Manufacturing of sintered flux focusing permanent magnets using an apparatus having an asymmetrically formed magnetic device

Abstract

An apparatus (460, 560) and method for manufacturing a sintered flux focusing permanent magnet (250, 350) are described. The apparatus includes (a) a mold (470, 570); and (b) a first magnetic device (461, 561-1, 561-2) and a second magnetic device (464, 564). The first magnetic device (461; 561-1, 561-2) includes a first yoke structure (463; 563-1, 563-2) having a first shape, and the second magnetic device (464, 564) includes a second yoke structure (466, 566) having a second shape. The second shape is spatially different from the first shape. In addition, the spatial difference in the shapes of the two yoke structures (463, 466; 563-1, 563-2, 566) causes a non-uniform magnetic field, so that the magnetic field within the mold cavity (472, 572) is associated with an extended angular distribution of magnetic flux lines. A sintered flux focusing permanent magnet (250, 350) manufactured using the method, an electromechanical transducer (140) including the sintered flux focusing permanent magnet (250, 350), and a wind turbine (100) are further described.

Description

Technical Field

[0001] The invention relates to an apparatus and a method for producing a sintered flux focusing permanent magnet. Furthermore, the invention relates to a sintered flux focusing permanent magnet produced by means of said method, and to an electromechanical transducer and a wind turbine comprising at least one such sintered magnet. Background Art

[0002] Permanent magnetic materials are used in a number of different application areas. Probably the most important application areas technically and economically are electromechanical transducers, i.e. electric motors and generators. Electric motors equipped with at least one permanent magnet (PM) convert electrical energy into mechanical energy by generating a temporarily changing magnetic field with the aid of windings or coils. This temporarily changing magnetic field interacts with the magnetic field of the PM, which is generated, for example, in the rotational movement of the rotor assembly of the electric motor relative to the stator assembly. In a physically complementary manner, the generator converts mechanical energy into electrical energy.

[0003] A generator is a core component of any power plant for generating electrical energy. This applies to power plants that capture mechanical energy directly, for example hydroelectric power plants, tidal power plants and wind power plants also known as wind turbines. However, this also applies to power plants that (i) firstly use chemical energy, for example from burning fossil fuels or from nuclear energy, in order to generate thermal energy and (ii) secondly convert the generated thermal energy into mechanical energy by means of appropriate thermodynamic processes.

[0004] The efficiency of a generator is probably the most important factor for optimizing the production of electrical energy. For a PM generator, it is essential that the magnetic flux generated by the permanent magnets (PM) is strong. This can be best achieved using sintered rare earth magnets, for example, using an NdFeB material composition. However, the spatial magnetic field distribution generated by the PM also has an impact on the generator efficiency. In the latter case, it is often advantageous when using a PM device or PM arrangement with a non-uniform magnetic domain arrangement pattern, which intentionally produces a non-uniform magnetic field strength or flux density, especially in the air gap between the rotor assembly and the stator assembly.

[0005] It is known to configure a non-uniform magnetic domain arrangement pattern in a PM in order to achieve so-called "flux focusing". WO2012 / 141932A2 discloses a PM magnet arrangement in which PMs of different magnetizations are combined so that "magnetic focusing" is achieved. EP3276642 A1 discloses a sintered rare earth PM with a focusing magnetic arrangement pattern, which has an integrally formed or single-piece PM body. EP2762838 A2 discloses an apparatus and method for manufacturing a PM, wherein a non-uniform external magnetic field is applied during the sintering process in order to magnetize different regions of the PM in different directions. In this document, flux focusing permanent magnets are abbreviated as FFPM.

[0006] To manufacture FFPM, there is a need for an apparatus for generating a suitable non-uniform magnetic field present in the mold cavity in order to magnetize the magnetic powder compressed in the mold cavity. Summary of the invention

[0007] An apparatus for manufacturing a sintered flux focusing permanent magnet, a method for manufacturing a sintered flux focusing permanent magnet, a sintered flux focusing permanent magnet, an electromechanical transducer and a wind turbine for generating electric power according to the present invention may meet this need.

