Coil Structure

Abstract

The purpose of the present invention is to provide a coil structure capable of increasing the magnetic field that causes a current flowing through a coil to generate inside an object. The coil structure of the present invention is configured by winding a conducting wire, wherein 40% to 100% of the total length thereof is wound on a single conical surface, and the angle between the generatrix and the central axis of the single conical surface is preferably 48° to 60°.

Description

[Technical Field]

[0001] This application claims priority based on Japanese Patent Application No. 2021-45298, the contents of which are incorporated herein by reference. The present invention relates to a coil structure suitable for generating a magnetic field inside the human head or the like. [Background technology]

[0002] Transcranial magnetic stimulation (TMS), which generates a magnetic field at specific parts of the brain, has been proposed for the treatment of depression and other conditions.

[0003] Figure 9 shows the appearance and conceptual diagram of a conventional TMS device. The patient sits on the couch of the TMS device, places headgear 91 on the patient's head, and generates a magnetic field in a specific part of the brain by emitting a magnetic field from the coil built into the headgear. The dotted line 92 in the figure conceptually shows the magnetic field generated by the device, while reference numeral 93 denotes the operation panel, reference numeral 94 denotes the power driver, and reference numeral 95 denotes the cooling unit. Summary of the Invention [Problem to be solved by the invention]

[0004] When a current is passed through a coil to generate a magnetic field, it is inevitable that the coil will generate heat. If the heat generated by the coil is large, a large-scale device will be required to cool the coil. The object of the present invention is to provide a coil structure that can increase the magnetic field generated inside the target object in response to the current passed through the coil. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have completed the present invention as described below. [1] A coil structure in which a conductor is wound, with 40 to 100% of the total length wound around a single conical surface. [2] The coil structure of [1], wherein the angle between the generatrix and the central axis of the one conical surface is 48° to 60°. [3] A coil structure according to [1] or [2] intended for use on the human head. [4] A coil structure in which a conducting wire is wound in a conical shape along the periphery of a spherical body along an axis connecting a point of application where a predetermined magnetic flux density is desired and a point on the surface of the spherical body, and the relationship between the distance (z) between the point of application and the center of the coil and the distance (a) from the axis of the periphery of the spherical body is a≦2. 1 / 2 In the case of ×z, the coil structure is characterized by being wound with a coil diameter that is between the generatrix and the periphery of the spherical body, so that the angle between the axis and the generatrix is ​​48 to 60 degrees. [5] The coil structure of [4], having a core inside at least a portion of the coil structure. [Effects of the Invention]

[0006] According to the present invention, the magnetic field generated inside the cone shape increases relative to the current flowing through the coil, which allows the current flowing through the coil to be relatively small, thereby further simplifying the device for cooling the coil. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of the application of a coil according to the invention to a human head; [Figure 2] The radius a of the coil and the distance z to the point A where you want to act are defined. [Figure 3] This is a plot of the relationship between the coil radius a and the magnetic flux density B. [Figure 4] The coil radius that gives the maximum value of magnetic flux density shown in Figure 3 is plotted as ● against the distance z between the point of action and the coil center, and the plot ◯ represents the outer diameter of the object being acted upon. [Figure 5] FIG. [Figure 6-1] FIG. 1 is a cross-sectional view of a spiral coil. [Figure 6-2] FIG. 1 is a cross-sectional view of a spiral coil. [Figure 6-3] FIG. 1 is a cross-sectional view of a spiral coil. [Figure 7] FIG. 10 is a schematic diagram of another example of a coil structure according to the present invention. [Figure 8-1] 1 is a plot showing a portion of a cross section of a coil structure according to the present invention, illustrating suitable winding diameters for a helical coil. [Figure 8-2] 1 is a plot showing a portion of a cross section of a coil structure according to the present invention, illustrating suitable winding diameters for a helical coil. [Figure 8-3] 1 is a plot showing a portion of a cross section of a coil structure according to the present invention, illustrating suitable winding diameters for a helical coil. [Figure 8-4] 1 is a plot showing a portion of a cross section of a coil structure according to the present invention, illustrating suitable winding diameters for a helical coil. [Figure 8-5] 1 is a plot showing a portion of a cross section of a coil structure according to the present invention, illustrating suitable winding diameters for a helical coil. [Figure 9] 1 is an external view and conceptual diagram of a conventional TMS device. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below with reference to the accompanying drawings, in which: The illustrated embodiments are merely examples and are not intended to limit the present invention.

