Optically excited magnetic sensor module

Abstract

An optically excited magnetic sensor module is provided that can apply a uniform magnetic field to a cell in which an alkali metal is sealed. [Solution] The sensor module (1) includes a cell (11) in which an alkali metal is sealed, and a coil unit that generates a magnetic field that acts on the cell (11). The coil unit includes a support frame (30) formed in a rectangular parallelepiped shape and arranged to surround the cell (11), and a plurality of coils (40) provided on the support frame (30). The support frame (30) includes a pair of first surfaces (31A, 31B) facing each other in the X direction and a pair of second surfaces (32A, 32B) facing each other in the Y direction perpendicular to the X direction. The plurality of coils (40) include a pair of first coils (41A, 41B). The first coil (41A) extends from the first surface (31A) across the second surfaces (32A, 32B), and the first coil (41B) extends from the first surface (31B) across one and the other of the second surfaces (32A, 32B).

Description

[Technical Field]

[0001] The present invention relates to an optically excited magnetic sensor module. [Background technology]

[0002] An example of an optically excited magnetic sensor is the optically pumped magnetic sensor described in Patent Document 1. In the magnetic sensor described in Patent Document 1, multiple coils are provided on the outer surface of a cell in which an alkali metal is sealed. The multiple coils are composed of a pair of coils arranged on the X-axis with the cell sandwiched between them, a pair of coils arranged on the Y-axis with the cell sandwiched between them, and a pair of coils arranged on the Z-axis with the cell sandwiched between them. These coils generate an AC magnetic field that cancels out the magnetic field in the cell region. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-217690 Summary of the Invention [Problem to be solved by the invention]

[0004] In an optically excited magnetic sensor, a coil generates a magnetic field that acts on a cell, and a probe light is used to detect changes in the magnetic field within the cell. In this case, to ensure detection accuracy, it is preferable that the magnetic field generated within the cell by the coil is uniform.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optically excited magnetic sensor module that can apply a uniform magnetic field to a cell in which an alkali metal is sealed. [Means for solving the problem]

[0006] The optically excited magnetic sensor module of the present invention is [1] "an optically excited magnetic sensor module comprising: a cell in which an alkali metal is sealed; and a coil unit that generates a magnetic field acting on the cell, the coil unit being formed in a shape along a rectangular parallelepiped; a support frame body arranged to surround the cell; and a plurality of coils provided on the support frame body, the support frame body including a pair of first surfaces facing each other in a first direction and a pair of second surfaces facing each other in a second direction perpendicular to the first direction, the plurality of coils including a pair of first coils, one of the pair of first coils extending from one of the pair of first surfaces across one and the other of the pair of second surfaces, and the other of the pair of first coils extending from the other of the pair of first surfaces across one and the other of the pair of second surfaces."

[0007] In this photo-excited magnetic sensor module, one of a pair of first coils included in the multiple coils extends from one of a pair of first surfaces of the support frame across one and the other of a pair of second surfaces, and the other of the pair of first coils extends from the other of the pair of first surfaces of the support frame across one and the other of the pair of second surfaces. This allows the magnetic field generated in the cell by the first coil to be uniform. Therefore, this photo-excited magnetic sensor module allows a uniform magnetic field to act on the cell in which the alkali metal is sealed. Furthermore, the coil unit includes a support frame formed in a shape along a rectangular parallelepiped and arranged to surround the cell, and multiple coils provided on the support frame. By providing multiple coils on the support frame formed in a shape along a rectangular parallelepiped, the coil unit can be conveniently arranged inside the coil unit (support frame).

[0008] The optically excited magnetic sensor module of the present invention may be [2] "the optically excited magnetic sensor module according to [1], wherein the plurality of coils further include a pair of second coils, one of which extends from one of the pair of second surfaces across one and the other of the pair of first surfaces, and the other of which extends from the other of the pair of second surfaces across one and the other of the pair of first surfaces." In this case, the magnetic field generated in the cell by the second coil can be made uniform.

[0009] The optically excited magnetic sensor module of the present invention may be [3] "the optically excited magnetic sensor module according to [1] or [2], wherein the plurality of coils further include a pair of third coils, each of which extends across the pair of first surfaces and the pair of second surfaces so as to surround the support frame, and the pair of third coils face each other in a third direction perpendicular to the first direction and the second direction." In this case, the magnetic field generated in the cell by the third coil can be made uniform.

[0010] The optically excited magnetic sensor module of the present invention may be [4] "the optically excited magnetic sensor module according to [3], wherein the support frame has a shape in which the length along the third direction is longer than the length along the first direction and the length along the second direction." In this case, the magnetic field generated within the cell by the third coil can be made uniform.

[0011] The photo-excited magnetic sensor module of the present invention may be [5] "the photo-excited magnetic sensor module according to any one of [1] to [4], wherein the support frame and the plurality of coils are formed of a flexible circuit board." In this case, the support frame and the plurality of coils can be configured to be bendable.

[0012] The optically excited magnetic sensor module of the present invention may be [6] "an optically excited magnetic sensor module according to any one of [1] to [5], wherein D / L is 0.2 or more and 0.8 or less, where D is the distance between the pair of first coils on the pair of second surfaces along the first direction and L is the length of the support frame along the first direction." In this case, the magnetic field generated in the cell by the first coil can be made more uniform.

[0013] The photo-excited magnetic sensor module of the present invention may be [7] "the photo-excited magnetic sensor module according to any one of [1] to [6], further comprising a cell case that houses the cell, and the support frame is disposed outside the cell case so as to surround the cell via the cell case." In this case, for example, heat insulating properties can be improved by disposing a heat insulating material inside the cell case.

[0014] The photo-excited magnetic sensor module of the present invention may be [8] "the photo-excited magnetic sensor module according to any one of [1] to [7], wherein the pair of first coils are configured by a single conductive path." In this case, the configuration of the first coils can be simplified.

