 is a functional configuration diagram of an arithmetic control unit according to the present embodiment. The figure explaining alignment when there is no magnetic field. The figure explaining the change of alignment by a magnetic field. The figure explaining the change of the polarization plane of linearly polarized light by permeate | transmitting a gas cell. The figure explaining the change of the polarization plane of 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 according to the drawings.
In addition, in order to make each member in each drawing into a size that can be recognized in each drawing, each member is illustrated with different scales.

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

  The 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. Note that an apparatus that measures some information (for example, one component, size, presence or 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 emitted by the measurement object is a magnetocardiogram (a magnetic field generated from the electrophysiological activity of the heart) or the magnetoencephalogram. Here, the case where the magnetic field measurement apparatus 1 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 in which pump light and probe light are used in common. The configuration is not limited to the one-beam system, and a so-called two-beam system may be configured in which a light source for irradiating pump light and a light source for irradiating probe light are separated. As shown in FIG. 1, the magnetic field measurement apparatus 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, the direction (irradiation direction) in which the laser light (also referred to as irradiation light) 18a emitted from the light source 18 passes through the gas cell 12 is taken as the third direction (Z direction in this embodiment). The vibration direction of the linearly polarized light component of the irradiation light is taken as a second direction (Y direction in the present embodiment). A direction orthogonal to the second direction (Y direction) and the third direction (Z direction) is taken 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 defined as the axial direction of the orthogonal coordinate system, and hereinafter referred to as the X axis direction, the Y axis direction, and the Z axis direction, respectively. Do.

  In FIG. 1, the Z-axis direction is the vertical direction, which is the height direction of the magnetic field measurement apparatus 1 (vertical direction in FIG. 1). The X-axis direction and the Y-axis direction are horizontal directions, in which the upper surfaces of the base 3 and the table 4 extend. The height direction (left and right direction in FIG. 1) of the subject 9 lying down 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 inner bottom surface of the magnetic shield device 6 (main body 6a), and extends to the outer side of the main body 6a along the X-axis direction which is the movable direction of the subject 9. The table 4 includes a first table 4a, a second table 4b, and a third table 4c. On the base 3, a first table 4a which is moved along the X-axis direction by the linear motion mechanism 3a is installed. On the first table 4a, a second table 4b which is moved up and down in the Z-axis direction by an elevator (not shown) is installed. A third table 4c is provided on the second table 4b for moving along the Y-axis direction on the rail by a linear motion mechanism (not shown).

  The magnetic shield device 6 includes a rectangular cylindrical main body 6a having an opening 6b. The inside of the main body 6a is hollow, and the cross-sectional shape of a plane (a plane perpendicular to the X-axis direction in the Y-Z cross section) formed in the Y-axis direction and the Z-axis direction is substantially square. When measuring the magnetocardiogram, the subject 9 is accommodated inside the main body 6 a in a state of 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 6 b of the main body 6 a. The size of the magnetic shield device 6 is, for example, about 200 cm in length in the X-axis direction, and about 90 cm on one side of the opening 6 b. Then, the subject 9 lying on the table 4 can move along the X axis direction along the table 4 along the X axis direction into and out of the magnetic shield device 6 from the opening 6 b.

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

  A magnetic field generator 8 is installed inside the main body 6a. The magnetic field generator 8 is formed of a 3-axis Helmholtz coil, and can generate a predetermined magnetic field in the axial direction of the X axis, the Y axis, and the Z axis with respect to the measurement area 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 along the X-axis direction) 8X and a second magnetic field generator (a pair of Helmholtzes facing along the Y-axis direction) A coil 8Y and a third magnetic field generator (a pair of Helmholtz coils opposed along the Z-axis direction) 8Z are included. An area in the main body 6 a of the magnetic shield device 6 which is a target for measuring the magnetocardiogram of the magnetic field measurement apparatus 1 is a measurement area 5. The chest 9 a, which is the measurement position in the subject 9, and the magnetic sensor 10 are disposed in the measurement area 5.

  As shown in FIGS. 2, 3 and 4, the diameters of the Helmholtz coil 8X, the Helmholtz coil 8Y, and the Helmholtz coil 8Z included in the magnetic field generator 8 are larger than the diameter of the measurement area 5. That is, the measurement area 5 is included in an area 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 these Helmholtz coils 8X, 8Y, 8Z, the center of the measurement area 5 and the center of the magnetic sensor 10 be substantially coincident. In this way, in the measurement area 5, it is possible to accurately measure the magnetic field which is a three-dimensional vector.

  The distance between the pair of opposing Helmholtz coils is preferably larger than the diameter of the other Helmholtz coils. For example, as shown in FIG. 2, FIG. 3 and FIG. 4, it is preferable that the distance between the pair of opposing Helmholtz coils 8X is larger than the diameters of the Helmholtz coils 8Y and the Helmholtz coils 8Z. In this way, a parallel 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.

  In FIGS. 2, 3 and 4, it is assumed that the distance between a pair of Helmholtz coils 8X (for example, in FIG. 2, the distance along the X axis between the Helmholtz coil 8X on the left and the Helmholtz coil 8X on the right) is It is assumed that the diameter is smaller than the diameters of the other Helmholtz coils 8Y and Helmholtz coils 8Z. In this case, the Helmholtz coil 8X enters the inside of a cylindrical region having the bottom surface of the pair of Helmholtz coils 8Y (or 8Z). Then, distortion occurs in the magnetic field formed by the pair of Helmholtz coils 8Y (or 8Z), and it is difficult to generate a parallel uniform magnetic field along the Y axis (or Z axis) near 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 Helmholtz coils 8Z, in the cylindrical region having the pair of Helmholtz coils 8Y (or 8Z) as the bottom. The Helmholtz coil 8X is disposed on the outside. Then, distortion of the magnetic field formed by the pair of Helmholtz coils 8Y (or 8Z) is suppressed by the Helmholtz coil 8X, and a parallel uniform magnetic field is generated along the Y axis (or Z axis) near the measurement region 5 It becomes possible.

  Thus, it is preferable that the pair of Helmholtz coils 8Y and the pair of Helmholtz coils 8Z be disposed outside the cylindrical region having the bottom of the pair of Helmholtz coils 8X. A pair of Helmholtz coils 8Z and a pair of Helmholtz coils 8X are disposed outside a cylindrical area having the bottom of the pair of Helmholtz coils 8Y, and outside a cylindrical area having the bottom of the pair of Helmholtz coils 8Z as the bottom. Preferably, a pair of Helmholtz coils 8X and a pair of Helmholtz coils 8Y are disposed.

  Although the shape of the Helmholtz coil is described as being circular in the present embodiment, the shape of the Helmholtz coil is not limited to a circular shape, and may be a polygon such as a quadrilateral. When the shape of the Helmholtz coil is a polygon, other Helmholtz coils which are orthogonal to the height direction of the prism are arranged outside the prismatic region having the bottom surface of the pair of Helmholtz coils.

  The magnetic sensor 10 is fixed to the ceiling of the main body 6 a via the support member 7. The magnetic sensor 10 measures the intensity component of the magnetic field in the Z-axis direction of the measurement area 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 4a and the third table 4c are moved so that the chest 9a, which is the measurement position in the subject 9, faces the magnetic sensor 10, and the chest 9a The second table 4 b is raised 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 from the outside due to the environment such as geomagnetism or urban noise is present in the measurement area 5 where the gas cell 12 is disposed. Is preferred. If the original magnetic field is present, the influence thereof causes a reduction in sensitivity to the magnetic field generated by the measurement object (the subject 9) and a reduction in measurement accuracy. In the present embodiment, the magnetic shield device 6 suppresses the inflow of the magnetic field from the outside into the measurement area 5. And by the magnetic field generator 8 arrange | positioned inside the main-body part 6a, measurement area | region 5 vicinity can be maintained in the low magnetic field near zero magnetic field.