[0008] According to a first aspect of the present invention, there is provided an apparatus for manufacturing a sintered flux focusing permanent magnet. The provided apparatus comprises: (a) a mould having a mould cavity for receiving a powder of a permanent magnet material; and (b) a first magnetic device and a second magnetic device, both for generating a magnetic field for magnetizing the powder contained in the mould cavity. The first magnetic device comprises a first (magnetic) yoke structure having a first shape, and the second magnetic device comprises a second (magnetic) yoke structure having a second shape, which is spatially different from the first shape. In addition, the spatial difference in the shapes of the two yoke structures causes a non-uniform magnetic field, so that the magnetic field in the mould cavity is associated with the spread angular distribution of the magnetic flux lines.

[0009] The described device is based on the idea that by choosing a spatially asymmetric design of a magnet system comprising two magnetic devices and for magnetizing the (compressed) powder present in the cavity, it is easy to generate a suitable inhomogeneous magnetic field at least in the region of the cavity.

[0010] The described spread angular distribution of magnetic flux lines can be used in particular to produce a spread angular distribution of magnetic domain alignment directions within a flux focusing permanent magnet (FFPM) to be produced, which spread angular distribution produces a focused magnetization of the sintered block. Thus, outside the majority of the FFPM, a magnetic focus or at least a magnetic focusing region can be defined. In this point or in this region, the magnetic flux density caused by the corresponding FFPM is increased compared to points or regions outside the focus and the corresponding focusing region.

[0011] By designing the shape and / or geometric shape of the yoke structure in an appropriate (asymmetric) manner, an extended angular distribution of the flux lines can be generated, which results in the desired focused flux magnetization design.

[0012] The yoke structure, which may also be referred to as a pole piece, may be made of a ferromagnetic material, in particular iron or cobalt iron for higher saturation. In contrast, the mold may be made of a non-magnetic material, and in particular a non-ferromagnetic material. The (currently) preferred mold material is stainless steel. However, other mold materials that provide mechanical rigidity may also be used.

[0013] According to an embodiment of the present invention, (a) at least one of the two magnetic devices comprises at least one electromagnetic coil for generating at least a portion of a magnetic field, and (b) the corresponding yoke structure is configured for guiding and / or for shaping the magnetic field generated by the corresponding electromagnetic coil.

[0014] Using at least one electromagnetic coil supported by a suitable yoke structure to generate the magnetic field may provide the advantage that the magnetic field and corresponding magnetic flux (density) at least in selected areas of the mould cavity may be significantly increased.

[0015] By setting the current flowing through the individual coils, the strength of the magnetic field generated by each magnetic device can be appropriately adjusted. By varying the current flowing through each coil independently, not only the strength but also the direction of the magnetic field lines can be varied towards the desired characteristics of the generated magnetic field.

[0016] According to another embodiment of the invention, the device comprises the following features:

[0017] (A) With respect to the mold cavity, the first yoke structure and the second yoke structure are located at opposite sides, and (B) the first yoke structure has a first outer yoke surface facing the mold cavity, and the second yoke structure has a second outer surface facing the mold cavity, wherein the first outer yoke surface has a curvature different from that of the second outer yoke surface.

[0018] By designing the respective outer yoke surfaces in a suitable manner, the direction of the magnetic field lines emerging from the respective yoke can be selected. Thus, the extent of the angular distribution of the magnetic flux lines can be adjusted in an easy and effective manner.

[0019] According to another embodiment of the present invention, the first outer yoke surface has (at least within a portion of the first outer yoke surface) a first radius of curvature, and the second outer yoke surface has (at least within a portion of the second outer yoke surface) a second radius of curvature different from the first radius of curvature.

[0020] V: This may provide an advantage that a higher alignment angle can be achieved at the side edge of the FFPM and with respect to the magnetic domain arrangement direction of the side edge of the FFPM.

[0021] According to another embodiment of the invention, the mold cavity comprises one of the following features regarding the two outer yoke surfaces:

[0022] (A) The first outer yoke surface (463a) is convex, and the second outer yoke surface (466a) is convex;

[0023] (B) The first outer yoke surface is convex, and the second outer yoke surface is concave;

[0024] (C) The first outer yoke surface is concave and the second outer yoke surface is convex; and

[0025] (D) The first outer yoke surface is concave, and the second outer yoke surface is concave.