[0015] The optically excited magnetic sensor module of the present invention may be [9] "an optically excited magnetic sensor module according to [5], wherein the support frame and the plurality of coils are formed by bending the flexible circuit board, the flexible circuit board having a plurality of planar portions corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, and a light passing opening through which at least the pump light passes is formed in the planar portion of the plurality of planar portions corresponding to the pair of first surfaces, and one of the pair of second surfaces is formed by overlapping two planar portions of the flexible circuit board, each of which has a positioning opening formed therein, and the two planar portions are overlapped so that the positioning openings of the two planar portions overlap with each other." In this case, the two planar portions can be aligned by overlapping the two planar portions so that the positioning openings overlap with each other.

[0016] The photo-excited magnetic sensor module of the present invention may be

[10] "the photo-excited magnetic sensor module according to [5] or [9], wherein the support frame and the plurality of coils are formed by bending the flexible circuit board, the flexible circuit board has a plurality of flat portions corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, respectively, and a long hole extending along the boundary line is formed at the boundary between the plurality of flat portions." In this case, the formation of the long hole extending along the boundary line makes it possible to easily bend the flexible circuit board at the boundary line.

[0017] The optically excited magnetic sensor module of the present invention may be

[11] "the optically excited magnetic sensor module according to [5], [9] or

[10] , wherein the flexible circuit board has a lead-out portion drawn in a direction away from the support frame, and the lead-out portion has pad portions electrically connected to the pair of first coils." In this case, the lead-out portion can separate the pad portions from the cell, and the magnetic field generated in the pad portions can be prevented from affecting the magnetic field in the cell. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an optically excited magnetic sensor module that can apply a uniform magnetic field to a cell in which an alkali metal is sealed. [Brief explanation of the drawings]

[0019] [Figure 1] 10A and 10B are diagrams for explaining the operation of the optically excited magnetic sensor module. [Figure 2] FIG. 2A is a perspective view of the optically excited magnetic sensor module, and FIG. 2B is a perspective view of the optically excited magnetic sensor module with the outer cover removed. [Figure 3] FIG. 3 is a perspective view of the optically excited magnetic sensor module with the casing cover of the casing removed from FIG. 2(b). [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] 4 is a plan view of the photo-excited magnetic sensor module in a state where a case lid of the cell case is removed from FIG. 3. FIG. [Figure 6] FIG. 2 is a diagram showing a coil unit. [Figure 7] FIG. 2 is a diagram illustrating a first coil. [Figure 8] FIG. 4 is a diagram illustrating a second coil. [Figure 9] FIG. 10 is a diagram illustrating a third coil. [Figure 10] FIG. 2 is a diagram illustrating a first coil. [Figure 11] FIG. 4 is a diagram illustrating a second coil. [Figure 12] FIG. 10 is a diagram illustrating a third coil. [Figure 13] FIG. 10(a) is a diagram illustrating a coil of a comparative example, and FIG. 10(b) is a diagram illustrating a first coil of an embodiment. [Figure 14] 10(a) is a table showing the calculation results for the comparative example, and FIG. 10(b) is a table showing the calculation results for the example. [Figure 15] 10A and 10B are diagrams for explaining the operation of an optically excited magnetic sensor module according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0021] 1 to 5 is an optically pumped magnetometer (OPM) and is used, for example, to measure biomagnetic fields. For example, the sensor module 1 can be used as a magnetoencephalograph that measures magnetic fields generated in the brain, or a magnetocardiograph or magnetospinograph that measures magnetic fields generated in the heart or spinal cord. [Sensor module configuration]

[0022] 1 to 5, the sensor module 1 includes a cell unit 2, a housing 3 that houses the cell unit 2, and an outer cover 4 that covers the outer surface of the housing 3. The cell unit 2 has a cell 11, a heater 12, a heat insulating member 13, and a cell case 14, and is at least partially surrounded by a coil unit 15. The sensor module 1 further includes a light source 21, a lens 22, a mirror 23, a quarter-wave plate 24, a photodetector 25, a connector member 26, and a connector cover 27. [Sensor module operation]

[0023] The operation of the sensor module 1 (the principle of detecting changes in a magnetic field) will be described with reference to FIG. 1. During measurement, the sensor module 1 (cell 11) is placed near the object to be measured. The cell 11 is filled with a gas GS containing an alkali metal. During measurement, the alkali metal in the cell 11 is heated by a heater 12, and the cell 11 is filled with alkali metal vapor. In this state, laser light L output from a light source 21 passes through the cell 11. The laser light L is circularly polarized by a quarter-wave plate 24 and enters the cell 11. This circularly polarized laser light L optically pumps (optically excites) the alkali metal vapor in the cell 11 to make it spin-polarized. In other words, the laser light L functions as pump light that optically pumps the alkali metal vapor in the cell 11 to make it spin-polarized.

[0024] The laser light L that passes through the cell 11 is detected by the photodetector 25. At this time, the intensity of the laser light L detected by the photodetector 25 (i.e., the degree to which the laser light L is absorbed by the alkali metal vapor in the cell 11) changes depending on the spin polarization state of the alkali metal vapor in the cell 11. Here, the spin polarization state of the alkali metal vapor in the cell 11 changes under the influence of the magnetic field of the measurement target. Therefore, changes in the magnetic field of the measurement target can be detected based on the detected intensity of the laser light L. In this way, the laser light L also functions as probe light for detecting the spin polarization state of the alkali metal vapor in the cell 11. In this case, the sensor module 1 is a single-laser sensor module in which the laser light L serves as both pump light and probe light. [Configuration of each part of the sensor module]

[0025] The configuration of each part of the sensor module 1 will be described with reference to Figures 2 to 5. The following description will be made with reference to the X direction (first direction), the Y direction (second direction) perpendicular to the X direction, and the Z direction (third direction) perpendicular to both the X and Y directions shown in Figures 2 to 5. The housing 3 is formed into a substantially rectangular parallelepiped shape from, for example, a resin material, and has a housing main body 3a and a housing lid 3b. Figure 2(b) shows a state in which the housing lid 3b is attached, and Figure 3 shows a state in which the housing lid 3b is removed.

