Assembly for generating a unidirectional surface magnetic field - Patent Application 20070122947

Abstract

An assembly (E) for generating a surface magnetic field comprising first and second ferromagnetic segments (6, 6') superimposed in the direction y, said assembly comprising: - at least two permanent magnets, called upper magnets (3, 4, 5), arranged so as to partially surround the first ferromagnetic segment, except for at least one surface of the first ferromagnetic segment, called the first surface (S1); - at least two permanent magnets, referred to as lower magnets (3', 4', 5'), arranged so as to partially surround the second ferromagnetic segment, except for at least one surface of the second ferromagnetic segment, referred to as the second surface (S2); - at least one permanent magnet, referred to as central magnet (2), which is disposed between the first and second magnetic segments so as to be adjacent to the first and second surfaces, while defining an area of ​​the first surface not covered by the central magnet, referred to as the first area, and an area of ​​the second surface not covered by the central magnet, referred to as the second area, where the first area faces the second area; Further provided with Magnetization of permanent magnets (M3; M4; M5; M 3’ ;M 4’ ;M 5’ ) is designed to generate a surface magnetic field in an area (1) comprised between the first region and the second region, such that the surface magnetic field is substantially in a direction y having a predetermined orientation.

Description

[Technical Field]

[0001] The present invention relates to the technical field of structures comprising permanent magnets and ferromagnetic elements for producing magnetic fields with predetermined and controlled characteristics. [Background technology]

[0002] Permanent magnets are anisotropic or "directional" materials that possess a magnetization direction under certain conditions. As soon as an external magnetic field is applied to these materials, the magnetic moments (spin and orbit) of their electrons align parallel to this field, and they become "magnetized." At this time, they generate an intrinsic static magnetic field. Some permanent magnets have preferred planes of easy magnetization and prefer specific directions within these planes. In contrast to paramagnetic materials, when the external magnetic field is removed, the magnetic moments of permanent magnets tend to maintain their orientation and therefore retain a large amount of magnetization (called remanence). As a result, permanent magnets can generate a large intrinsic static magnetic field, even in the absence of an external magnetic field.

[0003] In contrast to hard ferromagnetic materials, in the case of paramagnetic materials, when the external magnetic field is removed, the magnetic moments orient themselves apart and they no longer generate an intrinsic static magnetic field.

[0004] Materials that exhibit a large amount of remanence are referred to as "hard" ferromagnetic materials. These materials can also exhibit high coercivity. The "coercivity" of a ferromagnetic material refers to the strength of the magnetic field that must be applied to the material to demagnetize it once it has initially reached its saturation magnetization.

[0005] The distribution of remanence depends on the orientation of the material, its geometric shape, and other properties of the material. Permanent magnets are composed of both paramagnetic elements (samarium, neodymium, etc.) and ferromagnetic elements (iron, cobalt, etc.). During the fabrication of permanent magnets, crystalline structures are created that exhibit spontaneously oriented intra-domain magnetization, known as magnetic anisotropy.

[0006] Soft ferromagnetic materials are macroscopically isotropic or omnidirectional. Compared to hard ferromagnetic materials, they have little remanence and very weak coercivity (less than 1000 A / m), so when they are no longer exposed to an external magnetic field, they only generate a weak intrinsic static magnetic field. These materials include pure iron, plain steel alloys with low carbon content, and more exotic materials such as vanadium permendur, which is composed of iron, cobalt, and vanadium. These materials are capable of concentrating and redirecting magnetic flux from other sources, such as electromagnetic coils or permanent magnets. Therefore, they are often combined with the latter to form structures capable of generating high magnetic fields (>1 T).

[0007] Numerous structures are known that include permanent magnets for generating a magnetic field in a controlled manner, possibly combined with soft ferromagnetic material to concentrate the magnetic flux. Thus, Figure 1 shows six different structures (a)-(f) for generating a substantially uniform magnetic field in a given "empty" volume (i.e., the volume away from the magnets and away from the ferromagnetic segments).

[0008] In Figure 1, permanent magnets are represented by unshaded shapes with black outlines, while shaded areas with black outlines represent elements made of soft ferromagnetic material. Solid black arrows represent the direction of magnetization of the permanent magnets, and unshaded arrows represent the main direction of the magnetic field created within the volume.

[0009] Structure (e) in Figure 1 is a "Halbach" configuration known in the art and used to counteract the magnetic field of wafers up to 200 mm in diameter, which have a magnetic field of approximately 1 T, particularly for the fabrication of spintronic read heads for RAM (Random Access Memory). For this type of application, it is necessary to use large cylindrical magnets of the Halbach type, weighing several metric tons. The weight, volume, and cost of such a structure are disadvantageous, especially for applications that do not require the magnetization of such large volumes, such as reactive ion etching.

[0010] Currently, there is no satisfactory solution for generating a unidirectional surface field without magnetizing a large volume.

[0011] The present invention aims to overcome this problem. To this end, the subject of the present invention is an assembly comprising first and second ferromagnetic segments and a plurality of permanent magnets arranged to surround the first and second ferromagnetic segments, except for at least a first region of the first ferromagnetic segment and a second region of the second ferromagnetic segment, where the first region faces the second region. The magnetization of the permanent magnets is designed to generate a surface magnetic field in the area comprised between the first and second regions, such that the surface magnetic field is substantially in a predetermined direction.

