JP2012163393A - Magnetic field measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology which improves measurement accuracy of a magnetic field by controlling temperature of each cell in a magnetic field measurement device for measuring the magnetic field by lining up a plurality of cells.SOLUTION: The magnetic field measurement device includes: a cell array having the plurality of cells containing a plurality of atoms to be excited by pump light; magnetic field detection sections for exciting the atoms in the cells by irradiating each cell with the pump light, and detecting the magnetic fields in each cell by detecting probe light which is penetrated through each cell; temperature control sections for controlling the temperature of each cell in accordance with input control values; and a controller for carrying out a first process in which the temperature of each cell is adjusted so that detection results of the magnetic field of each cell to be detected in the magnetic field detection sections at the time when a prescribed magnetic field is impressed to the cell array become a reference value, and control values showing the temperature of each cell when becoming the reference value are stored in a storage section for every cell as temperature information, and for carrying out a second process in place of the first process, in which the control value based on the temperature information in the storage section is inputted to the temperature control section and the result detected by the magnetic field detection section is outputted.

Description

  The present invention relates to a magnetic field measurement apparatus.

  Magnetic sensors using optical pumping are used in biomagnetic measuring devices that detect magnetic fields emitted from the brain, heart, etc. of living bodies. As such a magnetic sensor, each cell in which gas is sealed is irradiated so that pump light having a circularly polarized component and probe light having a linearly polarized component are orthogonal to each other, and a magnetic field emitted from a living body is generated by the probe light. There is something to detect. Patent Document 1 below discloses such an optical pumping atomic magnetometer.

JP 2009-236599 A

By the way, when measuring a wide part of a living body by arranging a plurality of independent cells, if the atoms and gases in each cell are not uniform, the magnetic field sensitivity varies. Magnetic field sensitivity increases as the number of optically pumped atoms increases. Therefore, by adjusting the cell temperature, the atomic density in the cell can be increased to increase the magnetic field sensitivity, but the magnetic field sensitivity of each cell is uniform. Otherwise, the magnetic field cannot be measured accurately.
The present invention provides a technique for improving the measurement accuracy of a magnetic field by controlling the temperature of the cell in a magnetic field measurement apparatus that measures a magnetic field by arranging a plurality of cells.

  A magnetic field measurement apparatus according to the present invention includes a cell array having a plurality of cells including therein an atomic group composed of a plurality of atoms excited by pump light, and irradiating each cell of the cell array with pump light. Magnetic field detection means for detecting the magnetic field in each cell by exciting the atoms in each cell and detecting the probe light transmitted through each cell, and the control provided corresponding to each cell in the cell array The temperature control means for controlling the temperature of each cell according to the value, the storage means for storing temperature information for each cell, and the control for applying a constant magnetic field to the cell array and inputting it to the temperature control means The control value when the detection result of the magnetic field of each cell detected by the magnetic field detection means by changing the value becomes a predetermined reference value is specified for each cell, and specified. The first processing for storing the control value for each cell as the temperature information in the storage means, and the control value based on the temperature information stored in the storage means instead of the first processing And a control means for performing a second process of inputting to the temperature control means and outputting the detection result by the magnetic field detection means. According to this configuration, the temperature of each cell is controlled so that the sensitivity of each cell becomes uniform, and the measurement accuracy of the magnetic field can be improved.

  Moreover, the magnetic field measurement apparatus according to the present invention includes a measurement unit that measures the temperature in the magnetic field measurement apparatus, the storage unit stores temperature information for each cell for each temperature, and the control unit includes: In the first process, the control value for each cell is specified for each temperature measured by the measuring means, the specified control value is stored in the storage means as the temperature information, and in the second process, It is good also as reading the said temperature information for every said cell according to the temperature measured by the said measurement means from the said memory | storage means, and inputting the said control value based on the said temperature information to the said temperature control means. According to this configuration, since the temperature of each cell is controlled according to the temperature, a certain measurement accuracy can be obtained even if the temperature changes.

  Moreover, the magnetic field measurement apparatus according to the present invention includes an acquisition unit that acquires information indicating the light amount of the pump light in the magnetic field measurement device, and the storage unit is configured to change the temperature for each cell for each light amount of the pump light. The information is stored, and the control means specifies the control value for each cell for each light amount indicated by the information acquired by the acquisition means in the first process, and the specified control value is set as the temperature information. In the second process, the temperature information for each cell corresponding to the amount of light indicated by the information acquired by the acquisition unit is read from the storage unit and based on the temperature information. The control value may be input to the temperature control means. According to this configuration, since the temperature of each cell is controlled according to the light amount of the pump light, it is possible to obtain a certain measurement accuracy even if the light amount of the pump light changes.

