JP3653253B2 - Magnetic field generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic field generator, and more particularly to a magnetic field generator for MRI.
[0002]
[Prior art]
An example of a technique for reducing leakage flux in an MRI magnetic field generator is disclosed in Japanese Utility Model Publication No. 5-41530. Here, on the main surface of the plate-shaped yoke, by arranging a shield magnet consisting of eight ferrite magnets in an annular shape at a position corresponding to the outer periphery of the permanent magnet structure attached on the back surface side, the leakage flux Is suppressed.
[0003]
[Problems to be solved by the invention]
However, with this related technology, it is difficult to effectively suppress the leakage flux in the MRI magnetic field generator that generates a high magnetic field of 0.3 T or more. Even when the magnetic field generator for MRI that generates such a high magnetic field is configured as an open type, it is difficult to effectively suppress the leakage magnetic flux.
In the related art described above, since the shielding magnet is exposed to the outside of the magnetic field generator, there is a possibility of attracting magnetic bodies such as tools and chains during assembly and transportation. When such a thing occurs, since the shielding magnet itself is a sintered body, the shielding magnet may be damaged at the time of attraction. Moreover, when the magnetic body attracted and adhered to the shielding magnet is large, there is a problem that it cannot be removed by human power.
[0004]
Furthermore, recent magnetic field generators for MRI have legs. The leg portion is made of a magnetic material and is attached after the shielding magnet is bonded to the main surface of the plate-shaped yoke. However, the leg portion may be attracted to the shielding magnet and the worker may be in danger.
The above-described adverse effects are remarkable when a rare earth sintered magnet having a strong magnetic force is used as a shielding magnet in order to reduce the magnet weight.
[0005]
In recent years, magnetic field generating devices having an open portion of 150 degrees or more continuously as viewed from the center of the magnetic field generating space in front of the device have been proposed and are becoming popular. In such a device, leakage of magnetic flux becomes large at the open portion. This problem becomes more conspicuous in the case where the front of the apparatus is formed in a slope shape in order to reduce the weight of the apparatus, or in a magnetic field generator that generates a strong magnetic field of 0.3 T or more. If the plate yoke in front of the device is thickened, the leakage magnetic flux will be reduced to some extent, but in a magnetic field generator having an open part of 150 degrees or more continuously, the support structure is unstable and the plate yoke is thickened. I can't.
[0006]
Therefore, a main object of the present invention is to provide a magnetic field generator that can more effectively suppress an unnecessary magnetic field generated outside the magnetic field generator, in other words, a leakage magnetic flux.
Another object of the present invention is to provide a magnetic field generator capable of preventing the shield magnet from being damaged.
Another object of the present invention is to provide a magnetic field generator that can be safely assembled.
[0007]
[Means for Solving the Problems]
  In order to achieve the above-described object, the magnetic field generator according to claim 1 includes a pair of plate-like yokes that are opposed to each other with a gap formed therebetween, and two magnetically coupling a pair of plate-like yokes. Permanent magnets arranged on one main surface facing each of the following support yokes and a pair of plate yokes,First shield magnet and second shield magnet provided respectively on the open front and rear of the other main surface of at least one plate-shaped yoke, A first spacer inserted between the plate yoke and the first shield magnet, and a second spacer inserted between the plate yoke and the second shield magnetIs provided.
  The magnetic field generator according to claim 2 is a pair of plate-like yokes arranged to face each other with a gap formed therebetween, at least one of permanent magnets arranged on one opposing main surface of each of the pair of plate-like yokes A shielding magnet provided on the other main surface of the plate-shaped yoke,A spacer inserted between the plate yoke and the shielding magnet,And a cover member provided on the shielding magnet.
[0008]
The magnetic field generator according to claim 3 is the magnetic field generator according to claim 2, wherein the cover member is a nonmagnetic member.
The magnetic field generator according to claim 4 is the magnetic field generator according to claim 3, wherein the distance between the outer surface of the cover member and the surface of the shielding magnet is set to 2 mm or more. .