[0012] Compared to the magnet assembly shown in Figure 1, the solution of the present invention makes it possible to reduce the volume of the magnet by magnetizing a less large volume, and is therefore more compact, lighter and cheaper than prior art solutions. Summary of the Invention [Means for solving the problem]

[0013] To this end, the subject of the present invention is an assembly for generating a surface magnetic field comprising first and second ferromagnetic segments superimposed in the direction y, said assembly comprising: at least two permanent magnets, referred to as upper magnets, arranged so as to partially surround the first ferromagnetic segment, except for at least one surface of the first ferromagnetic segment, referred to as the first surface; at least two permanent magnets, referred to as bottom magnets, arranged so as to partially surround the second ferromagnetic segment, except for at least one surface of the second ferromagnetic segment, referred to as the second surface; at least one permanent magnet, referred to as a central magnet, disposed between the first and second magnetic segments, defining an area of ​​its first surface, referred to as a first region, that is not covered by the central magnet, and an area of ​​its second surface, referred to as a second region, that is not covered by the central magnet, the first region facing the second region; Further provided with The magnetization of the permanent magnets and the arrangement of the at least one central magnet are designed to create a surface magnetic field in an area that is included between the first region and the second region, but not between the two central magnets, such that the surface magnetic field is substantially in a direction y having a predetermined orientation.

[0014] According to one embodiment, the magnetization of the permanent magnet is such that said surface field lies in a plane yz, where z is perpendicular to the direction y, the magnetization of the upper magnet is such that the magnetization resulting from said arrangement of the upper magnet, referred to as the upper magnetization, is substantially in a direction y having said predetermined orientation; the lower magnet is such that the magnetization resulting from said arrangement of the lower magnet, referred to as the lower magnetization, is substantially in a direction y having said predetermined orientation; said at least one central magnet exhibits a magnetization, referred to as central magnetization, substantially in a direction y having an orientation opposite to said predetermined orientation.

[0015] Preferably, in this embodiment, the upper magnet is an upper magnet, referred to as the central upper magnet, arranged above the first ferromagnetic segment in the direction y and presenting a magnetization in the direction y with said predetermined orientation; two upper magnets, referred to respectively as first and second lateral upper magnets, arranged one on each side of the first ferromagnetic segment in a direction x perpendicular to the direction y and to the direction z, the first and second lateral upper magnets exhibiting magnetizations in the direction x with opposite orientations; Including, and wherein the lower magnet is a lower magnet, referred to as the central lower magnet, arranged below the second ferromagnetic segment in the direction y and presenting a magnetization in the direction y with said predetermined orientation; two lower magnets, called first and second lateral lower magnets respectively, arranged one on each side of the second ferromagnetic segment in the direction x, Including, the first lower lateral magnet is disposed facing the first upper lateral magnet, and the second lower lateral magnet is disposed facing the second upper lateral magnet; The first and second lateral lower magnets exhibit magnetization in direction x with opposite orientations.

[0016] More preferably, the first and second lateral lower magnets exhibit magnetizations in direction x with opposite orientations.

[0017] According to one embodiment, the dimension of the first ferromagnetic segment in the direction x is less than the dimension of the central upper magnet in the direction x, and the dimension of the second ferromagnetic segment in the direction x is less than the dimension of the central lower magnet in the direction x.

[0018] According to one embodiment, the upper magnet further comprises two upper magnets, referred to as first and second additional lateral upper magnets, respectively, arranged one on each side of the first ferromagnetic segment in the direction z, the first and second additional lateral upper magnets exhibiting magnetizations in the direction z with opposite orientations; the lower magnet further comprises two lower magnets, referred to as first and second additional lateral lower magnets, respectively, disposed one on each side of the second ferromagnetic segment in the direction z; the first additional lower lateral magnet is disposed facing the first additional upper lateral magnet, and the second additional lower lateral magnet is disposed facing the second additional upper lateral magnet; The first and second additional lateral lower magnets exhibit magnetization in direction z with opposite orientations.

[0019] According to one embodiment, the assembly comprises two permanent magnets, referred to as first and second additional magnets, arranged one on each side of the at least one central magnet in direction z, the first and second additional lateral upper magnets exhibiting magnetization in direction y having an orientation opposite to the predetermined orientation.

[0020] According to one embodiment, the first and second side upper magnets are not positioned adjacent to the central upper magnet, and the first and second side lower magnets are not positioned adjacent to the central lower magnet.

[0021] According to one embodiment, the magnetization of the permanent magnet is such that the sum of the upper and lower magnetic flux is equal or substantially equal to the central magnetic flux.

[0022] According to one embodiment, the first ferromagnetic segment includes a chamfer or rounded edge formed in a region opposite the first surface, and the second ferromagnetic segment includes a chamfer or rounded edge formed in a region opposite the second surface.

[0023] According to one embodiment, the permanent magnet and the first and second ferromagnetic segments are arranged such that the assembly exhibits planar symmetry in a plane normal to the direction y.

[0024] According to one embodiment, the magnetization and arrangement of the permanent magnets are designed such that the strength of the surface magnetic field in the area between the first and second regions is 1 T or greater.

[0025] According to one embodiment, the permanent magnet is a neodymium magnet, for example a NdFeB or PrNdB magnet, and the assembly further comprises a cooling system designed to reduce the temperature of the permanent magnet, the magnetization and arrangement of the permanent magnet and said cooling system being designed such that the strength of said surface magnetic field in said area comprised between the first region and the second region is 1.5 T or more.

[0026] According to one embodiment, all permanent magnets are of substantially the same size, same magnetization, same magnetic flux density, same mass, same material, and same grade.