[0026] By choosing suitable curvatures for the two outer yoke surfaces, an extended angular distribution of appropriate and well-defined magnetic flux lines can be produced in a simple and effective manner. Depending on the specific application, the curvature of the outer yoke surfaces can be regular (without any corners and edges ("blocks and protrusions") or irregular.

[0027] At least one of the two outer yoke surfaces may have a shape that is at least approximately cylindrical. This results in a one-dimensional (1D) magnetic flux focusing, which results in a linearly extending focal region. Such magnetic focusing corresponds to optical focusing with the aid of a cylindrical optical lens. Alternatively, at least one of the outer yoke surfaces may have a shape that is at least approximately spherical. This results in a two-dimensional (2D) magnetic flux focusing, which results in an at least approximately focal point. Such magnetic focusing corresponds to optical focusing with the aid of a spherical optical lens.

[0028] According to another embodiment of the present invention, the first yoke structure comprises a first yoke substructure and a second yoke substructure, and the two yoke substructures are spatially separated from each other. In this configuration of the above-mentioned specific features of the device, according to this configuration, the first shape is different from the second shape by two sub-shapes, and the two sub-shapes are spatially separated from each other.

[0029] The use of at least three yoke structures in addition to the two yoke structures, by "split" the first yoke structure into two yoke substructures, may allow the generation of a highly spatially inhomogeneous magnetic field within the mold cavity. This may be particularly advantageous when producing sintered magnet blocks for FFPMs, which have a small focal length. The focal length may thus be defined as the distance between the focal point or focal region and the main surface of the FFPM.

[0030] It should be mentioned that there is no major limitation on the number of substructures. The second yoke substructure may also be subdivided into at least two substructures.

[0031] It is further mentioned that the yoke structure and / or the yoke substructure have the same (external) shape or at least two of them have different (external) shapes. In this respect, it is pointed out that when all external shapes are geometrically identical, the above-defined features are achieved by dividing the (entire) first outer yoke surface into two sub-surfaces, each sub-surface being assigned to a yoke substructure, according to which the (entire) first outer yoke surface has a different curvature than the second outer yoke surface.

[0032] With at least one of the at least three yoke(sub)structures now magnetized by means of a magnetic field generated by an electromagnetic coil, there is an opportunity to modify (the inhomogeneity of) the overall magnetic field by choosing an appropriate current flowing through the electromagnetic coil. This may allow the described device to be used to manufacture FFPMs with different flux focusing properties.

[0033] According to another aspect of the present invention, a method for manufacturing a sintered flux focusing permanent magnet by means of the above-mentioned apparatus is provided. The provided method comprises: (a) filling a permanent magnet material powder into a mold cavity of a mold; (b) generating a magnetic field for magnetizing the powder contained in the mold cavity by means of a first magnetic device and a second magnetic device; (c) compacting the powder contained in the mold cavity by means of a mold, magnetizing and compacting to produce a magnetized compacted block of the powder; (d) sintering the magnetized compacted block in a sintering furnace for producing a flux focusing permanent magnet; and (e) taking out the flux focusing permanent magnet from the sintering furnace.

[0034] Furthermore, the described method is based on the idea that with an appropriate spatially asymmetric design of a magnet system comprising two magnetic devices and used for magnetizing the (compressed) powder, FFPMs with a desired diffusion angle distribution of the magnetic domain alignment direction can be produced very easily.

[0035] It is mentioned that the step of generating a magnetic field to obtain a magnetic arrangement and the step of compacting the powder are usually completed at least in part simultaneously.

[0036] It is further mentioned that after the sintering step, further or post-processing may be performed in order to end up with a FFPM sheet, which may be used, for example, for a rotor component of a generator. Such post-processing may include, for example, surface finishing to smooth the surface of the sintered material and / or applying an outer surface layer, which makes the surface of the FFPM sheet less sensitive to external impacts. Furthermore, post-processing may include shaping of the sintered FFPM in order to have the desired geometry. Such shaping may be achieved, for example, by conventional milling.

[0037] According to another embodiment of the invention, the permanent magnet material comprises a rare earth material, in particular NdFeB. This may provide the advantage that very strong PMs may be manufactured without generating a lot of waste (rare earth materials are generally very expensive) for achieving the desired PM geometry.

