coil

Abstract

To reduce loss in a coil with a wire wound once or multiple times in a spiral.SOLUTION: A coil 100A includes a wire 1 wound around a central axis 2 once or multiple times in a spiral shape. The wire 1 includes a conductor 10 whose cross-sectional shape 11 in a plane including the central axis 2 is elongated. The cross-sectional shape 11 is curved such that the first end 12 and the second end 13 in the longitudinal direction are separated from the central axis 2.SELECTED DRAWING: Figure 2

Description

[Technical Field] 【0001】 This disclosure relates to coils. [Background technology] 【0002】 Conventionally, coils obtained by winding a wire with a circular cross-section conductor have been widely used. However, it is known that in such coils, the skin effect and proximity effect of the wire cause uneven distribution of current flow. Therefore, when alternating current flows through the coil, losses occur due to these effects, resulting in a problem of reduced power transmission efficiency. 【0003】 Therefore, efforts are being made to reduce the above-mentioned losses in the coil. For example, Japanese Patent Publication No. 2021-100102 (Patent Document 1) discloses a coil in which a wire having a conductor with a non-circular cross-sectional shape is wound multiple times in a spiral shape. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Japanese Patent Publication No. 2021-100102 [Overview of the project] [Problems that the invention aims to solve] 【0005】 The method of winding the wire in a coil varies depending on the application of the coil. The technology disclosed in Patent Document 1 applies to coils in which the wire is wound multiple times in a spiral shape, and does not apply to coils in which the wire is wound once or multiple times in a spiral shape. In other words, Patent Document 1 does not disclose how to reduce losses in coils in which the wire is wound once or multiple times in a spiral shape. 【0006】 This disclosure addresses the above-mentioned problems and aims to reduce losses in coils comprising wires wound once or multiple times in a spiral. [Means for solving the problem] 【0007】 A coil relating to one aspect of this disclosure comprises a wire wound once or multiple times in a spiral around a central axis. The wire includes an elongated conductor having a cross-sectional shape in a plane containing the central axis. The cross-sectional shape is curved such that the first and second ends in the longitudinal direction are away from the central axis. 【0008】 According to the above coil, the generation of reverse current and the uneven distribution of current in the conductor are suppressed. As a result, losses can be reduced in coils that have wires wound once or multiple times in a spiral. [Effects of the Invention] 【0009】 According to this disclosure, losses in a coil comprising a wire wound once or multiple times in a spiral can be reduced. [Brief explanation of the drawing] 【0010】 [Figure 1] This is a perspective view of the coil according to Embodiment 1. [Figure 2] This is a cross-sectional view showing the coil of the first embodiment. [Figure 3] This is a cross-sectional view showing a coil of the second embodiment. [Figure 4] This is a cross-sectional view showing a coil of the third embodiment. [Figure 5] This is a cross-sectional view showing an example of an electric wire containing insulating material. [Figure 6] This is a cross-sectional view showing another example of an electric wire containing insulating material. [Figure 7] This is a cross-sectional view showing the coil of the first reference example. [Figure 8] This is a cross-sectional view showing the coil of the second reference example. [Figure 9] This is a cross-sectional view showing the coil of the third reference example. [Figure 10] This is a cross-sectional view showing the coil of the fourth reference example. [Figure 11] This is a cross-sectional view showing the coil of the fifth reference example. [Figure 12] It is a diagram showing the current distribution in the conductor cross-section of models No. 1A to 38A, 27A1, and 27A2 when the frequency is 100 kHz. [Figure 13] It is a graph showing the Q values of each model in Embodiment 1 when the coil diameter d is 50 mm and the frequency is 100 kHz. [Figure 14] It is a graph showing the Q values of each model in Embodiment 1 when the coil diameter d is 100 mm and the frequency is 100 kHz. [Figure 15] It is an external perspective view of the coil according to Embodiment 2. [Figure 16] It is a cross-sectional view showing the coil of the fourth embodiment. [Figure 17] It is a cross-sectional view showing the coil of the fifth embodiment. [Figure 18] It is a cross-sectional view showing the coil of the sixth embodiment. [Figure 19] It is a cross-sectional view showing the coil of the seventh embodiment. [Figure 20] It is a cross-sectional view showing the coil of the sixth reference example. [Figure 21] It is a cross-sectional view showing the coil of the seventh reference example. [Figure 22] It is a cross-sectional view showing the coil of the eighth reference example. [Figure 23] It is a cross-sectional view showing the coil of the ninth reference example. [Figure 24] It is a cross-sectional view showing the coil of the tenth reference example. [Figure 25] It is a cross-sectional view showing the coil of the eleventh reference example. [Figure 26] It is a diagram showing the current distribution in the conductor cross-section of models No. 1B to 15B when the frequency is 100 kHz. [Figure 27] It is a diagram showing the current distribution in the conductor cross-section of models No. 16B to 30B when the frequency is 100 kHz. [Figure 28] It is a diagram showing the current distribution in the conductor cross-section of models No. 31B to 38B, 27B1, and 27B2 when the frequency is 100 kHz. [Figure 29]This figure shows the current distribution in the conductor cross-section of models No. 2B1~2B3, 18B1~18B3, and 21B1~21B3 at a frequency of 100kHz. [Figure 30] This figure shows the current distribution in the conductor cross-section of models No. 24B1~24B3, 27B3~27B5, and 30B1~30B3 at a frequency of 100kHz. [Figure 31] This graph shows the Q values ​​of each model in Embodiment 2 when the coil diameter d is 50 mm and the frequency is 100 kHz. [Figure 32] This graph shows the Q values ​​of each model in Embodiment 2 when the coil diameter d is 100 mm and the frequency is 100 kHz. [Figure 33] This is a perspective view of the coil according to Embodiment 3. [Figure 34] This is a cross-sectional view showing the coil of the eighth embodiment. [Figure 35] This graph shows the Q values ​​of each model in Embodiment 3 when the coil diameter d is 50 mm and the frequency is 100 kHz. [Figure 36] This graph shows the Q values ​​of each model in Embodiment 3 when the coil diameter d is 100 mm and the frequency is 100 kHz. [Modes for carrying out the invention] 【0011】 Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, identical or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated. Furthermore, the embodiments or modifications described below may be selectively combined as appropriate. 【0012】 <Embodiment 1> Figure 1 is an external perspective view of the coil according to Embodiment 1. As shown in Figure 1, the coil 100A according to Embodiment 1 comprises an electric wire 1 wound once around a central axis 2. The diameter of the coil 100A (hereinafter referred to as "coil diameter") is d. 【0013】 Figure 2 is a cross-sectional view showing the coil of the first embodiment. Figure 3 is a cross-sectional view showing the coil of the second embodiment. Figure 4 is a cross-sectional view showing the coil of the third embodiment. Figures 2 to 4 show cross-sectional views of coil 100A in a plane including the central axis 2. As shown in Figures 2 to 4, the electric wire 1 is wound once around the central axis 2 at a distance of d / 2 from the central axis 2. Note that only a portion of coil 100A is depicted in Figures 2 to 4. That is, the cross-section of coil 100A located to the left of the central axis 2 is not shown in Figures 2 to 4. 【0014】 As shown in Figures 2 to 4, the electric wire 1 includes a conductor 10 whose cross-sectional shape 11 in a plane containing the central axis 2 is non-circular. The cross-sectional shape 11 of the conductor 10 is shaped to avoid or bypass areas where reverse current is likely to flow and areas where current is unlikely to flow. As a result, the loss of the conductor 10 is reduced. Specifically, the cross-sectional shape 11 is elongated, and the first end 12, which is one end in the longitudinal direction, and the second end 13, which is the other end in the longitudinal direction, are curved away from the central axis 2. This suppresses the generation of reverse current and the uneven distribution of current in the conductor 10 when an alternating current is passed through the coil 100A. 