[0027] Another subject of the invention is a system comprising a number of assemblies according to the invention stacked in the direction y.

[0028] Other features, details and advantages of the invention will become apparent on reading the description given with reference to the accompanying drawings, given as an example, in which: [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 shows schematic diagrams of six different configurations (a)-(f) for generating a substantially uniform magnetic field within a given "empty" volume. [Figure 2A] 2A, 2B and 2C show a cross section UU' in the plane yx, a cross section VV' in the plane yz and a perspective view of an assembly according to a preferred embodiment of the invention. [Figure 2B] 2A, 2B and 2C show a cross section UU' in the plane yx, a cross section VV' in the plane yz and a perspective view of an assembly according to a preferred embodiment of the invention. [Figure 2C]2A, 2B and 2C show a cross section UU' in the plane yx, a cross section VV' in the plane yz and a perspective view of an assembly according to a preferred embodiment of the invention. [Figure 2D] FIG. 2D shows a particular embodiment of the assembly of the invention along cross section VV'. [Figure 3] FIG. 3 shows a particular embodiment of the assembly of the invention along cross section UU'. [Figure 4] FIG. 4 shows a cross section in the plane yx of an assembly according to one embodiment of the invention. [Figure 5] FIG. 5 shows a cross section in the plane yx of an assembly according to a variant of the embodiment in FIG. [Figure 6] FIG. 6 shows a system including a number of assemblies according to the invention stacked in the direction y. [Figure 7] FIG. 7 shows a cross section in the plane yx of a segment of an assembly according to one embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] In the drawings, elements are not drawn to scale and like reference numbers designate like elements unless otherwise indicated.

[0031] In the remainder of this document, the term "permanent magnet(s)" refers to hard ferromagnetic materials that exhibit anisotropy such that they have a preferred axis of magnetization. When an external magnetic field is applied to them, these materials become magnetized and generate a magnetic field, and continue to generate this field even when the external magnetic field is no longer applied.

[0032] In the remainder of this document, the term "magnetization orientation" refers to the orientation of the preferred magnetization direction of a permanent magnet.

[0033] "Magnetization orientation +y" is used to refer to a magnetization direction in the direction of axis y that has a positive orientation relative to axis y, and "magnetization orientation -y" is used to refer to a magnetization direction in the direction of axis y that has a negative orientation.

[0034] More generally, to indicate that a magnetization or magnetic field has a direction along the axis y with a positive orientation, the magnetization or magnetic field will be said to be "oriented in the direction +y." If no sign is specified for a direction, no orientation is specified, and "direction y" corresponds to a direction along the axis y.

[0035] Here and in the following text, the term "substantially in a given direction" means that the vector quantity has a direction parallel to the given direction, ±25°.

[0036] Detailed Description Figures 2A and 2B show schematic cross sections UU' in plane yx and VV' in plane yz, respectively, of an assembly E according to a preferred embodiment of the present invention for generating a surface magnetic field in a substantially predetermined direction - in direction y in the example of Figures 2A and 2B.

[0037] Figure 2C shows a schematic perspective view of part of the assembly E according to the embodiment in Figures 2A and 2B. In Figure 2C, cross sections UU' and VV' are shown. The coordinate system xyz forms an orthogonal coordinate system.

[0038] 2C, only the upper segment of assembly E is shown for easier visualization, taking into account the fact that, according to the illustrated embodiment, the assembly exhibits planar symmetry in the plane Pxz. As will be explained in more detail later, the planar symmetry property of assembly E is optional, but is advantageous from a magnetic point of view.

[0039] In Figure 2A, by way of non-limiting example, the various elements shown are drawn to scale (which can be achieved based on a single magnet geometry). Additionally, Figure 2A shows the magnetic field lines generated by assembly E. All results, including field line or magnetic field strength calculations, are the result of simulations produced by finite element calculation software, such as FEMM or Comsol.

[0040] In its most general form, the assembly E of the invention comprises first and second ferromagnetic segments 6, 6' superimposed in the direction y, and at least five permanent magnets arranged so as to partially surround the first ferromagnetic segment 6 and the second ferromagnetic segment 6'. The magnetization of the permanent magnets is designed to create a surface magnetic field in the area comprised between the first and second regions R1, R2 of the ferromagnetic segments not covered by the permanent magnets, such that the surface magnetic field is substantially in a predetermined direction.

[0041] More specifically, the assembly of the present invention comprises at least two permanent magnets, referred to as upper magnets, arranged so as to partially surround the first ferromagnetic segment 6, except for at least one surface of the first ferromagnetic segment, referred to as the first surface S1. The magnetization resulting from the arrangement of the upper magnets, referred to as the upper magnetization, is M S It is expressed as:

[0042] Additionally, the assembly E comprises at least two permanent magnets, referred to as lower magnets, which are arranged so as to partially surround the second ferromagnetic segment 6′, except for at least one surface of the second ferromagnetic segment, referred to as the second surface S2. The magnetization resulting from the arrangement of the lower magnets, referred to as the lower magnetization, is M I It is expressed as:

[0043] Finally, the assembly comprises at least one permanent magnet, referred to as central magnet 2, disposed between the first and second magnetic segments 6, 6'. In embodiments in which the assembly comprises several central magnets 2, the latter are arranged in abutment with one another so as to form a "compound" central magnet (see, for example, Figures 3 and 4). The central magnet 2 (or, in some cases, central magnets 2) is arranged so as to adjoin the first and second surfaces, defining a first region R1 of the first surface S1 not covered by the central magnet 2, and a second region R2 of the second surface S2 not covered by the central magnet 2. Within the assembly, the first region R1 faces the second region R2 in such a way that an area 1 is defined. The magnetization resulting from the arrangement of the central magnet(s), referred to as central magnetization, is M C It is expressed as:

[0044] In the embodiment in FIGS. 2A-2C, by way of non-limiting example, the assembly comprises five upper magnets: an upper magnet, called the central upper magnet 3, arranged above the first ferromagnetic segment 6 in the direction y. The magnetization of the central magnet 3 is denoted M3. - two upper magnets 4 and 5, called first and second lateral upper magnets, respectively, arranged one on each side of the first ferromagnetic segment in the direction x. The magnetizations of magnets 4 and 5 are denoted M4 and M5, respectively. - two upper magnets 4A and 5A, called first and second additional lateral upper magnets, respectively, arranged one on each side of the first ferromagnetic segment in the direction z. The magnetization of the magnets 4A and 5A is M 4A and M 5A These magnets 4A and 5A are optional and are configured to prevent the magnetic flux from escaping through the face of the first segment 6 normal to the direction z in the example of Figures 2A-2C. They mainly affect the upper vertical edge of the area 1, where they are configured to avoid an excessive reduction in the strength of the magnetic field.

[0045] In the embodiment in FIGS. 2A-2C, by way of non-limiting example, the assembly comprises five lower magnets: a lower magnet, called central lower magnet 3′, arranged below the second ferromagnetic segment 6′ in the direction y. The magnetization of the central lower magnet 3′ is M 3’ It is expressed as: - Two lower magnets 4' and 5', called first and second lateral lower magnets, respectively, arranged one on each side of the second ferromagnetic segment in the direction x. The first lateral lower magnet 4' is arranged facing the first lateral upper magnet 4, and the second lateral lower magnet 5' is arranged facing the second lateral upper magnet 5. The magnetizations of the magnets 4' and 5' are respectively M 4’ and M 5’ Here and in the following text, the term "magnet A disposed facing magnet B" means that the surface of magnet A is disposed facing the surface of magnet B. - two lower magnets 4A' and 5A', called first and second additional lateral lower magnets, respectively, arranged one on each side of the second ferromagnetic segment in the direction z. The magnetizations of the magnets 4A' and 5A' are respectively M 4A’ and M 5A’ Like magnets 4A and 5A, these magnets 4A' and 5A' are optional and are configured to prevent magnetic flux from escaping through the face of second segment 6' normal to direction z in the example of Figures 2A-2C. They primarily affect the lower vertical edge of area 1, where they are configured to avoid excessive reduction in the strength of the magnetic field.

[0046] In the embodiment of FIGS. 2A-2C, by way of non-limiting example, the assembly has a magnetization M=M c The central magnet 2 has a

[0047] Each of the permanent magnets mentioned in this description may be a single magnet or may be formed of multiple "element" magnets.

[0048] The permanent magnets of the present invention each exhibit a magnetization designed to create a surface magnetic field in the region 1 that is included between the first region R1 and the second region R2, but not between the two central magnets, such that the surface magnetic field is substantially in the direction y having a predetermined orientation. In other words, by virtue of their arrangement relative to the ferromagnetic segments 6, 6' and their magnetization, the permanent magnets concentrate magnetic flux through the regions R1 and R2 to create a unidirectional surface magnetic field in the region 1.

[0049] The term "surface magnetic field" means that the magnetic field is substantially uniform along the surface contained between the first and second regions within an area 1. The fact that area 1 is a three-dimensional area does not in any way preclude the fact that the magnetic field is uniform along the surface within this area 1 (i.e., a "surface" magnetic field).

[0050] It will be understood that the above results can be obtained by numerous arrangements and permutations of the permanent magnets without departing from the scope of the invention, so long as they satisfy the conditions set forth above.

[0051] Thus, by way of non-limiting example, thanks to their arrangement and magnetization, the permanent magnets of the embodiment in FIGS. 2A-2C generate a surface magnetic field in the plane yz with orientation +y in Zone 1.

[0052] To this end, the central top magnet 3 exhibits a magnetization M3 in the direction +y, and the first and second lateral top magnets 4 and 5 each exhibit a magnetization M4, M5 in the direction x with an opposite orientation. In addition, the additional lateral top magnets 4A and 5A each exhibit a magnetization M in the direction z with an opposite orientation. 4A , M 5A The magnetization of the upper magnet is the upper magnetization M S In addition, the central magnet 2 has a central magnetization M C Finally, the central lower magnet 3' exhibits a magnetization M2 in the direction +y, so that the magnet is oriented in the -y direction. 3’ and the first and second lateral lower magnets 4' and 5' respectively have magnetizations M in the direction x with opposite orientations. 4’ , M5’ In addition, the additional lateral lower magnets A' and 5A' each exhibit a magnetization M in a direction z having an opposite orientation. 4A’ , M 5A’ The magnetization of the lower magnet is the lower magnetization M I is oriented in the +y direction.

[0053] More generally, to obtain a surface magnetic field in the plane yz and substantially oriented in the direction +y in the area 1, it is necessary: -The magnetization of the upper magnet is the upper magnetization M S is substantially oriented in the direction +y; -The magnetization of the lower magnet is I are also substantially oriented in the direction +y, - the magnetization of the central magnet(s) is the central magnetization M C is substantially oriented in the direction −y.