  In the magnetic field measurement apparatus according to the present invention, the control unit of the magnetic field measurement apparatus may obtain the reference value based on a detection result of the magnetic field of each cell in the first process. According to this configuration, the temperature of each cell can be controlled based on the detection result of the magnetic field in each cell.

It is a figure which shows the structural example of the magnetic field measuring device which concerns on embodiment. It is a figure explaining the pump light and probe light which irradiate to the magnetic sensor array which concerns on embodiment. (A) is a figure explaining the pump light irradiation part which concerns on embodiment. (B) is a figure explaining the probe light irradiation part which concerns on embodiment. It is a figure which shows the relationship between the detection result and control value of the magnetic field of each cell which concern on embodiment. It is a figure which shows the example of the temperature information which concerns on embodiment. It is a figure which shows the example of the temperature information which concerns on a modification (1).

<Embodiment>
(Constitution)
FIG. 1 is a block diagram showing a configuration of a magnetic field measurement apparatus according to an embodiment of the present invention. The magnetic field measurement apparatus 1 includes a cell array 10, a temperature control unit 20 that controls the temperature of the cell array 10, a magnetic field detection unit 30 that detects a magnetic field in the cell array 10, a control unit 40, an operation unit 50, and a storage unit 60.

  The cell array 10 is configured by arranging a plurality of cells (10a, 10b, 10c, 10d) in a line. Each cell is made of a material such as glass that transmits light, and is an independent object having a cubic shape including predetermined atoms therein. Predetermined atoms in each cell are excited by circularly polarized light and spin-polarized atoms. For example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) And alkali metals such as francium (Fr). Each cell may contain a buffer gas such as helium (He) or nitrogen (N) in addition to these alkali metal atoms. The alkali metal atoms may be in a gaseous state when detecting magnetism, and may not always be in a gaseous state. In the present embodiment, four cells of the cell array 10 are arranged in a line. However, the number of cells may be plural, and may be plural. In this embodiment, an example is used in which each cell is an independent object.However, for example, the cell may be formed by partitioning a rectangular parallelepiped so as not to be affected by adjacent cells, and the influence of adjacent cells may be reduced. Each cell may be communicated by a hole provided in a part of the partition between the cells so as not to be received. In short, the cell array 10 only needs to have a plurality of partitioned spaces. Moreover, although the shape of the cell of this embodiment is a cube shape, the shape of a cell is not restricted to this shape.

  The temperature control unit 20 has a temperature control unit (20a, 20b, 20c, 20d) corresponding to each cell. Each temperature control unit is an example of temperature control means, and is provided outside the cell so as to correspond to each cell (10a, 10b, 10c, 10d), and a heating / cooling device for heating / cooling the cell is provided. The temperature of each cell is adjusted by controlling the heating and cooling device according to the control value (power value) input by the control unit 40.

  The magnetic field detection unit 30 includes magnetic field detection units (30a, 30b, 30c, 30d) that detect magnetic fields in the cells (10a, 10b, 10c, 10d). Each magnetic field detection unit is an example of a magnetic field detection means, and pump light for spin-polarizing atoms in each cell in the same direction is directed from the top surface to the bottom surface of each cell indicated by the broken-line arrows in FIG. -Pump light irradiation unit (not shown) for irradiation in the -z-axis direction) and probe light for detecting the magnetic field in each cell are irradiated in the side surface direction (-y-axis direction) of each cell indicated by the solid line arrow in FIG. A probe light irradiating section (not shown) for detecting the probe light transmitted through each cell and detecting a magnetic field in each cell by detecting the probe light. Here, the pump light irradiation unit, the probe light irradiation unit, and the detection unit will be described.

  FIG. 3A is a diagram showing the pump light irradiation units (310a, 310b, 310c, 310d) and the respective cells shown in FIG. As shown to Fig.3 (a), each pump light irradiation part is provided for every cell. Each of the pump light irradiation units has a light source that outputs laser light having a circularly polarized component as pump light. Each light source irradiates a corresponding cell with pump light having a circularly polarized component as indicated by a dashed arrow. When the pump light irradiated from each pump light irradiation unit enters each cell, atoms in each cell are spin-polarized in the same direction by the pump light.