[0038] It is to be mentioned that other components of the permanent magnet material may include ferrite and / or SmCo.

[0039] According to another aspect of the present invention, a sintered magnetic flux-focused permanent magnet made by performing the above-described method is provided.

[0040] According to another aspect of the present invention, an electromechanical transducer, in particular a generator, is provided. The provided electromechanical transducer comprises a stator assembly and a rotor assembly. The rotor assembly comprises a support structure and at least one sintered flux focusing permanent magnet, as described above, wherein the flux focusing permanent magnet is mounted to the support structure.

[0041] By designing the generator in such a way that the focus and corresponding focus areas are located within the air gap between the stator assembly and the rotor assembly, the power that can be generated by the generator can be significantly increased.

[0042] According to another aspect of the present invention, a wind turbine for generating electric power is provided. The wind turbine provided comprises (a) a tower, (b) a wind rotor arranged at a top portion of the tower and comprising at least one blade; and (c) an electromechanical transducer as described above. The electromechanical transducer is mechanically coupled to the wind rotor.

[0043] The wind turbine provided is also called a wind energy device, which is based on the idea that the above-mentioned electromechanical transducer allows to realize a wind turbine having an improved efficiency in the conversion of mechanical power into electricity, which conversion is done by the generator including the FFPM. This can help to increase the attractiveness of wind turbine technology for renewable electricity production compared to other technologies such as solar power plants.

[0044] It is noted that embodiments of the present invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims, while other embodiments have been described with reference to device type claims. However, a person skilled in the art will gather from the above and following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter, any combination between features relating to different subject matters, in particular any combination between features of method type claims and features of device type claims, is considered to be disclosed with this document.

[0045] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment.The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A wind turbine according to an embodiment of the present invention is shown.

[0047] Figure 2 The schematic diagram shows Figure 1 Generators of wind turbines.

[0048] Figure 3A magnetic flux-focused permanent magnet (FFPM) made according to an embodiment of the present invention is shown.

[0049] Figure 4 An apparatus for manufacturing an FFPM is shown, which has two magnetic devices having yoke structures of different shapes.

[0050] Figure 5 An apparatus for manufacturing FFPM is shown, which comprises three magnetic devices for unevenly magnetizing the magnetic material powder in the mold cavity. DETAILED DESCRIPTION

[0051] The illustrations in the drawings are schematic diagrams. It is noted that in different drawings, similar or identical elements or features are provided with the same reference numerals or with reference numerals which differ from the corresponding reference numerals only within the first digit. In order to avoid unnecessary repetition, elements or features which have already been explained with respect to the previously described embodiments are not explained again at a later point in the description.

[0052] Figure 1 A wind turbine 100 according to an embodiment of the invention is shown. The wind turbine 100 comprises a tower 120, which is mounted on a foundation not shown. On top of the tower 120 a nacelle 122 is arranged. Between the tower 120 and the nacelle 122 a yaw angle adjustment device 121 is provided, which enables the nacelle 122 to be rotated about a vertical axis not shown, which is aligned with the longitudinal extension of the tower 120. By controlling the yaw angle adjustment device 121 in a suitable manner it can be ensured that during normal operation of the wind turbine 100 the nacelle 122 is always properly aligned with the current wind direction.

[0053] The wind turbine 100 further comprises a wind rotor 110 having three blades 114 . In Figure 1 In the perspective view, only two blades 114 can be seen. The rotor 110 is rotatable about the axis of rotation 110a. The blade 114 mounted at the hub 112 extends radially with respect to the rotation axis 110a.

[0054] A blade angle adjustment device 116 is provided between the hub 112 and the blades 114, respectively, to adjust the blade pitch angle of each blade 114 by rotating the corresponding blade 114 around an axis not shown, which is substantially aligned parallel to the longitudinal extension of the corresponding blade 114. By controlling the blade angle adjustment device 116, the blade pitch angle of the corresponding blade 114 can be adjusted so that at least when the wind is not too strong, the maximum wind force can be obtained from the available mechanical power of the wind-driven wind rotor 110.