  As shown in FIG. 5, the magnetic sensor 10 includes a light source 18, a gas cell 12, and light detectors 14 and 15. The light source 18 outputs a laser beam 18a of a wavelength according to the absorption line of cesium. The wavelength of the laser beam 18a is not particularly limited, but in the present embodiment, for example, it is set to a wavelength of 894 nm corresponding to the D1 line. The light source 18 is a tunable laser, and the laser beam 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 arithmetic 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 through 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. 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 and make it travel in the + X direction, and let a part of the laser beam 18a pass through it and travel in the -Y direction Let The first reflection mirror 25 reflects all the incident laser light 18a in the + X direction. The laser beam 18 a 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 reflectance of each mirror is set so that the light intensity of the laser beam 18a of each light path becomes the same light intensity.

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

  The laser beam 18 a of one optical path is divided into four optical paths by the fourth half mirror 26, the fifth half mirror 27, the sixth half mirror 28, and the second reflecting mirror 29. The reflectance of each mirror is set so that the light intensity of the laser beam 18a of each light path becomes the same light intensity. Therefore, the laser beam 18a is split into 16 light paths. And the reflectance of each mirror is set so that the light intensity of the laser beam 18a of each light path becomes the same intensity.

  16 gas cells 12 of 4 rows and 4 columns are provided in the optical path of the laser beam 18a on the + Z direction side of the fourth half mirror 26, the fifth half mirror 27, the sixth half mirror 28 and the second reflecting mirror 29 It is done. The laser beam 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 void inside, and the void is filled with a gas of alkali metal as a medium that changes the optical characteristics of light according to the magnetic field of the measurement area 5 (see FIG. 1). . The alkali metal is not particularly limited, and potassium, rubidium or cesium can be used. In the present embodiment, for example, cesium is used as the alkali metal.

  A polarization splitter 13 is installed on the + Z direction side of each gas cell 12. The polarization splitter 13 is an element that splits the incident laser beam 18a into laser beams 18a of two polarization components orthogonal to each other. For the polarization splitter 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 splitter 13, and a photodetector 15 is installed on the + X direction side of the polarization splitter 13. The laser beam 18a that has passed through the polarization splitter 13 enters the light detector 14, and the laser beam 18a reflected by the polarization splitter 13 enters the light detector 15. The light detector 14 and the light detector 15 output a signal corresponding to the amount of light received by the incident laser beam 18 a to the calculation control unit 30.

  It is desirable that the photodetectors 14 and 15 be made of a nonmagnetic material, as it may affect the measurement if the photodetectors 14 and 15 generate a magnetic field. The magnetic sensor 10 has heaters 16 provided on both sides in the X-axis direction and on 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 of a type that heats by passing steam or hot air through the 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 a measurement target) detected by the magnetic sensor 10 in the measurement area 5 enters the magnetic sensor 10 from the −Z direction side. The magnetic field vector B passes the fourth half mirror 26 to the second reflecting mirror 29, passes through the gas cell 12, passes through the polarization splitter 13, and exits from the magnetic sensor 10.

  The magnetic sensor 10 is a sensor called an optical pumping magnetic sensor or an optical pumping atomic magnetic sensor. The cesium in the gas cell 12 is heated to be in a gas state. Then, by irradiating the cesium gas with laser light 18a that has become linearly polarized, the cesium atoms are excited and the directions of the magnetic moments are aligned. In this state, when the magnetic field vector B passes through the gas cell 12, 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. There is a positive correlation between the size of the Larmor precession and the amount of change in the rotation angle of the deflection surface of the laser beam 18a. Therefore, the strength 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 splitter 13 splits the laser beam 18a transmitted through the gas cell 12 into linearly polarized light of two components in axial directions (α-axis and β-axis shown in FIG. 11) orthogonal to each other. One of the separated linear polarizations is guided to the photodetector 14, and the other linear polarization is guided to the photodetector 15. The light detector 14 and the light detector 15 receive linearly polarized light of each of two orthogonal components, generate a signal corresponding to the amount of received light, and output the signal to the calculation control unit 30. By detecting the intensity of each linear polarization, it is possible to detect the rotation angle of the deflection surface of the laser beam 18a. Then, the strength of the magnetic field vector B can be detected from the change in the rotation angle of the deflection plane of the laser beam 18a.

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

  As shown in FIG. 7, the calculation 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 operation performed to the processing unit 40. The operation unit 31 inputs various instructions such as an instruction to start magnetic field measurement.

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

  The processing unit 40 may be, for example, a microprocessor such as a central processing unit (CPU) or a graphics processing unit (GPU) or an electronic component such as an application specific integrated circuit (ASIC) or an integrated circuit (IC) memory. To be realized. The processing unit 40 controls the operation of the calculation control unit 30 by executing various calculation processes based on predetermined programs 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 magnetic measurement processing (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 process according to the present embodiment, for example, before measurement of a magnetic field generated by a measurement object such as the heart or brain of a human body, the original of the measurement area 5 in a state where the measurement object is not placed. The magnetic field C _x is calculated. Then, in a state where the magnetic field generator 8 generates a bias magnetic field which cancels the original magnetic field C _x , the magnetic field generated by the object to be measured is measured. That is, the measurement of the magnetic field generated by the measurement object (the subject 9) is performed in a state where the external magnetic field (original magnetic field) flowing into the measurement area 5 is reduced.

  The irradiation control unit 41 controls the irradiation of the 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 linear polarization plane included in the irradiation light, and the like, in addition to the start and end of the 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 the X, Y, 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. Although the details will be described 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) components 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.

In addition, the magnetic field generation control unit 42 sets 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 ) at the time of measurement. The magnetic field generator 8 (8X, 8Y, 8Z) generates a synthetic magnetic field (B _b + A) of

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

In the state where the magnetic field generator 8 (8X, 8Y, 8Z) generates the artificial magnetic field vector A (A _x , A _y , A _z ), the source magnetic field calculation unit 43 converts the signal output from the magnetic sensor 10 Based on this, an original magnetic field vector C (C _x , C _y , C _z ) is calculated. Specifically, the magnetic sensor measurement value obtained based on a signal output from the magnetic sensor 10 (squared difference W _-) was used as a spin polarization M _x, at a certain time t, X-axis direction component of the artificial magnetic field vector A 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 one or more combinations.

Then, a simultaneous equation consisting of three or more equations obtained by substituting each of the acquired combinations into equation 17 described later is defined, and a predetermined arithmetic operation process for solving this simultaneous equation is executed to obtain an original magnetic field vector. Calculate C (C _x , C _y , C _z ). The calculated original magnetic field C (C _x , C _y , C _z ) is stored in the storage unit 50 as 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 Do. The determined bias magnetic field B _b (B _bx , B _by , B _bz ) is stored in the storage unit 50 as bias magnetic field data 54.