[0054] Therefore, the assembly of the present invention, among its various variants and embodiments, allows for the controlled creation of a substantially unidirectional surface magnetic field. Compared to the magnet assembly shown in Figure 1, the solution of the present invention requires a smaller magnet volume by magnetizing a volume that is not as large as in the prior art. The solution of the present invention is therefore more compact, lighter, and cheaper than the prior art solutions.

[0055] The dimension of regions R1, R2 in direction x relative to the thickness in x of region 1 (effective surface magnetic field) is a critical parameter of the present invention because if this distance is too large, the magnetic flux leaving regions R1 and R2 will traverse a larger surface area, reducing the strength of the magnetic field within region 1 and resulting in a less efficient use of the permanent magnet. Conversely, if this distance is too small, the magnetic field may become too strong at certain points in region 1, potentially causing undesirable demagnetization effects of the permanent magnet near these points of high field strength.

[0056] Also, according to a preferred embodiment of the present invention, the dimensions of regions R1 and R2 in a direction perpendicular to the plane in which the surface magnetic field is generated are designed so that the strength of the surface magnetic field in area 1 is equal to or greater than 1 T, and preferably less than an intensity that would even cause partial demagnetization of the permanent magnet.

[0057] Preferably, the permanent magnets of assembly E are neodymium magnets, for example PrNdB magnets, and the assembly is equipped with a cooling system designed to reduce the temperature of the permanent magnets to a temperature below 10 K, preferably below 4 K. In this embodiment, the magnetization and positioning of the permanent magnets and the cooling system are designed such that the surface magnetic field strength is 1.5 T or greater in zone 1.

[0058] Preferably, and as shown in Figure 2A, the first lateral lower magnet 4' exhibits a magnetization with an opposite orientation (-x in the example of Figure 2A) to that of the first lateral upper magnet 4 (in this case +x). This makes it possible to loop the magnetic fields entering regions R1 and R2. For the same reason, preferably, the first additional lateral lower magnet 4A' in Figure 2B exhibits a magnetization in direction z with an opposite orientation to that of the first additional lateral upper magnet 4A.

[0059] The ferromagnetic segments 6, 6' are preferably soft ferromagnetic materials, since these materials allow a greater concentration of magnetic flux than hard ferromagnetic elements, since soft ferromagnetic materials have a greater saturation magnetization H than hard ferromagnetic materials. S (For pure iron, M S =2.19 T). The ferromagnetic segments 6, 6' contain, for example, iron, cobalt, nickel, magnesium, silicon, iron-nickel or iron-cobalt alloys.

[0060] Alternatively, the ferromagnetic segments 6, 6' are made of a hard ferromagnetic material, for example, made of an alloy of aluminum (Al), nickel (Ni), and cobalt (Co), or made of neodymium-iron-boron (NdFeB) or praseodymium-iron-boron (PrFrB). These materials are less preferable than soft ferromagnetic materials because they have a lower saturation magnetization than the latter. However, their saturation magnetization depends on their temperature. Also, according to one embodiment of the present invention in which the ferromagnetic segments 6, 6' are made of a hard ferromagnetic material, the assembly further comprises a cooling system designed to reduce the temperature of the ferromagnetic segments 6, 6' (and possibly of the permanent magnets) to, for example, a temperature of 4 K. As a result, the value of the saturation magnetization of the segments 6, 6' is increased, which makes it possible to obtain a surface magnetic field strength in the direction y in the area 1 greater than 1.5 T.

[0061] As a non-limiting example, in the example shown in FIGS. 2A-2C, the ferromagnetic segments 6, 6′ are rectangular parallelepiped structures, and the upper, lower, and central magnets are arranged such that each face of the ferromagnetic segments 6, 6′ faces a permanent magnet.

[0062] Alternatively, according to another embodiment, the ferromagnetic segments 6, 6' have a shape different from a rectangular parallelepiped structure, for example a cylindrical structure, as long as this shape allows the magnetic flux to be concentrated so that it exits through the regions R1 and R2 with the generation of a unidirectional surface magnetic field.

[0063] As described above, in the embodiment of FIGS. 2A-2C, the permanent magnet and the first and second ferromagnetic segments of the assembly are arranged such that the assembly is aligned with the plane P XZ The central magnets 2 are arranged to exhibit planar symmetry in the y direction. This symmetry is optional and allows for the creation of a system comprising multiple assemblies stacked in the y direction without significant degradation in performance by canceling the magnetic flux created by the central magnet 2 through the field created by the stack of the central lower magnet 3' and the central upper magnet 3 of another assembly (see FIG. 6).

[0064] FIG. 2D shows a schematic representation of a particular embodiment of the assembly in FIGS. 2A-2C along cross section VV' shown in FIG. 2C.

[0065] In this particular embodiment, the assembly further comprises two permanent magnets AS1, AS2, referred to as first and second additional magnets. The additional magnets AS1, AS2 are disposed one on each side of the central magnet in the direction z (i.e., one on each outer vertical edge of the area 1), and each have a magnetization M in the same direction as the surface magnetic field, with an orientation opposite to the predetermined orientation of the surface magnetic field generated in the area 1. AS1 , M AS2 It presents.

[0066] The additional magnets AS1, AS2 mainly affect the vertical edges of Zone 1, where they are configured to avoid excessive reduction in the strength of the magnetic field, in other words, these magnets AS1, AS2 aim to make the strength of the generated magnetic field more uniform in z within Zone 1.