[0026] 4 and 5, the housing 3 is provided with a cell unit arrangement section 3c in which the cell unit 2 is arranged, an optical member arrangement section 3f in which the light source 21, lens 22, and mirror 23 are arranged, and a photodetector arrangement section 3g in which the photodetector 25 is arranged. The optical member arrangement section 3f is provided with an optical path section 3h, which is a space through which the laser light L output from the light source 21 and directed toward the cell unit 2 travels. The photodetector arrangement section 3g is arranged on the opposite side of the cell unit arrangement section 3c from the optical path section 3h.

[0027] The light source 21 is, for example, a vertical cavity surface emitting laser, and outputs laser light L. In this example, the light source 21 is mounted on a connector member .

[0028] The lens 22 collimates the laser light L output from the light source 21. The mirror 23 reflects the laser light L collimated by the lens 22 toward the cell unit 2. The quarter-wave plate 24 is disposed between the mirror 23 and the cell unit 2. The quarter-wave plate 24 imparts a phase difference of π / 2 (=λ / 4) between the vertically polarized components of the incident light. The quarter-wave plate 24 converts the linearly polarized laser light L output from the light source 21 into circularly polarized light.

[0029] The cell unit 2 is arranged in the cell unit arrangement section 3c. The cell unit 2 has a cell 11 in which a gas GS containing an alkali metal is sealed. The cell unit 2 will be described in detail later. Circularly polarized laser light L converted by a quarter-wave plate 24 is incident on the cell unit 2. The laser light L incident on the cell unit 2 passes through the cell 11 and is emitted from the cell unit 2 toward the photodetector 25. In this example, the laser light L passes through the cell 11 along the X direction. The photodetector 25 is arranged in the photodetector arrangement section 3g. The photodetector 25 is, for example, a photodiode, and detects the laser light L that has passed through the cell unit 2.

[0030] The connector member 26 is provided on one side in the Z direction of the housing 3. The heater 12, the coil unit 15, the light source 21, and the photodetector 25 are electrically connected to the connector member 26, and the connector member 26 is used for electrically connecting these components to the outside. A connector cover 27 is detachably attached to the connector member 26. As shown in FIG. 2, the outer cover 4 is formed in a substantially rectangular parallelepiped shape, and covers the outer surface of the housing 3 except for the surface on the side where the connector cover 27 is arranged (one side in the Z direction). [Cell unit]

[0031] 3 to 5, the cell unit 2 will be described in detail. As described above, the cell unit 2 has a cell 11, a heater 12, a heat insulating member 13, and a cell case 14, and is at least partially surrounded by a coil unit 15. The cell 11, the heater 12, and the heat insulating member 13 are housed in the cell case 14, and the coil unit 15 is disposed outside the cell case 14.

[0032] The cell 11 has a main body 11a and a protruding portion 11b. The cell 11 is formed of a translucent material such as glass or silicon. The cell 11 is filled with a gas GS consisting of an alkali metal and an inert gas. The alkali metal filled in the cell 11 is, for example, one or more of potassium, lithium, sodium, rubidium, and cesium. The inert gas filled in the cell 11 is, for example, one or more of helium, neon, argon, krypton, xenon, nitrogen, and hydrogen. The main body 11a is, for example, a rectangular parallelepiped container portion. The protruding portion 11b is a tubular portion connected to the main body 11a, and is sealed off after being used as a passage for gas introduction and exhaust, such as for introducing the gas GS.

[0033] The heater 12 is disposed in a state of being thermally connected to the cell 11, and in this embodiment, is provided on the surface of the main body 11a of the cell 11 (in this example, the surface on one side in the Y direction). The heater 12 is formed, for example, in a sheet shape including a metal wire (resistor) that generates heat when electricity is applied. In this example, the heater 12 is formed including a titanium wire and is fixed to the cell 11 by an adhesive layer. The heater 12 generates heat when electricity is applied, thereby heating the cell 11.

[0034] The heat insulating member 13 is disposed within the cell case 14 so as to be positioned outside the cell 11. In this example, the heat insulating member 13 is composed of a plurality of plate-shaped members 13a. The plurality of plate-shaped members 13a are disposed to fill the space between the cell 11 and the cell case 14. More specifically, the plurality of plate-shaped members 13a are disposed in the space between the main body 11a of the cell 11 and the cell case 14 so as to fill as few gaps as possible except for the area of ​​the main body 11a through which the laser light L passes. In the space between the protrusion 11b of the cell 11 and the cell case 14, the plurality of plate-shaped members 13a are disposed so as to completely surround and fill the entire protrusion 11b while leaving an area spaced apart from the outer surface of the protrusion 11b of the cell 11. The plate-shaped members 13a are members whose heat insulating properties are enhanced, for example, by forming an air layer inside. The cell case 14 is formed, for example, in a substantially rectangular parallelepiped shape from a resin material, and includes a case main body 14a and a case lid 14b. Fig. 3 shows a state in which case lid 14b is attached, and Fig. 5 shows a state in which case lid 14b is removed. Note that hatching of plate-shaped member 13a is omitted in Fig. 4.

[0035] As shown in FIG. 5, the case body 14a has a pair of first walls 14c facing each other in the X direction and a pair of second walls 14d facing each other in the Z direction. A plurality of (two in this example) plate-like members 13a are disposed between each of the first walls 14c and the cell 11, and a plurality of (four in this example) plate-like members 13a are disposed between each of the second walls 14d and the cell 11. Although not shown, heat insulating members 13 (a plurality of plate-like members 13a) are also disposed between the cell 11 and a Y-direction wall (a wall facing the case lid 14b in the Y direction) of the case body 14a, and between the case lid 14b and the cell 11. Thus, in this example, the cell 11 is housed in the cell casing 14 with the heat insulating member 13 interposed between the cell 11 and the cell casing 14. As shown in Figure 4, one of the pair of first wall portions 14c has an opening 14e through which laser light L reflected by the mirror 23 and heading toward the cell 11 passes, and the other of the pair of first wall portions 14c has an opening 14f through which laser light L that has passed through the cell 11 passes.

