Optically pumped magnetic sensor module

Abstract

This optically pumped magnetic sensor module comprises: a cell in which an alkali metal is sealed; and a coil unit that generates a magnetic field to act on the cell. The coil unit has a support frame body formed in a shape conforming to a rectangular parallelepiped and disposed so as to surround the cell, and a plurality of coils provided on the support frame body. The support frame body 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 include a pair of first coils. One of the pair of first coils extends from one of the pair of first surfaces over both of the pair of second surfaces. The other of the pair of first coils extends from the other of the pair of first surfaces over both of the pair of second surfaces.

Description

Optically Pumped Magnetic Sensor Module

[0001] One aspect of the present disclosure relates to an optically pumped magnetic sensor module.

[0002] As an optically pumped magnetic sensor, for example, there is an optical pumping type magnetic sensor described in Patent Document 1. In the magnetic sensor described in Patent Document 1, a plurality of coils are provided on the outer surface of a cell in which an alkali metal is enclosed. The plurality of coils are composed of a pair of coils arranged on the X-axis sandwiching the cell, a pair of coils arranged on the Y-axis sandwiching the cell, and a pair of coils arranged on the Z-axis sandwiching the cell. These coils generate an alternating magnetic field that cancels out the magnetic field in the region of the cell.

[0003] Japanese Unexamined Patent Application Publication No. 2013 - 217690

[0004] In an optically pumped magnetic sensor, there are cases where while generating a magnetic field acting on a cell by a coil, the change in the magnetic field in the cell is detected using probe light. In this case, in order to ensure the detection accuracy, it is preferable that the magnetic field generated in the cell by the coil is uniform.

[0005] Therefore, one aspect of the present disclosure aims to provide an optically pumped magnetic sensor module capable of applying a uniform magnetic field to a cell in which an alkali metal is enclosed.

[0006] An optically excited magnetic sensor module relating to one aspect of the present disclosure is: [1] "An optically excited magnetic sensor module comprising: a cell containing an alkali metal; a coil unit for generating a magnetic field acting on the cell, wherein the coil unit is formed in a shape along a rectangular parallelepiped and has a support frame arranged to surround the cell; and a plurality of coils provided on the support frame, wherein 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 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 a plurality of coils extends from one of a pair of first surfaces on the support frame to one and the other of a pair of second surfaces, and the other of the pair of first coils extends from the other of a pair of first surfaces on the support frame to one and the other of a pair of second surfaces. This makes it possible to homogenize the magnetic field generated within the cell by the first coil. Therefore, this photo-excited magnetic sensor module can apply a uniform magnetic field to a cell containing alkali metals. Furthermore, the coil unit has a support frame formed in the shape of a rectangular parallelepiped and arranged to surround the cell, and a plurality of coils provided on the support frame. By configuring a coil unit by providing a plurality of coils on a support frame formed in the shape of a rectangular parallelepiped in this way, a cell, or a cell case housing the cell, can be suitably arranged inside the coil unit (support frame).

[0008] An optically excited magnetic sensor module relating to one aspect of the present disclosure 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 the pair of second coils extending from one of the pair of second surfaces across one and the other of the pair of first surfaces, and the other of the pair of second coils extending 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 within the cell by the second coils can be made uniform.

[0009] An optically excited magnetic sensor module relating to one aspect of the present disclosure 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 the pair of third coils extending 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 and second directions." In this case, the magnetic field generated within the cell by the third coils can be made uniform.

[0010] An optically excited magnetic sensor module relating to one aspect of this disclosure may be the optically excited magnetic sensor module according to [3], wherein the support frame has a shape in which the length in the third direction is longer than each of the length in the first direction and the length in the second direction. In this case, the magnetic field generated in the cell by the third coil can be made uniform.

[0011] An optically excited magnetic sensor module relating to one aspect of this disclosure may be [5] "an optically excited magnetic sensor module according to any one of [1] to [4], wherein the support frame and the plurality of coils are composed of a flexible circuit board." In this case, the support frame and the plurality of coils can be made bendable.