[0009]
  The magnetic field generator according to claim 5 is a pair of plate-like yokes arranged to face each other with a gap formed therebetween, a permanent magnet arranged on one opposing main surface of each of the pair of plate-like yokes, at least one of them A shielding magnet provided on the other main surface of the plate-shaped yoke,A spacer inserted between the plate yoke and the shielding magnet,And a non-magnetic leg portion formed on the other main surface of the plate-like yoke on which the shielding magnet is provided.
  The magnetic field generation device according to claim 6 is a pair of plate yokes that are arranged to face each other in a gap, a permanent magnet that is arranged on one opposing main surface of each of the pair of plate yokes, A support yoke provided so as to magnetically couple plate yokes and form an open portion having an open angle of 150 degrees or more continuously as viewed from the center of a uniform magnetic field space between permanent magnets.,Shielding magnet provided on the other main surface corresponding to the open part of at least one plate-shaped yoke, And a spacer inserted between the plate yoke and the shielding magnetIs provided.
[0010]
  The magnetic field generator according to claim 7 is the magnetic field generator according to claim 6, wherein the other principal surface of the plate yoke has a slope so that the plate yoke is thin, and the shield magnet is provided on the slope. Is provided.
  The magnetic field generator according to claim 8 is the magnetic field generator according to claim 6 or 7, wherein a magnetic field of 0.3 T or more is generated in the uniform magnetic field space.
  The magnetic field generator according to claim 9 is the magnetic field generator according to any one of claims 1 to 8, wherein the shielding magnet is a rare earth sintered magnet.
  A magnetic field generator according to a tenth aspect is the magnetic field generator according to any one of the first to eighth aspects, wherein the spacer is a magnetic member.
[0011]
  In the present invention, the leakage magnetic flux can be reduced by providing the shielding magnet. In addition, since the shield magnet can be moved away from the plate yoke by providing a spacer, the magnetic saturation of the plate yoke can be alleviated, and the shield magnet can be attached to the other of the plate yoke without using a spacer. The magnetic field strength of the air gap can be improved as compared with the case where it is arranged directly on the main surface.
  In the magnetic field generator according to claim 1, it is possible to prevent unnecessary magnetic flux from leaking from the front of the device by providing the first shielding magnet in front of the open side of the other main surface of the plate-shaped yoke. Furthermore, the leakage magnetic flux generated behind the device can be reduced by the second shielding magnet.
  In the magnetic field generator according to the second aspect, since the shielding magnet is protected by the cover member, the shielding magnet can be prevented from being damaged.
[0012]
In the magnetic field generator according to claim 3, since the cover member is a non-magnetic member, the leakage magnetic flux can be reliably reduced without shorting the magnetic flux generated by the shielding magnet.
In the magnetic field generator according to claim 4, since the distance between the outer surface of the cover member and the surface of the shielding magnet is set to 2 mm or more, the attractive force of the shielding magnet to the magnetic member can be weakened. . Therefore, when a magnetic member (for example, a tool) is adsorbed, it is easy to remove the adsorbed magnetic member from the cover member.
[0013]
In the magnetic field generator according to the fifth aspect, since the leg portion is made of a non-magnetic material, the leg portion can be prevented from being attracted by the shielding magnet during assembly work, and the operator is not exposed to danger.
In the open type magnetic field generator, since the leakage magnetic flux on the open part side is large, it is not possible to provide a shielding magnet at a position corresponding to the open part of the plate yoke as in the magnetic field generator according to claim 6. Great effect.
[0014]
  When a part of the plate yoke is cut to reduce the weight of the device, the leakage magnetic flux increases, so that a shielding magnet is provided in a thin portion of the plate yoke as described in claim 7. Is effective.
  As described in claim 8, the present invention is suitable for a magnetic field generator that generates a magnetic field of 0.3 T or more in a uniform magnetic field space. In such a magnetic field generating device that generates a strong magnetic field, the leakage magnetic flux is further increased. Therefore, it is effective to provide a shielding magnet.
  By using a rare earth sintered magnet having a large magnetic force as a shielding magnet and using a spacer as described in claim 9, leakage flux can be more effectively suppressed without magnetic saturation with a small amount of magnet.
