Method for manufacturing a Halbach magnet array and a Halbach magnet array

Abstract

To provide a method capable of easily manufacturing a Halbach magnet array with a large ratio of the magnetic flux density on the front side and the back side.SOLUTION: The manufacturing method of a Halbach magnet array includes the steps of: (a) magnetizing at least one first magnetic piece and at least one second magnetic piece in a direction parallel to a first direction; and (b) magnetizing a third magnetic piece in a direction parallel to a second direction perpendicular to the first direction. The first magnetic piece and the second magnetic piece are arranged alternately in the second direction with the third magnetic piece interposed therebetween. Each of the first magnetic pieces is joined to the adjacent third magnetic piece via a non-magnetic layer of thickness t1, and each of the second magnetic pieces is joined to the adjacent third magnetic piece via a non-magnetic layer of thickness t2, where t1 and t2 satisfy t1<t2.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a Halbach magnet array, and to a Halbach magnet array. [Background technology]

[0002] Patent Document 1 describes a Halbach magnetic circuit that includes a plurality of permanent magnets having a plurality of regions magnetized in different directions.

[0003] 1, the Halbach magnetic circuit 120 generally includes a plurality of permanent magnets 101 arranged in one direction, with the magnetization directions of adjacent permanent magnets 101 forming a predetermined angle (e.g., 90°). Due to such an arrangement, one side (front side) of the Halbach magnetic circuit 120 has a high surface magnetic flux density, and the opposite side (back side) has a low surface magnetic flux density or ideally has zero surface magnetic flux density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-092988 A Summary of the Invention [Problem to be solved by the invention]

[0005] When manufacturing a Halbach magnetic circuit by bonding multiple magnetized magnets, accurate position control is difficult due to repulsion between the magnets, and a large external force is required. Therefore, such a manufacturing method is not suitable for mass production. On the other hand, when manufacturing a Halbach magnetic circuit by bonding multiple unmagnetized magnetic bodies and magnetizing each magnetic body in a predetermined direction, and when manufacturing a Halbach magnetic circuit by forming multiple regions magnetized in different directions on one permanent magnet as in Patent Document 1, the ratio of magnetic flux density between the front and back surfaces of the Halbach magnetic circuit tends to be small.

[0006] Accordingly, a method capable of easily manufacturing a Halbach magnet array having a large ratio of magnetic flux density between the front and back surfaces, and a Halbach magnet array manufactured thereby are provided.

Means for Solving the Problems

[0007] According to one aspect of the present invention, a method for manufacturing a Halbach magnet array, comprising: a) magnetizing at least one first magnetic body piece and at least one second magnetic body piece in a direction parallel to a first direction, wherein the at least one first magnetic body piece and the at least one second magnetic body piece are alternately arranged in a second direction perpendicular to the first direction with a third magnetic body piece interposed therebetween, each of the at least one first magnetic body piece is joined to the adjacent third magnetic body piece via a non-magnetic layer having a thickness t1, each of the at least one second magnetic body piece is joined to the adjacent third magnetic body piece via a non-magnetic layer having a thickness t2, the thickness t1 and the thickness t2 satisfy t1 < t2, the at least one first magnetic body piece and the at least one second magnetic body piece have an easy magnetization axis parallel to the first direction, the third magnetic body piece has an easy magnetization axis parallel to the second direction, the magnetization direction of the at least one first magnetic body piece and the magnetization direction of the at least one second magnetic body piece are different by 180°, and b) magnetizing the third magnetic body piece in a direction parallel to the second direction so that the third magnetic body piece has an S pole facing the adjacent first magnetic body piece and an N pole facing the adjacent second magnetic body piece, A method is provided that includes these steps in this order.