[0012] An optically excited magnetic sensor module relating to one aspect of the present disclosure may be [6] "an optically excited magnetic sensor module according to any one of [1] to [5], wherein 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, and D / L is 0.2 or more and 0.8 or less." In this case, the magnetic field generated in the cell by the first coil can be made even more uniform.

[0013] An optically excited magnetic sensor module relating to one aspect of the present disclosure may be [7] "an optically excited magnetic sensor module according to any one of [1] to [6], further comprising a cell case for housing the cell, wherein the support frame is arranged outside the cell case so as to surround the cell via the cell case." In this case, for example, an insulating material can be placed inside the cell case to improve heat insulation.

[0014] An optically excited magnetic sensor module relating to one aspect of the present disclosure may be [8] "an optically 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] An optically excited magnetic sensor module relating to one aspect of the present disclosure may be the optically excited magnetic sensor module according to [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, at least the planar portion corresponding to the pair of first surfaces has a light-passing aperture through which pump light passes, one of the pair of second surfaces is formed by overlapping two planar portions of the flexible circuit board, a positioning aperture is formed in each of the two planar portions, and the two planar portions are overlapped such that the positioning apertures of the two planar portions overlap each other, as described in [5]. In this case, the two planar portions can be aligned by overlapping the two planar portions so that their positioning apertures overlap each other.

[0016] An optically excited magnetic sensor module relating to one aspect of the present disclosure may be the optically excited magnetic sensor module according to

[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 corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, and elongated holes extending along the boundary lines are formed at the boundaries between the plurality of planar portions." In this case, the formation of elongated holes extending along the boundary lines allows the flexible circuit board to be easily bent at the boundary lines.

[0017] An optically excited magnetic sensor module relating to one aspect of the present disclosure may be the optically excited magnetic sensor module according to

[11] "the flexible circuit board having a lead portion extended away from the support frame, and the lead portion having a pad portion electrically connected to the pair of first coils." In this case, the lead portion can be used to move the pad portion away from the cell, thereby suppressing the magnetic field generated at the pad portion from affecting the magnetic field inside the cell.

[0018] According to one aspect of this disclosure, it is possible to provide a photo-excited magnetic sensor module that can apply a uniform magnetic field to a cell containing an alkali metal.

[0019] This is a diagram illustrating the operation of the optically excited magnetic sensor module. (a) is a perspective view of the optically excited magnetic sensor module, and (b) is a perspective view of the optically excited magnetic sensor module with the outer cover removed. This is a perspective view of the optically excited magnetic sensor module with the housing lid removed from Figure 2(b). This is a cross-sectional view along line IV-IV in Figure 3. This is a plan view of the optically excited magnetic sensor module with the case lid removed from the cell case from Figure 3. This is a diagram illustrating the coil unit. This is a diagram illustrating the first coil. This is a diagram illustrating the second coil. This is a diagram illustrating the third coil. This is a diagram illustrating the first coil. This is a diagram illustrating the second coil. This is a diagram illustrating the third coil. (a) is a diagram illustrating the coil of the comparative example, and (b) is a diagram illustrating the first coil of the embodiment. (a) is a table showing the calculation results for the comparative example, and (b) is a table showing the calculation results for the embodiment. This is a diagram illustrating the operation of the optically excited magnetic sensor module according to a modified example.

[0020] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant descriptions will be omitted.

[0021] The optically pumped magnetic sensor module 1 (hereinafter also referred to as "sensor module 1") shown in Figures 1 to 5 is an optically pumped magnetic sensor (OPM) and is used, for example, for measuring biomagnetic fields. As an example, sensor module 1 can be used as a magnetoencephalograph (MEG) to measure magnetic fields generated in the brain, or as a magnetocardiograph (CG) or magnetospinal meter (SP2) to measure magnetic fields generated in the heart or spinal cord. [Configuration of the sensor module]

[0022] As shown in Figures 1 to 5, the sensor module 1 comprises 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 comprises 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] Referring to Figure 1, the operation of the sensor module 1 (the principle of detecting magnetic field changes) will be explained. During measurement, the sensor module 1 (cell 11) is placed near the object to be measured. The cell 11 is filled with gas GS containing alkali metals. During measurement, the alkali metals in the cell 11 are heated by the heater 12, and the cell 11 is filled with alkali metal vapor. In this state, the laser light L output from the light source 21 passes through the cell 11. The laser light L is incident on the cell 11 in a state of circular polarization by the quarter-wave plate 24. This circularly polarized laser light L causes the alkali metal vapor in the cell 11 to be put into a spin-polarized state by optical pumping (photoexcitation). In other words, the laser light L functions as a pump light that puts the alkali metal vapor in the cell 11 into a spin-polarized state by optical pumping.