  As described in claim 10, when the spacer is made of a magnetic member, the leakage magnetic flux can be further reduced.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 to 4, an MRI magnetic field generator 10 according to an embodiment of the present invention is an open-type device, and a pair of plate yokes 14 a and 14 b that are opposed to each other by forming a gap 12. including. The plate yoke 14a includes a front portion 16a and a rear portion 18a on the open side. The upper surface of the front portion 16a is an inclined surface 20a, and the plate yoke 14a is formed thin toward the front of the open portion, so that the weight of the yoke is reduced. Similarly, the plate yoke 14b includes a front portion 16b and a rear portion 18b on the open side. In order to reduce the weight of the yoke, the front portion 16b is formed thinner than the rear portion 18b, and the lower surface of the front portion 16b is connected to the lower surface of the rear portion 18b through the inclined surface 20b.
[0016]
Permanent magnets 22a and 22b are arranged on the opposing surface sides of the plate yokes 14a and 14b, and magnetic pole pieces 24a and 24b are fixed to the opposing surface sides of the permanent magnets 22a and 22b. The pair of plate yokes 14a and 14b are magnetically coupled by two columnar support yokes 26 disposed between both ends of the rear portions 18a and 18b. The plate yokes 14a and 14b and the support yoke 26 are made of soft iron. Thus, in the open type magnetic field generator 10, the support yoke 26 is disposed at the rear of the device. With such a configuration, as shown in FIG. 3, a uniform magnetic field space 12a is formed between the permanent magnets 22a and 22b, and a magnetic flux as indicated by an arrow Y is generated. At this time, as shown in FIG. 2, the supporting yoke is such that the opening angle α of the opening portion is continuously 150 degrees or more when viewed from the center P of the uniform magnetic field space 12a formed between the permanent magnets 22a and 22b. 26 is arranged. An open part means the space where the support yoke 26 does not exist.
[0017]
Two rectangular square plate spacers 28 are symmetrically arranged on the upper surface of the rear portion 18a of the plate yoke 14a, and a substantially square square plate shielding magnet 30 is disposed on the spacer 28. Be placed. In other words, the two shielding magnets 30 are provided behind the upper surface of the plate yoke 14a. As can be seen from FIG. 2, each shield magnet 30 on the plate yoke 14 a has a portion 30 a that protrudes from the outer peripheral edge A <b> 1 (formed on the back side) of the permanent magnet 22 a and does not overlap the support yoke 26. It arrange | positions so that the gap G may be formed. As shown by arrow B in FIG. 3, the support yoke 26 becomes a magnetic path, and magnetic flux concentrates on the connecting portion between the plate yoke 14 a and the support yoke 26, so that the plate yoke 14 a positioned in the gap G The part is easily magnetically saturated. By arranging the shielding magnet 30 so as to avoid the region where magnetic saturation is likely to occur in this way, leakage magnetic flux can be suppressed without promoting magnetic saturation, and the magnetic field strength at the center of the gap 12 can be secured.
[0018]
Further, a rectangular square plate spacer 32 is arranged on the slope 20a on the upper surface of the front portion 16a of the plate yoke 14a, and a rectangular square plate shielding magnet 34 is arranged on the spacer 32. The In other words, the shielding magnet 34 is provided in front of the open side of the upper surface of the plate yoke 14a. In general, the open magnetic field generator 10 has a large leakage magnetic flux on the open side. Therefore, the magnetic flux leakage can be further suppressed by arranging the shielding magnet 34 on the front portion 16a of the apparatus in this way.