[0067] In the embodiment in FIG. 2D, the additional magnets AS1, AS2 each have a magnetization M oriented in the direction −y to achieve the above-mentioned effect. AS1 , M AS2 It presents.

[0068] The use of additional magnets AS1, AS2 is compatible with all embodiments of the present invention.

[0069] FIG. 3 shows a schematic representation of a particular embodiment of the assembly in FIGS. 2A-2C along cross section UU′ shown in FIG. 2C. Elements in FIG. 3 are drawn to scale. The embodiment in FIG. 3 is an improvement over the structure in FIGS. 2A-2C to minimize demagnetization, especially when the permanent magnet is made of FeNdB.

[0070] To avoid the problem of localized partial demagnetization, the structure of assembly E was modified in the following ways compared to that in FIG. 2A: -The upper and lower magnets are offset by 7 mm in the +x direction. -Permanent magnet corners are rounded,

[0071] A space of approximately 1 mm was introduced between the upper and lower magnets. In this embodiment, all of the permanent magnets are identical (also referred to as "element magnets"). Here, the term "identical" means that the permanent magnets are of substantially the same dimensions, same magnetization, same magnetic flux density, same mass, same material, and same grade, except for tolerances associated with standard manufacturing processes used by those skilled in the art. This allows for easier design and manufacturing.

[0072] As a non-limiting example, the permanent magnet in FIG. 3 has dimensions of 15×15 mm 2 and made of FeNdB (minimum grade N48) at 300 K, assembly E comprises 16 element magnets: - 4 central magnets 2 -Two central top magnets 3 -Two lateral upper magnets 4, 5 - two additional lateral upper magnets 4A, 5A (not shown in Figure 3) -Two central bottom magnets 3' -Two lateral lower magnets 4', 5' - Two additional lateral lower magnets 4A', 5A' (not shown in Figure 3).

[0073] In addition, the ferromagnetic segments 6 and 6' have dimensions 4 x 19 mm, in which the magnetic flux is concentrated. 2 Considering the fact that the ferromagnetic segments 6 and 6' and the central magnet 2 are always attracted to each other, a gap is unfavorable, so the ferromagnetic segments 6 and 6' are placed directly on the central magnet 2.

[0074] The assembly of the embodiment in FIG. 3 has dimensions (in the plane xy) of 0.5×30 mm with a distance of 0.5 mm between the central magnets 2. 2 The device is configured to generate an average unidirectional magnetic field of 1.02 T with a maximum magnetic field H of 1250 kA / m within an area of ​​100 m.

[0075] 3 shows a weak partial demagnetization of the magnetization, mainly in front of the ferromagnetic segments 6 and 6′, for components with coercive forces greater than 1100 kA / m and opposite to the direction of magnetization for the side lower magnets 4′, 5′ and side upper magnets 4, 5. In addition, the direction of magnetization is tilted near the central upper magnet 2 and central lower magnet 2′.

[0076] Moving the side upper magnets closer to the central upper magnet (and the side lower magnets closer to the central lower magnet) does not significantly strengthen the surface field, while the demagnetization is still increased.

[0077] Also, preferably, in all embodiments of the present invention, the first and second side upper magnets are not positioned adjacent to the central upper magnet, and the first and second side lower magnets are not positioned adjacent to the central lower magnet. The distance between these magnets is designed to reduce weakening of the surface magnetic field while still minimizing demagnetization of the side lower and upper magnets. It will be understood that this distance depends on the parameters of the magnets (dimensions, placement, magnetization, etc.) and on the parameters of the ferromagnetic segments 6, 6'. Furthermore, separating the magnets allows the mass of the assembly to be mechanically supported by a structure independent of the magnets, especially when forces do not allow for adhesive bonding, which is particularly advantageous when multiple assemblies are stacked (see FIG. 6).

[0078] The presence of the side upper magnets 4, 5 (and side lower magnets 4', 5', respectively) reverses the direction of the force exerted by the central upper magnet 3 (and central lower magnet 3', respectively), thus potentially minimizing the force exerted by the side upper and lower magnets on the central upper and lower magnets of the assembly.

[0079] In the embodiment in FIG. 3, the vertical end of the assembly E is preferably connected to a "C" shaped metal armature CM of small thickness (less than 1 mm) to loop the residual magnetic flux.

[0080] Figure 4 shows a schematic cross section in the plane yx of an assembly E according to one embodiment of the present invention. In Figure 4, by way of non-limiting example, the various elements shown are drawn to scale. In addition, the field lines of the magnetic field generated by the assembly E are shown.

[0081] As in the embodiment in Figure 3, the permanent magnets are all identical in the embodiment in Figure 4. It should be understood that this feature is optional.

[0082] In contrast to the embodiments shown previously in the figures, in the embodiment in Fig. 4 the ferromagnetic segments 6, 6' each have a cross section in the shape of an isosceles triangle in the plane yx. The angle opposite region R1 can be removed to suppress the demagnetizing field.

[0083] The ferromagnetic segment 6 has two upper surfaces covered by central upper magnets 31 and 32, and a lower surface S1 partially covered by central magnets 21 and 22 so as to define a region R1.

[0084] Similarly, the ferromagnetic segment 6 has two lower faces covered by the central lower magnets 31 and 32', and an upper face S2 partially covered by the central magnets 23 and 24 so as to define a region R2.

[0085] Each central magnet has a central magnetization M C exhibits a magnetization designed to have orientation -y.

[0086] Therefore, the surface magnetic field generated in area 1 is oriented in the direction +y.