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

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

[0026] As shown in Figures 4 and 5, the housing 3 contains a cell unit arrangement section 3c where the cell unit 2 is placed, an optical component arrangement section 3f where the light source 21, lens 22, and mirror 23 are placed, and a photodetector arrangement section 3g where the photodetector 25 is placed. The optical component arrangement section 3f has an optical path section 3h, which is the 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 located on the opposite side of the optical path section 3h from the cell unit arrangement section 3c.

[0027] The light source 21 is, for example, a vertical cavity surface-emitting laser, which outputs laser light L. In this example, the light source 21 is mounted on the connector member 26.

[0028] The lens 22 aligns the laser light L output from the light source 21. The mirror 23 reflects the laser light L, which has been aligned by the lens 22, toward the cell unit 2. The quarter-wave plate 24 is positioned between the mirror 23 and the cell unit 2. The quarter-wave plate 24 introduces 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 located in the cell unit arrangement section 3c. The cell unit 2 has a cell 11 containing an alkali metal gas GS. Details of the cell unit 2 will be described later. Circularly polarized laser light L, converted by the 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 located 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 of the housing 3 in the Z direction. The heater 12, coil unit 15, light source 21, and photodetector 25 are electrically connected to the connector member 26, and the connector member 26 is used for the electrical connection of each of these parts to the outside. A connector cover 27 is detachably attached to the connector member 26. As shown in Figure 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 located (one side in the Z direction). [Cell Unit]

[0031] The details of the cell unit 2 will be explained with reference to Figures 3 to 5. As described above, the cell unit 2 includes 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, heater 12, and heat insulating member 13 are housed inside the cell case 14, and the coil unit 15 is positioned outside the cell case 14.

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

[0033] The heater 12 is positioned in a state of thermal connection with the cell 11, and in this embodiment, it is provided on the surface of the main body portion 11a of the cell 11 (in this example, one surface in the Y direction). The heater 12 is configured in a sheet shape and includes, for example, a metal wire (resistor) that generates heat when an electric current is passed through it. In this example, the heater 12 is composed of a titanium wire and is fixed to the cell 11 by an adhesive layer. The heater 12 generates heat when an electric current is passed through it and heats the cell 11.

[0034] The heat insulating member 13 is positioned inside the cell case 14 so as to be located 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 arranged to fill the space between the cell 11 and the cell case 14. More specifically, in the space between the main body portion 11a of the cell 11 and the cell case 14, the plurality of plate-shaped members 13a are arranged to fill as little gap as possible except for the laser light L transmission area in the main body portion 11a, and in the space between the protrusion 11b of the cell 11 and the cell case 14, they are arranged to surround and fill the entire protrusion 11b while having a region 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 by, for example, the formation of an air layer inside. The cell case 14 is formed in a substantially rectangular parallelepiped shape from, for example, a resin material, and has a case body portion 14a and a case lid portion 14b. Figure 3 shows the case with the lid 14b attached, and Figure 5 shows the case with the lid 14b removed. Note that the hatching of the plate-shaped member 13a is omitted in Figure 4.

[0035] As shown in Figure 5, the case body 14a has a pair of first wall portions 14c facing each other in the X direction and a pair of second wall portions 14d facing each other in the Z direction. Multiple (two in this example) plate-like members 13a are arranged between each first wall portion 14c and the cell 11, and multiple (four in this example) plate-like members 13a are arranged between each second wall portion 14d and the cell 11. Although not shown, heat insulating members 13 (multiple plate-like members 13a) are also arranged between the wall portion in the Y direction of the case body 14a (the wall portion facing the case lid portion 14b in the Y direction) and the cell 11, and between the case lid portion 14b and the cell 11. Thus, in this example, the cell 11 is housed in the cell case 14 with the heat insulating members 13 interposed between it and the cell case 14. As shown in Figure 4, one of the pair of first wall portions 14c has an opening 14e through which the 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 the laser light L that has passed through the cell 11 passes.