[0055] As from Figure 1 As can be seen in FIG. 1 , a gearbox 124 is arranged inside the nacelle 122. The gearbox 124 serves to convert the number of revolutions of the rotor 110 into a higher number of revolutions of a shaft 125, which is coupled to an electromechanical transducer 130 in a known manner. The electromechanical transducer is a generator 130.

[0056] At this point it is noted that the gearbox 124 is optional and the generator 140 may also be coupled directly to the rotor 110 via the shaft 125 without changing the number of revolutions. In this case, the wind turbine is a so-called direct drive (DD) wind turbine.

[0057] Furthermore, a brake 126 is provided to stop operation of the wind turbine 100 or to reduce the rotational speed of the rotor 110 , for example in an emergency.

[0058] The wind turbine 100 further comprises a control system 143 for operating the wind turbine 100 in an efficient manner. Besides controlling eg the yaw angle adjustment device 121, the depicted control system 153 is also used for adjusting the blade pitch angles of the rotor blades 114 in an optimized manner.

[0059] According to the basic principles of electrical engineering, the generator 130 includes a stator assembly 135 and a rotor assembly 140. In the embodiment described here, the generator 130 is implemented in a so-called "inner stator-outer rotor" configuration, wherein the rotor assembly 140 surrounds the stator assembly 135. This means that the non-illustrated permanent magnets and corresponding magnet assemblies of the rotor assembly 140 travel around an arrangement of multiple non-illustrated coils of the inner stator assembly 135, which coils generate induced currents generated by picking up the time-varying magnetic flux from the traveling permanent magnets.

[0060] According to the embodiments described herein, each permanent magnet (PM) assembly comprises at least three sintered flux-focused permanent magnets (FFPMs) made of an Nd-Fe-B material component.

[0061] Figure 2 A schematic diagram of a generator 130 is shown in cross-section. The generator 130 includes a stator assembly 135. The stator assembly 135 includes a stator support structure 237 including a stack of multiple laminations and a plurality of stator windings 239 housed within the stator support structure 237. The windings 239 are interconnected in a known manner by means of electrical connections not shown.

[0062] The rotor assembly 140 of the generator 130 is separated from the stator assembly 135 by an air gap ag, which includes a rotor support structure 242 that provides a mechanical base for mounting a plurality of FFPMs 250 . In Figure 2In this case, the rotation axis of the rotor assembly 140 is indicated by reference numeral 230a.

[0063] In the exemplary embodiment described here, three FFPMs arranged adjacent to each other are arranged at each angular position of the rotor assembly 140 . It should be mentioned that Figure 2 In the figure, for ease of illustration, only three FFPM250 assigned to one angular position are shown. In practice, multiple FFPM250 are mounted to the rotor support structure 242 according to the size of the generator 130. The FFPM250 is preferably arranged in a matrix-like structure around a curved surface area of ​​the support structure 242, which has a substantially cylindrical geometry around the generator axis 240a.

[0064] As from Figure 2 As can be seen in FIG. 2 , the FFPM 250 is not mounted directly to the rotor support structure 242. Instead, a back plate 244 made of a ferromagnetic material, such as iron, is provided. The back plate 244 is provided in order to ensure proper magnetic flux guidance. This significantly reduces the strength of the magnetic stray fields in an advantageous manner.

[0065] Figure 3 A magnetic flux-focused permanent magnet (FFPM) 350 made in accordance with an embodiment of the present invention is shown in more detail.

[0066] The FFPM 350 is magnetized in a manner that gives an extended angular distribution of magnetic domain alignment directions 352. According to the embodiments described herein, each magnetic domain alignment direction 352 follows a straight magnetization line. The straight lines are angled or tilted relative to each other in a fan-shaped manner. Specifically, the extended angular distribution of the straight magnetization lines produces a focus 354 in the area above the main surface 350a of the FFPM 350, and the focus 354 is characterized by a local maximum of the magnetic field and corresponding magnetic flux density generated by the FFPM 350.

[0067] According to the exemplary embodiment described herein, the depicted magnetic domain arrangement pattern is symmetrical with respect to a symmetry axis 354a. In this document, the symmetry axis 354a is also referred to as the magnetic axis. The magnetic axis 354a is the normal axis of the major surface 350a, which runs through the focal point 354.