【0015】 If the first end 12 and the second end 13 are tapered, current distribution tends to become uneven in these areas. Therefore, it is preferable that the first end 12 and the second end 13 are tapered so that the entire structure is rounded. 【0016】 When the reference line 18 is defined as a straight line passing through the center point 16 of the cross-sectional shape 11 and perpendicular to the line segment 17 connecting the first end 12 and the second end 13, it is preferable that the cross-sectional shape 11 is symmetrical with respect to the reference line 18. This further suppresses the generation of reverse current and the uneven distribution of current in the conductor 10 when an alternating current is passed through the coil 100A. 【0017】 The reference line 18 defines the orientation of the conductor 10. As shown in Figures 2 to 4, it is preferable that the reference line 18 is perpendicular to the central axis 2 in any part of the wire 1. This further suppresses the generation of reverse current and the uneven distribution of current in the conductor 10. 【0018】 As described above, the cross-sectional shape 11 is curved such that the first end 12 and the second end 13 move away from the central axis 2. Therefore, the cross-sectional shape 11 has a concave first edge 14 facing outward from the coil 100A and a convex second edge 15 facing the central axis 2. 【0019】 The cross-sectional shape 11 is preferably formed such that the distance t between the first edge 14 and the second edge 15 is constant. The distance t is preferably 2 times or less the skin depth (the depth at which the current becomes 1 / e of the surface current) at the operating frequency of the coil 100A. 【0020】 As shown in Figure 2, the cross-sectional shape 11a of the conductor 10 in the coil 100A of the first embodiment is an arc shape with a central angle θs. That is, the first edge 14 and the second edge 15 are arc shapes with a central angle θs. This further suppresses the generation of reverse current and the uneven distribution of current in the conductor 10. The cross-sectional shape 11a is symmetric with respect to the reference line 18. 【0021】 When the conductor 10 has an arc-shaped cross-section 11a, the simulation results described later show that the central angle θs is preferably 15° to 345°, more preferably 60° to 345°, even more preferably 105° to 345°, even more preferably 120° to 345°, particularly preferably 180° to 345°, and most preferably 240° to 345°. By having the central angle θs at the above values, the generation of reverse current and the uneven distribution of current in the conductor 10 are more effectively suppressed. The central angle θs is calculated, for example, as the arithmetic mean of the measured angles at the cross-sectional shape 11a at any 10 locations on the electric wire 1. 【0022】 When the conductor 10 has an arc-shaped cross-section 11a and the spacing t is constant, the radius R1 of the first edge 14 with respect to the center point O of the arc is calculated using the spacing t, the central angle θs, and the required conductor cross-sectional area (area of ​​the cross-sectional shape 11a). 【0023】 For example, 2mm at a frequency of 100kHz 2 When a considerable conductor cross-sectional area is required, the radius R1 is determined using the spacing t (mm) and the central angle θs (°). R1 = (2 × 360 / θs - πt) 2 ) / 2tπ It is expressed as follows. Note that the interval t and radius R1 are calculated, for example, as the arithmetic mean of the measured values ​​at 10 arbitrary positions in the cross-sectional shape of the electric wire 1. 【0024】 As shown in Figure 3, the cross-sectional shape 11b of the conductor 10 in the coil 100A of the second embodiment is V-shaped (a V-shape rotated by 90°). Specifically, the cross-sectional shape 11b has a bend 20 at the center point 16. The region from the bend 20 to the first end 12 and the region from the bend 20 to the second end 13 each extend linearly in a direction inclined with respect to the central axis 2. The cross-sectional shape 11b is symmetric with respect to the reference line 18. 【0025】 If the bent portion 20 is pointed, current distribution is likely to become uneven in this area. Therefore, it is preferable that the outer side of the bent portion 20 (the side facing the central axis 2 in Figure 3) has a chamfered shape. 【0026】 When the conductor 10 has a V-shaped cross-sectional shape 11b, the simulation results described later show that the angle θv formed on the inside of the bent portion 20 is preferably 90° to 165°, more preferably 105° to 165°, even more preferably 120° to 165°, and particularly preferably 120° to 150°. The angle θv is calculated, for example, as the arithmetic mean of the measured angles at the cross-sectional shape of 10 arbitrary positions on the electric wire 1. 【0027】 When the conductor 10 has a V-shaped cross-sectional shape 11b and the spacing t is constant, the length L1 is calculated by the spacing t, the angle θv, and the required conductor cross-sectional area (area of ​​the cross-sectional shape 11b), with L1 being half the length of the first edge 14. 【0028】 As shown in Figure 4, the cross-sectional shape 11c of the conductor 10 in the coil 100A of the third embodiment is U-shaped (a U-shape rotated 90 degrees). Specifically, the cross-sectional shape 11c has two bent portions 21 and 22. The portion of the cross-sectional shape 11 between the bent portions 21 and 22 extends linearly parallel to the central axis 2. The region from the bent portion 21 to the first end 12 and the region from the bent portion 22 to the second end 13 each extend linearly in a direction inclined with respect to the central axis 2. The cross-sectional shape 11c is symmetric with respect to the reference line 18. Therefore, the angle θ formed inside the bent portions 21 and 22 U They are identical. 【0029】 If the bent portions 21 and 22 are pointed, current distribution is likely to become uneven in these areas. Therefore, it is preferable that the outer side of the bent portions 21 and 22 (the side facing the central axis 2 in Figure 4) be chamfered. 【0030】 When the conductor 10 has a U-shaped cross-sectional shape 11c, the simulation results described later show that the angle θu formed inside the bent portions 21 and 22 is preferably 105 to 165°, and more preferably 105 to 150°. The angle θu is calculated, for example, as the arithmetic mean of the measured angles at 10 arbitrary positions in the cross-sectional shape of the electric wire 1. 【0031】 When the conductor 10 has a U-shaped cross-sectional shape 11c and the spacing t is constant, the lengths L2 and L3 are calculated by the spacing t, the angle θu, and the required conductor cross-sectional area (area of ​​the cross-sectional shape 11), where L2 is the length from the bent portion 21 of the first edge 14 to the first end 12 (or from the bent portion 22 to the second end 13), and L3 is the length between the bent portions 21 and 22 of the first edge 14. 【0032】 The conductor 10 is made of, for example, flat braided copper wire, copper plate, copper tape, or copper foil. Furthermore, the material of the conductor 10 is not limited to copper; it may be made of a metal other than copper. 【0033】 The electric wire 1 may include an insulating material covering the conductor 10. Alternatively, the conductor 10 may not be covered with an insulating material and may be a bare conductor. 【0034】 Figure 5 is a cross-sectional view showing an example of an electric wire including an insulating material. Figure 5 shows an electric wire 1 in which the entire conductor 10 is covered with an insulating material 30. For example, as shown in Figure 5(a), the electric wire 1 may include an insulating material 30 that covers the entire conductor 10 and has a periphery that corresponds to the periphery of the conductor 10. Alternatively, as shown in Figure 5(b), the electric wire 1 may include an insulating material 30 that covers the entire conductor 10 and has a rectangular periphery. 【0035】 Figure 6 is a cross-sectional view showing another example of a wire containing an insulating material. Figure 6 shows a wire 1 in which only a portion of the conductor 10 is covered by the insulating material 30. For example, as shown in Figure 6(a), the wire 1 may comprise a hollow cylindrical insulating material 30 having an outer circumference that contacts the first edge 14 of the conductor 10. Alternatively, as shown in Figure 6(b), the wire 1 may comprise a hollow cylindrical insulating material 30 having an inner circumference that contacts the second edge 15 of the conductor 10. 