[0036] As shown in Figure 3, the coil unit 15 is located outside the cell case 14. The coil unit 15 is composed of, for example, multiple coils, which generate a magnetic field acting on the cell 11. The sensor module 1 generates a magnetic field acting on the cell 11 using the coil unit 15 and detects changes in the magnetic field within the cell 11 using laser light L (probe light).

[0037] The coil unit 15 generates a corrective magnetic field, for example, so that the influence of magnetic fields other than the magnetic field being measured on the cell 11 approaches zero. For example, the coil unit 15 may generate a magnetic field in the opposite direction to the Earth's magnetic field so that the influence of the Earth's magnetic field is canceled out. Alternatively or in addition to this, the coil unit 15 may generate a modulated magnetic field that acts on the cell 11. For example, the coil unit 15 may generate an alternating magnetic field modulated at a predetermined frequency for increased sensitivity, or it may generate a modulated magnetic field to enable detection of the direction of magnetic field change (positive and negative directions in each axis). In this example, the coil unit 15 is made of a flexible circuit board and is arranged to surround the four sides of the cell case 14 (cell 11) (sides of the cell case 14 other than each second wall portion 14d) (sides of the cell 11 other than the two sides in the extending direction of the protrusion 11b), 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 includes 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 the shape of 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 case 14 so that it can be positioned on the outside of the cell case 14 along the cell case 14. More specifically, the support frame 30 is formed in a rectangular cylindrical shape so as to surround the cell case 14 (cell 11) when viewed from the Z direction. The support frame 30 has a pair of first surfaces 31A and 31B that face each other in the X direction (first direction) and a pair of second surfaces 32A and 32B that face each other in the Y direction (second direction). The first surfaces 31A and 31B are flat surfaces perpendicular to the X direction and parallel to each other, and the second surfaces 32A and 32B are flat surfaces perpendicular to the Y direction and parallel to each other. The first surfaces 31A and 31B cover a pair of surfaces of the cell case 14 in the X direction, and the second surfaces 32A and 32B cover a pair of surfaces of the cell case 14 in the Y direction. In this way, the support frame 30 is positioned outside the cell case 14 so as to surround the cell 11 via the cell case 14. In this example, the support frame 30 does not cover a pair of surfaces of the cell case 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 in the Z direction is longer than the length in the X direction and the length in the Y direction. In this example, when viewed from the Y direction, the support frame 30 is formed in a rectangular shape having a longer side in the Z direction and a shorter side in the X direction.

[0040] The plurality of coils 40 includes 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 plurality of coils 40 are made of a flexible printed circuit board 50 (FPC). An FPC is a flexible, bendable printed circuit board. The support frame 30 and the plurality of coils 40 are made by bending the flexible circuit board 50 (Figure 6). More specifically, as shown in the unfolded views in Figures 10 to 12, the first to third coils 41A to 43B are formed as a circuit on the flexible circuit board 50, and the support frame 30 and the plurality of coils 40 are made by bending the flexible circuit board 50 to take 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] Figure 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 that apply a magnetic field in the X direction to the cell 11.

[0042] As shown in Figure 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 located on the first surface 31A, a second portion 41Ab located on the second surface 32A, and a third portion 41Ac located on the second surface 32B. The first portion 41Aa consists of a pair of opposite sides in the Z direction and extends along the outer edge of the first surface 31A. The second portion 41Ab consists of a pair of opposite sides in the Z direction and extending along the outer edge of the second surface 32A, and a side connected to those sides and extending straight along the Z direction. The third portion 41Ac consists of a pair of opposite sides in the Z direction and extending along the outer edge of the second surface 32B, and a side connected to those sides and extending straight along the Z direction. As shown in Figure 10, the first coil 41A is formed in a rectangular shape in the flexible circuit board 50 before it is bent.

