JPS61274305A - Uniform magnetic field generating device - Google Patents

Abstract

PURPOSE:To obtain the central magnetic field of identical intensity with the permanent magnet of small volume, and realize cost reduction, small size and lightweight of the equipment, by magnetizing the parmanent magnet part of each block in the radial direction of the ring constituted by the blocks, and making the field direction inward for one of the half ring part and outward for the other half ring part. CONSTITUTION:The ring 17 to generate the magnetic field is constitued by arranging several blocks 16 in the form of ring. The blocks 16 are composed of the parmanent magnet part 18 and the high permeability part 19 like ferrite and iron, etc. The former constitutes the inside periphery of the ring 17, and the latter does the outside periphery of the ring 17. The permanent magnet part 18 is magnetized in the direction shown by the arrow 21, which indicates the radial direction of the ring 17. In other words, the direction of magnetization is nearly perpendicular to the upper and the lower sides of the trapezoidal block. One of the half ring part 17 containing, for example, the block 16a is magnetized toward inside, and the other half ring part 17 containing the block 16b is magnetized toward outside. These rings 17 to generate the magnetic field are arranged on the same axis center as that of the ring 17, and several rings are installed in the axial direction with some spacing. Thus the magnetic flux posses through the high-permeability material part with little leakage to outside, so that the volume of permanent magnet can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention applies to, for example, nuclear magnetic resonance
The present invention relates to a uniform magnetic field generating device that provides the required uniform magnetic field of T).

"Prior Art" In a conventional homogeneous magnetic field generator of this type, two permanent magnets have different magnetic pole ends facing each other, and the curved ends of these permanent magnets are connected by a yoke made of a high magnetic permeability material. Published Patent Publication No. 59-501995 “NHR Image Forming Apparatus, No. 5
As shown in the figure, one block 11 of a plurality of permanent magnets is arranged in a ring shape, and in order to create a closed circuit with the entire block, the direction of magnetization is changed for each block 11 as shown by the arrow 12, and the magnetization inside the ring is changed. A uniform magnetic field 13 was generated, and a ring made up of a plurality of blocks had the same axis and were arranged offset in the axial direction, so that the ring had a cylindrical shape as a whole.

"Problems to be Solved by the Invention" An NMR-CT uniform magnetic field generator requires a uniform magnetic field over a wide range, and is required to be inexpensive, lightweight, and as little susceptible to external influences as possible. However, in the former magnetic field generator, the yoke is large in order to reduce the leakage magnetic field, and the size is 1
Both become very large at heavy times. On the other hand, in the latter case, only permanent magnets are used, and the amount of permanent magnets used is large, the leakage magnetic field is small, and the direction of magnetization 12 is changed from the block 11 to increase efficiency, which requires less time and effort for magnetization and assembly. mosquito\
9, the cost is high, and leakage magnetic flux occurs as shown by the arrow 14 in FIG. 5.

"Means for Solving the Problems" This invention eliminates such problems and improves NMR-CT
It is designed to more closely meet the requirements of magnetic field generators.

According to this invention, the magnetic field generating ring is divided into at least two blocks along the circumferential direction, and these blocks have a permanent magnet portion on the inner circumferential side of the ring, and a high magnetic permeability material on the outer circumferential side. It is considered as a department. The permanent magnet portion of each block is magnetized in the radial direction of the ring made up of seven blocks, and the magnetization is directed inward in one half of the ring and outward in the curved half. Since the high magnetic permeability material part is provided on the outer periphery of the ring in this way, there is little magnetic flux passing through this high magnetic permeability material part and leaking to the outside, and since the high magnetic permeability material part is used, the permanent magnet's The magnetization direction is constant in the radial direction, and magnetization is easy.

"Embodiment" FIGS. 1 and 2 show an embodiment of the uniform magnetic field generator of the present invention. A plurality of blocks 16 are arranged in a ring shape to constitute a magnetic field generating ring 17. In each example, ten blocks 16 form a regular octagonal magnetic field generating ring 17. One opposing side of the octagon is each composed of 22 blocks 16a and 16b,
Each side of the pond is composed of one block of the same size, and the surface perpendicular to the axis of the ring 17 is trapezoidal.

Each block 16 has a permanent magnet portion 1 on the inner peripheral surface side of the ring 17.
8. On the outer peripheral surface side, high magnetic permeability material such as ferrite or iron 1
It is said to be 9. The permanent magnet part 18 is magnetized in the radial direction of the ring 17 as shown by the arrow 21, in this example, in a direction substantially perpendicular to the top and bottom sides of each trapezoidal block, and the direction of magnetization is in one half of the ring 17, In this example block 16
The side including a faces inward with respect to ring 17, and ring 1
The other half of 7, that is, the side including block 16b, faces outward.