[0009] The coil structure of the present invention is particularly useful when it is necessary to generate a magnetic field in a location where it is impossible to install a conductor. For example, it is suitable when it is necessary to generate a magnetic field inside the human head (inside the brain). Other examples of its application include, but are not limited to, locations that are difficult to remove, such as the chest or abdominal organs of animals, including humans.

[0010] According to the present invention, there are no particular limitations on the conductors used or the method of connecting to the power source, and conventionally known techniques relating to coil manufacturing can be used as appropriate.

[0011] FIG. 1 is a schematic diagram of the application of a coil according to the present invention to a human head. FIG. 1(A) is a schematic external view, and FIG. 1(B) shows a simplified cross section of a single-turn circular coil passing through the central axis 15. Reference numerals 13 and 14 represent cross sections of the coil itself, with current flowing from 14 to the back of the page and from 13 to the front of the page. This figure defines the distance z between point A and the coil center, as well as the coil radius a. The coil structure of the present invention, comprised of conductor wire 11, is conical and, in this configuration, is attached to a human head 12. Point A in the figure is the location inside the head (brain) where a predetermined magnetic field is desired to be generated. Point B in the figure is the intersection of the surface 16 of the target spherical body and the central axis 15 of the coil, which is the very edge of the target head.

[0012] Referring to Figure 1(B), we consider the optimal shape of the cone formed by the coil. Here, curve 16 in Figure 1(B) indicates the limiting position at which the conductor can be placed. In other words, the conductor cannot be placed inside circle 16. As a specific example, curve 16 can be thought of as the surface of a human head. Line 15 is the central axis of the cone formed by the coil structure. Point B mentioned above is located at the intersection of central axis 15 and curve 16. Point A, as mentioned above, is the location where a specified magnetic field is desired to be generated. The conductors that make up the coil are represented by symbols 13 and 14. In the figure, r is the distance between point A and curve 16. Considering the points 13 and 14 on the conductor, let a be the distance from them to central axis 15, and let Z be the distance from the projection point of symbol 13 onto central axis 15 to point A.

[0013] As an assumed example, consider placing a coil on the outside of a sphere with a radius of about 100 mm, and deriving the structure of the coil that will generate the required magnetic flux density (for example, about 50 mT) at the center. Figure 2 is a cross-sectional view including the central axis of the coil. If the distance AC between the center C of the coil and point A where a magnetic field with a specified magnetic flux density is desired is z, and the coil radius is a, then the magnetic flux density B [T] at point A is:

number

[0014] Figure 3 is a plot of the relationship between the coil radius and magnetic flux density B when z, the distance from the coil center to the point of application, is used as a parameter. This plot, for example when the distance is 10 mm or 20 mm, makes it clear that there is an optimum value for the coil radius that can deliver the highest magnetic flux. This optimum value can be expressed by differentiating the above equation, and the relationship is a=2 1 / 2 × z. For example, if z is 60 mm, the radius a is 84.85 mm. Therefore, the coil diameter is calculated by using the distance z to the part that generates a specified magnetic flux as a = 2 1 / 2 The coil designed with a radius a according to xz is the coil that can generate the strongest magnetic flux density.

[0015] Therefore, when the symbols a and z are defined as above, the radius a of the coil that gives the maximum magnetic flux density at a certain point is a = 2 1 / 2 The optimal shape is a coil with coils aligned along the xz axis arranged on a concentric axis. However, this shape is like a megaphone, with a small diameter near the target area and a larger diameter the further away, and it may not be possible to place it inside the target area. For example, if the target is simply a sphere, under these conditions, a=2 1 / 2 To design a coil radius that satisfies ×z, when the distance between the target area and the coil center is determined, for example, when z = 40 mm, the optimal radius a = 56.6 mm. However, considering the above conditions, a radius of 91.5 mm or less is inside the target area and cannot be placed, so it is designed with the minimum diameter of the sphere. When the distance to the area is 80 mm, the optimal diameter is larger than the minimum diameter of the sphere, so it is possible to design with the optimal diameter. This can be explained in Figure 4. The circle plot surrounded by an ellipse indicates that the optimal coil diameter cannot be achieved because the area is close to the affected area, so the coil diameter must be designed to follow the shape of the sphere. The circle plot surrounded by an ellipse indicates that the coil diameter can be designed with the optimal diameter.