[0043] As shown in Figure 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 symmetric 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 (center C of the main body portion 11a of the cell 11). The first coil 41B has a first portion 41Ba located on the first surface 31B, a second portion 41Bb located on the second surface 32A, and a third portion 41Bc located on the second surface 32B. The first portion 41Ba consists of a pair of opposite sides in the Z direction and extends along the outer edge of the first surface 31B. The second portion 41Bb consists of a pair of opposite sides in the Z direction and extending along the outer edge of the second surface 32A, and a side connected to those sides and extending straight along the Z direction. The third portion 41Bc consists of a pair of edges that face each other in the Z direction and extend along the outer edge of the second surface 32B, and an edge that is connected to those edges and extends straight along the Z direction. As shown in Figure 10, the first coil 41B is formed in a rectangular shape in the flexible circuit board 50 before it is bent.

[0044] When 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 preferably be 0.4 or more and 0.7 or less, or more preferably 0.5 or more and 0.6 or less.

[0045] FIG. 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 across from the second surface 32A to the first surfaces 31A and 31B. The second coils 42A and 42B have a shape obtained by rotating the first coils 41A and 41B 90° around a straight 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 arranged on the second surface 32A, a second portion 42Ab arranged on the first surface 31A, and a third portion 42Ac arranged on the first surface 31B. The first portion 42Aa consists of a pair of opposing side portions in the Z direction and extends along the outer edge of the second surface 32A. The second portion 42Ab consists of a pair of opposing side portions in the Z direction that extend along the outer edge of the first surface 31A and side portions connected to those side portions and extending straight along the Z direction. The third portion 42Ac consists of a pair of opposing side portions in the Z direction that extend along the outer edge of the first surface 31B and side portions connected to those side portions and extending straight along the Z direction. As shown in FIG. 11, in the flexible circuit board 50 before being bent, the second coil 42A is formed in a rectangular shape.

[0047] As shown in FIG. 8, the second coil 42B extends across from the second surface 32B to the first surfaces 31A and 31B. The second coil 42B has a shape symmetric 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 opposite side portions in the Z direction and extends along the outer edge of the second surface 32B. The second portion 42Bb consists of a pair of opposite side portions that extend along the outer edge of the first surface 31A in the Z direction and side portions connected to those side portions and extending straight along the Z direction. The third portion 42Bc consists of a pair of opposite side portions that extend along the outer edge of the first surface 31B in the Z direction and side portions connected to those side portions and extending straight along the Z direction. As shown in FIG. 11, in the flexible circuit board 50 before being bent, the second coil 42B is formed in a rectangular shape.

[0048] FIG. 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] As shown in FIG. 9, the third coils 43A and 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 and 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] As shown in Figures 10 to 12, the flexible circuit board 50 has a plurality (six in this example) of planar portions 51, 52, 53, 54, 55, and 56 that correspond to the first surfaces 31A, 31B and the second surfaces 32A, 32B of the support frame 30. Planar portions 51 and 55 correspond to the first surface 31A. When the flexible circuit board 50 is bent to take the shape of the support frame 30, the planar portions 51 and 55 overlap to form the first surface 31A. Planar portion 52 corresponds to the first surface 31B. Planar portions 53 and 56 correspond to the second surface 32A. When the flexible circuit board 50 is bent to take the shape of the support frame 30, the planar portions 53 and 56 overlap to form the second surface 32A. Planar portion 54 corresponds to the second surface 32B.

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

[0052] An opening 58 is formed in the center of each of the planar portions 53 and 54 corresponding to the second surfaces 32A and 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. 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 planar portion 56, which is superimposed with the planar portion 53 to form the second surface 32A. In this example, the opening 59 is formed in the same circular shape as the light-passing opening 57 and the opening 59. When the flexible circuit board 50 is bent to form the support frame 30, the opening 58 formed in the planar portion 53 and the opening 59 formed in the planar portion 56 overlap each other. This positions the two planar portions 53 and 56. In other words, when bending the flexible circuit board 50 to form the support frame 30, the two planar portions 53 and 56 are superimposed so that the opening 58 formed in the planar portion 53 and the opening 59 formed in the planar portion 56 overlap each other. In this way, the opening 58 formed in the planar portion 53 and the opening 59 formed in the planar portion 56 function as positioning openings.