[0087] Compared to the embodiment in FIG. 3, the embodiment in FIG. 4 makes it possible to reduce the number of permanent magnets.

[0088] Preferably, the embodiment in FIG. 4 has magnetizations M in the same direction as the surface magnetic field, each of which has an orientation opposite to the predetermined orientation of the surface magnetic field, arranged one on each side of the central magnet in the direction z. AS1 , MAS2 The magnet further includes two additional permanent magnets AS1 and AS2.

[0089] 4 further comprises two additional lateral upper magnets 4A and 5A, one disposed on each side of the first ferromagnetic segment 6 in the direction z, and two additional lateral lower magnets 4A' and 5A', one disposed on each side of the second ferromagnetic segment 6' in the direction z. The additional lateral upper magnets 4A and 5A (and the additional lateral lower magnets 4A' and 5A', respectively) each exhibit magnetization in the direction z with opposite orientations.

[0090] Figure 5 shows a schematic cross section in the plane yx of an assembly E according to a variant of the embodiment in Figure 3. In this variant, by way of non-limiting example, the ferromagnetic segments 6, 6' are of a structure with a parallelepiped cross section in the plane xy.

[0091] 5, the dimension of the first ferromagnetic segment 6 in the direction x is less than the dimension in the direction x of the central upper magnet(s) arranged above the ferromagnetic segment 6. Similarly, the dimension of the second ferromagnetic segment 6' in the direction x is less than the dimension in the direction x of the central lower magnet(s) arranged below the ferromagnetic segment 6'. Shortening the segments 6 and 6' on the horizontal side opposite the regions R1 and R2 relative to the magnets 3 and 3' makes it possible to increase the strength of the magnetic flux in the area 1. This feature is optional and is compatible with all embodiments of the present invention.

[0092] Additionally, in this embodiment, the first ferromagnetic segment includes a chamfer formed in the region opposite the first surface S1, and the second ferromagnetic segment includes a chamfer formed in the region opposite the second surface S2. These chamfers are configured to increase the strength of the magnetic flux in Region 1 by concentrating more of the magnetic flux through Regions R1 and R2. This feature is optional and is compatible with all embodiments of the present invention.

[0093] Compared to Figure 3, the embodiment in Figure 5 does not include a shift of the top and bottom magnets to the right, does not include magnets with rounded corners, and the assembly of the embodiment in Figure 5 is configured to generate an average unidirectional magnetic field of 1.01 T with H=1590 kA / m in Zone 1, and demagnetization is more pronounced compared to the embodiment in Figure 3.

[0094] Alternatively, the first ferromagnetic segment includes a rounded edge formed in an area opposite the first surface S1, and the second ferromagnetic segment includes a rounded edge formed in an area opposite the second surface S2. These rounded edges are configured to reduce the strength of the demagnetizing field for magnets 4 and 4'. This feature is optional and compatible with all embodiments of the present invention.

[0095] Additionally, optionally, as shown in FIG. 7, grooves 7 are machined in the ferromagnetic segments 6, 6′ in the surface in contact with the central magnet 2 in the direction z to suppress demagnetizing fields in the corners of the magnet 2 on the area 1 side.

[0096] 6 shows a system ST comprising several assemblies E according to the invention stacked in the direction y. The system of the invention therefore makes it possible to generate a unidirectional surface magnetic field in several rows of areas 1.

[0097] Preferably, the magnetization of the permanent magnets of each assembly E of the system ST in FIG. 6 is such that the sum of the upper and lower magnetic fluxes is equal or substantially equal to the central magnetic flux. Here, the term "substantially equal" means that the norm of the sum of the upper and lower magnetic fluxes is equal to the norm of the central magnetic flux, ±5%. The sum of the upper and lower magnetic fluxes having the same direction as the central magnetic flux but opposite orientation within the assembly E is locally canceled on average. As a result, it is possible to stack the assemblies E without significant degradation in performance by canceling the leakage flux created by the central magnet 2 through that created by the stack of central lower magnet 3' and central upper magnet 3.

[0098] Preferably, the system ST comprises a "C" shaped metal armature CM to loop the magnetic field at the vertical end of the system ST.

[0099] Optionally, the concentration of magnetic flux within the ferromagnetic segments 6, 6' may also be at least temporarily facilitated by superconducting tape shielding the outgoing magnetic flux instead of or in combination with one or more of the permanent magnets.

[0100] The structures of the assemblies detailed in the description and figures are given as examples and are intended to illustrate the present invention. They should not be considered to limit the scope of the present invention in any way. Various modifications and variations of the above-described structures, fabrication processes, and their applications and uses will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. In particular, optimization and / or modification of the structure may be based on multiple parameters, including the magnetic field, its uniformity, the dimensions of Area 1, the volume of the magnet, temperature, etc.

Claims

1. An assembly (E) for generating a surface magnetic field comprising first and second ferromagnetic segments (6, 6') superimposed in the direction y, said assembly comprising: at least two permanent magnets, called upper magnets (3, 4, 5, 4A, 5A), arranged so as to partially surround said first ferromagnetic segment (6), except for at least one surface of said first ferromagnetic segment, called first surface (S1); at least two permanent magnets, called lower magnets (3', 4', 5', 4A', 5A'), arranged so as to partially surround said second ferromagnetic segment, except for at least one surface of said second ferromagnetic segment, called second surface (S2); at least one permanent magnet, called central magnet (2), disposed between the first and second magnetic segments, defining an area of ​​the first surface not covered by the central magnet, called first area (R1), and an area of ​​the second surface not covered by the central magnet, called second area (R2), the first area facing the second area; Further provided with The magnetization of the permanent magnet (M ３ ;M ４ ;M ５ ;M ４Ａ ;M ５Ａ ;M ３’ ;M ４’ ;M ５’ ;M ４Ａ’ ;M ５Ａ’ ), and the arrangement of the at least one central magnet is designed to create a surface magnetic field in a region (1) that is included between the first region and the second region but not between two central magnets, such that the surface magnetic field is substantially in the direction y having a predetermined orientation.