[0016] As an example of the coil shape resulting from the above considerations, the shape shown in Figure 7 can be considered. With this shape, when a high frequency current of 100 [A] and 200 [kHz] is applied to the coil central axis and 80 mm inside from the surface of the shape to be irradiated, the magnetic flux density is calculated to be approximately 5.0 [mT]. For example, if the required magnetic flux density is 40 [mT], it is necessary to stack 6 to 8 coils per unit length. In other words, the relationship between the coil radius and the distance z from the center of the coil to a point on the central axis (point of action) that generates the specified magnetic flux density is approximately a = 2 1 / 2 A coil having a coil relationship that satisfies ×z is preferred, and also, for a coil that generates a magnetic field inside an object where a coil cannot be placed inside, if the distance (z') from the axis of the coil to the surface of the object is smaller than 1.4 times the distance (z) to the point of application, that value is used as the coil radius, and if it is greater, a coil characterized by having a radius that is 1.4 times the distance z to the point of application is also preferred.

[0017] A specific example of such a coil structure is a coil structure in which a conductor is wound to form a single conical surface. Here, the angle between the generatrix and the central axis of the cone that forms the conical surface is preferably 48° to 60°, with the optimum angle being 54.7°. FIG. 5 is an explanatory diagram of a cone, showing the generatrix 51, the central axis 52, and the angle θ they form. Due to the convenience of connecting to a power source, etc., it is not necessary for the entire conductor to be present on the conical surface of the coil structure; specifically, it is sufficient if 40 to 100% of the total length of the conductor is on the single conical surface. Note that, in the case of the above-mentioned a=2, 1 / 2 The process of deriving the optimal angle of 54.7° from the equation × z is as follows: From the above equation, tanθ=a / z=2 1 / 2 is the angle θ calculated as the solution of

[0018] Figure 6-1 is a diagram of the layout of a spiral coil cross section, showing how the centers of coil cross sections 62 are aligned along the 54.7° angle between bus bar 61 and coil central axis 60. The actual coil cross section shape is rectangular or circular, as shown in 62, and when wound into a coil, the coil has an inner diameter and an outer diameter. The angle formed by the innermost end face of the coil is smaller than 54.7°, and the angle formed by the outermost end face of the coil is larger than 54.7°. When actually passing a high-frequency current, the current concentrates at the inner end face or outer end face of the coil due to the skin effect, so in some cases it may be appropriate to shape the bus bar so that half of its longitudinal thickness is shifted inward or outward.

[0019] For example, if the coil cross sections 62, 64, and 66 are rectangular and the long side of the rectangular cross section is 64 mm, and the center of the coil cross section 63 is formed along an angle of 54.7°, the angle θ between the central axis and the line 64 connecting the inner end face of the coil at the end position of 100 mm, which is the maximum diameter of the conical coil, and the apex of the cone, is i is tanθ i =(100×2 1 / 2 -64 / 2) / 100, θ i = 48.09°. On the other hand, the outer end of the coil is tanθ o =(100×2 1 / 2 +64 / 2) / 100, the angle θ of the generatrix 65 o Therefore, if a conical coil is generated with the angle between the bus 51 and the coil central axis 52 set to 48° to 60°, it is possible to align the inner side surface or the outer side surface, where the current density is high, with the optimum radius.

[0020] Note that Figure 6-2 shows an example of a coil wound so that the center of the cross section of the terminal coil (reference numeral 64) at a position 100 mm aligns with the busbar 63, which forms an angle of 48° with the central axis 60, and Figure 6-3 shows an example of a coil wound so that the center of the cross section of the terminal coil (reference numeral 66) at a position 100 mm aligns with the busbar 65, which forms an angle of 60° with the central axis 60.

[0021] Figure 7 is a schematic diagram of another example of a coil structure according to the present invention. This coil structure has a portion 71 in which the conductor wire is wound on a conical surface and a portion 72 in which the conductor wire is wound on a cylindrical surface. In the embodiment shown in Figure 7, portion 71 accounts for approximately 50% of the total length of the conductor wire. A core may be embedded in the hollow portion of the coil in portion 72. Examples of materials for the core include iron, ferrite, and amorphous metal materials.