[0054] In the planar sections 51, 52, 53, 54, 55, and 56, elongated holes H are formed at the boundaries between two adjacent planar sections, extending along the boundary line. The formation of these elongated holes H facilitates the bending of the flexible circuit board 50 at the boundary line.

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

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

[0057] As shown in Figure 10, the first coils 41A and 41B are composed of a single conductive path. That is, the first coils 41A and 41B are composed of a single circuit portion P1 that does not have any electrically interrupted parts. In Figure 10, the circuit portion of the circuit portion P1 that constitutes the first coils 41A and 41B is shown by a solid line, and the circuit portion for canceling the magnetic field is shown by a diagonal line. In the circuit portion for canceling the magnetic field, the effect of the generated magnetic field is canceled by current flowing in both directions. In Figure 10, the path through which current flows in the circuit portion P1 is shown by an arrow. These points are the same for Figures 11 and 12. The first coils 41A and 41B are electrically connected to pad portion 61A of pad portion 61 via wiring portion 62 formed in lead-out portion 60.

[0058] As shown in Figure 11, the second coils 42A and 42B are composed of a single conductive path. That is, the second coils 42A and 42B are composed of a single circuit portion P2 that does not have any electrically interrupted parts. The second coils 42A and 42B are electrically connected to the pad portion 61B of the pad portion 61 via the wiring portion 63 formed in the lead portion 60.

[0059] As shown in Figure 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 a single circuit portion P3 that does not have any electrically interrupted parts. The third coils 43A and 43B are electrically connected to the pad portion 61C of the pad portion 61 via a wiring portion 64 formed in the lead portion 60. In this example, the flexible circuit board 50 also has a lead portion 65 that extends from a planar portion 56 corresponding to the second surface 32A of the support frame 30. The lead portion 65 is superimposed on the lead portion 60 when the flexible circuit board 50 is bent. A pad portion 65a is formed at the tip of the lead portion 65, and the third coils 43A and 43B are electrically connected to the pad portion 65a via a wiring portion 66 formed in the lead portion 65. A pad portion 60a is formed at the position corresponding to the pad portion 65a in the lead portion 60. Since the pad portion 65a is electrically connected to the pad portion 60a, one end and the other end of the third coils 43A and 43B are electrically connected to each other.

[0060] Figures 13 and 14 are diagrams illustrating the results of simulation-based calculations and comparisons of magnetic field uniformity in the embodiment and comparative example. The embodiment shown in Figure 13(b) corresponds to the 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 sides 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 Figure 13(a), the pair of first coils 141 are placed only on the first surfaces 31A and 31B, respectively. Other points are the same as in the embodiment.

[0061] Figure 14 shows the calculation results. "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 embodiment, compared to the comparative example, the standard deviation and maximum error of the magnetic flux density were approximately 1 / 5 smaller 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 uniformity of the magnetic field was improved by approximately 5 times. Furthermore, since the uniformity of the magnetic field in the Z direction, as well as the magnetic field in the X direction generated by the first coil, was improved, it can be seen that the occurrence of interaxial crosstalk can be suppressed. [Function and Effects]

[0062] In the sensor module 1, the first coil 41A (one of the pair of first coils 41A and 41B) extends from the first surface 31A (one of the pair of first surfaces 31A and 31B) of the support frame 30 across the second surfaces 32A and 32B (one and the other of the pair of second surfaces 32A and 32B), and the first coil 41B (the other of the pair of first coils 41A and 41B) extends from the first surface 31B (the other of the pair of first surfaces 31A and 31B) of the support frame 30 across the second surfaces 32A and 32B. This makes it possible to homogenize the magnetic field generated within the cell 11 by the first coils 41A and 41B. Therefore, the sensor module 1 can apply a uniform magnetic field to the cell 11 containing alkali metals. Furthermore, the coil unit 15 has a support frame 30 formed in the shape of a rectangular parallelepiped and arranged to surround the cell 11, and a plurality of coils 40 provided on the support frame 30. By configuring the coil unit 15 by providing a plurality of coils 40 on the support frame 30 formed in the shape of a rectangular parallelepiped, the cell 11, or the cell case 14 that houses the cell 11, can be suitably arranged inside the coil unit 15 (support frame 30). In optically excited magnetic sensors, such as the sensor module 1, detection is sometimes performed while applying a magnetic field to the cell. If the uniformity of the magnetic field is low, the detection sensitivity may decrease 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 make the magnetic field uniform. On the other hand, there are cases where heat insulating material or a cell case is placed around the cell, and because of spatial constraints, it may be difficult to adopt a coil shape that makes it easy to create a uniform magnetic field. In this regard, the sensor module 1 configures a coil unit 15 by providing the first coils 41A and 41B (multiple coils 40) having the shape described above on the support frame 30, thereby enabling the arrangement of components around the cell 11 while homogenizing the magnetic field.