2. the magnetization of the permanent magnet is such that the surface magnetic field lies in a plane yz, where z is a direction perpendicular to the direction y; - the magnetization (M ３ ;M ４ ;M ５ ) is the magnetization (M) resulting from the placement of the upper magnet, referred to as the upper magnetization. Ｓ ) is substantially in the direction y with said predetermined orientation; the magnetization (M ３’ ;M ４’ ;M ５’ ) is the magnetization (M) resulting from the placement of the lower magnet, called the lower magnetization. Ｉ ) is substantially in the direction y with said predetermined orientation; - said at least one central magnet (2) has a magnetization (M, called central magnetization) substantially in said direction y, which has an orientation opposite to said predetermined orientation; ２ 10. The assembly of claim 1, wherein:

3. The upper magnet is - arranged above the first ferromagnetic segment in the direction y, and having the magnetization (M ３ ) an upper magnet, referred to as the central upper magnet (3), two upper magnets (4, 5), called first and second lateral upper magnets respectively, arranged one on each side of the first ferromagnetic segment in a direction x perpendicular to the direction y and to the direction z, the first and second lateral upper magnets having magnetizations (M ４ , M ５ two upper magnets (4, 5), Including, The lower magnet is - arranged below the second ferromagnetic segment in the direction y, and having the magnetization (M ３’ a lower magnet, referred to as the central lower magnet (3'), two lower magnets (4', 5'), called first and second lateral lower magnets respectively, arranged one on each side of the second ferromagnetic segment in the direction x; Including, The first lower lateral magnet (4') is arranged facing the first upper lateral magnet (4), and the second lower lateral magnet (5') is arranged facing the second upper lateral magnet (5), The first and second lateral lower magnets have magnetizations (M ４’ , M ５’ 3. The assembly of claim 2, wherein:

4. The first and second lateral lower magnets have magnetizations (M ４’ , M ５’ 4. The assembly according to claim 1, wherein the first and second electrodes are arranged in a plane parallel to each other.

5. 5. The assembly of claim 3, wherein a dimension of the first ferromagnetic segment in the direction x is less than a dimension of the central upper magnet in the direction x, and a dimension of the second ferromagnetic segment in the direction x is less than a dimension of the central lower magnet in the direction x.

6. the upper magnet further comprises two upper magnets (4A, 5A), referred to as first and second additional side upper magnets, respectively, arranged one on each side of the first ferromagnetic segment in the direction z, the first and second additional side upper magnets exhibiting magnetizations in the direction z with opposite orientations; the lower magnet further comprises two lower magnets (4A', 5A'), referred to as first and second additional lateral lower magnets, respectively, arranged one on each side of the second ferromagnetic segment in the direction z; the first additional lower lateral magnet is disposed facing the first additional upper lateral magnet, and the second additional lower lateral magnet is disposed facing the second additional upper lateral magnet; 6. An assembly according to any one of claims 3 to 5, wherein the first and second additional lateral lower magnets exhibit magnetizations in the direction z having opposite orientations.

7. 7. The assembly of claim 3, further comprising two permanent magnets, referred to as first and second additional magnets, arranged one on each side of the at least one central magnet in the direction z, the first and second additional lateral upper magnets exhibiting magnetization in the direction y having an orientation opposite to the predetermined orientation.

8. 8. The assembly of claim 3, wherein the first and second upper side magnets are not positioned adjacent to the central upper magnet, and the first and second lower side magnets are not positioned adjacent to the central lower magnet.

9. Assembly according to any one of claims 2 to 8, wherein the magnetisation of the permanent magnet is such that the sum of the upper and lower magnetic flux is equal or substantially equal to the central magnetic flux.

10. 10. The assembly of claim 2, wherein the first ferromagnetic segment includes a chamfer or rounded edge formed in a region opposite the first surface, and the second ferromagnetic segment includes a chamfer or rounded edge formed in a region opposite the second surface.

11. 11. The assembly according to claim 2, wherein the permanent magnet and the first and second ferromagnetic segments are arranged such that the assembly exhibits planar symmetry in a plane having a normal to the direction y.

12. 12. The assembly of claim 1, wherein the magnetization and arrangement of the permanent magnets are designed such that the strength of the surface magnetic field in the area between the first region and the second region is 1 T or greater.

13. the permanent magnet is a neodymium magnet, for example, a NdFeB or PrNdB magnet, and the assembly further comprises a cooling system designed to reduce the temperature of the permanent magnet; 13. The assembly of claim 1, wherein the magnetization and arrangement of the permanent magnet and the cooling system are designed such that the strength of the surface magnetic field in the area comprised between the first region and the second region is 1.5 T or greater.

14. Assembly according to any one of claims 1 to 13, wherein all the permanent magnets are of substantially the same size, same magnetization, same magnetic flux density, same mass, same material and same quality.

15. A system (ST) comprising a plurality of assemblies according to any one of claims 1 to 14 stacked in the direction y.

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