[0036] 3, the coil unit 15 is disposed outside the cell case 14. The coil unit 15 is configured to include, for example, a plurality of coils, which generate a magnetic field that acts on the cell 11. In the sensor module 1, the coil unit 15 generates a magnetic field that acts on the cell 11, and the sensor module 1 detects changes in the magnetic field within the cell 11 using laser light L (probe light).

[0037] The coil unit 15 generates a correction magnetic field so that the influence of magnetic fields other than the magnetic field to be measured on the cell 11 approaches zero. For example, the coil unit 15 may generate a magnetic field in the opposite direction to the geomagnetic field so as to cancel the influence of the geomagnetic field. Alternatively or additionally, the coil unit 15 may generate a modulated magnetic field acting on the cell 11. For example, the coil unit 15 may generate an AC magnetic field modulated at a predetermined frequency to improve sensitivity, or may generate a modulated magnetic field to enable detection of the direction of magnetic field change (positive / negative direction on each axis). In this example, the coil unit 15 is formed of a flexible circuit board and is disposed to surround four surfaces of the cell casing 14 (cell 11) (surfaces other than the second wall portions 14d of the cell casing 14) (surfaces other than the two surfaces in the extension direction of the protrusion 11b of the cell 11), and is drawn out to one side in the Z direction and electrically connected to the connector member 26. Details of the coil unit 15 will be described later. [Coil unit]

[0038] The coil unit 15 will be described in detail with reference to Figures 3 and 6 to 12. The coil unit 15 has a support frame 30 and a plurality of coils 40 provided on the support frame 30.

[0039] The support frame 30 is formed in a shape that follows a rectangular parallelepiped. In this example, the support frame 30 is formed in a shape that corresponds to the outer shape of the rectangular parallelepiped cell casing 14 so that it can be placed outside the cell casing 14 along the cell casing 14. More specifically, the support frame 30 is formed in a rectangular cylindrical shape so as to surround the cell casing 14 (cells 11) when viewed from the Z direction. The support frame 30 has a pair of first surfaces 31A, 31B that face each other in the X direction (first direction) and a pair of second surfaces 32A, 32B that face each other in the Y direction (second direction). The first surfaces 31A, 31B are flat surfaces that are perpendicular to the X direction and parallel to each other, and the second surfaces 32A, 32B are flat surfaces that are perpendicular to the Y direction and parallel to each other. The first surfaces 31A and 31B cover a pair of surfaces of the cell casing 14 in the X direction, and the second surfaces 32A and 32B cover a pair of surfaces of the cell casing 14 in the Y direction. In this way, the support frame 30 is disposed outside the cell casing 14 so as to surround the cell 11 via the cell casing 14. In this example, the support frame 30 does not cover a pair of surfaces of the cell casing 14 in the Z direction, but the support frame 30 may cover at least one of the pair of surfaces. The support frame 30 has a shape in which the length along the Z direction is longer than the lengths along the X direction and the Y direction. In this example, the support frame 30 is formed in a rectangular shape when viewed from the Y direction, with long sides along the Z direction and short sides along the X direction.

[0040] The multiple coils 40 include a pair of first coils 41A, 41B, a pair of second coils 42A, 42B, and a pair of third coils 43A, 43B. These first to third coils 41A to 43B are provided on the support frame 30 and extend along the support frame 30. In this example, the support frame 30 and the multiple coils 40 are formed by a flexible printed circuit board (FPC) 50. An FPC is a flexible, bendable printed circuit board. The support frame 30 and the multiple coils 40 are formed by bending the flexible circuit board 50 ( FIG. 6 ). More specifically, as shown in the developed views of FIGS. 10 to 12 , the first to third coils 41A to 43B are formed as circuits on the flexible circuit board 50, and the support frame 30 and the multiple coils 40 are formed by bending the flexible circuit board 50 to form the shape of the support frame 30. In Figure 10, the second coils 42A, 42B and the third coils 43A, 43B are omitted, in Figure 11 the first coils 41A, 41B and the third coils 43A, 43B are omitted, and in Figure 12 the first coils 41A, 41B and the second coils 42A, 42B are omitted.

[0041] 7 schematically shows the main body 11a of the cell 11, the support frame 30, and the first coils 41A and 41B. The first coils 41A and 41B are arranged to face each other in the X direction. The first coils 41A and 41B are coils for applying a magnetic field in the X direction to the cell 11.

[0042] As shown in FIG. 7 , the first coil 41A extends from the first surface 31A across the second surface 32A and the second surface 32B. The first coil 41A has a first portion 41Aa disposed on the first surface 31A, a second portion 41Ab disposed on the second surface 32A, and a third portion 41Ac disposed on the second surface 32B. The first portion 41Aa consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the first surface 31A. The second portion 41Ab consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the second surface 32A, and a side connected to the pair of sides and extending straight along the Z direction. The third portion 41Ac consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the second surface 32B, and a side connected to the pair of sides and extending straight along the Z direction. As shown in FIG. 10, in the flexible circuit board 50 before being folded, the first coil 41A is formed in a rectangular shape.

[0043] As shown in FIG. 7, the first coil 41B extends from the first surface 31B across the second surface 32A and the second surface 32B. The first coil 41B has a shape symmetrical to the first coil 41A with respect to a plane perpendicular to the X direction and passing through the center of the support frame 30 (the center C of the main body 11a of the cell 11). The first coil 41B has a first portion 41Ba disposed on the first surface 31B, a second portion 41Bb disposed on the second surface 32A, and a third portion 41Bc disposed on the second surface 32B. The first portion 41Ba consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the first surface 31B. The second portion 41Bb consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the second surface 32A, and a side connected to the first and second sides and extending straight along the Z direction. The third portion 41Bc is composed of a pair of sides that face each other in the Z direction and extend along the outer edge of the second surface 32B, and a side that is connected to the sides and extends straight along the Z direction. As shown in Fig. 10, in the flexible circuit board 50 before being folded, the first coil 41B is formed in a rectangular shape.