【0036】 The material of the insulating material 30 is not limited to the following, but is preferably an electrically insulating polymer composition, such as 1 × 10 12 It is more preferable that the polymer composition has a volume resistivity of Ω·cm or more. 【0037】 (simulation) Using the analysis software Femtet® (Version 2018.1.2.70140), models of multiple coils with different conductor cross-sectional shapes and conductor orientations were evaluated under the analysis conditions shown in Table 1. 【0038】 [Table 1] 【0039】 The models under evaluation include the models corresponding to the coils 100A of the first to third embodiments shown in Figures 2 to 4, respectively, as well as the models corresponding to the coils of the first to fifth reference examples shown below. The coils of the first to fifth reference examples include a wire wound once around a central axis 2, similar to the coil 100A shown in Figure 1. 【0040】 Figure 7 is a cross-sectional view showing the coil of the first reference example. As shown in Figure 7, the wire provided in the coil of the first reference example has a conductor 10 whose planar cross-sectional shape 11d containing the central axis 2 is circular. The diameter D of the cross-sectional shape 11d is calculated from the required conductor cross-sectional area (area of ​​the cross-sectional shape 11d). 【0041】 Figure 8 is a cross-sectional view showing the coil of the second reference example. As shown in Figure 8, the wire provided in the coil of the second reference example has a conductor 10 whose cross-sectional shape 11e in a plane including the central axis 2 is I-shaped. The cross-sectional shape 11e is elongated, similar to the cross-sectional shapes 11a to 11c. However, the cross-sectional shape 11e is straight. A reference line 18 that passes through the center point 16 of the cross-sectional shape 11e and is perpendicular to the line segment 17 connecting the first end 12 and the second end 13 defines the orientation of the conductor 10 having the cross-sectional shape 11e. As shown in Figure 8, the reference line 18 is perpendicular to the central axis 2. That is, the cross-sectional shape 11e extends along the central axis 2. The longitudinal length L4 of the cross-sectional shape 11e is calculated by the distance t between the edge of the cross-sectional shape 11e on the central axis 2 side and the edge on the opposite side of the central axis 2, and the required conductor cross-sectional area (area of ​​the cross-sectional shape 11e). 【0042】 Figure 9 is a cross-sectional view showing the coil of the third reference example. As shown in Figure 9, the wire provided in the coil of the third reference example has a conductor 10 whose planar cross-sectional shape 11f containing the central axis 2 is O-shaped. The inner diameter R2 of the cross-sectional shape 11f is given by the distance t between the outer and inner edges of the cross-sectional shape 11f and the required conductor cross-sectional area (cross-sectional shape 11 f It is calculated by (the area of) and 【0043】 Figure 10 is a cross-sectional view showing the coil of the fourth reference example. As shown in Figure 10, the wires provided in the coil of the fourth reference example have conductors 10 having the same cross-sectional shape 11a as the first embodiment shown in Figure 2. However, in the fourth reference example, the conductors 10 are arranged so that the reference straight line 18 is parallel to the central axis 2. That is, the conductors 10 in the fourth reference example take on a position where the reference straight line 18 is rotated by 90° on the plane containing the central axis 2, compared to the position of the conductors 10 in the first embodiment. 【0044】 Figure 11 is a cross-sectional view showing the coil of the fifth reference example. As shown in Figure 11, the wire provided in the coil of the fifth reference example has a conductor 10 having the same cross-sectional shape 11a as the first embodiment shown in Figure 2. However, in the fifth reference example, the conductor 10 is arranged such that the concave first edge 14 faces the central axis 2 and the convex second edge 15 faces outward from the coil. That is, the conductor 10 in the fifth reference example takes on a position obtained by rotating the reference straight line 18 by 180° on the plane containing the central axis 2 from the position of the conductor 10 in the first embodiment. 【0045】 Table 2 shows a list of the conductor cross-sectional shapes used in the model under evaluation. The cross-sectional shape has a cross-sectional area of ​​2 mm² in the plane containing the central axis 2. 2It is designed to be as follows: The cross-sectional shape of No. 1 is the circular cross-sectional shape 11d shown in Figure 7. The cross-sectional shape of No. 2 is the I-shaped cross-sectional shape 11e shown in Figure 8. The length L4 of the cross-sectional shape of No. 2 is designed so that the spacing t is 0.4 mm. The cross-sectional shape of No. 3 is the O-shaped cross-sectional shape 11f shown in Figure 9. The inner diameter R2 of the cross-sectional shape of No. 3 is designed so that the spacing t is 0.4 mm. The cross-sectional shapes of No. 4 to 9 are the V-shaped cross-sectional shapes 11b shown in Figure 3, and have different angles θv from each other. The length L1 of the cross-sectional shapes of No. 4 to 9 is designed so that the spacing t is 0.4 mm and the angle θv is 90° to 165° (15° intervals). The cross-sectional shapes of No. 10 to 15 are the U-shaped cross-sectional shapes 11c shown in Figure 4, and have different angles θu from each other. The cross-sectional shapes of No. 10 to 15 are designed so that the length L3 has a spacing t of 0.4 mm, a length L2 of 2.5 mm, and an angle θu of 90° to 165° (at 15° intervals). The cross-sectional shapes of No. 16 to 38 are the arc-shaped cross-sections 11a shown in Figure 2, and each has a different central angle θs. The radii R1 of the cross-sectional shapes of No. 16 to 38 are designed so that the spacing t is 0.4 mm and the central angle θs is 15° to 345° (at 15° intervals). 【0046】 [Table 2] 【0047】 The models under evaluation include models No. 1A to 38A, 27A1, and 27A2. Model No. 1A corresponds to a coil in which a wire with the cross-sectional shape of No. 1 is wound once around a central axis 2 (the coil in the first reference example shown in Figure 7). Model No. 2A corresponds to a coil in which a wire with the cross-sectional shape of No. 2 is wound once around a central axis 2, and the reference line 18 of the cross-sectional shape is perpendicular to the central axis 2 (the coil in the second reference example shown in Figure 8). Model No. 3A corresponds to a coil in which a wire with the cross-sectional shape of No. 3 is wound once around a central axis 2 (the coil in the third reference example shown in Figure 9). 【0048】 Models No. 4A to 9A correspond to coils (coil 100A in the second embodiment shown in Figure 3) in which a wire having the cross-sectional shapes of No. 4 to 9 is wound once around the central axis 2. 【0049】 Models No. 10A to 15A correspond to coils (coil 100A in the third embodiment shown in Figure 4) in which a wire having the cross-sectional shapes of No. 10 to 15 is wound once around the central axis 2. 【0050】 Models No. 16A to 38A correspond to coils (coil 100A in the first embodiment shown in Figure 2) in which a wire having a conductor with the cross-sectional shape of No. 16 to 38 is wound once around a central axis 2. Models No. 4A to 38A correspond to coils having a conductor that is positioned such that the second edge 15 faces the central axis 2 and the reference straight line 18 is perpendicular to the central axis 2. 【0051】 Model No. 27A1 corresponds to a coil (the coil in the fourth reference example shown in Figure 10) in which a wire having the cross-sectional shape of No. 27 is wound once around the central axis 2 so that the reference straight line 18 is parallel to the central axis 2. 【0052】 Model No. 27A2 corresponds to a coil (the coil in the fifth reference example shown in Figure 11) in which a wire having the cross-sectional shape of No. 27 is wound once around the central axis 2 such that the first edge 14 faces the central axis 2 and the reference straight line 18 is perpendicular to the central axis 2. 【0053】 Tables 3 to 5 show the simulation results for each model with a coil diameter d of 50 mm. Furthermore, Tables 6 to 8 show the simulation results for each model with a coil diameter d of 100 mm. Tables 3 and 6 show the inductance (nH) at each frequency, Tables 4 and 7 show the resistance (Ω) at each frequency, and Tables 5 and 8 show the Q value at each frequency. The Q value is expressed as 2πfL / R, where L is the inductance and R is the resistance. A higher Q value indicates less loss. 