[0008] According to one aspect of the present invention, a Halbach magnet array, comprising: at least one first magnetic body piece having magnetization parallel to a first direction, and At least one second magnetic body piece having magnetization in a direction different from the magnetization direction of the first magnetic body piece by 180°; At least one third magnetic body piece having magnetization parallel to a second direction perpendicular to the first direction; and having the at least one first magnetic body piece and the at least one second magnetic body piece are alternately arranged in the second direction with the third magnetic body piece interposed therebetween; the third magnetic body piece has an S pole facing the adjacent first magnetic body piece and an N pole facing the adjacent second magnetic body piece; each of the at least one first magnetic body pieces is joined to the adjacent third magnetic body piece via a non-magnetic layer having a thickness t1; each of the at least one second magnetic body pieces is joined to the adjacent third magnetic body piece via a non-magnetic layer having a thickness t2; a Halbach magnet array is provided in which the thickness t1 and the thickness t2 satisfy t1 < t2.

[0009] By the manufacturing method of the present invention, a Halbach magnet array having a large ratio of the magnetic flux density on the front surface to that on the back surface can be easily manufactured.

Brief Description of Drawings

[0010] [Figure 1] FIG. 1 is a diagram schematically showing an example of a conventional Halbach magnetic circuit. [Diagram 2] FIG. 2 is a flowchart of the manufacturing method according to the embodiment. [Diagram 3] FIG. 3 is a diagram schematically showing an example of an array used for the step of magnetizing the first magnetic body piece. [Figure 4] FIG. 4 is a diagram schematically showing an example of a Halbach magnet array manufactured by the manufacturing method according to the embodiment. [Diagram 5] FIG. 5 is a diagram showing the ratio of the magnetic flux on the front surface and the ratio of the magnetic flux on the back surface to the sum of the magnetic fluxes on the front and back surfaces of the test bodies of Example 1, 2 and Comparative Examples 1-4.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the embodiments will be described with reference to the drawings as appropriate. The present invention is not limited to the following embodiments, and various design modifications can be made without departing from the spirit of the present invention described in the claims. In the drawings referred to in the following description, the same members or members having similar functions may be given the same reference numerals, and repeated description may be omitted. The dimensional ratios of the drawings may differ from the actual ratios for convenience of explanation, and some members may be omitted from the drawings. In addition, in this application, a numerical range expressed using the symbol "~" includes the numerical values ​​written before and after the symbol "~" as the lower limit and upper limit, respectively. In this application, vertical means substantially vertical, and parallel means substantially parallel.

[0012] As shown in FIG. 2, a manufacturing method for a Halbach magnet array includes a step (S1) of magnetizing a first magnetic piece and a second magnetic piece, and a step (S2) of magnetizing a third magnetic piece.

[0013] a) Magnetization of the first magnetic piece and the second magnetic piece First, at least one unmagnetized first magnetic piece, at least one unmagnetized second magnetic piece, and at least one third magnetic piece are prepared. The first magnetic piece, the second magnetic piece, and the third magnetic piece include a permanent magnet material. Examples of the permanent magnet material include Nd-Fe-B magnetic material, Sm-Co magnetic material, Sm-Fe-N magnetic material, ferrite magnetic material, and Al-Ni-Co magnetic material. The first magnetic piece, the second magnetic piece, and the third magnetic piece have magnetic anisotropy. That is, the first magnetic piece, the second magnetic piece, and the third magnetic piece each have an easy axis of magnetization and an axis of hard magnetization. The first magnetic piece, the second magnetic piece, and the third magnetic piece may have any shape. For example, each magnetic piece may have a columnar shape having a substantially rectangular (particularly substantially square) or substantially partially annular bottom surface. The first magnetic piece, the second magnetic piece, and the third magnetic piece may have the same shape and size. When the first magnetic piece, the second magnetic piece, and the third magnetic piece have a columnar shape (i.e., a rectangular parallelepiped shape) with a substantially rectangular bottom surface of the same dimensions, the magnetization easy axis of the first magnetic piece and the second magnetic piece may be perpendicular to a set of parallel faces perpendicular to the bottom surface, and the magnetization easy axis of the third magnetic piece may be perpendicular to another set of parallel faces perpendicular to the bottom surface. When the first magnetic piece, the second magnetic piece, and the third magnetic piece have a columnar shape with a substantially partially annular bottom surface of the same dimensions, the magnetization easy axis of the first magnetic piece and the second magnetic piece may be parallel to the radial direction of the partial annular ring, and the magnetization easy axis of the third magnetic piece may be parallel to the circumferential direction of the partial annular ring. The first magnetic piece, the second magnetic piece, and the third magnetic piece can be manufactured by a commonly known manufacturing method. The first magnetic piece 1, the second magnetic piece, and the third magnetic piece may be commercially available magnetic pieces.