Target magnetic field calculating unit 45, the measurement object is disposed, in a state in which the magnetic field generator 8 is producing the bias magnetic field B _b, on the basis of a signal output from the magnetic sensor 10, the measuring object is generated A target magnetic field vector B (B _x , B _y , B _z ) is calculated. Specifically, the measurement value obtained based on a signal output from the magnetic sensor 10 (squared difference W _-) and spin polarization M _x a, at a certain time t, the artificial magnetic field vector A X-axis direction component A _x A combination of the value A _x (t) and the value A _y (t) of the Y-axis direction component A _y with the spin polarization M _x (t), where the spin polarization M _x is different Get a combination of

Then, a simultaneous equation consisting of three or more equations obtained by substituting each of the acquired combinations into Equation 17 is defined, and a predetermined arithmetic operation process for solving this simultaneous equation is executed to obtain the original magnetic field vector C (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 target. The calculated target magnetic field vector B (B _x , B _y , B _z ) is stored in the storage unit 50 as the measured magnetic field data 55. Further, 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 the magnetic sensor measurement data 56.

  The storage unit 50 is configured by a storage device such as a read only memory (ROM), a random access memory (RAM), or a hard disk. The storage unit 50 stores programs, data, and the like for the processing unit 40 to control the arithmetic control unit 30 in an integrated manner, and is used as a work area of the processing unit 40. Operation data and the like from the operation unit 31 are temporarily stored. In this 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. Be done.

[principle]
The measurement principle of the magnetic field in the magnetic field measurement apparatus 1 will be described. FIG. 8 is a view for explaining the alignment in the absence of a magnetic field. FIG. 9 is a diagram for explaining the change in alignment due to the magnetic field. FIGS. 10 and 11 are diagrams for explaining the change in the polarization plane of linearly polarized light due to transmission through the gas cell. FIG. 12 is a view showing the relationship between the alignment azimuth angle θ and the detection result of the probe light.

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

(A) Optical pumping The gas of alkali metal atoms enclosed in the gas cell 12 is a pump light adjusted to a wavelength corresponding to the transition of the state of hyperfine structure quantum number F to F '(= F-1) of the D1 line. By irradiating (the light passing through the gas cell 12 in the present embodiment), the spins that are directed approximately in antiparallel (in the reverse direction) (spin-polarized) atoms become a group in which the same number of mixed atoms are mixed. This state is called alignment. Although the spin polarization of one atom relaxes with the passage of time, since the pump light is CW (continuous wave) light, the formation and relaxation of spin polarization are repeated concurrently and continuously. As a result, stationary spin polarization is formed as a whole of the atomic group.

  When the measurement area 5 has a zero magnetic field, the alignment is represented by a probability distribution of magnetic moments of atoms. When the pump light is linearly polarized as in the present embodiment, the shape thereof is, as shown in FIG. 8, the vibration direction of the electric field of the linearly polarized pump light in the X-Y plane (in the present embodiment, the Y axis direction It becomes the shape of area | region R which connected two ellipses extended along 2.).

(B) Action of Magnetic Field If there is any magnetic field in the measurement area 5, the alkali metal atoms start precession with the direction of the magnetic field vector (the magnetic field received by the gas cell 12) as the axis of rotation. Then, as shown in FIG. 9, the direction of alignment (the direction along the major axis of the ellipse) is obtained by the addition of an optical pumping action by the pump light and a relaxation action caused by gas atoms colliding with the inner wall of the gas cell 12 or the like. Changes to rotate about the origin O.

  The alignment direction is in a steady state in an arrangement rotated by an angle (θ) according 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 a Y-axis direction which is a vibration direction of the electric field of the pump light is set as an alignment azimuth angle θ. The alignment azimuth angle θ mainly increases according to the magnetic field strength in the Z-axis direction.

(C) Probing A situation is considered in which a probe beam (a beam passing through the gas cell 12 in the present embodiment) having a linearly polarized component oscillating in the Y axis direction with an electric field vector E ₀ passes through the atomic group in this state. That is, as shown in FIG. 10, linearly polarized light whose oscillation direction of the electric field of the probe light is along the Y-axis direction is made to pass through the gas cell 12 in the + Z direction. In FIG. 10, the origin O corresponds to the position of the atomic group (gas atoms enclosed in the gas cell 12), and the atomic group is optically pumped, whereby alignment is distributed in a region along the Y-axis direction. It is happening. In the Z-axis direction, the -Z direction side indicates linearly polarized light before transmitting the atomic group, and the + Z direction indicates linearly polarized light (transmitted light) transmitted through the atomic group.

When linearly polarized light passes through a group of atoms, the plane of linearly polarized light rotates due to linear dichroism, and its electric field vector changes to E ₁ . Linear dichroism is a property in which the transmittance of linearly polarized light differs between the direction θp along the alignment (see FIG. 9) and the direction θs perpendicular to the alignment (see FIG. 9). Specifically, since the component in the direction θs perpendicular to the alignment is more absorbed 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 view showing the state of rotation of the polarization plane before and after linearly polarized light passes through the atomic group, in an X-Y plane perpendicular to the Z-axis direction which 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 vibration direction of the electric field is the Y-axis direction. By alignment, the component in the direction θp of the probe light is transmitted at the transmittance t _p , and the component in the direction θs is transmitted at the transmittance t _s . Since t _p > t _s due to linear dichroism, the polarization plane of the probe light transmitted through the gas cell 12 rotates so as to approach the direction θp. Thus the light which has passed through the gas cell 12 comes to have an electric field vector E _1.

Specifically, a component along the alignment of the electric field vector E ₀ is denoted by E _0P, a component along the direction perpendicular to the traveling direction of alignment and the linearly polarized light of the electric field vector E ₀ is denoted by E _{0 s.} Further, a component along the alignment of the electric field vector E ₁ is expressed as E _1P, a component along the direction perpendicular to the traveling direction of alignment and the linearly polarized light the electric field vector E ₁ 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 .

A direction along the alignment angle formed with the vibration direction of the electric field of the probe light (hereinafter, referred to as "alignment azimuth".) When the theta, from the above relationship, the electric field vector E ₁ direction θp and direction θs Each component is calculated by Equation 4 below.

As described above, the probe light transmitted through the gas cell 12 is polarized by the polarization splitter 13 with respect to the Y-axis direction which is the irradiation direction of the probe light. 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 light detectors 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 and β axes according to Equation 6 and Equation 7 below. 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 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 squared difference between the square sum W ₊ of the axial component of the axis W _- and shows. The alignment azimuth angle θ = 0 is a state where the measurement area 5 has a zero magnetic field (see FIG. 8). However, the transmittance t _p of the component in the direction θ _{p is} 1 and the transmittance t _s of the component in the direction θ _{s is} 0.8.

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 almost linearly with the alignment azimuth angle θ in the range of the alignment azimuth angle θ of −45 degrees to +45 degrees, high sensitivity can be obtained. In addition, since the center of the linear change is 0 degrees and the range of the linear change is wider than that of the other (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 magnetocardiogram 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 is present in the measurement area 5, the sensitivity is reduced due to the influence thereof, and the measurement accuracy is lowered. Normally, in order to measure the magnetic field to be measured such as the magnetocardiogram or the magnetocardiogram, under an environment where the magnetic shield device 6 suppresses the entry of the magnetic field from the outside into the measurement area 5 (in a state where the external magnetic field is small) Although it is performed, it is difficult for the magnetic shield device 6 to sufficiently reduce the external magnetic field to such an extent that the measurement is not affected. In other words, the entry of the external magnetic field can often not be completely shielded by the magnetic shield device 6. A magnetic shield that can completely shield the magnetism is large in size, expensive, and expensive to install and operate.