【0054】 [Table 3] 【0055】 [Table 4] 【0056】 [Table 5] 【0057】 [Table 6] 【0058】 [Table 7] 【0059】 [Table 8] 【0060】 Figure 12 shows the current distribution in the conductor cross-section of models No. 1A to 38A, 27A1, and 27A2 at a frequency of 100 kHz. Figure 12 shows the current distribution when the coil diameter d of each model is 50 mm. Note that Figure 12 shows the current distribution in the conductor cross-section where the central axis 2 is on the left side. 【0061】 Figure 13 is a graph showing the Q values ​​of each model in Embodiment 1 when the coil diameter d is 50 mm and the frequency is 100 kHz. Figure 14 is a graph showing the Q values ​​of each model in Embodiment 1 when the coil diameter d is 100 mm and the frequency is 100 kHz. In Figures 13 and 14, the horizontal axis represents the central angle θs, angles θv, and θu, and the vertical axis represents the Q value. In Figures 13 and 14, the point where θs = 360° represents the value obtained from the model corresponding to the coil of the third reference example. Also, the point where θs = 0° and the points where θv, θu = 180° represent the values ​​obtained from the model corresponding to the coil of the second reference example. 【0062】 As shown in Figures 13 and 14, No. 1 corresponds to the first reference example, which has a circular cross-sectional shape. A The Q values ​​of models No. 4A to 38A, which correspond to the coils of the first to third embodiments, are higher than those of model No. 1A. This is because, as shown in Figure 12, the current distribution is significantly uneven in model No. 1A, which corresponds to the first reference example with a circular cross-sectional shape, whereas the current distribution is suppressed in models No. 4A to 38A, which correspond to the coils of the first to third embodiments. 【0063】 The Q values ​​of models No. 16A to 38A, corresponding to the coil (arc-shaped) of the first embodiment, tend to be higher than those of models No. 4A to 15A, corresponding to the coils (V-shaped and U-shaped) of the second and third embodiments. This is because, as shown in Figure 12, in V-shaped and U-shaped conductors having bent portions 20 to 22, the current tends to be unevenly distributed at these bent portions, whereas in the arc-shaped conductor, the uneven distribution of current caused by the bends is suppressed. 【0064】 The models of No. 27A, 27A1, and 27A2 all correspond to coils having an arcuate conductor with θs = 180°. However, it is found that the Q value of the model of No. 27A corresponding to the coil of the first embodiment is higher than that of the models of No. 27A1 and 27A2 corresponding to the coils of the fourth and fifth reference examples. This is because the convex second edge 15 (see FIG. 2) faces the central axis 2, suppressing the uneven distribution of current as shown in FIG. 12. 【0065】 As shown in FIGS. 13 and 14, among the models corresponding to coils having an arcuate conductor, the Q value of the model with a central angle θ S ranging from 15° to 345° is confirmed to be higher than that of the models corresponding to coils having circular and I-shaped cross-sectional conductors. Also, the Q value of the model with a central angle θ S ranging from 105° to 345° is confirmed to be higher than that of the models corresponding to coils having conductors of other cross-sectional shapes. The Q value becomes even higher when the central angle θ S ranges from 180° to 345°, and it is further confirmed that the Q value becomes even higher when the central angle θ S ranges from 240° to 345°. 【0066】 Among the models corresponding to coils having a V-shaped conductor, the Q value is high when the angle θv ranges from 105° to 165°, and it is particularly high when the angle θv ranges from 120° to 150°. 【0067】 Among the models corresponding to coils having a U-shaped conductor, the Q value is high when the angle θu ranges from 105° to 165°, and it is particularly high when the angle θu ranges from 105° to 150°. 【0068】 <Embodiment 2> FIG. 15 is an external perspective view of the coil according to Embodiment 2. As shown in FIG. 15, the coil 100B according to Embodiment 2 is different from the coil 100A according to Embodiment 1 in that the electric wire 1 is wound around the central axis 2 in a spiral shape a plurality of times. 【0069】 Figure 16 is a cross-sectional view showing the coil of the fourth embodiment. Figure 17 is a cross-sectional view showing the coil of the fifth embodiment. Figure 18 is a cross-sectional view showing the coil of the sixth embodiment. Figures 16 to 18 show cross-sectional views of the coil 100B in a plane including the central axis 2. As shown in Figures 16 to 18, the electric wire 1 is wound spirally multiple times around the central axis 2 such that the distance from the central axis 2 is d / 2. d is the coil diameter. Note that only a portion of the coil 100B is depicted in Figures 16 to 18. That is, the cross-section of the coil 100B located to the left of the central axis 2 is not shown in Figures 16 to 18. 【0070】 As shown in Figures 16 to 18, the electric wire 1 according to Embodiment 2 has the same characteristics as those of Embodiment 1. 【0071】 In other words, the electric wire 1 includes a conductor 10 whose cross-sectional shape 11 in a plane containing the central axis 2 is non-circular. The cross-sectional shape 11 is elongated and curved so that one end in the longitudinal direction, the first end 12, and the other end in the longitudinal direction, the second end 13, are separated from the central axis 2, in order to avoid or bypass areas where current flow is difficult. Furthermore, it is preferable that the first end 12 and the second end 13 are tapered so that the entire shape is rounded. 【0072】 Furthermore, it is preferable that the cross-sectional shape 11 is symmetrical with respect to a reference line 18 that passes through the center point 16 and is perpendicular to the line segment 17 connecting the first end 12 and the second end 13. At any point on the electric wire 1, it is preferable that the reference line 18 is perpendicular to the central axis 2. 【0073】 Furthermore, the concave first edge 14 faces outward from the coil 100B, and the convex second edge 15 faces the central axis 2. The cross-sectional shape 11 is preferably formed such that the distance t between the first edge 14 and the second edge 15 is constant. The distance t is preferably twice or less the skin depth (the depth at which the current becomes 1 / e of the surface current) at the operating frequency of the coil 100B. 【0074】 As shown in Figure 16, the cross-sectional shape 11a of the conductor 10 provided in the coil 100B of the fourth embodiment is arc-shaped, similar to the first embodiment of Embodiment 1 shown in Figure 2. When winding a conductor 10 having the cross-sectional shape 11a so that the coil diameter d is 50 mm, simulation results described later show that the central angle θs is preferably 15° to 330°, more preferably 60° to 285°, even more preferably 90° to 240°, and particularly preferably 105° to 240°. When winding a conductor 10 having the cross-sectional shape 11a so that the coil diameter d is 100 mm, the central angle θs is preferably 60° to 345°, more preferably 120° to 345°, and even more preferably 180° to 300°. S By having the above value, the uneven distribution of current is more effectively suppressed. 【0075】 As shown in Figure 17, the cross-sectional shape 11b of the conductor 10 provided in the coil 100B of the fifth embodiment is V-shaped, similar to the second embodiment of Embodiment 1 shown in Figure 3. When winding a conductor 10 having the cross-sectional shape 11b so that the coil diameter d is 50 mm, the angle θv formed on the inside of the bent portion 20 is preferably 120° to 165°, as shown in the simulation results described later. When winding a conductor 10 having the cross-sectional shape 11b so that the coil diameter d is 100 mm, the angle θv is preferably 90° to 165°, more preferably 105° to 165°, and even more preferably 120° to 165°. By having the angle θv at the above values, the uneven distribution of current is more effectively suppressed. 