[0068] Figure 4An apparatus 460 is shown for manufacturing a block in the form of a pressed magnet powder which can be sintered in a furnace to become a FFPM. Specifically, the apparatus 460 is used to magnetize and compact a magnetic material powder 495. The subsequent sintering of the resulting magnetized compacted block is carried out in a sintering furnace not shown. The apparatus 460 comprises a mold 470 in which a mold cavity 472 is formed. The mold cavity 472 can be closed by a mold member not shown, which is used to compact the magnetic material powder 495, which must be filled into the mold cavity 472 according to the usual process for manufacturing sintered magnets. The mold member not depicted performs movement in a direction perpendicular to the plane of the drawing.

[0069] The device 460 further includes means for generating a magnetic field applied to the compacted powder 495 during the sintering process. These magnetic field generating devices include a first magnetic device 461 and a second magnetic device 464 . In Figure 4 In the embodiment shown in , the first magnetic device 461 generates a magnetic north pole N, and the second magnetic device 464 generates a magnetic south pole S. According to known equipment, the first magnetic device 461 includes (i) a first electromagnetic coil 462 for generating a magnetic field, and (ii) a first yoke structure 463 for guiding and / or for shaping the magnetic field (line) present in the mold cavity 472. Correspondingly, the second magnetic device 464 includes (i) a second electromagnetic coil 465 and (ii) a second yoke structure 466.

[0070] According to the exemplary embodiment described here, the first yoke structure 463 assigned to the north pole and the second yoke structure 466 assigned to the south pole have different geometric shapes. Specifically, the bending radii of the outer surfaces of the two yoke structures 463, 466 are different from each other. Figure 4 As can be seen in the figure, the first yoke structure 463 includes a curved first outer yoke surface 463a, which (in a portion of the surface 463a) has a first radius of curvature R1. Correspondingly, the second yoke structure 466 includes a curved second outer yoke surface 466a, which (in a portion of the surface 466a) has a second radius of curvature R2 different from the first radius of curvature R1.

[0071] Figure 5 An apparatus 560 for manufacturing an FFPM block from a magnet powder prepared for sintering in a furnace is shown according to another embodiment of the invention.

[0072] according to Figure 4 In the embodiment shown in FIG. 5 , the apparatus 560 includes a mold 570 having a mold cavity 572 for accommodating magnetic material powder 595. In addition, a mold member not shown is used to compact the magnetic material powder 595 filled in the mold cavity 572. The movement of the mold member is along a direction perpendicular to the plane of the drawing.

[0073] Device 560 and Figure 4 The difference of the device 460 shown in FIG. 5 is that the spatially inhomogeneous magnetic field / magnetic flux within the mold cavity 572 is generated not only by two magnetic devices, but by three magnetic devices. Therefore, the two magnetic devices are realized by dividing the first magnetic device 461 into two magnetic sub-devices (the first magnetic sub-device 561-1 and the second magnetic sub-device 561-2). Figure 5 In the embodiment shown in , the first magnetic sub-device 561-1 includes an electromagnetic coil 562-1 and a first yoke sub-structure 563-1. Thus, the second magnetic sub-device 561-2 includes an electromagnetic coil 562-2 and a second yoke sub-structure 563-2. Both yoke sub-structures 561-1 and 561-2 define a magnetic north pole from the perspective of the mold cavity 572.

[0074] The magnetic south pole is generated by a second magnetic device 564, which includes an electromagnetic coil 565 and a second yoke structure 566.

[0075] It is worth mentioning that in Figure 5 In the embodiment shown in , all outer yoke surfaces facing the mold cavity 572 have the same convex curvature. However, this is not required. A suitable non-uniform magnetic field within the mold cavity 572 can also be achieved with differently shaped or curved outer yoke surfaces.