  Therefore, in the present embodiment, after using the magnetic shield device 6, an external magnetic field (referred to as an original magnetic field C) leaking into the magnetic shield device 6 is measured and reduced by the magnetic field generator 8. And measure the magnetic field of the measurement target. However, when the external magnetic field is low originally or when 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 the range of alignment azimuth angle θ of −45 degrees to +45 degrees, the square difference W ₋ is an X-axis direction component M _x of the spin polarization (M _x , M _y , M _z ) (hereinafter, approximately proportional to the referred to as the spin polarization M _x). The spin polarization M _x corresponds to a magnetization value which is an X-axis direction component of a magnetization vector obtained by synthesizing the magnetic moment of the atom. For this reason, in the following, the squared difference W ₋ is treated as the spin polarization M _x . In this embodiment, paying attention to the spin polarization M _x , how the value of the spin polarization M _x corresponds to each component B _x , B _y and B _z of the magnetic field vector B applied to the gas cell 12 We will derive a relational expression that indicates whether it changes.

The time evolution of the spin polarization (M _x , M _y , M _z ) of the alignment generated by the optical pumping is approximated by Bloch equations shown in the following Equations 8 to 10. γ _F represents the gyromagnetic ratio determined by the type of medium gas (alkali metal atom gas) in the gas cell 12. Also, Γ ₀ represents the relaxation rate of spin polarization (M _x , M _y , M _z ), and Γ _p represents the optical pumping rate. M _p is the maximum magnetization when all the spins of the alkali metal atom group are aligned in one direction.

Since the pumping light and the probe light are constantly irradiated to the gas cell 12 with a constant power, the stationary solution of spin polarization (M _x , M _y , M _z ) is the left side of Eqs. Each can be solved as zero. The solution is obtained by Equations 11 to 13.

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

(D) Measurement of magnetic Well, the magnetic field generator 8 (8X, 8Y, 8Z) by, with respect to the gas cell 12, X, Y, each Z-axis direction, the artificial magnetic field _{A (A x, A y,} A z) Consider the case of generating and 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) generated by the magnetic field generator 8 as shown in Formula 15. The vector sum of _z ) and the original magnetic field vector C (C _x , C _y , C _z ) is obtained. The original magnetic field C is a magnetic field present in the measurement area 5 when the artificial magnetic field A is zero.

Here, the component _Az in the Z-axis direction of the artificial magnetic field vector A is set to zero ( _Az = 0). Further, the component A _x in the X axis direction of the artificial magnetic field vector A is a function A ₁₀ f (t) having an amplitude A ₁₀ , and the component A _y in the Y axis direction is 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 area 5 is expressed by the following formula 16. Note that the amplitude A ₁₀ and the amplitude A ₂₀ by a factor having a dimension of the magnetic field, the function f (t) and function and g (t) is a non-dimension (dimensionless) function.

Substituting Equation 16 into the spin polarization M _x of Equation 11, Equation 17 is obtained.

If A ₁₀ = A ₂₀ = A ₀ , control and calculation become easy, and these equations become equation 18 below.

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 original magnetic field vector C, which is an unknown number, are calculated as follows. That is, measurement is performed using the magnetic field measurement apparatus 1, and at a certain time t, the component A _x (t) in the X axis direction of the artificial magnetic field A by the magnetic field generator 8 and the component A _y (t) in the Y axis direction , And a combination of spin polarization M _x (t) (ie, the output value W ₋ of the magnetic sensor 10), and three or more combinations having different spin polarization M _x (t) are acquired.

Then, for each combination, a simultaneous equation of three formulas obtained by substituting the artificial magnetic fields A _x (t), A _y (t) and the spin polarization M _x (t) into the formula 19 is obtained Generate By solving this simultaneous equation, it is possible to calculate each component (C _x , C _y , C _z ) of the original magnetic field vector C which is an unknown number.

In Equation 19, the constants a and c may also be unknowns. That is, it is assumed that Equation 19 includes five unknowns of each component (C _x , C _y , C _z ) of the original magnetic field vector C and the constants a and c. In this case, measurement is performed using the magnetic field measurement apparatus 1, 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) Get five combinations with different polarization M _x (t). Then, each equation is substituted for each value into equation 19 to generate simultaneous equations of five equations. By solving this simultaneous equation, it is possible to calculate each component (C _x , C _y , C _z ) of the original magnetic field vector C which is an unknown quantity, and the constants a and c.

Furthermore, it is a combination of an artificial magnetic field A _x (t), A _y (t) and a spin polarization M _x (t), and a combination of six or more different spin polarization M _x (t) is acquired And 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 ( Calculate C _x , C _y , C _z ) and constants a, c.

In addition, the amplitude A ₀ of the time functions f (t) and g (t), which are artificial magnetic fields A _x and A _y , is compared with the X axis component C _x of the original magnetic field C and the Y axis component C _y If it is sufficiently small (generally 1/10 or less, A ₀ <(C _x / 10), A ₀ <(C _y / 10)), equation 19 is simplified to equation 20, and measurement becomes easier. .

Thus, 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 are calculated using Expression 19 and Expression 20. From the above, 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 component A _{x in} the X axis direction of the artificial magnetic field A takes fixed values f _i (i = 1,..., N) which are n different levels respectively. The time function g (t) of the Y-axis direction component _Ay takes fixed values g _j (j = 1,..., M) which are m different levels. At the same time, a total of n × m measurement periods τ k (k = i,..., N × m) corresponding to all combinations of fixed values f _i and g _j of the time functions g (t) and f (t), respectively. The time functions f (t), g (t) are defined such that c) exists.

In the present embodiment, as described above, in order to calculate each component (C _x , C _y , C _z ) of the original magnetic field vector C, the artificial magnetic field A _x (t), A _y (t) at a certain time t And spin polarization M _x (t), and it is necessary to obtain three or more combinations in which spin polarization M _x (t) is different. That is, it is necessary to determine fixed values f _i and g _j taken by the time functions f (t) and g (t), respectively, so that three or more measurement periods τ k (k 存在 3) exist.

And, the spin polarization M _x in the measurement period τ k 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 respectively is From each of 20, the following Equation 21 and Equation 22 are obtained. Here, it is denoted _{f (t) = f i,} g a (t) = g _j become upon spin polarization M _x (t) at M _xij.

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

If the coefficients a and c are both unknowns, 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, and the other of n or m is an integer of 3 or more, and a total of 6 or more M _xij are measured. . When changing only the X side, n is an integer of 5 or more and 5 or more of M _xij are measured. When changing only the Y side, m is an integer of 5 or more and 5 or more of M _xij are measured.

If A ₁₀ = A ₂₀ = A ₀ as in the above, control and calculation become easy, and Formula 21 and Formula 22 become the following Formula 23 and Formula 24, respectively.

[Flow of processing]
FIG.13 and FIG.14 is a flowchart explaining the flow of the magnetic field measurement process which concerns on this embodiment. This process is a process that is realized when each unit of the processing unit 40 illustrated in FIG. 7 executes the magnetic field measurement program 51. A case where a measurement object is a human body (the subject 9) and cardiac magnetism (a magnetic field generated from electrophysiological activity of the heart) or the magnetoencephalogram 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 of irradiation light including a linearly polarized light component that also serves as pump light and probe light (step S01). Next, the source magnetic field C is measured. Specifically, the magnetic field generation controller 42 controls the magnetic field generator 8 to generate an artificial magnetic field A (A _x = A ₀ f _i , A _y = A ₀ g _j , 0) corresponding to the combination (i, j) of the object. ) 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 fixed values 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 The combination of the time function g (t) with the number j (j = 1 to m) of the fixed value g is repeatedly executed (step S04). That is, when all the combinations of (i, j) are not completed (step S 04: NO), the processes of steps S 02 and S 03 are performed on the combinations of (i, j) for which the process is not executed. To be executed.