[0019]
Spacers 28 and 32 have a thickness of 30 mm, for example, and are made of electromagnetic soft iron. The shield magnets 30 and 34 are formed so as to assemble a magnet having a rectangular parallelepiped shape of approximately 35 × 50 × 50 mm, for example, and to have magnetization in a direction opposite to the direction of the leakage magnetic flux. As magnets used for the shielding magnets 30 and 34, neodymium sintered magnets (R—Fe—B based sintered magnets), samarium cobalt magnets, alnico magnets, and ferrite magnets can be used. Among these, ferrite magnets are heavy and demagnetization may occur at a low temperature of about −20 ° C. during transportation. If a magnet having a high energy product is used, a high shielding effect can be obtained, and it is also necessary to reduce the size of the apparatus by thinning the magnet. Therefore, it is desirable to use a rare earth sintered magnet. The coercive force is usually 1000 kA / m or more, but a material having a higher coercive force is desirable when the temperature becomes high during transportation. For example, NEOMAX-47 manufactured by Sumitomo Special Metals is used as the permanent magnets 22a and 22b, and NEOMAX-39SH manufactured by Sumitomo Special Metals is used as the shield magnets 30 and 34, for example. R-Fe-B sintered magnets are disclosed in US Pat. Nos. 4,770,723 and 4,792,368.
[0020]
As shown in FIG. 4, the spacer 28 is fixed to the plate yoke 14 a by a spacer mounting screw 36, and the spacer 28 and the shielding magnet 30 are covered by a cover member 38. The cover member 38 is made of a nonmagnetic member such as SUS304, and is attached to the upper surface of the rear portion 18a of the plate yoke 14a by the cover attachment screw 40. The spacer 32 is fixed by a spacer mounting screw 42, and the spacer 32 and the shielding magnet 34 are covered by a cover member 44. The cover member 44 is also made of a nonmagnetic member made of, for example, SUS304 (stainless steel) or the like, and is attached onto the inclined surface 20a of the front portion 16a of the plate yoke 14a by a cover attachment screw 46. The shield magnets 30 and 34 are composed of a plurality of magnets, and each magnet is bonded on the spacers 28 and 32 with the same poles adjacent to each other. Therefore, when the adhesion is removed, the magnet alone may jump out due to the repulsive force, but the cover members 38 and 44 prevent this. At this time, the distance T1 between the outer surface of the cover member 38 and the surface of the shielding magnet 30 and the distance T2 between the outer surface of the cover member 44 and the surface of the shielding magnet 34 are each set to 2 mm or more. Is done.
[0021]
As shown in FIG. 5, two spacers 28 are symmetrically arranged on the lower surface of the rear portion 18b of the plate-like yoke 14b on the plate-like yoke 14b side, and are shielded on the spacer 28. A magnet 30 is arranged. In other words, the two shielding magnets 30 are provided behind the lower surface of the plate yoke 14b. As can be seen from FIG. 5, each shield magnet 30 on the plate yoke 14 b protrudes from the outer peripheral edge A <b> 2 of the permanent magnet 22 b and forms a gap G without overlapping the support yoke 26. Placed in. Further, a spacer 32 is disposed on the flat surface of the lower surface of the front portion 16b of the plate yoke 14b, and a shield magnet 34 is disposed on the spacer 32. In other words, the shield magnet 34 is provided in front of the open side of the lower surface of the plate yoke 14b.
Also on the plate-like yoke 14b side, as in the case of the plate-like yoke 14a shown in FIG. 4, the spacer 28, the shielding magnet 30, the spacer 32, and the shielding magnet 34 are made by the cover member. It is covered and each member is fixed.
[0022]
As described above, the shielding magnets 30 and 34 are protected by the cover members 38 and 44, respectively, so that the shielding magnets 30 and 34 can be prevented from being damaged. Further, since the cover members 38 and 44 are non-magnetic members, the magnetic flux generated by the shielding magnets 30 and 34 is not short-circuited or shielded, and the leakage magnetic flux can be reliably reduced.
Further, since the distances T1 and T2 are set to 2 mm or more, even if the magnetic member is attracted to the shielding magnets 30 and 34, the attractive force can be weakened, and the attracted magnetic member is attached to the cover members 38 and 44. It becomes easy to remove from.
[0023]
Legs 48 are attached to the lower surface of the plate yoke 14b at positions corresponding to the two support yokes 26, respectively, and two flat portions of the lower surface of the front portion 16b of the plate yoke 14b are provided on the flat surface. A leg 50 is attached. The legs 48 and 50 are made of a nonmagnetic material. As a result, the legs 48 and 50 can be prevented from being attracted by the shielding magnets 30 and 34 during assembly work, and the operator is not exposed to danger.