【0076】 As shown in Figure 18, the cross-sectional shape 11c of the conductor 10 provided in the coil 100B of the sixth embodiment is U-shaped, similar to the third embodiment of Embodiment 1 shown in Figure 4. When winding a conductor 10 having the cross-sectional shape 11c so that the coil diameter d is 50 mm, simulation results described later show that the angle θu formed inside the bent portions 21 and 22 is preferably 105° to 165°, more preferably 120° to 165°, and even more preferably 120° to 150°. When winding a conductor 10 having the cross-sectional shape 11c so that the coil diameter d is 100 mm, the angle θu is preferably 90° to 165°, more preferably 90° to 150°, and even more preferably 105° to 135°. By having the angle θu at the above values, the uneven distribution of current is more effectively suppressed. 【0077】 Figure 19 is a cross-sectional view showing the coil of the seventh embodiment. As shown in Figure 19, the cross-sectional shape 11a of the conductor 10 provided in the coil 100B of the seventh embodiment is as shown in Figure 2 It is arc-shaped, similar to the first embodiment shown. However, the coil 100B of the seventh embodiment differs from the coil 100B of the fourth embodiment in that the reference straight line 18 is not perpendicular to the central axis 2 in a part of the electric wire 1. 【0078】 The electric wire 1 is wound spirally three or more times around the target section 3 of the central axis 2. In the example shown in Figure 19, the electric wire 1 is wound 10 times. The electric wire 1 has a first part 1a wound around a first section 3a located at one end of the target section 3, a second part 1b wound around a second section 3b located at the other end of the target section 3, and a third part 1c wound around a third section 3c located between the first section 3a and the second section 3b of the target section 3. The reference line 18c in the third part 1c is perpendicular to the central axis 2. The reference line 18a in the first part 1a is inclined with respect to the reference line 18c corresponding to the third part 1c in a direction that causes the intersection points 40a, 40c with the central axis 2 to move away from each other. In the second part 1b, the reference line 18b is inclined in a direction that causes the intersection points 40b and 40c with the central axis 2 to move away from each other, relative to the reference line 18c corresponding to the third part 1c. The degree of inclination is represented by the angle φ between the reference lines 18a and 18c and the line perpendicular to the central axis 2. 【0079】 The orientation of the conductor 10 in the first part 1a, the second part 1b, and the third part 1c may be made different from each other by twisting the electric wire 1, or by joining the first part 1a, the second part 1b, and the third part 1c while the orientations of the conductor 10 are different from each other. 【0080】 In the example shown in Figure 19, the number of turns in the first part 1a and the second part 1b is 3, and the number of turns in the third part 1c is 4. However, the number of turns in the first part 1a, the second part 1b, and the third part 1c is not limited to these. 【0081】 As shown by the simulation results described later, in the conductor 10 of the first part 1a and the second part 1b, current tends to flow on the side farther from the third part 1c. Therefore, as shown in Figure 19, by tilting the reference lines 18a and 18b in the first part 1a and the second part 1b, the conductor 10 is positioned in the part where current flows easily, and the uneven distribution of current in the conductor 10 is suppressed. 【0082】 In Embodiment 2, the electric wire 1 may also include an insulating material that covers the conductor 10. The insulating material may cover the entire conductor 10, as shown in Figure 5, or it may cover a part of the conductor 10, as shown in Figure 6. Alternatively, the insulating material may cover the entire conductor 10, which is wound multiple times in a spiral shape and extends along the central axis 2. 【0083】 (simulation) Each model of multiple coils with different conductor cross-sectional shapes and conductor orientations was evaluated according to the same method as in Embodiment 1. 【0084】 The models under evaluation include the models corresponding to the coils of the 4th to 7th embodiments shown in Figures 16 to 19, respectively, as well as the models corresponding to the coils of the 6th to 11th reference examples shown below. The coils of the 6th to 11th reference examples include a wire wound multiple times in a spiral around a central axis 2, similar to coil 100B shown in Figure 15. 【0085】 Figure 20 is a cross-sectional view showing the coil of the sixth reference example. As shown in Figure 20, the cross-sectional shape 11d of the conductor 10 provided in the coil of the sixth reference example is circular, similar to the first reference example shown in Figure 7, and is defined by the diameter D (see Figure 7). 【0086】 Figure 21 is a cross-sectional view showing the coil of the seventh reference example. As shown in Figure 21, the cross-sectional shape 11e of the conductor 10 provided in the coil of the seventh reference example is I-shaped, similar to the second reference example shown in Figure 8, and is defined by the longitudinal length L4 (see Figure 8) and the distance t (see Figure 8) between the edge on the side of the central axis 2 and the edge on the opposite side of the central axis 2. In any part of the wire, the reference straight line 18 is perpendicular to the central axis 2. 【0087】 Figure 22 is a cross-sectional view showing the coil of the eighth reference example. As shown in Figure 22, the cross-sectional shape 11f of the conductor 10 provided in the coil of the eighth reference example is O-shaped, similar to the third reference example shown in Figure 9, and is defined by the distance t between the outer and inner edges (see Figure 9) and the inner diameter R2 (see Figure 9). 【0088】 Figure 23 is a cross-sectional view showing the coil of the ninth reference example. As shown in Figure 23, the wire provided in the coil of the ninth reference example has a conductor 10 having the same cross-sectional shape 11a as the fourth embodiment shown in Figure 16. However, in the ninth reference example, the wire 1 is arranged such that the reference straight line 18 is parallel to the central axis 2 in any portion. That is, the cross-sectional shape 11a in the ninth reference example takes the position obtained by rotating the reference straight line 18 by 90° on the plane containing the central axis 2 from the position in the fourth embodiment. 【0089】 Figure 24 is a cross-sectional view showing the coil of the 10th reference example. As shown in Figure 24, the wire provided in the coil of the 10th reference example has a conductor 10 having the same cross-sectional shape 11a as the 4th embodiment shown in Figure 16. However, in the 10th reference example, the wire 1 is arranged such that the concave first edge 14 faces the central axis 2 and the convex second edge 15 faces outward from the coil. That is, the cross-sectional shape 11a in the 10th reference example takes the position obtained by rotating the reference straight line 18 by 180° on the plane containing the central axis 2 from the position in the 4th embodiment. 【0090】 Figure 25 is a cross-sectional view showing the coil of the 11th Reference Example. As shown in Figure 25, the conductor 10 of the electric wire provided in the coil of the 11th Reference Example has the same cross-sectional shape 11e as the 7th Reference Example shown in Figure 21. However, the coil of the 11th Reference Example differs from the coil of the 7th Reference Example in that the reference straight line 18 is not perpendicular to the central axis 2 in a part of the electric wire. Specifically, similar to the 7th embodiment, the electric wire has a first portion 1a wound around a first section 3a located at one end of the target section 3, a second portion 1b wound around a second section 3b located at the other end of the target section 3, and a third portion 1c wound around a third section 3c located between the first section 3a and the second section 3b of the target section 3. The reference straight line 18c in the third portion 1c is perpendicular to the central axis 2. The reference line 18a in the first part 1a is inclined in a direction that causes the intersection points 40a and 40c with the central axis 2 to move away from each other, relative to the reference line 18c corresponding to the third part 1c. The reference line 18b in the second part 1b is inclined in a direction that causes the intersection points 40b and 40c with the central axis 2 to move away from each other, relative to the reference line 18c corresponding to the third part 1c. The degree of inclination is represented by the angle φ between the reference lines 18a and 18c and the normal to the central axis 2. The number of turns in the first part 1a and the second part 1b is 3, and the number of turns in the third part 1c is 4. 