  FIG. 3B is a diagram illustrating each cell, the probe light irradiation unit (320a, 320b, 320c, 320d), and the detection unit (330a, 330b, 330c, 330d) illustrated in FIG. As shown in FIG. 3B, each probe light irradiation unit and each detection unit are provided for each cell. Each probe light irradiation unit has a light source that outputs laser light having a linearly polarized light component as probe light. Each light source irradiates a corresponding cell with probe light having a linearly polarized light component. The probe light irradiated to each cell is incident on each cell, and the incident light is rotated by the polarization plane according to the rotational force of the atoms precessed by the influence of the magnetic field in each cell. Transparent. Each detector has a photodetector, and separates the probe light transmitted through each cell into a P-polarized component and an S-polarized component and receives the light with each photodetector. Each detection unit analyzes an electrical signal corresponding to the amount of light received by each photodetector, obtains the rotation angle of the polarization plane of the probe light received for each cell, and detects the magnetic field value corresponding to the rotation angle. In this example, the magnetic field in the x-axis direction shown in FIG. 3B is detected.

  Returning to FIG. 1, the description of the configuration is continued. The control unit 40 is an example of a control unit, and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU executes a control program stored in advance in the ROM, thereby performing a calibration process as a first process and a magnetic field detection process for detecting a magnetic field emitted from a living body as a second process in accordance with a user operation. Do.

  The controller 40 uses a coil (not shown) provided for each cell as a calibration process, applies a constant magnetic field in the x-axis direction of FIG. Each probe light irradiation unit and each detection unit are controlled to detect a magnetic field in each cell (10a, 10b, 10c, 10d). Then, the control value for adjusting the temperature of each cell is changed and input to the temperature control unit 20 so that the detection result of the magnetic field in each cell becomes a predetermined reference value, and the detection result of the reference value is obtained. A control value is specified for each cell, and the control value for each specified cell is stored in the storage unit 60 as temperature information. In the present embodiment, a value corresponding to the value of the applied magnetic field is used as an example of the reference value. Moreover, the control part 40 inputs into the temperature control unit 20 the control value based on the temperature information of each cell memorize | stored in the memory | storage part 60 as a magnetic field detection process, and each pump light irradiation part, each probe light irradiation part, and each The detection unit is controlled to detect a magnetic field emitted from the living body and to output a detection result.

  The operation unit 50 includes operation means such as an operation switch that accepts an instruction operation for calibration and an operation switch that accepts an instruction to measure a magnetic field of a living body, and sends an operation signal indicating the operated content to the control unit 40. The storage unit 60 is an example of a storage unit, and is configured by a non-volatile storage medium. Under the control of the control unit 40, the control value of each temperature control unit for each cell specified by the calibration process is used as temperature information. Remember.

(Operation example)
Next, an operation example of the magnetic field measurement apparatus 1 will be described. The control unit 40 of the magnetic field measurement apparatus 1 has a circularly polarized component from each of the pump light irradiation units (310a, 310b, 310c, 310d) when an operation for instructing the calibration process is performed via the operation unit 50. While irradiating each cell (10a, 10b, 10c, 10d) of the cell array 10 with pump light, probe light having a linearly polarized light component from each probe light irradiation unit (320a, 320b, 320c, 320d) is supplied to each cell. Irradiation is performed so as to be orthogonal to the pump light irradiated to (10a, 10b, 10c, 10d) in the cell. And the control part 40 applies the fixed magnetic field of the direction orthogonal to pump light and probe light using the coil which is not shown in figure.

  Atoms in each cell are excited by pump light and spin-polarized in the same direction, and perform precession by changing the direction of the magnetic moment according to the applied magnetic field. The probe light is incident on each cell, and passes through each cell by rotating the polarization plane according to the magnitude of the magnetic field received by the atoms in each cell. The probe light transmitted through each cell is received by the detection unit corresponding to the cell. Each detection unit (330a, 330b, 330c, 330d) analyzes an electrical signal corresponding to the light amount of the probe light to determine the rotation angle of the polarization plane of the probe light, detects the magnetic field in the corresponding cell, and controls the control unit 40. The detection result is output to.

  The control unit 40 changes the control value input to the temperature control unit corresponding to the cell until the detection result of the reference value corresponding to the applied magnetic field value is obtained for each cell, and the reference value detection result is obtained. The control value when specified is specified. Then, the control unit 40 stores the control value specified for each cell in the storage unit 60 in association with the cell number for identifying the cell as temperature information. For example, when the detection result of the magnetic field with respect to the control value of the temperature control unit for each cell is represented by the waveform shown in FIG. 4, as the control value of each cell (10a, 10b, 10c, 10d) whose detection result is the reference value, P2, P4, P1, and P3 are specified. In this case, as shown in FIG. 5, the storage unit 60 stores temperature control information 150 that associates a cell number for identifying each cell with temperature information corresponding to the cell.