In the magnetic field generator 10, the spacer 28, the shielding magnet 30 and the cover member 38 are attached to the plate yoke 14a as follows.
[0024]
Referring to FIG. 6, first, both end portions of plate yoke 14a are supported by support base 52, and four guide rods 54 are erected at predetermined positions on plate yoke 14a. The shield magnet 30 is fixed at a predetermined position on the spacer 28 with an adhesive or the like, and the spacer 28 in this state is lifted by a crane or the like and carried onto the plate-like yoke 14a. The guide bar 54 is inserted into each hole 56 of the spacer 28, and the spacer 28 is lowered. As a result, the spacer 28 and the shielding magnet 30 are arranged at predetermined positions on the plate yoke 14a. Thereafter, the guide rod 54 is removed, and instead, a spacer mounting screw 36 is screwed in, and the spacer 28 is fixed on the plate yoke 14a. Then, the cover member 38 is placed on the fixed spacer 28 and shield magnet 30, and the cover member 38 is attached to the plate yoke 14 a by the cover attachment screw 40.
The same applies to the spacer 34, the shielding magnet 36, and the cover member 44. Similarly, the spacers 30 and 34, the shielding magnets 32 and 36, and the cover members 38 and 44 are attached to the lower surface of the plate yoke 14b.
[0025]
An experimental example of such a magnetic field generator 10 will be described.
In each of the cases (1) to (5) shown in FIG. 7, the magnetic field intensity at the center P of the uniform magnetic field space 12a and the magnetic field becomes 1 mT above the center P of the plate yoke 14a from the center P of the uniform magnetic field space 12a. The distance to the position (magnetic field 1 mT line) was measured. If the distance to the magnetic field 1 mT line is small, it means that the leakage magnetic flux is small. Here, a spacer and a shielding magnet were attached to each of the three positions of the plate-like yokes 14a and 14b shown in FIGS. 1 to 3 and 5 according to the cases (1) to (5). did.
[0026]
(1) When the mounting member, ie, the spacer and the shield magnet are not mounted, the magnetic flux flows through the plate yoke 14a as shown in FIG. 8 (a), and the result shown in FIG. 7 is obtained. It was.
[0027]
(2) When only the spacers 28 and 32 made of iron are attached to the plate yokes 14a and 14b, the thickness of the plate yokes 14a and 14b is substantially as shown in FIG. 8 (b). Although the magnetic field strength was improved to increase, the leakage flux was only slightly reduced.
[0028]
(3) When the shielding magnets 30 and 34 are directly attached to the plate yokes 14a and 14b, the leakage magnetic flux is reduced, but the shielding magnets 30 and 34 themselves are attached as shown in FIG. When the plate yokes 14a and 14b are partially magnetically saturated by the generated magnetic flux, the permeability is partially lowered, and the magnetic field strength at the center P of the uniform magnetic field space 12a is reduced.
[0029]
(4) When the shield magnets 30 and 34 are attached to the spacers 28 and 32 made of a non-magnetic member (SUS304) and attached to the plate yokes 14a and 14b, the shield magnets 30 and 34 Away from the yokes 14a and 14b. Therefore, although the leakage magnetic flux is slightly increased as compared with the case (3), the magnetic flux generated by the shielding magnets 30 and 34 itself affects the magnetic resistance of the plate yokes 14a and 14b as shown in FIG. 8 (d). Therefore, magnetic saturation in the plate yokes 14a and 14b was suppressed, and the magnetic field strength at the center P of the uniform magnetic field space 12a was improved accordingly. However, a part of the magnetic flux generated by the shielding magnets 30 and 34 flows to the plate yokes 14a and 14b.
[0030]
(5) When the shield magnets 30 and 34 are attached to the spacers 28 and 32 made of iron and are attached to the plate yokes 14a and 14b, as shown in FIG. 8 (e), the shield magnet 30 Since the magnetic flux generated by the magnetic fluxes 34 and 34 mainly passes through the spacers 28 and 32 and does not affect the magnetic resistance of the plate yokes 14a and 14b, and the spacers 28 and 32 are made of iron, they are substantially plate-shaped joints. Since the thicknesses of the irons 14a and 14b are increased, the magnetic saturation can be suppressed to improve the magnetic field strength, and the leakage magnetic flux can be reduced.