When the process of step S02 and step S03 ends for all combinations of (i, j) (step S04: YES), the original magnetic field calculation unit 43 determines the artificial magnetic fields A _x and A _y and the obtained measured values (square difference W _-) using a combination of the original magnetic field vector C (C _x, C _y, to calculate the C _z) (step S05). Subsequently, the bias magnetic field determining 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 object to be measured is placed close to the magnetic sensor 10 (step S07). Then, the magnetic field B generated by the object to be measured is measured. Specifically, the magnetic field generation control unit 42 sets the artificial magnetic field A (A _x = A ₀ f _i , A _y = A ₀ g _j , 0) corresponding to the combination (i, j) of the object, and the bias magnetic field B _The magnetic field generator 8 generates a synthetic magnetic field with _b (step S08). Then, a measured value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 in this state is acquired (step S09).

The processes in steps S08 and S09 are the number i (i = 1 to n) of fixed values 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 The combination of the time function g (t) and the number j (j = 1 to m) of the fixed value g is repeatedly executed (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 combinations of (i, j) for which the process is not executed. To be executed.

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

As specific examples of the magnetic field measurement apparatus 1 configured as described above, three examples in which the artificial magnetic field A (A _x , A _y , A _z ) is specifically shown will be described below.

[First embodiment]
The first embodiment is an embodiment in which the time function f (t) taken as the component A _{x in} the X-axis direction 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) to be the Y-axis direction component A _y has 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 drawing, graphs of artificial magnetic fields A _x and A _y and spin polarization M _x are shown in order from the top with the horizontal axis as a common time t.

The time function f (t) takes f ₁ = 0, f ₂ = 1 as the fixed value f _i , and the time function g (t) takes the fixed value g _j as g ₁ = 0, g ₂ = 1 ,I take the. Therefore, the component A _{x in} the X-axis direction 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 "and take the binary value. The component A _{y in the} Y-axis direction is such that “A ₀ g ₁ = 0” which is a constant magnetic field of Y side first level and “A ₀ g ₂ = A ₀ ” which is a constant magnetic field of Y side second level Take two values.

Then, there are four measurement periods τ1 to τ4 corresponding to all combinations of fixed values f ₁ and f ₂ of the time function f (t) and 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 one another. In other words, it is necessary to calculate the original magnetic field vector C (C _x , C _y , C _z ) using Equation 19 and it is the X-side i-th level (i = 1, 2) that is the X-axis direction component A _x of the artificial magnetic field A ), A Y-side j-th level (j = 1, 2) as the Y-axis direction component _Ay , and a spin polarization M _x as the magnetization value, Three or more combinations with different M _x can be obtained.

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

Then, Expression 23 of the spin polarization M _x , which is the 1-1st magnetization value, is Expression 26 below.

Further, in the second measurement period τ2 in which i = 2 and j = 1, time function f (τ2) = f ₂ = 1 and g (τ 2) = g ₁ = 0. That is, a constant magnetic field of the X-side second level as the X-axis direction component A _x of the artificial magnetic field A is a constant magnetic field in the Y-side first level as the Y-axis direction component A _y, are generated, respectively. Accordingly, Equation 16 of the magnetic field B applied to the gas cell 12 is Equation 27 below.

Then, Expression 23 of the spin polarization M _x , which is the 2-1st magnetization value, is Expression 28 below.

Further, in the third measurement period τ3 in which i = 1 and J = 2, the time function f (τ3) = f ₁ = 0 and g (τ 3) = g ₂ = 1. That is, a constant magnetic field of the X-side first level as the X-axis direction component A _x of the artificial magnetic field A is a constant magnetic field in the Y-side second level as the Y-axis direction component A _y, are generated, respectively. Accordingly, Equation 16 of the magnetic field B applied to the gas cell 12 is Equation 29 below.

Then, Formula 23 of the spin polarization M _x , which is the 1-2nd magnetization value, is Formula 30 below.

Further, in the fourth measurement period τ4 in which i = j = 2, the time function f (τ4) = f ₂ = 1 and g (τ 4) = g ₂ = 1. That is, a constant magnetic field of the X-side second level as the X-axis direction component A _x of the artificial magnetic field A is a constant magnetic field in the Y-side second level as the Y-axis direction component A _y, are generated, respectively. Accordingly, Equation 16 of the magnetic field B applied to the gas cell 12 is Equation 31 below.

Then, Formula 23 of the spin polarization M _x , which is the second-2 magnetization value, is Formula 32 below.

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

Second Embodiment
The second embodiment is an embodiment in which the time function f (t) taken as the component A _{x in} the X-axis direction 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), which is the Y-axis direction component A _y , has three fixed values g ₁ , G ₂ and g ₃ and at least one of the three fixed values g ₁ , g ₂ and 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. The figure shows graphs of the artificial magnetic fields A _x and A _y and the spin polarization M _{x with} the horizontal axis as time t. Moreover, in order to make the change of the spin polarization M _x easy to understand, the lower graph shows a part of the upper graph with the vertical axis direction enlarged.

The time function f (t) takes f ₁ = 0, f ₂ = 1 and f ₃ = −1 as the fixed value f _i , and the time function g (t) takes the fixed value g _j g ₁ = Take 0, g ₂ = 1, g ₃ = -1. Therefore, the artificial magnetic fields A _x and A _y both take three 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. In other words, it is a combination of the artificial magnetic fields A _x and A _y and the spin polarization M _x required to calculate the original magnetic field vector C (C _x , C _y and C _z ) using Eq. Three or more combinations with different extreme M _x can be obtained.

Specifically, in the first measurement period τ1 where i = j = 1, the time function f (τ1) = f ₁ = 0 and g (τ 1) = g ₁ = 0. Accordingly, Equation 16 of the magnetic field B applied to the gas cell 12 is Equation 33 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 34 below.

Further, in the second measurement period τ2 in which i = 2 and j = 1, time function f (τ2) = f ₂ = 1 and g (τ 2) = g ₁ = 0. Accordingly, Formula 16 of the magnetic field B applied to the gas cell 12 is Formula 35 below.

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

In the third measurement period τ3 in which i = 3 and j = 1, the time function f (τ3) = f ₃ = −1, g (τ 3) = g ₁ = 0. Accordingly, Formula 16 of the magnetic field B applied to the gas cell 12 is Formula 37 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 38 below.

Further, in the fourth measurement period τ4 in which i = 1, j = 2, the time function f (τ4) = f ₁ = 0 and g (τ 4) = g ₂ = 1. Accordingly, Equation 16 of the magnetic field B applied to the gas cell 12 is Equation 39 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 40 below.

Further, in the fifth measurement period τ5 where i = j = 2, the time function f (τ5) = f ₂ = 1 and g (τ 5) = g ₂ = 1. Therefore, Equation 16 of the magnetic field B applied to the gas cell 12 is Equation 41 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 42 below.

Further, in the sixth measurement period τ6 in which i = 3 and j = 2, time function f (τ6) = f ₃ = −1, g (τ 6) = g ₂ = 1. Accordingly, Expression 16 of the magnetic field B applied to the gas cell 12 is Expression 43 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 44 below.