[0044] If the distance between the first coils 41A and 41B along the X direction on the second surfaces 32A and 32B is D and the length of the support frame 30 along the X direction is R, D / R is 0.2 or more and 0.8 or less. D / R may be preferably 0.4 or more and 0.7 or less, and more preferably 0.5 or more and 0.6 or less.

[0045] 8 schematically shows the main body 11a of the cell 11, the support frame 30, and the second coils 42A and 42B. The second coils 42A and 42B are arranged to face each other in the Y direction. The second coils 42A and 42B are coils for applying a magnetic field in the Y direction to the cell 11.

[0046] As shown in FIG. 8 , the second coil 42A extends from the second surface 32A across the first surface 31A and the first surface 31B. The second coils 42A and 42B have a shape obtained by rotating the first coils 41A and 41B by 90 degrees around a line parallel to the Z direction and passing through the center C of the cell 11. The second coil 42A has a first portion 42Aa disposed on the second surface 32A, a second portion 42Ab disposed on the first surface 31A, and a third portion 42Ac disposed on the first surface 31B. The first portion 42Aa consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the second surface 32A. The second portion 42Ab consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the first surface 31A, and a side connected to the first side and extending straight along the Z direction. The third portion 42Ac is made up of a pair of sides that face each other in the Z direction and extend along the outer edge of the first surface 31B, and a side that is connected to the sides and extends straight along the Z direction. As shown in Fig. 11, in the flexible circuit board 50 before being folded, the second coil 42A is formed in a rectangular shape.

[0047] As shown in FIG. 8, the second coil 42B extends from the second surface 32B across the first surface 31A and the first surface 31B. The second coil 42B has a shape symmetrical to the second coil 42A with respect to a plane perpendicular to the Y direction and passing through the center of the support frame 30 (the center C of the main body 11a of the cell 11). The second coil 42B has a first portion 42Ba disposed on the second surface 32B, a second portion 42Bb disposed on the first surface 31A, and a third portion 42Bc disposed on the first surface 31B. The first portion 42Ba consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the second surface 32B. The second portion 42Bb consists of a pair of sides facing each other in the Z direction and extending along the outer edge of the first surface 31A, and a side connected to the first side and extending straight along the Z direction. The third portion 42Bc is composed of a pair of sides that face each other in the Z direction and extend along the outer edge of the first surface 31B, and a side that is connected to the sides and extends straight along the Z direction. As shown in Fig. 11, in the flexible circuit board 50 before being folded, the second coil 42B is formed in a rectangular shape.

[0048] 9 schematically shows the main body 11a of the cell 11, the support frame 30, and the third coils 43A and 43B. The third coils 43A and 43B are arranged to face each other in the Z direction. The third coils 43A and 43B are coils for applying a magnetic field in the Z direction to the cell 11.

[0049] 9, the third coils 43A, 43B extend across the first surfaces 31A, 31B and the second surfaces 32A, 32B so as to surround the support frame 30 when viewed from the Z direction. The third coils 43A, 43B extend straight along the Y direction on the first surfaces 31A, 31B, and extend straight along the X direction on the second surfaces 32A, 32B.

[0050] 10 to 12, the flexible circuit board 50 has a plurality of (six in this example) flat surfaces 51, 52, 53, 54, 55, and 56 corresponding to the first surfaces 31A and 31B and the second surfaces 32A and 32B of the support frame 30. The flat surfaces 51 and 55 correspond to the first surface 31A. When the flexible circuit board 50 is bent into the shape of the support frame 30, the flat surfaces 51 and 55 are superimposed to form the first surface 31A. The flat surface 52 corresponds to the first surface 31B. The flat surfaces 53 and 56 correspond to the second surface 32A. When the flexible circuit board 50 is bent into the shape of the support frame 30, the flat surfaces 53 and 56 are superimposed to form the second surface 32A. The flat surface 54 corresponds to the second surface 32B.

[0051] A light passing opening 57 through which the laser light L passes is formed in the center of each of the flat portions 51, 52 corresponding to the first surfaces 31A, 31B. When the flexible circuit board 50 is bent to form the support frame 30, the pair of light passing openings 57 face each other in the X direction and form an incident region through which the laser light L enters the cell 11. In this example, the light passing opening 57 is formed in a circular shape.

[0052] An opening 58 is formed in the center of each of the flat portions 53, 54 corresponding to the second surfaces 32A, 32B. The pair of openings 58 face each other in the Y direction when the flexible circuit board 50 is bent to form the support frame 30. The laser light L does not enter the openings 58. In this example, the openings 58 are formed in the same circular shape as the light passing opening 57.

[0053] An opening 59 is formed in the center of the flat portion 56, which is overlapped with the flat portion 53 to form the second surface 32A. In this example, the opening 59 is formed in the same circular shape as the light passage opening 57 and the opening 59. When the flexible circuit board 50 is folded to form the support frame 30, the opening 58 formed in the flat portion 53 and the opening 59 formed in the flat portion 56 overlap each other. This positions the two flat portions 53 and 56. In other words, when the flexible circuit board 50 is folded to form the support frame 30, the two flat portions 53 and 56 are overlapped so that the opening 58 formed in the flat portion 53 and the opening 59 formed in the flat portion 56 overlap each other. In this way, the opening 58 formed in the flat portion 53 and the opening 59 formed in the flat portion 56 function as positioning openings.

[0054] A slot H extending along the boundary line is formed at the boundary between two adjacent flat surfaces among the flat surfaces 51, 52, 53, 54, 55, and 56. The formation of the slot H makes it easier to bend the flexible circuit board 50 at the boundary line.

[0055] The flexible circuit board 50 further has a lead-out portion 60 drawn out in a direction away from the support frame 30. In this example, the lead-out portion 60 extends from the flat portion 53 corresponding to the second surface 32A of the support frame 30. A plurality of pad portions 61 (six in this example) electrically connected to the plurality of coils 40 are formed at the tip of the lead-out portion 60. The lead-out portion 60 is drawn out to one side in the Z direction from the support frame 30, and is electrically connected to the connector member 26 at the plurality of pad portions 61. Note that although the lead-out portion 60 is not shown in FIG. 3, in reality the lead-out portion 60 extends from the second surface 32A toward the connector member 26.