[0031]
Therefore, according to the magnetic field generator 10, since the shield magnets 30 and 34 can be moved away from the plate yokes 14a and 14b by providing the spacers 28 and 32, respectively, the plate yokes 14a and 14b Magnetic saturation can be relaxed and the magnetic field strength of the air gap 12 can be improved. Further, when the spacers 28 and 32 are made of a magnetic member such as iron, the leakage magnetic flux can be reduced. In particular, in an open-type magnetic field generator such as the magnetic field generator 10, the magnetic flux tends to concentrate locally at the joint portion of the yoke, and magnetic saturation is likely to occur at that portion. It is.
Further, by using a rare earth sintered magnet having a large magnetic force as the shielding magnets 30 and 34 and using the spacers 28 and 32, it is possible to more effectively suppress the leakage flux without causing magnetic saturation with a small amount of magnets.
[0032]
If the shield magnets 30 and 34 are directly attached to the plate yokes 14a and 14b, respectively, a strong attractive force is generated between the plate yokes 14a and 14b and the shield magnets 30 and 34, and the shield. It becomes difficult to arrange the magnets 30 and 34 at predetermined positions with high accuracy and safety. However, in the magnetic field generator 10, the shield magnets 30 and 34 are attached in advance to the spacers 28 and 32, and the spacers 28 and 32 are attached to the main surfaces of the plate yokes 14a and 14b in that state. The shield magnets 30 and 34 can be easily arranged at predetermined positions on the spacers 28 and 32, and the magnetic field generator 10 can be assembled safely. When a rare earth sintered magnet is used as the shielding magnets 30 and 34, it is more effective.
[0033]
Generally, if the thickness of the plate-shaped yoke is increased, the leakage magnetic flux is reduced. However, if a magnetic field of 0.35 T is generated, for example, the thickness of the plate-shaped yoke becomes 30 cm. At this time, the magnetic field generator is approximately 20 tons, and the floor strength is required, so that the installation location is restricted and the transportation becomes difficult. Therefore, the thickness of the plate yoke cannot be increased any more. Therefore, the thickness of the plate yoke is set so thin that the magnetic flux is not saturated. For example, like the magnetic field generator 10, the front portions 16a and 16b of the plate yokes 14a and 14b are formed thin in order to reduce the weight of the device. In this case, in the region where the magnetic flux is concentrated, the yoke inevitably becomes magnetically saturated and the magnetic flux leaks. Therefore, in the magnetic field generator 10, the shield magnets 30 and 34 are respectively disposed through the spacer members 28 and 32 at necessary portions such as thin portions of the plate yokes 14a and 14b. Leakage magnetic flux can be suppressed while reducing the weight of the magnetic field generator 10 without increasing the thickness of the irons 14a and 14b themselves.
In particular, the present invention is suitable for a magnetic field generator that generates a strong magnetic field of 0.3 T or more in the uniform magnetic field space 12a.
[0034]
Furthermore, since the MRI apparatus is installed in a hospital, there is a possibility that electronic equipment in the hospital may malfunction if there is a large amount of leakage magnetic flux. In addition, if a person wearing a pacemaker enters the strong magnetic field region, the pacemaker may malfunction. Therefore, in order to limit the area where a magnetic field of 0.5 mT or more is generated to a narrow area, a large-scale magnetic shield work is required or a large installation space is required. However, according to the present invention, since the leakage magnetic flux can be reduced, the above-mentioned problems can be improved.
[0035]
The spacer and the shielding magnet may be provided only on one of the plate yokes 14a and 14b.
The present invention can also be applied to a magnetic field generator using one support yoke or four support yokes, for example, a magnetic field generator as disclosed in Japanese Patent Application Laid-Open No. 2000-139874. .