Further, in the seventh measurement period τ7 where i = 1, j = 3, the time function f (τ7) = f ₁ = 0 and g (τ 7) = g ₃ = −1. Accordingly, Expression 16 of the magnetic field B applied to the gas cell 12 is Expression 45 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 46 below.

In the eighth measurement period τ8 in which i = 2 and j = 3, the time function f (τ8) = f ₂ = 1 and g (τ 8) = g ₃ = −1. Accordingly, Expression 16 of the magnetic field B applied to the gas cell 12 is Expression 47 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 48 below.

Further, in the ninth measurement period τ9 where i = j = 3, time function f (τ9) = f ₃ = −1, g (τ 9) = g ₃ = −1. Accordingly, Expression 16 of the magnetic field B applied to the gas cell 12 is Expression 49 below.

Then, Formula 23 of the spin polarization M _x becomes Formula 50 below.

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

The magnetization value (M _x4 ) obtained from the magnetic field measurement apparatus 1 in the fourth measurement period τ4 is substituted into the left side of Expression 40 to obtain a fourth equation. The magnetization value (M _x5 ) obtained from the magnetic field measurement apparatus 1 in the fifth measurement period τ5 is substituted into the left side of Expression 42 to obtain a fifth equation. The magnetization value (M _x6 ) obtained from the magnetic field measurement apparatus 1 in the sixth period τ6 is substituted into the left side of Expression 44 to obtain the sixth equation.

The magnetization value (M _x7 ) obtained from the magnetic field measurement apparatus 1 in the seventh measurement period τ7 is substituted into the left side of Expression 46 to obtain the seventh equation. The magnetization value (M _{x 8} ) obtained from the magnetic field measurement apparatus 1 in the eighth measurement period τ8 is substituted into the left side of Expression 48 to obtain an eighth equation. The magnetization value (M _x9 ) obtained from the magnetic field measurement apparatus 1 in the ninth measurement period τ9 is substituted into the left side of Expression 50 to obtain the ninth equation. Then, these nine equations are simultaneously established to calculate an unknown source magnetic field vector C (C _x , C _y , C _z ).

Third Embodiment
The third embodiment is an embodiment in which only an uniaxial component (X-axis component) is generated and applied as an artificial magnetic field A (corresponding to application example 2). That is, this corresponds to the case where g (t) = 0 in Expression 17 of the spin polarization M _x . Further, the time function f (t), which is the component A _{x in} the X axis direction of the artificial magnetic field A, takes three fixed values f ₁ , f ₂ , f ₃ , and the three fixed values f ₁ , f ₂ , f ₃ One is zero.

That is, for example, the component A _{x in} the X-axis direction of the artificial magnetic field A is “A ₀ f _i = 0” which is a constant magnetic field on the X side and “A ₀ f” which is a constant magnetic field on the X side. _There are three values, ₂ = A ₀ ", and" A ₀ f ₃ = -A ₀ ", which is a constant magnetic field at the X-side third level. Therefore, Equation 21, Equation 22 of spin polarization M _x, respectively, the following equation 51, the equation 52.

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, it is assumed that the time function f (t) takes f ₁ = 0, f ₂ = 1, f ₃ = −1 as the fixed value f _i . Then, these three measurement periods τ1 to τ3 are identical to the measurement periods τ1 to τ3 in the second embodiment described above.

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

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

In addition, in the third measurement period τ3 in which i = 3 and j = 1 (g ₁ = 0), a constant magnetic field at the X-side third level is generated as the component A _{x in} the X-axis direction of the artificial magnetic field A. The magnetic field B applied to the gas cell 12 is Expression 37, and the spin polarization M _{x, which} is the 3-1st magnetization value, is Expression 38.

Thus, the spin polarization M _x in each of the measurement periods τ1 to τ3 is different. Therefore, it is a combination of the artificial magnetic fields A _x and A _y and the spin polarization M _x necessary for calculation of the original magnetic field vector C (C _x , C _y and C _z ) using Eq. Three or more combinations with different extreme M _x can be obtained.

Fourth Embodiment
The fourth embodiment is an embodiment in which only an uniaxial component (Y-axis component) is generated and applied as an artificial magnetic field A (corresponding to application example 6). That is, this corresponds to the case where f (t) = 0 in Expression 17 of the spin polarization M _x . Also, the time function g (t), which is the Y-axis direction component _{Ay of} the artificial magnetic field A, takes three fixed values g ₁ , g ₂ and g ₃ , and these three fixed values g ₁ , g ₂ and g ₃ 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 _There are three values, ₂ = A ₀ ", and" A ₀ g ₃ = -A ₀ ", which is a constant magnetic field at the Y-side third level. Therefore, Equation 21, Equation 22 of spin polarization M _x, respectively, the following equation 53, the equation 54.

In this case, there are three measurement periods τ1 to τ3 corresponding to the fixed values g _{1 to} g _{3 of} the artificial magnetic field A, respectively. For example, it is assumed that the time function g (t) takes g ₁ = 0, g ₂ = 1, g ₃ = -1 as the fixed value g _j . Then, these three measurement periods τ1 to τ3 are identical to the measurement periods τ1 to τ3 in the second embodiment described above.

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

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

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

Thus, the spin polarization M _x in each of the measurement periods τ1 to τ3 is different. Therefore, it is a combination of the artificial magnetic fields A _x and A _y and the spin polarization M _x necessary for calculation of the original magnetic field vector C (C _x , C _y and C _z ) using Eq. Three or more combinations with different extreme M _x can be obtained.

Fifth Embodiment
The fifth embodiment is an embodiment in which a predetermined magnetic field is generated in the measurement area 5 instead of setting the measurement area 5 in a state where no measurement object is placed to the zero magnetic field as in the above-described example. . A magnetic field desired to be produced in the measurement area 5 in a state where no measurement object is placed is referred to as a target magnetic field. If you want a predetermined magnetic field instead of the target magnetic field at zero magnetic field, the measurement value obtained based on a signal output from the magnetic sensor 10 in step S03 shown in FIG. 13 (squared difference W _-) and artificial at that time After acquiring the combination with the values of the magnetic fields A _x and A _y , the following processing is performed.

As a first step, the obtained measured value (squared difference W _-) and artificial magnetic field A _x, by using the combination of A _y, a magnetic field of the measuring region 5, is calculated as a raw magnetic field C (corresponding to step S05) . Subsequently, in the second step, the measurement target (the subject 9) is disposed in the measurement area 5 (corresponding to step S07). In the fifth embodiment, applying a target magnetic field for the predetermined magnetic field rather than a zero field, the bias magnetic field B _b to cancel the calculated original field C in the measurement region 5 (Step S06 and Step S08 ) Is not done.

  Subsequently, as a third step, a magnetic field of the difference between the target magnetic field, which is a predetermined magnetic field desired to be formed in the measurement area 5, and the original magnetic field C, is generated by the first magnetic field generator 8X, the second magnetic field generator 8Y, and the third magnetic field generation. 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 synthesized, and a predetermined magnetic field can be created in the measurement area 5 as a target magnetic field. The order of the second and third steps may be reversed.

Then, as a fourth step, the measurement value obtained based on a signal the second step is conducted third step is output from the magnetic sensor 10 in the period has ended (squared difference W _-) using a measuring The magnetic field B generated by the object is measured (corresponding to step S11). Thereby, in the state where measurement field 5 is made into the predetermined target magnetic field, magnetic field B which a measurement subject generated can be measured.