[0056] 10 to 12 show the arrangement of the first to third coils 41A to 43B on the flexible circuit board 50 before bending. As described above, the first to third coils 41A to 43B are formed as a circuit on the flexible circuit board 50. The first to third coils 41A to 43B are arranged, for example, on planes (layers) at different heights in the thickness direction of the flexible circuit board 50, and this allows them to be formed so as to have portions that intersect with each other when viewed from the thickness direction of the flexible circuit board 50.

[0057] As shown in FIG. 10, the first coils 41A and 41B are configured with a single conductive path. That is, the first coils 41A and 41B are configured with one circuit portion P1 without any electrically disconnected portions. In FIG. 10, the circuit portion of the circuit portion P1 that configures the first coils 41A and 41B is indicated by solid lines, and the circuit portion for canceling the magnetic field is indicated by diagonal lines. In the circuit portion for canceling the magnetic field, the influence of the generated magnetic field is canceled by current flowing in both directions. In FIG. 10, the path of current flow through the circuit portion P1 is indicated by arrows. This also applies to FIGS. 11 and 12. The first coils 41A and 41B are electrically connected to the pad portion 61A of the pad portion 61 via the wiring portion 62 formed on the lead-out portion 60.

[0058] 11, the second coils 42A, 42B are configured by a single conductive path. That is, the second coils 42A, 42B are configured by one circuit portion P2 that does not have any electrically disconnected portions. The second coils 42A, 42B are electrically connected to the pad portion 61B of the pad portion 61 via the wiring portion 63 formed on the lead-out portion 60.

[0059] As shown in FIG. 12 , the third coils 43A and 43B are configured by a single conductive path. That is, the third coils 43A and 43B are configured by one circuit portion P3 without any electrically disconnected portions. The third coils 43A and 43B are electrically connected to a pad portion 61C of the pad portion 61 via a wiring portion 64 formed on the lead-out portion 60. In this example, the flexible circuit board 50 further includes a lead-out portion 65 extending from the flat portion 56 corresponding to the second surface 32A of the support frame 30. The lead-out portion 65 overlaps with the lead-out portion 60 when the flexible circuit board 50 is bent. A pad portion 65a is formed at the tip of the lead-out portion 65, and the third coils 43A and 43B are electrically connected to the pad portion 65a via a wiring portion 66 formed on the lead-out portion 65. A pad portion 60a is formed on the lead-out portion 60 at a position corresponding to the pad portion 65a. The pad portion 65a is electrically connected to the pad portion 60a, so that one end side and the other end side of the third coils 43A, 43B are electrically connected to each other.

[0060] 13 and 14 are diagrams illustrating the results of a comparison of the magnetic field uniformity calculated by simulation in the example and the comparative example. The example shown in FIG. 13(b) corresponds to a configuration in which the first coils 41A and 41B described above are provided. The main body 11a of the cell 11 is a cube with a side length of 2 mm, and the length of the support frame 30 is 10 mm in the X direction, 10 mm in the Y direction, and 12 mm in the Z direction. The center C of the main body 11a of the cell 11 coincides with the center of the support frame 30. In the modified example shown in FIG. 13(a), a pair of first coils 141 are disposed only on the first surfaces 31A and 31B, respectively. The other aspects are the same as those of the example.

[0061] The calculation results are shown in Figure 14. "Position error in the Z direction" represents the amount of deviation of the first coil from the target position along the Z direction. From the tables in Figures 14(a) and 14(b), it can be seen that in the example, the standard deviation and maximum error of the magnetic flux density were about 1 / 5 smaller than those in the comparative example for both the magnetic field in the X direction and the magnetic field in the Z direction generated within the main body 11a of the cell 11, and the magnetic field uniformity was improved by about 5 times. Furthermore, it can be seen that the uniformity of the magnetic field generated by the first coil was improved not only in the X direction but also in the Z direction, thereby suppressing the occurrence of crosstalk between axes. [Action and effect]

[0062] In the sensor module 1, the first coil 41A (one of the pair of first coils 41A, 41B) extends from the first surface 31A (one of the pair of first surfaces 31A, 31B) of the support frame 30 across the second surfaces 32A, 32B (one and the other of the pair of second surfaces 32A, 32B), and the first coil 41B (the other of the pair of first coils 41A, 41B) extends from the first surface 31B (the other of the pair of first surfaces 31A, 31B) of the support frame 30 across the second surfaces 32A, 32B. This makes it possible to homogenize the magnetic field generated in the cell 11 by the first coils 41A, 41B. Therefore, the sensor module 1 allows a homogenous magnetic field to act on the cell 11 in which the alkali metal is sealed. The coil unit 15 includes a support frame 30 formed in a rectangular parallelepiped shape and arranged to surround the cell 11, and multiple coils 40 provided on the support frame 30. By providing multiple coils 40 on the support frame 30 formed in a rectangular parallelepiped shape to form the coil unit 15, the cell 11 or the cell case 14 housing the cell 11 can be conveniently arranged inside the coil unit 15 (support frame 30). In optically excited magnetic sensors, such as the sensor module 1, detection may be performed while a magnetic field is applied to the cell. If the magnetic field is not uniform, the detection sensitivity may be reduced due to the influence of a magnetic field on an axis different from the axis of the object to be detected, so it is necessary to homogenize the magnetic field. However, thermal insulating materials or a cell case may be arranged around the cell, which may limit the space available, making it difficult to adopt a coil shape that easily creates a uniform magnetic field. In this regard, in the sensor module 1, the first coils 41A, 41B (multiple coils 40) having the above-mentioned shape are provided on the support frame 30 to form the coil unit 15, thereby making it possible to arrange components around the cell 11 while making the magnetic field uniform.