[0036]
【The invention's effect】
  According to this invention,Leakage magnetic flux can be reduced. Also,Can reduce the magnetic saturation of the plate yoke,Rather than using a shield magnet directly on the other main surface of the plate yoke without using a spacerThe magnetic field strength of the gap between a pair of plate yokesCan be improved.
  In addition, the shield member can be prevented from being damaged by using the cover member, and the leg portion can be prevented from being attracted to the shield magnet at the time of assembly work by configuring the leg portion with a non-magnetic material. Can be assembled safely.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of the present invention.
FIG. 2 is a plan view showing an embodiment of the present invention.
FIG. 3 is a front view showing an embodiment of the present invention.
FIG. 4 is an illustrative view showing a state in which a cover member is attached.
FIG. 5 is a bottom view showing an embodiment of the present invention.
FIG. 6 is an illustrative view showing one example of a method for assembling a shielding magnet and a spacer.
FIG. 7 is a table showing experimental results.
FIG. 8 is an illustrative view for explaining an experimental result.
[Explanation of symbols]
10 Magnetic field generator
12 gap
12a Uniform magnetic field space
14a, 14b Plate yoke
16a, 16b Front of plate yoke
18a, 18b Rear part of plate yoke
20a, 20b Plate yoke slope
22a, 22b Permanent magnet
24a, 24b Pole pieces
26 Supporting yoke
28, 32 Spacer
30, 34 Shield magnet
38, 44 Cover member
48, 50 legs
P Center of uniform magnetic field space
α Opening angle
T1, T2 Distance between the outer surface of the cover member and the surface of the shielding magnet

Claims (10)

A pair of plate-like yokes that are arranged opposite each other to form a void;
2 or less supporting yokes that magnetically couple the pair of plate yokes,
Permanent magnets arranged on one opposing main surface of each of the pair of plate yokes ,
A first shielding magnet and a second shielding magnet provided respectively on the open side front and rear of the other main surface of at least one of the plate-shaped yokes ;
A first spacer interposed between the plate yoke and the first shielding magnet; and
A magnetic field generator comprising a second spacer interposed between the plate yoke and the second shielding magnet . A pair of plate-like yokes that are arranged opposite each other to form a void;
Permanent magnets arranged on one opposing main surface of each of the pair of plate yokes,
A shielding magnet provided on the other main surface of at least one of the plate yokes,
A magnetic field generator comprising: a spacer interposed between the plate yoke and the shield magnet; and a cover member provided on the shield magnet.   The magnetic field generator according to claim 2, wherein the cover member is a nonmagnetic member.   The magnetic field generator according to claim 3, wherein a distance between an outer surface of the cover member and a surface of the shielding magnet is set to 2 mm or more. A pair of plate-like yokes that are arranged opposite each other to form a void;
Permanent magnets arranged on one opposing main surface of each of the pair of plate yokes,
A shielding magnet provided on the other main surface of at least one of the plate yokes,
A magnetic field comprising a spacer interposed between the plate yoke and the shield magnet, and a non-magnetic leg formed on the other main surface of the plate yoke on which the shield magnet is provided. Generator. A pair of plate-like yokes that are arranged opposite each other to form a void;
Permanent magnets arranged on one opposing main surface of each of the pair of plate yokes,
A support yoke provided so as to magnetically couple the pair of plate yokes and form an open portion having an open angle of 150 degrees or more continuously as viewed from the center of the uniform magnetic field space between the permanent magnets ;
A shielding magnet provided on the other principal surface corresponding to the open portion of at least one of the plate-shaped yokes ; and
A magnetic field generator comprising a spacer interposed between the plate yoke and the shield magnet .   The magnetic field generator according to claim 6, wherein the other surface of the plate-like yoke has a slope so that the plate-like yoke is thin, and the shield magnet is provided on the slope.   The magnetic field generator according to claim 6 or 7, wherein a magnetic field of 0.3T or more is generated in the uniform magnetic field space.   The magnetic field generator according to claim 1, wherein the shielding magnet is a rare earth sintered magnet. The magnetic field generator according to claim 1, wherein the spacer is a magnetic member.

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