  Also in the first to fourth embodiments described above, the target magnetic field is generated in the measurement area 5 by generating a magnetic field of the difference between the target magnetic field which is a predetermined magnetic field desired to be formed in the measurement area 5 and the original magnetic field C. As a predetermined magnetic field can be created. In the fifth embodiment, in order to offset the original magnetic field C leaking into the measurement area 5 from the outside, if the target magnetic field is a zero magnetic field, the magnetic field B generated by the object to be measured (strictly speaking, The component in the Z direction can be accurately measured.

Sixth Embodiment
The sixth embodiment is an embodiment in which a magnetic field of a predetermined three-dimensional vector is formed as a target magnetic field in the measurement area 5 in contrast to the fifth embodiment. In the sixth embodiment, the first and second steps are the same as in the fifth embodiment.

As a third step, the component in the X direction of the difference magnetic field between the target magnetic field which is a predetermined magnetic field formed in the measurement area 5 and the original magnetic field C (C _x , C _y , C _z ) is a constant X level first level A constant magnetic field added to the magnetic field is generated in the first magnetic field generator 8X, a magnetic field of the Y direction component of the difference magnetic field is generated in the second magnetic field generator 8Y, and a magnetic field of the Z direction component of the difference magnetic field is It is generated by the three magnetic field generator 8Z (corresponding to step S08). Thus, the magnetic field generator 8 (8X, 8Y, 8Z) artificial magnetic field A is applied by (A _x, A _y, A _z) with the original field _{C (C x, C y,} C z) and are synthesized, A magnetic field of a predetermined three-dimensional vector can be created in the measurement area 5 as a target magnetic field. The order of the second and third steps may be reversed.

Then, as a fourth step, the measurement value obtained based on a signal the second step is conducted third step is output from the magnetic sensor 10 in the period has ended (squared difference W _-) and the third alternating magnetic field The magnetic field B (B _x , B _y , B _z ) generated by the object to be measured is measured using the third and fourth alternating magnetic fields (corresponding to step S11). Thereby, the magnetic field B generated by the object to be measured can be measured in a state where the measurement area 5 is a target magnetic field of a predetermined three-dimensional vector.

Also in the first to fourth embodiments described above, X of the magnetic field of the difference between the target magnetic field, which is a predetermined magnetic field desired to be formed in the measurement area 5, and the original magnetic field C (C _x , C _y , C _z ) By generating a magnetic field of components in the Y, Z directions, a predetermined magnetic field can be created in the measurement area 5 as a target magnetic field. In the sixth embodiment, if the target magnetic field is a zero magnetic field so as to offset the original magnetic field C (C _x , C _y , C _z ) leaking into the measurement area 5 from the outside, the measurement object is generated. Can be accurately measured as a vector quantity.

[Function effect]
As described above, according to the magnetic field measurement apparatus 1 of the present embodiment, the irradiation light (probe light) of one direction (Z-axis direction) with respect to the gas cell 12 in which the gas (gas) such as alkali metal atom is enclosed is By the irradiation, the magnetic field vector (C _x , C _y , C _z ) of the measurement area 5 can be calculated.

Specifically, amplitudes taking 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 measurement value (square difference W ₋ ) obtained based on the signal output from the magnetic sensor 10 Get three or more combinations where M _x is different. Then, the magnetic field C (C _x , C _y , C _z ) is calculated from Expression 17 using these combinations, the spin polarization M _x, and the artificial magnetic fields A _x and A _y .

[Modification]
Note that the applicable embodiments of the present invention are not limited to the above-described examples, and it is needless to say that they can be appropriately changed without departing from the scope of the present invention.

(A) Bias magnetic field B _b
In the above embodiment, the magnetic field generator 8 generates a bias magnetic field B _b which cancels the original magnetic field C, and measures the magnetic field B (B _x , B _y , B _z ) generated by the object to be measured. However, the measurement may be performed without generating the bias magnetic field B _b . Specifically, first, as in the above-described embodiment, the original magnetic field C _x is measured in advance without an object to be measured. Thereafter, the measurement object is brought close to the magnetic sensor 10 and the magnetic field generated by the measurement object is measured. At this 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 synthetic magnetic field of the original magnetic field C, the magnetic field B of the object to be measured, and the artificial magnetic field A by the magnetic field generator 8. Accordingly, a magnetic field B obtained by subtracting the original magnetic field C _x measured in advance from the magnetic field C _x calculated using Formula 17 at this time becomes the magnetic field B generated by the object to be measured.

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

  DESCRIPTION OF SYMBOLS 1 magnetic field measuring device 5 measurement area 8 magnetic field generator 8 X first magnetic field generator (Helmholtz coil) 8 Y second magnetic field generator (Helmholtz coil) 8 Z third magnetic field generator (Helmholtz Coils, 9: object (object to be measured), 10: magnetic sensor, 12: gas cell (medium), 14, 15: light detector, 18: light source, 30: arithmetic control unit.

Claims (17)

The first direction, the second direction, and the third direction are orthogonal to each other,
A light source for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A first magnetic field generator that applies a magnetic field in the first direction to the measurement area;
A magnetic field measurement apparatus comprising the magnetic field measurement method is a magnetic field measurement method for measuring a magnetic field in the measurement area,
In the first magnetic field generator, as the magnetic field in the first direction, a constant magnetic field in the first direction side first level, a constant magnetic field in the first direction side second level, and the first direction side third level Generating a constant magnetic field of
Calculating the magnetic field of the measurement area using the detection result of the light detector and the magnetic field in the first direction;
Magnetic field measurement method including. The calculation of the magnetic field in the measurement area includes calculating a magnetization value indicating the component in the first direction of the magnetization vector of the medium based on the detection result of the light detector. A 1-1 magnetization value when a constant magnetic field of one level is generated, a 2-1 magnetization value when a constant magnetic field of the first direction side second level is generated, and It is to calculate the magnetic field of the measurement area using the 3-1st magnetization value when the constant magnetic field of the third direction on the one direction side is generated and the magnetic field of the first direction,
The magnetic field measurement method according to claim 1. In calculating the magnetic field of the measurement area, a constant magnetic field of the first direction side level (i = 1, 2, 3) which is a magnetic field of the first direction and a magnetic field of the first direction are generated. The following equation 1 is to be applied to each combination of the magnetization value when
The magnetic field measurement method according to claim 2.

However, the magnetic field of the measurement area is C = (C _x , C _y , C _z ), and x, y, z are space coordinates of the first direction, the second direction, and the third direction, respectively. M _xi is a magnetization value when a constant magnetic field at the first direction side i level is generated, a and c are constants, and A ₁₀ f _i is a constant magnetic field at the first direction side i level 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 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 for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A second magnetic field generator applying a magnetic field in the second direction to the measurement area;
A magnetic field measurement apparatus comprising the magnetic field measurement method is a magnetic field measurement method for measuring a magnetic field in the measurement area,
In the second magnetic field generator, as the magnetic field in the second direction, the constant magnetic field in the second direction side first level, the constant magnetic field in the second direction side second level, and the second direction side third level Generating a constant magnetic field of
Calculating the magnetic field of the measurement area using the detection result of the light detector and the magnetic field in the second direction;
Magnetic field measurement method including. The calculation of the magnetic field in the measurement area includes calculating a magnetization value indicating the component in the first direction of the magnetization vector of the medium based on the detection result of the light detector, and the second direction side second A 1-1 magnetization value when a constant magnetic field of one level is generated, a 1-2 magnetization value when a constant magnetic field of the second direction side second level is generated, and Calculating a magnetic field of the measurement area using a first to third magnetization value when a constant magnetic field at a second level and a third level are generated, and a magnetic field of the second direction;
The magnetic field measurement method according to claim 5. In calculating the magnetic field of the measurement area, a constant magnetic field of the second direction side j-th level (j = 1, 2, 3), which is a magnetic field of the second direction, and a magnetic field of the second direction are generated. The following equation 2 is to be applied to each combination of the magnetization value when
The magnetic field measurement method according to claim 6.