[0014] As shown in FIG. 3, a first magnetic body piece 1, a second magnetic body piece 2, and a third magnetic body piece 3 are arranged in a predetermined direction (the X direction in FIG. 3) to obtain an array body 10. Although a linear array body 10 is shown in FIG. 3, when the first magnetic body piece 1, the second magnetic body piece 2, and the third magnetic body piece 3 have a columnar shape with a substantially partial annular bottom surface, an annular array body 10 can be formed by arranging a predetermined number of the first magnetic body pieces 1, the second magnetic body pieces 2, and the third magnetic body pieces 3 in their circumferential direction. In the array body 10, the first magnetic body piece 1 and the second magnetic body piece 2 are alternately arranged with the third magnetic body piece 3 interposed therebetween. Each of the first magnetic body pieces 1 is joined to an adjacent third magnetic body piece 3 via a non-magnetic layer 5 having a thickness t1, and the second magnetic body piece 2 is joined to an adjacent third magnetic body piece 3 via a non-magnetic layer 5 having a thickness t2, and t1 < t2. The non-magnetic layer 5 may contain an adhesive (for example, an epoxy resin-based adhesive, an acrylic resin-based adhesive).

[0015] The non-magnetic layer 5 may have a thermal conductivity of 0.5 W / m·K or less, particularly 0.2 W / m·K or less. Thereby, when magnetizing the first magnetic body piece 1 and the second magnetic body piece 2 under the condition that the first magnetic body piece 1 and the second magnetic body piece 2 have a higher temperature than the third magnetic body piece 3, heat transfer from the first magnetic body piece 1 and the second magnetic body piece 2 to the third magnetic body piece 3 is suppressed. As a result, it is possible to effectively suppress the third magnetic body piece 3 from being magnetized by the magnetic field for magnetizing the first magnetic body piece and the second magnetic body piece. Similarly, in the step of magnetizing the subsequent third magnetic body piece, when magnetizing the third magnetic body piece 3 under the condition that the third magnetic body piece 3 has a higher temperature than the first magnetic body piece 1 and the second magnetic body piece 2, heat transfer from the third magnetic body piece 3 to the first magnetic body piece 1 and the second magnetic body piece 2 is suppressed. As a result, it is possible to effectively suppress the magnetic field for magnetizing the third magnetic body piece 3 from affecting the residual magnetization of the first magnetic body piece 1 and the second magnetic body piece 2 during the magnetization of the third magnetic body piece 3. Further, the non-magnetic layer 5 usually has a thermal conductivity of 0.01 W / m·K or more, but is not limited thereto.

[0016] In Figure 3, two first magnetic pieces 1 and one second magnetic piece 2 are arranged alternately with a third magnetic piece 3 in between, but as long as the first magnetic pieces 1 and the second magnetic pieces 2 can be arranged alternately, the array 10 may include more than two first magnetic pieces 1, more than one second magnetic piece 2, and more than two third magnetic pieces 3.

[0017] In the array 10, the magnetization easy axes (represented by hollow arrows in FIG. 3) of the first magnetic piece 1 and the second magnetic piece 2 are parallel to the first direction (Z direction in FIG. 3), and the magnetization easy axis (represented by hollow arrows in FIG. 3) of the third magnetic piece 3 is parallel to the second direction (X direction in FIG. 3). Here, the first direction and the second direction are perpendicular to each other. Also, the second direction is parallel to the arrangement direction of the first magnetic piece 1, the second magnetic piece 2, and the third magnetic piece 3.