Next, an operation example of the magnetic field measurement process will be described. In the magnetic field measurement apparatus 1, when an instruction operation of a magnetic field measurement process for measuring a magnetic field from a living body is performed via the operation unit 50, the control unit 40 reads the temperature control information 150 for each cell from the storage unit 60. The control unit 40 inputs a control value based on the temperature information stored in the temperature control information 150 to the temperature control unit (20a, 20b, 20c, 20d) corresponding to each cell number of the temperature control information 150. Each temperature control unit controls the heating and cooling device according to the control value input from the control unit 40. The control unit 40 irradiates each cell (10a, 10b, 10c, 10d) of the cell array 10 with pump light having a circularly polarized component from each of the pump light irradiation units (310a, 310b, 310c, 310d). The probe light having a linearly polarized light component is irradiated from each probe light irradiation unit (320a, 320b, 320c, 320d) so as to be orthogonal to the pump light.
The atoms in each cell are spin-polarized in the same direction by irradiation with pump light, and precess according to the magnetic field from the living body. The probe light enters each cell, and the plane of polarization is rotated according to the magnitude of the magnetic field received by the atoms in the cell, and passes through each cell. The probe light transmitted through each cell is received by the detection unit corresponding to each cell. Each detection unit (330a, 330b, 330c, 330d) analyzes an electrical signal corresponding to the light amount of the probe light to obtain a rotation angle of the polarization plane of the probe light, calculates a magnetic field value from the rotation angle, and controls the control unit 40. Output to. The control unit 40 outputs information indicating the value of each magnetic field output for each detection unit to a display device or the like (not shown).

  In the example of the present embodiment, the calibration process is performed in the state of the cell array, and the control value for controlling the temperature of each cell is set so that the detected value of the magnetic field detected at the position of each cell becomes the reference value. . Therefore, when measuring the magnetic field from a living body, the cells can be kept warm so that the sensitivity of each cell becomes uniform, and the measurement accuracy of the magnetic field can be improved.

<Modification>
The present invention is not limited to the above-described embodiment, and may be carried out by being modified as follows. Further, the following modifications may be combined.

(1) In the above-described embodiment, the control value of the temperature control unit for each cell is stored together with the information for identifying the cell. However, the temperature and control value of the place where the magnetic field measurement apparatus 1 is installed are stored. You may make it memorize | store. In this case, as an example of the measuring unit, a temperature measuring unit that measures the temperature may be provided in the magnetic field measuring device 1, or the magnetic field measuring device 1 may acquire temperature information from an external device by communication. In addition, an operation unit for inputting the temperature may be provided in the magnetic field measurement apparatus 1 so that the temperature information is acquired by a user input operation. In this modification, in the calibration process, the control unit 40 of the magnetic field measurement apparatus 1 stores in the storage unit 60 temperature information that associates the measured temperature with the control value of the temperature control unit for each cell. For example, for each temperature in the range of 15 ° C. to 30 ° C., the magnetic field in each cell is detected by the same method as in the embodiment, and input to the temperature control unit so that the detection result of the magnetic field in each cell becomes a reference value. By changing the control value, the control value when the reference value detection result is obtained is specified for each cell. And the control part 40 memorize | stores the control value specified about each cell in the memory | storage part 60 as temperature information, as shown in FIG. In addition, when starting the magnetic field measurement process, the control unit 40 acquires temperature information at the installation location of the magnetic field measurement device 1 and reads temperature information corresponding to the temperature of the acquired temperature information from the storage unit 60. The control unit 40 inputs a control value based on the read temperature information to the temperature control unit corresponding to each cell, and detects the magnetic field generated from the living body by the same method as in the embodiment.

(2) In the modified example (1) described above, the example in which the control value of the temperature control unit corresponding to each cell is stored for each temperature has been described. However, not only the temperature but also the amount of pump light irradiated to each cell You may make it memorize | store the control value of the temperature control part corresponding to each cell for every combination of a light quantity and a wavelength for every wavelength. In this case, as an example of the acquisition unit, an operation unit for the user to input information indicating the light amount and wavelength of the pump light is provided in the magnetic field measuring apparatus 1, and information indicating the light amount and wavelength is acquired by the user's input operation. You may make it do. For example, in the calibration process, when setting the control value of the temperature control unit for each cell according to the air temperature and the light amount, the control unit 40 determines the magnetic field in each cell for each air temperature and for each light amount of the pump light. Similarly, the control value of the temperature control unit of the cell is changed so that the detection result of the magnetic field for each cell becomes the reference value, and the control value and the cell when the detection result of the reference value is obtained are identified. The information is stored as temperature information together with the temperature and light quantity. When starting the magnetic field measurement process, the control unit 40 acquires information indicating the temperature at the installation location of the magnetic field measurement device 1 and the light amount of the pump light by an input operation by the user, and corresponds to the acquired temperature and light amount. The control value corresponding to each cell is read from the temperature information, and the read control value is input to each temperature control unit.