【0091】 The models under evaluation include models No. 1B to 38B, 2B1 to 2B3, 18B1 to 18B3, 21B1 to 21B3, 24B1 to 24B3, 27B1 to 27B5, and 30B1 to 30B3. Model No. 1B corresponds to a coil (the coil of the 6th reference example shown in Figure 20) in which a wire with a conductor of the No. 1 cross-sectional shape shown in Table 2 is wound spirally 10 times around a central axis 2. Model No. 2B corresponds to a coil (the coil of the 7th reference example shown in Figure 21) in which a wire with a conductor of the No. 2 cross-sectional shape is wound spirally 10 times around a central axis 2, and the reference line 18 of the cross-sectional shape is perpendicular to the central axis 2. Model No. 3B corresponds to a coil (the coil of the 8th reference example shown in Figure 22) in which a wire with a conductor of the No. 3 cross-sectional shape is wound spirally 10 times around a central axis 2. 【0092】 Models No. 4B to 9B correspond to coils (coil 100B of the fifth embodiment shown in Figure 17) in which a wire having the cross-sectional shapes of No. 4 to 9 is wound spirally 10 times around a central axis 2. 【0093】 Models No. 10B to 15B correspond to coils (coil 100B of the sixth embodiment shown in Figure 18) in which a wire having the cross-sectional shapes of No. 10 to 15 is wound spirally 10 times around a central axis 2. 【0094】 Models No. 16B to 38B correspond to coils (coil 100B of the fourth embodiment shown in Figure 16) in which a wire having the cross-sectional shapes of No. 16 to 38 is wound spirally 10 times around a central axis 2. 【0095】 Models No. 4B to 38B correspond to coils having a conductor that is positioned such that the second edge 15 faces the central axis 2 and the reference line 18 is perpendicular to the central axis 2. 【0096】 Model No. 27B1 corresponds to a coil (the coil in the 9th reference example shown in Figure 23) in which a wire having the cross-sectional shape of No. 27 is wound spirally 10 times around the central axis 2 so that the reference straight line 18 is parallel to the central axis 2. 【0097】 Model No. 27B2 corresponds to a coil (the coil of the 10th reference example shown in Figure 24) in which a wire having the cross-sectional shape of No. 27 is wound spirally 10 times around the central axis 2, such that the first edge 14 faces the central axis 2 and the reference line 18 is perpendicular to the central axis 2. 【0098】 Models No. 2B1 to 2B3 correspond to a coil (the coil of the 11th reference example shown in Figure 25) in which a wire with the cross-sectional shape of No. 2 is wound spirally 10 times around the central axis 2, such that the reference lines 18a and 18b of the first part 1a and the second part 1b are inclined with respect to the normal to the central axis 2, and the reference line 18c of the third part 1c is perpendicular to the central axis 2. Models No. 2B1 to 2B3 correspond to coils designed with angles φ (see Figure 25) of 30°, 45°, and 60°, respectively. The number of turns in the first part 1a and the second part 1b is set to 3, and the number of turns in the third part 1c is set to 4. 【0099】 Models No. 18B1~18B3, 21B1~21B3, 24B1~24B3, 27B3~27B5, and 30B1~30B3 correspond to a coil (the coil of the 7th embodiment shown in Figure 19) in which a wire having a conductor with a cross-sectional shape 11a is wound spirally 10 times around the central axis 2, such that the reference lines 18a and 18b of the first part 1a and the second part 1b are inclined with respect to the normal to the central axis 2, and the reference line 18c of the third part 1c is perpendicular to the central axis 2. The number of turns of the first part 1a and the second part 1b is 3, and the number of turns of the third part 1c is 4. 【0100】 Models No. 18B1 to 18B3 correspond to the coil 100B having a conductor with cross-sectional shape 11a of No. 18. Models No. 21B1 to 21B3 correspond to the coil 100B having a conductor with cross-sectional shape 11a of No. 21. Models No. 24B1 to 24B3 correspond to the coil 100B having a conductor with cross-sectional shape 11a of No. 24. Models No. 27B3 to 27B5 correspond to the coil 100B having a conductor with cross-sectional shape 11a of No. 27. Models No. 30B1 to 30B3 correspond to the coil 100B having a conductor with cross-sectional shape 11a of No. 30. 【0101】 Models No. 18B1, 21B1, 24B1, 27B3, and 30B1 correspond to coils designed with an angle φ (see Figure 19) of 30°. Models No. 18B2, 21B2, 24B2, 27B4, and 30B2 correspond to coils designed with an angle φ (see Figure 19) of 45°. Models No. 18B3, 21B3, 24B3, 27B5, and 30B3 correspond to coils designed with an angle φ (see Figure 19) of 60°. 【0102】 In each model, the pitch P1 between the wound wires (see Figures 16-25) is set to 6 mm. 【0103】 Tables 9 to 14 show the simulation results when the coil diameter d of each model is 50 mm. Furthermore, Tables 15 to 20 show the simulation results when the coil diameter d of each model is 100 mm. Tables 9, 10, 15, and 16 show the inductance (μH) at each frequency, Tables 11, 12, 17, and 18 show the resistance (Ω) at each frequency, and Tables 13, 14, 19, and 20 show the Q value at each frequency. 【0104】 [Table 9] 【0105】 [Table 10] 【0106】 [Table 11] 【0107】 [Table 12] 【0108】 [Table 13] 【0109】 Table 14 【0110】 Table 15 【0111】 Table 16 【0112】 Table 17 【0113】 Table 18 【0114】 Table 19 【0115】 Table 20 【0116】 Figure 26 shows the current distribution in the conductor cross-section of models No. 1B to 15B at a frequency of 100 kHz. Figure 27 shows the current distribution in the conductor cross-section of models No. 16B to 30B at a frequency of 100 kHz. Figure 28 shows the current distribution in the conductor cross-section of models No. 31B to 38B, 27B1, and 27B2 at a frequency of 100 kHz. Figure 29 shows the current distribution in the conductor cross-section of models No. 2B1 to 2B3, 18B1 to 18B3, and 21B1 to 21B3 at a frequency of 100 kHz. Figure 30 shows the current distribution in the conductor cross-section of models No. 24B1 to 24B3, 27B3 to 27B5, and 30B1 to 30B3 at a frequency of 100 kHz. Figures 26 to 30 show the current distribution when the coil diameter d of each model is 50 mm. Figures 26 to 30 show the current distribution in a conductor cross-section where the central axis 2 is located on the left side. 【0117】 Figure 31 is a graph showing the Q values ​​of each model in Embodiment 2 when the coil diameter d is 50 mm and the frequency is 100 kHz. Figure 32 is a graph showing the Q values ​​of each model in Embodiment 2 when the coil diameter d is 100 mm and the frequency is 100 kHz. In Figures 31 and 32, the horizontal axis represents the central angle θs, angles θv, and θu, and the vertical axis represents the Q value. In Figures 31 and 32, the point where θs = 360° represents the value obtained from the model corresponding to the coil of Reference Example 8. Also, the point where θs = 0° and the points where θv, θu = 180° represent the value obtained from the model corresponding to the coil of Reference Example 7 or Reference Example 11. 【0118】 Similar to Embodiment 1, it can be observed that the Q values ​​of models No. 4B to 38B, which correspond to the coils of Embodiments 4 to 6, are higher than those of model No. 1B, which corresponds to Reference Example 6, in which the cross-sectional shape of the conductor is circular. 【0119】 Furthermore, the Q values ​​of models No. 16B to 38B, which correspond to the arc-shaped coil of the fourth embodiment, tend to be higher than those of models No. 4B to 15B, which correspond to the V-shaped and U-shaped coils of the fifth and sixth embodiments. 【0120】 Models No. 27B, 27B1, and 27B2 all correspond to coils having an arc-shaped conductor with θs = 180°. However, it is observed that the Q value of model No. 27B, which corresponds to the coil in the 4th embodiment, is higher than that of models No. 27B1 and 27B2, which correspond to the coils in the 9th and 10th reference examples. 【0121】 Simulation results for a model corresponding to a coil with an arc-shaped conductor show that the Q value depends on the central angle θs. Specifically, when the coil diameter d is 50 mm, the Q value is high when the central angle θs is between 15° and 330°, even higher when the central angle θs is between 60° and 285°, even higher when the central angle θs is between 90° and 240°, and particularly high when the central angle θs is between 105° and 240°. When the coil diameter d is 100 mm, the Q value is high when the central angle θs is between 60° and 345°, even higher when the central angle θs is between 120° and 345°, and even higher when the central angle θs is between 180° and 300°. 