[0018] Next, the first magnetic piece 1 and the second magnetic piece 2 of the array 10 are magnetized in a direction parallel to the first direction. The magnetization directions of the first magnetic piece 1 and the second magnetic piece 2 differ by 180°.

[0019] The first magnetic piece 1 and the second magnetic piece 2 can be magnetized using any magnetizer. For example, the first magnetic piece 1 and the second magnetic piece 2 can be magnetized by placing them in a magnetic field (external magnetic field) generated by a magnetizing yoke.

[0020] The first magnetic piece 1 and the second magnetic piece 2 may be magnetized under the condition that the first magnetic piece 1 and the second magnetic piece 2 have a higher temperature than the third magnetic piece 3. This makes it possible to impart a sufficiently large residual magnetization to the first magnetic piece 1 and the second magnetic piece 2 while suppressing the third magnetic piece 3 from being magnetized by the magnetic field for magnetizing the first magnetic piece 1 and the second magnetic piece 2. This is because the higher the temperature of the magnetic piece when magnetizing, the higher the residual magnetization rate of the magnetic piece (i.e., the ratio of the residual magnetization to the saturation residual magnetization) generally becomes. The temperature dependence of the residual magnetization rate of the magnetic piece generally depends on the type of magnetic material contained as a main component in the magnetic piece, the presence or absence of element substitution in the magnetic material and the type of the substituted element, and the structure of the magnetic piece (e.g., crystal grain size).

[0021] For example, the first magnetic piece 1 and the second magnetic piece 2 may be magnetized while heating the first magnetic piece 1 and the second magnetic piece 2. In addition to or instead of that, the first magnetic piece 1 and the second magnetic piece 2 may be magnetized while cooling the third magnetic piece 3. The first magnetic piece 1 and the second magnetic piece 2 may be heated using any heating means (e.g., a hot plate resistance heater and a rubber heater). The first magnetic piece 1 and the second magnetic piece 2 may be heated and magnetized using a heater-attached magnetic yoke. The third magnetic piece 3 may be cooled using any cooling means (e.g., a water-cooled block).

[0022] b) Magnetization of the third magnetic piece Next, the third magnetic piece 3 is magnetized so that the third magnetic piece 3 has an S pole facing the adjacent first magnetic piece 1 and an N pole facing the adjacent second magnetic piece 2 .

[0023] The third magnetic piece 3 can be magnetized using any magnetizer. For example, the third magnetic piece 3 can be magnetized by placing the third magnetic piece 3 in a magnetic field (external magnetic field) generated by a magnetizing yoke.

[0024] The third magnetic body piece 3 may be magnetized under the condition that the third magnetic body piece 3 has a higher temperature than the first magnetic body piece 1 and the second magnetic body piece 2. Thereby, while suppressing the influence of the magnetic field for magnetizing the third magnetic body piece 3 on the residual magnetization of the first magnetic body piece 1 and the second magnetic body piece 2, a sufficiently large residual magnetization can be imparted to the third magnetic body piece 3. For example, the third magnetic body piece 3 may be magnetized while heating the third magnetic body piece 3. In addition to or instead of that, the third magnetic body piece 3 may be magnetized while cooling the first magnetic body piece 1 and the second magnetic body piece 2. The third magnetic body piece 3 can be heated using any heating means (for example, a hot plate resistance heater and a rubber heater). The heating and magnetization of the third magnetic body piece 3 may be performed using a magnetized yoke with a heater. The first magnetic body piece 1 and the second magnetic body piece 2 can be cooled using any cooling means (for example, a water-cooled block).