[0022] Figure 8-1 shows a cross section of the coil structure shown in Figure 7, and is a plot showing the appropriate winding diameter for a spiral coil. Reference numeral 81 in this plot indicates that the conductor wound on a conical surface is wound with a coil diameter that follows the contours of the subject, such as the head, to which the magnetic field is applied. Reference numeral 82 represents the range of possible coil radii for a conductor wound on a cylindrical surface. The following can be said from this plot: From the point of application, which is the origin (0,0) of the graph in Figure 8-1, up to a point 60 mm away, the coil winding diameter is determined and positioned according to reference numeral 81. In the region 82 between 60 mm and 100 mm, it is most effective to determine the winding diameter according to the optimal winding diameter 83. However, if the coil diameter is determined in the region 82 surrounded by the parallel line 84 and the optimal line 83, and a core is positioned inside, a stronger magnetic field can be generated. However, although Fig. 8-1 shows the distance from the point of action up to 100 mm, the coil may be wound to a position farther than 100 mm, and the present invention is not limited to a distance of 100 mm. Similarly, Fig. 8-1 does not draw a plot at the position 86 of the object, but extending the plot 81 beyond the position Z=0 and winding the coil does not reduce the effect.

[0023] As shown in Figure 8-1, an appropriate method for designing a coil is to consider the distance from the point of application 86 to the end portion 87 of the object as 100%, and then determine the coil diameter to follow the shape of the object up to 60% of the distance from the point of application, and from 60% or more, determine the coil diameter between the optimum diameter 83 and a cylindrical winding 84 wound with the same diameter. In Example 1, if the coil is an air-core coil without a core, the coil is wound along 88 as shown in Figure 8-2. In Example 2, the simplest configuration from the standpoint of manufacturing is to form the coil into a cylindrical shape along 88 as shown in Figure 8-3. Also, as a design method when the maximum depth of the point of application is 80 mm from the end 87 of the object, as shown in Figure 8-4, the coil is formed along the outer edge 891 of the object up to 80 x 60% = 48 mm, and from 48 mm onwards, the coil is formed with a constant radius as shown by reference numeral 892, or the coil is formed along the optimum diameter as shown by reference numerals 893 and 894, or the coil is wound with a constant diameter from the position of the end of the object onwards as shown by reference numerals 893 and 895. Each of these values ​​is one example, and depending on the size of the object, the depth of the point of application, and whether or not a core is built in, the horizontal axis of Figure 8-1 can be interpreted as a percentage representing the positional relationship between the point of application and the end of the object, and the coil radius can be designed so that the coil is located at reference numeral 81 and region 82. In another embodiment, as shown in Figure 8-5, in the region where the distance between the center position of each coil turn and the point of application is 0 to 60%, a coil with a rectangular cross-sectional shape as shown by reference numeral 896 is wound along the surface of the object, and in the region where the distance is 60% or more, the rectangular cross-sectional shape is gradually changed as shown by reference numeral 897, with the inner diameter of the coil turn kept constant and the outer diameter of the coil turn wound along the optimum plot. In this case, the coil shown by reference numeral 897 may be a coil in which the cross-section of a spirally integrated wire material is gradually changed, and since induced electromotive force can be used, the coils shown by reference numeral 897 may each be independent in a ring shape and not connected in series.

[0024] Also, in FIG. 8-5, an example is shown in which the coil cross sections are arranged at a pitch of 10 mm, but the pitch may be, for example, 5 mm, and the dimensions are not limited to those shown in the example.

[0025] As described above, according to the present invention, a magnetic field can be efficiently generated with a low current in a location where a conductor cannot be installed. Therefore, the current required for a desired magnetic field can be reduced, which is expected to suppress heat generation and simplify heat countermeasures. [Explanation of symbols]

[0026] 11 Conductor 12 Head 51 Generatrix 52 Center axis

Claims

1. A coil structure is formed by winding a conductor in a conical shape along the periphery of a spherical body along an axis connecting a point of action where a predetermined magnetic flux density is desired and a point on the surface of the spherical body, and a magnetic field is generated by passing a current through the conductor constituting the coil structure, and the relationship between the distance (z) between the point of action and the center of the coil and the distance (a) from the axis of the periphery of the spherical body is a≦2. １／２ In the case of xz, the coil structure is characterized in that it is wound with a coil diameter that is between the generatrix and the periphery of the spherical body, so that the angle between the axis and the generatrix is ​​48 to 60 degrees.

2. 10. The coil structure of claim 1, further comprising a core within at least a portion of the coil structure.

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