[0076] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the article "a" or "an" does not exclude a plurality. Elements described in connection with different embodiments may also be combined. It should also be noted that the reference numerals in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A device (460, 560) for manufacturing a sintered flux focusing permanent magnet (250, 350), the device (460, 560) comprising: A mold (470, 570) having a mold cavity (472, 572) for receiving permanent magnet material powder (495, 595); as well as A first magnetic device (461; 561-1, 561-2) and a second magnetic device (464, 564), both of which are used to generate a magnetic field for magnetizing the permanent magnet material powder (495, 595) contained in the mold cavity (472, 572); wherein, The first magnetic device (461; 561-1, 561-2) includes a first yoke structure (463; 563-1, 563-2) having a first shape, and the second magnetic device (464, 564) includes a second yoke structure (466, 566) having a second shape, the second shape being spatially different from the first shape, and The spatial difference in the shape of the two yoke structures (463, 466; 563-1, 563-2, 566) causes the magnetic field to be non-uniform, so that the magnetic field in the mold cavity (472, 572) is associated with an extended angular distribution of magnetic flux lines, wherein at least one of the first magnetic device (461; 561-1, 561-2) and the second magnetic device (464, 564) comprises at least one electromagnetic coil (462, 465; 562-1, 562-2, 565) for generating at least a portion of the magnetic field, and a corresponding yoke structure (463, 466; 563-1, 563-2, 566) is configured for guiding and / or for shaping the magnetic field generated by the corresponding electromagnetic coil (462, 465; 562-1, 562-2, 565), wherein, with respect to the mold cavity (472), the first yoke structure (463) and the second yoke structure (466) are located at opposite sides, and the first yoke structure (463) has a first outer yoke surface (463a) facing the mold cavity (472), and the second yoke structure (466) has a second outer yoke surface (466a) facing the mold cavity (472), wherein the first outer yoke surface (463a) has a curvature different from that of the second outer yoke surface (466a), Wherein, the first outer yoke surface (463a) has a first curvature radius (R1), and the second outer yoke surface (466a) has a second curvature radius (R2) different from the first curvature radius (R1).

2. The device (460) according to claim 1, wherein: With respect to the mold cavity (472), the two outer yoke surfaces (463a, 466a) include one of the following features: The first outer yoke surface (463a) is convex, and the second outer yoke surface (466a) is convex; The first outer yoke surface is convex and the second outer yoke surface is concave; The first outer yoke surface is concave and the second outer yoke surface is convex; and The first outer yoke surface is concave, and the second outer yoke surface is concave.

3. The device (560) according to claim 1 or 2, wherein: The first yoke structure includes a first yoke substructure (563-1) and a second yoke substructure (563-2), and the two yoke substructures (563-1, 563-2) are spatially separated from each other.

4. A method for manufacturing a sintered flux focusing permanent magnet (250, 350) by means of the apparatus according to any one of claims 1 to 3, the method comprising: Filling the permanent magnet material powder (495, 595) into the mold cavity (472, 572) of the mold (470, 570); generating the magnetic field for magnetizing the permanent magnet material powder (495, 595) contained in the mold cavity (472, 572) by means of the first magnetic device (461; 561-1, 561-2) and the second magnetic device (464, 564); Compacting the permanent magnet material powder (495, 595) contained in the mold cavity (472, 572) by means of a mold, the magnetization and compaction producing a magnetized compacted block of the permanent magnet material powder (495, 595); sintering the magnetized compacted mass in a sintering furnace to produce the flux focusing permanent magnet (250, 350); and The flux focusing permanent magnet (250, 350) is taken out from the sintering furnace.

5. The method according to claim 4, wherein: The permanent magnet material powder (495, 595) includes rare earth material.

6. The method according to claim 4, wherein: The permanent magnet material powder (495, 595) includes NdFeB.

7. A sintered flux focusing permanent magnet (250, 350) manufactured by performing the method as claimed in claim 5 or 6.

8. An electromechanical transducer (130), the electromechanical transducer (130) comprising: a stator assembly (135), and The rotor assembly (140) includes A support structure (242) and The at least one sintered flux focusing permanent magnet (250, 350) of claim 7, wherein the flux focusing permanent magnet (250, 350) is mounted to the support structure (242).

9. The electromechanical transducer (130) according to claim 8, wherein: The electromechanical transducer (130) is a generator.

10. A wind turbine (100) for generating electrical power, the wind turbine (100) comprising: Tower (120), a wind rotor (110) arranged at a top portion of the tower (120) and comprising at least one blade (114); as well as The electromechanical transducer (130) according to claim 8 or 9, wherein the electromechanical transducer (130) is mechanically coupled to the wind rotor (110).

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