[0025] In this way, a Halbach magnet array 20 as shown in FIG. 4 is manufactured. The Halbach magnet array 20 includes a first magnetic body piece 1 having magnetization parallel to a first direction (the Z direction in FIG. 4), a second magnetic body piece 2 having magnetization in a direction 180° different from the magnetization direction of the first magnetic body piece 1, and a third magnetic body piece 3 having magnetization parallel to a second direction (the X direction in FIG. 4) perpendicular to the first direction. The first magnetic body piece 1 and the second magnetic body piece 2 are alternately arranged in the second direction with the third magnetic body piece 3 interposed therebetween. The third magnetic body piece 3 has an S pole facing the adjacent first magnetic body piece 1 and an N pole facing the adjacent second magnetic body piece 2. Each of the first magnetic body pieces 1 is joined to the adjacent third magnetic body piece 3 via a non-magnetic layer 5 having a thickness t1, and the second magnetic body piece 2 is joined to the adjacent third magnetic body piece 3 via a non-magnetic layer 5 having a thickness t2, and the thicknesses t1 and t2 satisfy t1 < t2.

[0026] In the Halbach magnet array 20 obtained by the manufacturing method according to the embodiment, the thickness t2 of the non-magnetic layer 5 between the adjacent second magnetic piece 2 and third magnetic piece 3 is greater than the thickness t1 of the non-magnetic layer 5 between the adjacent first magnetic piece 1 and third magnetic piece 3. This increases the ratio of magnetic flux density on the front and back surfaces of the Halbach magnet array 20, as shown in the examples described below. In addition, in the manufacturing method according to the embodiment, since each magnetic piece is magnetized in a predetermined direction after bonding a plurality of unmagnetized magnetic pieces, no repulsive force is generated between the magnetic pieces when the magnetic pieces are bonded. Therefore, when bonding the magnetic pieces, no large external force is required to resist the repulsive force between the magnetic pieces, and accurate position control of the magnetic pieces is also easy. EXAMPLES

[0027] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0028] Examples 1 and 2, and Comparative Examples 1-3 Five magnetic pieces (sintered neodymium magnets) were prepared, each of which was a rectangular parallelepiped of 5 mm x 5 mm x 7 mm, with an easy magnetization axis perpendicular to the 5 mm x 7 mm surface. Two of the magnetic pieces were designated as the first magnetic piece, one as the second magnetic piece, and two as the third magnetic piece.

[0029] The first and second magnetic pieces were arranged alternately in a second direction perpendicular to the first direction, with the easy magnetization axes of the first and second magnetic pieces parallel to the first direction. A third magnetic piece was arranged between adjacent first and second magnetic pieces, with the easy magnetization axis of the third magnetic piece parallel to the second direction. The first, second, and third magnetic pieces were arranged so that their 5 mm × 5 mm faces were parallel to both the first and second directions. The adjacent first and third magnetic pieces, and the adjacent second and third magnetic pieces were bonded with a non-magnetic adhesive (thermal conductivity 0.2 W / m·K). The thickness t1 of the adhesive layer between the first magnetic piece and the third magnetic piece, and the thickness t2 of the adhesive layer between the second magnetic piece and the third magnetic piece were as shown in Table 1. However, in Table 1, S <M<Lである。

[0030] The first magnetic piece and the second magnetic piece were magnetized by an external magnetic field parallel to the first direction while being heated to 65° C. At this time, the magnetization direction of the first magnetic piece was set to a direction that differed by 180° from the magnetization direction of the second magnetic piece.

[0031] Next, while the third magnetic piece was heated to 65°C, the third magnetic piece was magnetized by an external magnetic field parallel to the second direction so that the third magnetic piece had a south pole facing the adjacent first magnetic piece and a north pole facing the adjacent second magnetic piece.

[0032] As a result, a test specimen having a Halbach array as shown in FIG. 4 was obtained.

[0033] Comparative Example 4 Five magnetic pieces (neodymium magnet sintered bodies) having the same magnetic anisotropy as in Example 1 were prepared. Each magnetic piece was magnetized in the direction of its easy axis of magnetization. Next, two of the magnetic pieces were designated as the first magnetic piece, one as the second magnetic piece, and two as the third magnetic piece, and they were arranged in the same manner as in Example 1. The first magnetic piece and the third magnetic piece adjacent to each other, and the second magnetic piece and the third magnetic piece adjacent to each other were bonded with an adhesive that is a non-magnetic material. The thickness t1 of the adhesive layer between the first magnetic piece and the third magnetic piece, and the thickness t2 of the adhesive layer between the second magnetic piece and the third magnetic piece were made as shown in Table 1. Thereby, a test body having a Halbach array as shown in FIG. 4 was obtained.