[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 end of the second coil 42B (the other of the pair of second coils 42A and 42B) extends from the second surface 32B (the other end of the pair of second surfaces 32A and 32B) across the first surfaces 31A and 31B. This makes it possible to equalize the magnetic field generated within the cell 11 by the second coils 42A and 42B.

[0064] The multiple coils 40 further include a pair of third coils 43A and 43B. Each third coil 43A or 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 and 43B face each other in the Z direction (third direction), which is perpendicular to the X direction (first direction) and the Y direction (second direction). This makes it possible to equalize the magnetic field generated within the cell 11 by the third coils 43A and 43B.

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

[0066] The support frame 30 and the multiple coils 40 are made of a flexible circuit board 50. This makes the support frame 30 and the multiple coils 40 bendable.

[0067] If D is the distance between the first coils 41A and 41B along the X direction on the second surfaces 32A and 32B, and R is the length of the support frame 30 along the X direction, then D / R is between 0.2 and 0.8. This makes it possible to further homogenize the magnetic field generated within the cell 11 by the first coils 41A and 41B. This numerical range is based on the following simulation results. With the length R of the support frame 30 along the X direction fixed, the magnetic field generated within the cell 11 was calculated by changing the distance D between the first coils 41A and 41B in increments of 0.1 mm, and its standard deviation was calculated. Based on these calculation results, a range in which the standard deviation is small was selected.

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

[0069] The first coils 41A, 41B, the second coils 42A, 42B, and the third coils 43A, 43B are connected by a single conductive path. This 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 planar portions 51 to 56 corresponding to the first surfaces 31A, 31B and the second surfaces 32A, 32B of the support frame 30. Among the planar portions 51 to 56, the planar portions 51 and 52 corresponding to the first surfaces 31A, 31B have light-passing apertures 57 through which laser light L passes. The second surface 32A is formed by overlapping two planar portions 53 and 56 of the flexible circuit board 50, and the planar portions 53 and 56 each have apertures 58 and 59 (positioning apertures), and the planar portions 53 and 56 are overlapped so that these apertures 58 and 59 overlap each other. As a result, the planar portions 53 and 56 can be aligned by overlapping them so that the apertures 58 and 59 overlap each other.

[0071] Elongated holes H are formed at the boundary between the planar portions 51 and 56, extending along the boundary line. As a result of the formation of elongated holes H extending along the boundary line, the flexible circuit board 50 can be easily bent at the boundary.

[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 is formed on the lead-out portion 60 that is electrically connected to the first coils 41A and 41B. As a result, the pad portion 61 can be moved away from the cell 11 by the lead-out portion 60, and the magnetic field generated in the pad portion 61 can be prevented from affecting the magnetic field inside the cell 11. [Modified example]

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

[0074] In the modified sensor module 1, the alkali metal vapor in cell 11 is brought into a spin-polarized state by optical pumping using pump light L1 output from light source 21A. Probe light L2 output from light source 21B and passing through cell 11 is detected by photodetector 25. Here, since the spin-polarized state of the alkali metal vapor in cell 11 changes under the influence of the magnetic field of the object being measured, the polarization direction of the probe light L2 that has passed through the alkali metal vapor is changed to tilt. The first photodetector 25A detects the intensity of the light component in the deflection direction corresponding to the polarization direction of the probe light L2 before the polarization direction change, and the second photodetector 25B detects the intensity of the light component in the deflection direction corresponding to the polarization direction of the probe light L2 after the polarization direction change. This allows the difference in the light intensity of the two polarization direction components in the probe light L2 to be detected. Based on this difference, the spin-polarized state of the alkali metal vapor in cell 11 can be detected, and consequently, changes in the magnetic field of the object being measured can be detected.