However, the magnetic field of the measurement area is C = (C _x , C _y , C _z ), and x, y, z are space coordinates of the first direction, the second direction, and the third direction, respectively. M _xj is a magnetization value when a constant magnetic field at the second direction side j level is generated, a and c are constants, and A ₂₀ g _j is a constant magnetic field at the second direction side j level 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 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 for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A first magnetic field generator that applies a magnetic field in the first direction to the measurement area;
A second magnetic field generator applying a magnetic field in the second direction to the measurement area;
A magnetic field measurement apparatus comprising the magnetic field measurement method is a magnetic field measurement method for measuring a magnetic field in the measurement area,
Generating, in the first magnetic field generator, a constant magnetic field of the first direction side first level and a constant magnetic field of the first direction side second level as the magnetic field in the first direction;
Generating, on the second magnetic field generator, a constant magnetic field on the second direction side first level and a constant magnetic field on the second direction side second level as the magnetic field in the second direction;
Calculating the magnetic field of the measurement area using the detection result of the light detector, the magnetic field in the first direction, and the magnetic field in the second direction;
Magnetic field measurement method including. The calculation of the magnetic field in the measurement area includes calculating a magnetization value indicating the component in the first direction of the magnetization vector of the medium based on the detection result of the light detector.
1) The first direction side first level constant magnetic field, and the second direction side first level constant magnetic field when the first direction side first level constant magnetic field is generated, and the first direction side first level A first constant magnetic field when the first constant magnetic field of the second direction and the second magnetic field when the second constant magnetic field of the second direction is generated; a second constant magnetic field of the first direction; The magnetization value of 2-1 when the constant magnetic field at the first level of two directions is generated, the constant magnetic field at the second level at the first direction, and the constant magnetic field at the second level at the second direction And two or more magnetization values of the second-2 magnetization values at the time of generation of
2) a magnetic field in the first direction;
3) a magnetic field in the second direction;
Calculating the magnetic field of the measurement area using
The magnetic field measurement method according to claim 9. The calculation of the magnetic field in the measurement area may be performed by the constant magnetic field of the first direction side i level (i = 1, 2), which is the magnetic field in the first direction, and the second magnetic field, which is the magnetic field in the second direction. Each combination of the direction-side j-th level (j = 1, 2) constant magnetic field and the magnetization value when the magnetic field in the first direction and the magnetic field in the second direction are generated is Calculating the magnetic field of the measurement area based on the filling.
The magnetic field measurement method according to claim 10.

However, the magnetic field of the measurement area is C = (C _x , C _y , C _z ), and x, y, z are space coordinates of the first direction, the second direction, and the third direction, respectively. M _x ij is a magnetization value when a constant magnetic field at the first direction side level i and a constant magnetic field at the second direction side level j are generated, and a and c are constants and A ₁₀ f _i is a constant magnetic field at the first direction side i level, and A ₂₀ g _j is a constant magnetic field at the second direction side j level. 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, and the second direction side first level constant field, and One of the constant magnetic fields on the second direction side 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 for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A first magnetic field generator for applying a magnetic field in the first direction to the medium;
A second magnetic field generator applying a magnetic field in the second direction to the medium;
A magnetic field measurement apparatus comprising a third magnetic field generator for applying a magnetic field in the third direction to the medium is a magnetic field measurement method for measuring the magnetic field in the measurement area,
Generating, on the first magnetic field generator, a first magnetic field on the first direction side as a magnetic field in the first direction;
A first step of calculating a magnetic field of the measurement area as an original magnetic field using a detection result of the light detector and a magnetic field in the first direction;
A second step of arranging an object to be measured in the measurement area;
A third step of generating a magnetic field of a difference between a target magnetic field, which is a magnetic field to be formed in the measurement area, and the original magnetic field in the first magnetic field generator, the second magnetic field generator and the third magnetic field generator; ,
A fourth step of measuring a magnetic field generated by the object to be measured using a detection result of the light detector during a period in which 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 for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A first magnetic field generator for applying a magnetic field in the first direction to the medium;
A second magnetic field generator applying a magnetic field in the second direction to the medium;
A magnetic field measurement apparatus comprising a third magnetic field generator for applying a magnetic field in the third direction to the medium is a magnetic field measurement method for measuring the magnetic field in the measurement area,
Generating, on the first magnetic field generator, a first magnetic field on the first direction side as a magnetic field in the first direction;
A first step of calculating a magnetic field of the measurement area as an original magnetic field using a detection result of the light detector and a magnetic field in the first direction;
A second step of arranging an object to be measured in the measurement area;
The first magnetic field is generated by applying a constant magnetic field obtained by adding a component in the first direction of the magnetic field in the first direction on the first direction side to a constant magnetic field on the first direction side. The second magnetic field generator generates a magnetic field of the second direction component of the difference magnetic field, and the third magnetic field generator generates a magnetic field of the third direction component of the difference magnetic field. The third step,
During the period in which the third step is performed and the second step is completed, the magnetic field generated by the object to be measured is detected using the detection result of the light detector and the constant magnetic field on the first direction side fourth level. And a fourth step of measuring the magnetic field. The first direction, the second direction, and the third direction are orthogonal to each other,
A light source for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A first magnetic field generator that applies a magnetic field in the first direction to the measurement area;
In the first magnetic field generator, as the magnetic field in the first direction, a constant magnetic field in the first direction side first level, a constant magnetic field in the first direction side second level, and the first direction side third level An arithmetic control unit for generating a constant magnetic field of the above-mentioned, and calculating the magnetic field of the measurement area using the detection result of the light detector 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 for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A second magnetic field generator applying a magnetic field in the second direction to the measurement area;
In the second magnetic field generator, as the magnetic field in the second direction, the constant magnetic field in the second direction side first level, the constant magnetic field in the second direction side second level, and the second direction side third level An arithmetic control unit that generates a constant magnetic field of the above-mentioned range, and using the detection result of the light detector and the magnetic field in the second direction to calculate the magnetic field in the measurement area;
Magnetic field measuring device equipped with The first direction, the second direction, and the third direction are orthogonal to each other,
A light source for emitting light,
A medium through which the light passes along the third direction to change an optical characteristic according to a magnetic field of a measurement area;
A photodetector for detecting the optical characteristic;
A first magnetic field generator that applies a magnetic field in the first direction to the measurement area;
A second magnetic field generator applying a magnetic field in the second direction to the measurement area;
Generating, in the first magnetic field generator, a constant magnetic field of the first direction side first level and a constant magnetic field of the first direction side second level as the magnetic field in the first direction;
Generating, on the second magnetic field generator, a constant magnetic field on the second direction side first level and a constant magnetic field on the second direction side second level as the magnetic field in the second direction;
Calculating the magnetic field of the measurement area using the detection result of the light detector, the magnetic field in the first direction, and the magnetic field in the second direction;
Magnetic field measuring device equipped with

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