[0034]

Table 1

[0035] Evaluation The magnetic fluxes on two surfaces perpendicular to the first direction of each test body were measured with a fluxmeter. Of the two surfaces, the surface with the larger magnetic flux was defined as the front surface, and the surface with the smaller magnetic flux was defined as the back surface. The ratio of the magnetic flux of each surface to the sum of the magnetic fluxes of the front surface and the back surface was determined. The results are shown in FIG. 5.

[0036] As shown in FIG. 5, for the test bodies of Examples 1 and 2 where t1 < t2, the ratio of the magnetic flux on the front surface was larger than that of the test bodies of Comparative Examples 1 and 3 where t1 = t2 or the test body of Comparative Example 2 where t1 > t2.

[0037] Note that the ratio of the magnetic flux on the front surface of the test bodies of Examples 1 and 2 was smaller than that of the test body of Comparative Example 4. However, the test body of Comparative Example 4 was produced by bonding magnetized magnetic pieces, and this production method is not suitable for mass production.

Explanation of Symbols

[0038] 1: First magnetic piece, 2: Second magnetic piece, 3: Third magnetic piece, 5: Non-magnetic layer, 10: Array body, 20: Halbach magnet array body

Claims

1. 1. A method of manufacturing a Halbach magnet array, comprising: a) magnetizing at least one first magnetic piece and at least one second magnetic piece in a direction parallel to a first direction, wherein the at least one first magnetic piece and the at least one second magnetic piece are alternately arranged in a second direction perpendicular to the first direction with a third magnetic piece interposed therebetween; each of the at least one first magnetic piece is joined to an adjacent third magnetic piece via a non-magnetic layer having a thickness t1; Each of the at least one second magnetic piece is joined to an adjacent third magnetic piece via a non-magnetic layer having a thickness t2, The thickness t1 and the thickness t2 satisfy t1<t2, the at least one first magnetic piece and the at least one second magnetic piece have an easy axis parallel to the first direction; the third magnetic piece has an easy axis parallel to the second direction; a magnetization direction of the at least one first magnetic piece and a magnetization direction of the at least one second magnetic piece differ from each other by 180°; b) magnetizing the third magnetic piece in a direction parallel to the second direction such that the third magnetic piece has a south pole facing the adjacent first magnetic piece and a north pole facing the adjacent second magnetic piece; A method comprising, in this order:

2. The method of claim 1 , wherein the non-magnetic layer has a thermal conductivity of 0.5 W / m·K or less.

3. The method of claim 1 or 2, wherein the non-magnetic layer comprises an adhesive.

4. A Halbach magnet array comprising: at least one first piece of magnetic material having a magnetization parallel to a first direction; At least one second magnetic piece having a magnetization direction that is 180° different from the magnetization direction of the first magnetic piece; at least one third magnetic piece having a magnetization parallel to a second direction perpendicular to the first direction; having The at least one first magnetic piece and the at least one second magnetic piece are alternately arranged in the second direction with a third magnetic piece therebetween, the third magnetic piece has a south pole facing the adjacent first magnetic piece and a north pole facing the adjacent second magnetic piece, Each of the at least one first magnetic piece is joined to the adjacent third magnetic piece via a non-magnetic layer having a thickness t1; Each of the at least one second magnetic piece is joined to the adjacent third magnetic piece via a non-magnetic layer having a thickness t2; The Halbach magnet array, wherein the thickness t1 and the thickness t2 satisfy t1<t2.

5. 5. The Halbach magnet array of claim 4, wherein the non-magnetic layer has a thermal conductivity of 0.5 W / m·K or less.

6. The Halbach magnet array of claim 4 or 5, wherein the non-magnetic layer comprises an adhesive.

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