[0063] The multiple coils 40 further include a pair of second coils 42A and 42B. The second coil 42A (one of the pair of second coils 42A and 42B) extends from the second surface 32A (one of the pair of second surfaces 32A and 32B) across the first surfaces 31A and 31B (one and the other of the pair of first surfaces 31A and 31B), and the other of the second coils 42B (the other of the pair of second coils 42A and 42B) extends from the second surface 32B (the other of the pair of second surfaces 32A and 32B) across the first surfaces 31A and 31B. This allows the magnetic field generated within the cell 11 by the second coils 42A and 42B to be uniform.

[0064] The multiple coils 40 further include a pair of third coils 43A, 43B. Each of the third coils 43A, 43B extends across the first surfaces 31A, 31B and the second surfaces 32A, 32B so as to surround the support frame 30. The third coils 43A, 43B face each other in the Z direction (third direction) perpendicular to the X direction (first direction) and the Y direction (second direction). This allows the magnetic field generated within the cell 11 by the third coils 43A, 43B to be uniform.

[0065] The support frame 30 has a shape in which the length along the Z direction is longer than both the length along the X direction and the length along the Y direction. This makes it possible to homogenize the magnetic field generated within the cell 11 by the third coils 43A, 43B. In other words, the third coils 43A, 43B having the above shape can be suitably used when the length of the support frame 30 along the Z direction is long.

[0066] The support frame 30 and the plurality of coils 40 are configured by a flexible circuit board 50. This allows the support frame 30 and the plurality of coils 40 to be configured to be bendable.

[0067] If the distance between the first coils 41A and 41B along the X direction on the second surfaces 32A and 32B is D and the length of the support frame 30 along the X direction is R, D / R is between 0.2 and 0.8. This allows the magnetic field generated within the cell 11 by the first coils 41A and 41B to be more uniform. This numerical range is based on the following simulation results. The magnetic field generated within the cell 11 was calculated by changing the distance D between the first coils 41A and 41B in 0.1 mm increments while keeping the length R of the support frame 30 along the X direction fixed, and the standard deviation was calculated. Based on the calculation results, a range in which the standard deviation became small was selected.

[0068] The support frame 30 is disposed outside the cell casing 14 so as to surround the cell 11 via the cell casing 14. This allows, for example, a heat insulating member 13 to be disposed inside the cell casing 14 to improve heat insulation.

[0069] The first coils 41A, 41B, the second coils 42A, 42B, and the third coils 43A, 43B are configured by a single conductive path, which simplifies the configuration of the first coils 41A, 41B, the second coils 42A, 42B, and the third coils 43A, 43B.

[0070] The support frame 30 and the multiple coils 40 are formed by bending a flexible circuit board 50. The flexible circuit board 50 has multiple flat portions 51-56 corresponding to the first surfaces 31A, 31B and second surfaces 32A, 32B of the support frame 30. Of the flat portions 51-56, the flat portions 51, 52 corresponding to the first surfaces 31A, 31B have light passing openings 57 through which the laser light L passes. The second surface 32A is formed by overlapping two flat portions 53, 56 of the flexible circuit board 50, and openings 58, 59 (positioning openings) are formed in the flat portions 53, 56, respectively. The flat portions 53, 56 are overlapped so that the openings 58, 59 overlap each other. As a result, by overlapping the flat portions 53, 56 so that the openings 58, 59 overlap each other, the flat portions 53, 56 can be aligned.

[0071] A slot H extending along the boundary line is formed at the boundary between the flat portions 51 to 56. As a result, the slot H extending along the boundary line allows the flexible circuit board 50 to be easily bent at the boundary line.

[0072] The flexible circuit board 50 has a lead-out portion 60 that is drawn out in a direction away from the support frame 30, and a pad portion 61 electrically connected to the first coils 41A and 41B is formed on the lead-out portion 60. This allows the pad portion 61 to be separated from the cell 11 by the lead-out portion 60, and makes it possible to suppress the magnetic field generated in the pad portion 61 from affecting the magnetic field within the cell 11. [Variations]

[0073] In the above embodiment, the sensor module 1 is configured as a one-laser system in which the laser light L serves as both the pump light and the probe light, but the sensor module 1 may also be configured as a two-laser system in which the pump light L1 and the probe light L2 are independent, as in the modified example shown in Fig. 15. The sensor module 1 of the modified example includes, instead of the light source 21, a light source 21A that outputs linearly polarized pump light L1 and a light source 21B that outputs circularly polarized probe light L2. Furthermore, in the sensor module 1 of the modified example, the photodetector 25 is configured as a differential detector consisting of a first photodetector 25A and a second photodetector 25B.

[0074] In the sensor module 1 of the modified example, the alkali metal vapor in the cell 11 is optically pumped by the pump light L1 output from the light source 21A to become spin-polarized. The probe light L2 output from the light source 21B and passing through the cell 11 is detected by the photodetector 25. Here, the spin-polarized state of the alkali metal vapor in the cell 11 changes due to the influence of the magnetic field of the object to be measured, so the polarization direction of the probe light L2 passing through the alkali metal vapor is changed so as to tilt. The first photodetector 25A detects the light intensity of the polarization direction component corresponding to the polarization direction of the probe light L2 before the polarization direction change, and the second photodetector 25B detects the light intensity of the polarization direction component corresponding to the polarization direction of the probe light L2 after the polarization direction change. This detects the difference in light intensity between the two polarization direction components of the probe light L2. Based on this difference, the spin-polarized state of the alkali metal vapor in the cell 11 can be detected, and thus changes in the magnetic field of the object to be measured can be detected.

[0075] In the case of the two-laser method, for example, the probe light L2 passes through the cell 11 along the X direction. The probe light L2 passes through a light passing opening 57 formed in the flat portions 51 and 52 of the flexible circuit board 50. The pump light L1 passes through the cell 11 along the Y direction perpendicular to the X direction. The pump light L1 passes through an opening 58 formed in the flat portions 53 and 54 of the flexible circuit board 50 (and an opening 59 formed in the flat portion 56).