[0075] In the two-laser system, for example, the probe light L2 passes through the cell 11 along the X direction. The probe light L2 passes through the light-passing apertures 57 formed in the planar 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 the apertures 58 (and apertures 59 formed in the planar portion 56) formed in the planar portions 53 and 54 of the flexible circuit board 50.

[0076] This disclosure is not limited to the embodiments and modifications described above. For example, the materials and shapes of each component are not limited to those described above, but can be made from a variety of materials and shapes. For example, the support frame 30 only needs to be positioned to surround at least a part of the cell 11 (main body 11a), and a part of the cell 11 may protrude outside the support frame 30. In the above embodiment, the support frame 30 had a long shape along the Z direction, but the support frame 30 may have a long shape along the X direction or the Y direction, or it may have a shape (cubic) with equal length along each direction. The support frame 30 and the plurality of coils 40 do not necessarily have to be made from 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, heater 12, heat insulating member 13, and 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 shapes described above, but may have any shape. For example, the second coils 42A and 42B may be placed 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 shapes described above, but may have any shape. For example, the third coils 43A and 43B may be placed only on the second surfaces 32A and 32B, respectively. The D / R described above may be less than 0.2 or greater 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 do not have to be composed of a single conductive path. For example, the first coils 41A and 41B may be composed of separate metal wires or circuits.

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

[0080] 1...Photo-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...Planar section, 57...Light-passing aperture, 58, 59...Aperture (positioning aperture), 60...Outlet section, 61, 61A, 61B, 61C...Pad section, H...Elongated hole.

Claims

1. An optically excited magnetic sensor module comprising: a cell containing an alkali metal; and a coil unit for generating a magnetic field acting on the cell, wherein the coil unit is formed in a shape along a rectangular parallelepiped and has a support frame body arranged to surround the cell; and a plurality of coils provided on the support frame body, wherein the support frame body 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; and 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 optically excited magnetic sensor module according to claim 1, wherein the plurality of coils further includes a pair of second coils, one of the pair of second coils extending from one of the pair of second surfaces across one and the other of the pair of first surfaces, and the other of the pair of second coils extending from the other of the pair of second surfaces across one and the other of the pair of first surfaces.

3. The optically excited magnetic sensor module according to claim 1 or 2, wherein the plurality of coils further include a pair of third coils, each of the pair of third coils extending 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 and second directions.

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

5. The photo-excited magnetic sensor module according to any one of claims 1 to 4, wherein the support frame and the plurality of coils are made of a flexible circuit board.

6. The optically excited magnetic sensor module according to any one of claims 1 to 5, wherein 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, and D / L is 0.2 or more and 0.8 or less.

7. The optically excited magnetic sensor module according to any one of claims 1 to 6, further comprising a cell case for housing the cell, wherein the support frame is disposed outside the cell case so as to surround the cell via the cell case.

8. The photo-excited magnetic sensor module according to any one of claims 1 to 7, wherein the pair of first coils are configured by a single conductive path.

9. The photo-excited magnetic sensor module according to claim 5, 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 planar portions corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, at least one of the plurality of planar portions corresponding to the pair of first surfaces has a light-passing aperture through which pump light passes, one of the pair of second surfaces is formed by overlapping two planar portions of the flexible circuit board, a positioning aperture is formed in each of the two planar portions, and the two planar portions are overlapped such that the positioning apertures of the two planar portions overlap each other.

10. The photo-excited magnetic sensor module according to claim 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 planar portions corresponding to the pair of first surfaces and the pair of second surfaces of the support frame, and elongated holes extending along the boundary lines are formed at the boundaries between the plurality of planar portions.

11. The photo-excited magnetic sensor module according to claim 5, 9, or 10, wherein the flexible circuit board has a pull-out portion that is pulled out in a direction away from the support frame, and the pull-out portion has a pad portion that is electrically connected to the pair of first coils.

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