【0122】 Furthermore, it is observed that the Q value increases significantly by tilting the reference straight lines 18a and 18b of the first portion 1a and second portion 1b of the electric wire 1, which are wound around the first portion 3a and second portion 3b located at both ends of the target section 3 of the central axis 2. As shown in Figures 27 and 28, in the conductor of the first portion 1a at the upper end, the current tends to concentrate on the upper side. On the other hand, in the conductor of the second portion 1b at the lower end, the current tends to concentrate on the lower side. Therefore, as shown in Figures 29 and 30, by tilting the orientation of the conductor in the direction in which the current tends to concentrate, the uneven distribution of current in the conductor is suppressed. 【0123】 Simulation results from a model corresponding to a coil with a V-shaped conductor show that the Q value depends on the angle θv. When the coil diameter d is 50 mm, the Q value is high when the angle θv is between 120° and 165°. When the coil diameter d is 100 mm, the Q value is high when the angle θv is between 90° and 165°, even higher when the angle θv is between 90° and 150°, and even higher when the angle θv is between 105° and 135°. 【0124】 Simulation results from a model corresponding to a coil with a U-shaped conductor show that the Q value depends on the angle θu. When the coil diameter d is 50 mm, the Q value is high when the angle θu is between 105° and 165°, higher when the angle θu is between 120° and 165°, and even higher when the angle θu is between 120° and 150°. When the coil diameter d is 100 mm, the Q value is high when the angle θu is between 90° and 165°, higher when the angle θu is between 90° and 150°, and even higher when the angle θu is between 105° and 135°. 【0125】 <Embodiment 3> Figure 33 is an external perspective view of the coil according to Embodiment 3. As shown in Figure 33, the coil 100C according to Embodiment 3 differs from the coil 100B according to Embodiment 2 in that the distance between the central axis 2 and the electric wire 1 increases or decreases along the central axis 2. In the example shown in Figure 33, the distance between the central axis 2 and the electric wire 1 increases as you move upwards from the central axis 2. As shown in Figure 33, the coil diameter d is the diameter of the portion of the electric wire 1 that is wound closest to the central axis 2. 【0126】 Figure 34 is a cross-sectional view showing the coil of the eighth embodiment. The coil 100C of the eighth embodiment is obtained by applying the configuration of Embodiment 3 to the coil 100B of the fourth embodiment shown in Figure 16. That is, as shown in Figure 34, the coil 100C of the eighth embodiment differs from the coil 100B of the fourth embodiment in that the distance between the central axis 2 and the electric wire 1 increases by a pitch P2 during one spiral winding of the electric wire 1 along the central axis 2. 【0127】 Similarly, by applying the configuration of Embodiment 3 to the coils 100B of the 5th to 7th embodiments shown in Figures 17 to 19, coils of the 9th to 11th embodiments (not shown) can be obtained, respectively. That is, the coil 100C of the 9th embodiment differs from the coil 100B of the 5th embodiment (see Figure 17) in that the distance between the central axis 2 and the wire 1 increases by a pitch P2 during the single spiral winding of the wire 1 along the central axis 2. The coil 100C of the 10th embodiment differs from the coil 100B of the 6th embodiment (see Figure 18) in that the distance between the central axis 2 and the wire 1 increases by a pitch P2 during the single spiral winding of the wire 1 along the central axis 2. The coil 100C of the 11th embodiment differs from the coil 100B of the 7th embodiment (see Figure 19) in that the distance between the central axis 2 and the wire 1 increases by a pitch P2 during the single spiral winding of the wire 1 along the central axis 2. 【0128】 (simulation) Each model of multiple coils with different conductor cross-sectional shapes was evaluated according to the same method as in Embodiment 2. 【0129】 The models under evaluation include the models corresponding to coil 100C of the 8th to 11th embodiments, as well as the models corresponding to the coils (not shown) of the 12th to 17th reference examples. The coils of the 12th to 17th reference examples are obtained by applying the configuration of Embodiment 3 to the coils of the 6th to 11th reference examples shown in Figures 20 to 25. That is, the coils of the 12th to 17th reference examples differ from the coils of the 6th to 11th reference examples, respectively, in that the distance between the central axis 2 and the electric wire 1 increases by a pitch P2 during one spiral winding of the electric wire 1 along the central axis 2. 【0130】 The models being evaluated are No.1C~38C, 2C1~2C3, 18C1~18C3, 21C1~21C3, 24 C1~ 24 C3, 27C1~27C5, 30 C1~ 30 Includes C3 models. No.1C~38C, 2C1~2C3, 18C1~18C3, 21C1~21C3,24 C1~ 24 C3, 27C1~27C5, 30 C1~ 30 The C3 models are No.1B~38B, 2B1~2B3, 18B1~18B3, 21B1~21B3, 24 B1~ 24 B3, 27B1~27B5, 30 B1~ 30 Compared to the B3 model, the only difference is that the distance between the central axis 2 and the wire 1 increases by a pitch P2 while the wire 1 is wound spirally once along the central axis 2. 【0131】 Specifically, model No. 1C corresponds to the coil of the 12th reference example, having a conductor with the cross-sectional shape of No. 1 shown in Table 2. Model No. 2C corresponds to the coil of the 13th reference example, having a conductor with the cross-sectional shape of No. 2. Model No. 3C corresponds to the coil of the 14th reference example, having a conductor with the cross-sectional shape of No. 3. Models No. 4C to 9C correspond to the coil 100C of the 9th embodiment, having conductors with the cross-sectional shapes of No. 4 to 9, respectively. Models No. 10C to 15C correspond to the coil 100C of the 10th embodiment, having conductors with the cross-sectional shapes of No. 10 to 15, respectively. Models No. 16C to 38C correspond to the coil 100C of the 8th embodiment, having conductors with the cross-sectional shapes of No. 16 to 38, respectively. Model No. 27C1 corresponds to the coil of the 15th reference example, having a conductor with the cross-sectional shape of No. 27. Model No. 27C2 corresponds to the coil of Reference Example No. 16, which has a conductor with the cross-sectional shape of No. 27. 【0132】 Models No. 2C1 to 2C3 correspond to the coil of the 17th reference example having a conductor with the cross-sectional shape of No. 2, where the angles φ between the reference lines 18a and 18b and the normal to the central axis 2 are designed to be 30°, 45°, and 60°, respectively. Models No. 18C1 to 18C3 correspond to the coil 100C of the 11th embodiment having a conductor with the cross-sectional shape of No. 18, where the angles φ between the reference lines 18a and 18b and the normal to the central axis 2 are designed to be 30°, 45°, and 60°, respectively. Models No. 21C1 to 21C3 correspond to the coil 100C of the 11th embodiment having a conductor with the cross-sectional shape of No. 21, where the angles φ between the reference lines 18a and 18b and the normal to the central axis 2 are designed to be 30°, 45°, and 60°, respectively. Models No. 24C1 to 24C3 correspond to coils 100C of the 11th embodiment having a conductor with the cross-sectional shape of No. 24, and are designed so that the angles φ between the reference lines 18a and 18b and the normal to the central axis 2 are 30°, 45°, and 60°, respectively. Models No. 27C3 to 27C5 correspond to coils 100C of the 11th embodiment having a conductor with the cross-sectional shape of No. 27, and are designed so that the angles φ between the reference lines 18a and 18b and the normal to the central axis 2 are 30°, 45°, and 60°, respectively. Models No. 30C1 to 30C3 correspond to coils 100C of the 11th embodiment having a conductor with the cross-sectional shape of No. 30, and are designed so that the angles φ between the reference lines 18a and 18b and the normal to the central axis 2 are 30°, 45°, and 60°, respectively. 【0133】 In each model, the pitch P1 between the wound wires (see Figure 34) is set to 6 mm, and the pitch P2 is set to 3 mm. 【0134】 Tables 21 to 26 show the simulation results when the coil diameter d of each model is 50 mm. Furthermore, Tables 27 to 32 show the simulation results when the coil diameter d of each model is 100 mm. Tables 21, 22, 27, and 28 show the inductance (μH) at each frequency, Tables 23, 24, 29, and 30 show the resistance (Ω) at each frequency, and Tables 25, 26, 31, and 32 show the Q value at each frequency. 