[0076] The present invention is not limited to the above-described embodiment and modifications. For example, the materials and shapes of each component are not limited to those described above, and various materials and shapes can be used. For example, the support frame 30 may be disposed so as to surround at least a portion of the cell 11 (main body portion 11a), and a portion of the cell 11 may protrude outside the support frame 30. In the above-described embodiment, the support frame 30 has a shape elongated along the Z direction. However, the support frame 30 may have a shape elongated along the X direction or the Y direction, or may have a shape with equal lengths in each direction (cubic shape). The support frame 30 and the multiple coils 40 do not necessarily have to be formed by a flexible circuit board 50.

[0077] The cell case 14 may be omitted. In this case, the support frame 30 may surround the cell 11 without the cell case 14. In this case, the cell 11, the heater 12, the heat insulating member 13, and the coil unit 15 may be arranged in the cell unit arrangement section 3c of the housing 3.

[0078] The pair of second coils 42A and 42B may be omitted. The second coils 42A and 42B are not limited to the above-described shapes and may have any shape. For example, the second coils 42A and 42B may be disposed only on the second surfaces 32A and 32B, respectively. The pair of third coils 43A and 43B may be omitted. The third coils 43A and 43B are not limited to the above-described shapes and may have any shape. For example, the third coils 43A and 43B may be disposed only on the second surfaces 32A and 32B, respectively. The above-described D / R may be smaller than 0.2 or larger than 0.8. At least one of the first coils 41A and 41B, the second coils 42A and 42B, and the third coils 43A and 43B may not be formed by a single conductive path. For example, the first coils 41A and 41B may be formed by metal wires or circuits separated from each other.

[0079] The opening 58 formed in the flat portions 53 and 54 of the flexible circuit board 50 and the opening 59 formed in the flat portion 56 may be omitted. As described above, in the case of the one-laser system (embodiment), the laser light L functioning as pump light and probe light passes through the light-passing opening 57. In the case of the two-laser system (variation), the pump light L1 passes through the light-passing opening 57, and the probe light L2 passes through the openings 58 and 59. That is, in either case, at least the pump light passes through the light-passing opening 57. The lead-out portion 60 may be omitted, and for example, a pad portion 61 may be formed on any of the flat portions 51 to 56. The long hole H does not have to be provided. [Explanation of symbols]

[0080] 1...optically excited magnetic sensor module, 11...cell, 14...cell case, 15...coil unit, 30...support frame, 40...coil, 31A, 31B...first surface, 32A, 32B...second surface, 41A, 41B...first coil, 42A, 42B...second coil, 43A, 43B...third coil, 50...flexible circuit board, 51-56...flat portion, 57...light passing opening, 58, 59...opening (positioning opening), 60...drawing portion, 61, 61A, 61B, 61C...pad portion, H...long hole.

Claims

1. a cell in which an alkali metal is sealed; a coil unit that generates a magnetic field that acts on the cell; the coil unit has a support frame formed in a shape along a rectangular parallelepiped and arranged to surround the cell, and a plurality of coils provided on the support frame; the support frame includes a pair of first surfaces facing each other in a first direction and a pair of second surfaces facing each other in a second direction perpendicular to the first direction, the plurality of coils includes a pair of first coils, one of the pair of first coils extends from one of the pair of first surfaces across one and the other of the pair of second surfaces, an optically excited magnetic sensor module, wherein the other of the pair of first coils extends from the other of the pair of first surfaces across one and the other of the pair of second surfaces;

2. the plurality of coils further includes a pair of second coils; one of the pair of second coils extends from one of the pair of second surfaces across one and the other of the pair of first surfaces, 2. The optically excited magnetic sensor module according to claim 1, wherein the other of the pair of second coils extends from the other of the pair of second surfaces across one and the other of the pair of first surfaces.

3. the plurality of coils further includes a pair of third coils; each of the pair of third coils extends across the pair of first surfaces and the pair of second surfaces so as to surround the support frame; 3. The optically excited magnetic sensor module according to claim 1, wherein the pair of third coils face each other in a third direction perpendicular to the first direction and the second direction.

4. 4. The optically excited magnetic sensor module according to claim 3, wherein the support frame has a shape in which its length along the third direction is longer than its length along the first direction and its length along the second direction.

5. 3. The optically excited magnetic sensor module according to claim 1, wherein the support frame and the plurality of coils are formed by a flexible circuit board.

6. 3. The optically excited magnetic sensor module of claim 1, wherein D / L is greater than or equal to 0.2 and less than or equal to 0.8, where D is the distance between the pair of first coils along the first direction on the pair of second surfaces and L is the length of the support frame along the first direction.

7. Further provided is a cell case that houses the cell, 3. The optically excited magnetic sensor module according to claim 1, wherein the support frame is disposed outside the cell case so as to surround the cell with the cell case interposed therebetween.

8. 3. The optically excited magnetic sensor module according to claim 1, wherein the pair of first coils are configured by a single conductive path.

9. the support frame and the plurality of coils are formed by bending the flexible circuit board, the flexible circuit board has a plurality of planar portions corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, a light passing opening through which at least the pump light passes is formed in the planar portions corresponding to the pair of first surfaces among the plurality of planar portions; one of the pair of second surfaces is formed by overlapping two planar portions of the flexible circuit board; 6. The optically excited magnetic sensor module according to claim 5, wherein a positioning opening is formed in each of the two planar portions, and the two planar portions are superimposed so that the positioning openings of the two planar portions overlap each other.

10. the support frame and the plurality of coils are formed by bending the flexible circuit board, the flexible circuit board has a plurality of planar portions respectively corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, 6. The optically excited magnetic sensor module according to claim 5, wherein a slot is formed at a boundary between the plurality of flat surfaces, the slot extending along the boundary line.

11. the flexible circuit board has a lead-out portion that is led out in a direction away from the support frame, 6. The optically excited magnetic sensor module according to claim 5, wherein the lead-out portion is formed with pad portions electrically connected to the pair of first coils.

Images