(3) In the embodiment and the modification described above, the example in which the light source of the pump light and the probe light is provided for each cell has been described. However, the pump light and the probe light from one light source are respectively used by using a branch coupler or the like. You may make it distribute and irradiate to each cell. In addition, for each cell, a single light source that serves as both pump light and probe light may be used to pump atoms in the cell and detect the probe light transmitted through the cell.

(4) In the above-described embodiment and modification, the example in which the value corresponding to the applied magnetic field is used as the reference value has been described. However, the reference value is obtained from the detection result of the magnetic field in each cell detected in the calibration process. You may make it ask. For example, among the detection values of the magnetic field in each cell, the detection value closest to the value corresponding to the applied magnetic field is specified for each cell, and the average value of each specified detection value or the minimum value of each specified detection value Or the mode value may be used as the reference value. Even if the detected value of each cell detected in the calibration process does not match the reference value, the detected value is detected if the difference between the detected value and the reference value is within a predetermined value range. The control value of the temperature control unit at this time may be stored as a control value corresponding to the cell.

(5) In the above-described embodiment, the example in which the calibration process and the magnetic field detection process are selectively performed according to the operation of the operation unit 50 by the user has been described. For example, the magnetic field detection process may be automatically started after the calibration process.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic field measuring apparatus, 10 ... Cell array, 10a, 10b, 10c, 10d ... Cell, 20 ... Temperature control unit, 20a, 20b, 20c, 20d ... Temperature control part, 30. .. Magnetic field detection unit, 30a, 30b, 30c, 30d ... Magnetic field detection unit, 40 ... Control unit, 50 ... Operation unit, 60 ... Storage unit, 310a, 310b, 310c, 310d ... Pump light irradiation unit, 320a, 320b, 320c, 320d ... Probe light irradiation unit, 330a, 330b, 330c, 330d ... detection unit

Claims (4)

A cell array having a plurality of cells including therein an atomic group composed of a plurality of atoms excited by pump light;
A magnetic field detection means for irradiating each cell of the cell array with pump light to excite the atoms in each cell, detecting probe light transmitted through each cell, and detecting a magnetic field in each cell;
Temperature control means provided corresponding to each cell of the cell array and controlling the temperature of each cell according to an input control value;
Storage means for storing temperature information for each cell;
Applying a constant magnetic field to the cell array, changing the control value input to the temperature control means, and detecting the magnetic field of each cell detected by the magnetic field detection means with a predetermined reference value Instead of the first process for specifying the control value for each cell and storing the control value for each specified cell in the storage means as the temperature information, Control means for performing a second process of inputting the control value based on the temperature information stored in the storage means to the temperature control means and outputting a detection result by the magnetic field detection means. Magnetic field measuring device. Equipped with measuring means to measure the temperature,
The storage means stores temperature information for each cell for each temperature,
In the first process, the control unit specifies the control value for each cell for each temperature measured by the measurement unit, stores the specified control value in the storage unit as the temperature information, and In the second process, the temperature information for each of the cells corresponding to the temperature measured by the measuring unit is read from the storage unit, and the control value based on the temperature information is input to the temperature control unit. The magnetic field measurement apparatus according to claim 1. An acquisition means for acquiring information indicating the amount of the pump light;
The storage means stores temperature information for each cell for each light amount of the pump light,
In the first process, the control unit specifies the control value for each cell for each light amount indicated by the information acquired by the acquisition unit, and stores the specified control value as the temperature information in the storage unit. In the second process, the temperature information for each cell corresponding to the light quantity indicated by the information acquired by the acquisition unit is read from the storage unit, and the control value based on the temperature information is read out from the storage unit. The magnetic field measurement apparatus according to claim 1, wherein the magnetic field measurement apparatus inputs the temperature control means.   4. The magnetic field measurement apparatus according to claim 1, wherein the control unit obtains the reference value based on a detection result of the magnetic field of each cell in the first process. 5.

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