【0135】 [Table 21] 【0136】 [Table 22] 【0137】 [Table 23] 【0138】 [Table 24] 【0139】 [Table 25] 【0140】 [Table 26] 【0141】 [Table 27] 【0142】 [Table 28] 【0143】 [Table 29] 【0144】 [Table 30] 【0145】 [Table 31] 【0146】 [Table 32] 【0147】 Figure 35 is a graph showing the Q values ​​of each model in Embodiment 3 when the coil diameter d is 50 mm and the frequency is 100 kHz. Figure 36 is a graph showing the Q values ​​of each model in Embodiment 3 when the coil diameter d is 100 mm and the frequency is 100 kHz. In Figures 35 and 36, the horizontal axis represents the central angle θs, angles θv, and θu, and the vertical axis represents the Q value. Note that in Figures 35 and 36, the point where θs = 360° is the first 14 The values ​​shown are obtained from the model corresponding to the coil in the reference example. Additionally, the points at θs=0° and θv,θu=180° represent values ​​obtained from the model corresponding to the coil in Reference Example 13 or Reference Example 17. 【0148】 Similar to Embodiment 1, it was observed that the Q values ​​of models No. 4C to 38C, which correspond to the coils of Embodiments 8 to 10, are higher than those of model No. 1C, which corresponds to Reference Example 12, in which the cross-sectional shape of the conductor is circular. 【0149】 Furthermore, the Q values ​​of models No. 16C to 38C, which correspond to the arc-shaped coil of the 4th embodiment, tend to be higher than those of models No. 4C to 15C, which correspond to the V-shaped and U-shaped coils of the 9th and 10th embodiments. 【0150】 Models No. 27C, 27C1, and 27C2 all correspond to coils having an arc-shaped conductor with θs = 180°. However, it is observed that the Q value of model No. 27C, which corresponds to the coil in the 8th embodiment, is higher than that of models No. 27C1 and 27C2, which correspond to the coils in the 15th and 16th reference examples. 【0151】 Simulation results for a model corresponding to a coil with an arc-shaped conductor show that the Q value depends on the central angle θs. Specifically, when the coil diameter d is 50 mm, the Q value is high when the central angle θs is between 60° and 345°, even higher when the central angle θs is between 90° and 300°, and even higher when the central angle θs is between 120° and 255°. When the coil diameter d is 100 mm, the Q value is high when the central angle θs is between 60° and 345°, even higher when the central angle θs is between 90° and 345°, even higher when the central angle θs is between 120° and 330°, and particularly high when the central angle θs is between 180° and 300°. 【0152】 Furthermore, it can be observed that the Q value increases significantly by tilting the reference straight lines 18a and 18b of the first portion 1a and second portion 1b of the electric wire 1 that is wound around the first section 3a and second section 3b located at both ends of the target section 3 of the central axis 2. 【0153】 Simulation results from a model corresponding to a coil with a V-shaped conductor show that the Q value depends on the angle θv. The Q value is high when the angle θv is between 105° and 165°, and even higher when the angle θv is between 120° and 150°. 【0154】 Simulation results from a model corresponding to a coil with a U-shaped conductor show that the Q value depends on the angle θu. It is high when the angle θu is between 105° and 165°, and even higher when the angle θu is between 120° and 150°. 【0155】 <Variation> In the above description, the cross-sectional shape 11 of the conductor 10 was shown as an arc shape, a V shape, and a U shape, but the cross-sectional shape 11 is not limited to these shapes. For example, the cross-sectional shape 11 of the conductor 10 may have three or more bends such that the first end 12 and the second end 13 are separated from the central axis 2. As the number of bends increases, the shape approaches an arc shape, and the uneven distribution of current becomes less likely, so it is preferable to have a larger number of bends. In that case, it is preferable that the outer surface of the bends is chamfered. 【0156】 <Examples of application> The coils 100A to 100C according to the above embodiments 1 to 3 can be suitably used as magnetic field coupled wireless power supply coils. Examples of magnetic field coupled wireless power supply coils include charging coils for relatively small wearable devices, smartphone charging coils, and battery charging coils for relatively large electric vehicles. In addition, such contactless power supply coils typically carry alternating currents of 85kHz, 6.78MHz, 13.56MHz, etc., and the coils 100A to 100C of this embodiment can be suitably used in applications where alternating currents of 10kHz or higher or 100kHz or higher are carried. 【0157】 Furthermore, the coils 100A to 100C according to the above embodiments 1 to 3 can be suitably used as resonant coils for electric field resonant coupling wireless power transfer. Examples of applications for electric field resonant coupling wireless power transfer include electric vehicles and trains. In such electric field resonant coupling wireless power transfer, alternating currents such as 6.78 MHz, 13.56 MHz, and 27.12 MHz are usually passed through, and the coils 100A to 100C of this embodiment can be suitably used in applications where alternating currents of 10 kHz or higher or 100 kHz or higher are passed through. A resonant coil for electric field resonant coupling wireless power transfer is a coil inserted in an electrical circuit including a power transmission coupler on the transmitting or receiving side of electric field coupling wireless power transfer to improve the power factor and generate a resonant state. 【0158】 The coils 100A to 100C according to the above embodiments 1 to 3 can be suitably used as a substitute for coils using Litz wire, particularly in high-frequency applications where the resistance of Litz wire, which is normally used as coil wire, becomes large, or in small-scale applications where Litz wire is difficult to use. "High frequency" preferably means a frequency of 1 MHz or higher, and more preferably a frequency of 5 MHz or higher. 【0159】 The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols] 【0160】 1 Electric wire, 1a First section, 1b Second section, 1c Third section, 2 Central axis, 3 Target section, 3a First section, 3b Second section, 3c Third section, 10 Conductor, 11, 11a~11f Cross-sectional shape, 12 First end, 13 Second end, 14 First edge, 15 Second edge, 16 Center point, 17 Line segment, 18, 18a~18c Reference straight line, 20~22 Bending section, 30 Insulating material, 40a~40c Intersection, 100A~100C Coil.

Claims

[Claim 1] It is a coil, It is equipped with a wire that is wound multiple times in a spiral around a central axis, The electric wire includes a conductor whose cross-sectional shape in a plane including the central axis is elongated. The cross-sectional shape is curved such that the first and second ends in the longitudinal direction are separated from the central axis. The electric wire is wound spirally three or more times around the target section of the central axis. The aforementioned electric wire is A first portion that is wound around a first section located at one end of the aforementioned target section, A second portion that is wound around the second section located at the other end of the aforementioned target section, It has a third portion that is wound around a third section located between the first section and the second section of the target section, When a line passing through the center point of the cross-sectional shape and perpendicular to the line segment connecting the first end and the second end is defined as the reference line, The reference line in the third part is perpendicular to the central axis, The reference line in the first part is inclined in a direction such that the points of intersection with the central axis move away from each other with respect to the reference line corresponding to the third part. A coil in which the reference line in the second part is inclined in a direction that causes the points of intersection with the central axis to move away from each other with respect to the reference line corresponding to the third part. [Claim 2] The coil according to claim 1, wherein the cross-sectional shape is symmetrical with respect to the reference line. [Claim 3] The coil according to claim 1 or 2, wherein the distance between the central axis and the electric wire increases or decreases along the central axis. [Claim 4] The coil according to claim 1 or 2, which is a magnetic field coupling type wireless power supply coil. [Claim 5] The coil according to claim 1 or 2, which is a resonant coil for electric field resonance coupling type wireless power transfer.

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