As shown in FIG. 2, such a magnetic field generating ring 17 is located on the same axis as the axis of the ring 17, and is arranged in a plurality of stages shifted in the axial direction. The overall structure is cylindrical.

Furthermore, in this example, the position and orientation of each block 16, and the ring 1
7 (the radial adjustment screw 24 is threadedly connected to the radial adjustment screw 24 and inserted through the radial adjustment screw 24, and the block 16 is fixed to the inner protruding end of the radial adjustment screw 24. Therefore, the adjustment screw 24 is rotated. When the block 16 moves, the block 16 moves inward or outward in the radial direction with respect to the axis of the ring 17, depending on the direction and amount of rotation. One end is fixed to block 16.

One end of a bolt 26 is fixed to each end of the ring 17 of the holding plate 23 in the axial direction, and each bolt 26 projects outside the frame through a long hole in the holding frame 22. A direction adjusting nut 27 is screwed together. Therefore, the axial adjustment nut 2
7 to rotate the holding plate 23. The position of the block 16 in the axial direction can be adjusted.

Further, one end of a bolt 28 is fixed to each side of the retaining plate 23 in the circumferential direction of the ring 17, and the bolt 28 protrudes outside the frame through an elongated hole formed in the retaining frame 22 along the axial direction. A direction adjusting nut 29 is screwed together. When the circumferential adjustment nut 29 is rotated, the retaining plate 23 and the block 16 are moved in the circumferential direction.

For each magnetic field generating ring 17, each holding frame 22 is connected to each other in ++ m order to form a polygonal shape, and the polygonal frame body 31
is supported by an L-shaped support 32. This support is the holding frame 2
Adjustment is made possible by an adjustment mechanism similar to the holding of block 16 by No. 2. In other words, one axis (X
The position along the axis) is adjusted by the X-axis adjustment mechanism 33, and the position along the y-axis in a plane perpendicular to the axis and perpendicular to the X-axis is
The shaft adjustment mechanism 34 adjusts the position, and the position along the axis is further adjusted by the two-axis adjustment mechanism 35.

The plurality of rings 17 are set on a pedestal 36 with their supports 32 arranged in the axial direction.

According to the above configuration, the magnetization direction of the permanent magnet portion 18 is in the radial direction of the ring, and since the direction is opposite between one half of the ring and the other half, as shown by the arrow 37 in FIG. A semicircular magnetic path is formed.

A uniform magnetic field 38 is created within the ring 17 . Further, since the high magnetic permeability material portion 19 is present, the semicircular magnetic path 37 passes through the high magnetic permeability material portion 19 and leaks less easily than the ring 17.

By adjusting the adjustment mechanism of each part, by moving each block 16 in various directions, and by moving the polygonal frame 31 in various directions, variations in the magnetic force of the permanent magnet part 18, variations in dimensional accuracy,
Furthermore, a uniform magnetic field 28 is obtained in a predetermined space without being affected by variations in the positions of various parts. Depending on the degree of the above-mentioned various variations, some or all of the above-mentioned various adjustment mechanisms can be omitted.

In addition, in order to improve the uniformity of the spatial magnetic field 28, it is necessary to provide a correction numeral (normal conductive shim, magnetic shim, etc.) on the inner or outer surface of the permanent magnet part 18, or to provide a plurality of magnetic field generators arranged in the axial direction. Both i in the axial direction of the ring 17
I! It is also possible to change the size of the permanent magnet portion 18 by using the ring 11 and the inner ring.

As shown in FIG. 4 (the two-magnetic field generating ring 17 is divided into two semicircular shapes in the circumferential direction to form two blocks 16, the inside of each block 16 is a permanent magnet part 18, and the outside is a highly transparent block). It may also be a magnetic material portion 19. Also, the shape of the magnetic field generating ring 17 is a polygon.

It may be oval to a circular curve.

"Effects of the Invention" According to the uniform magnetic field generating device of the present invention described above, as can be understood by comparing the magnetic fluxes in FIG. 3 and FIG. It is difficult to receive

In addition, since there is little leakage magnetic flux, the efficiency is high; in other words, the same central magnetic field strength can be obtained with fewer classes of permanent magnets, and it can be produced at a correspondingly lower cost.

Compared to the conventional magnetic plant generator with opposing magnetic poles and a yoke,
The device of this invention can also be designed along the magnetic circuit, so it can be made smaller and lighter, and the uniform magnetic field space can be widened. In the conventional device shown in Figure 5, the direction of the magnetic poles for each block is oriented in various directions, so it is very time-consuming to make a predetermined shape from a small magnet, and it is also time-consuming to process and magnetize it. Call me. On the other hand, in the apparatus of the present invention, since all the magnetic poles are in the radial direction, they can all be assembled in the same manner, and the machining 1 magnetization is also very advantageous.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of a uniform magnetic field generating device according to the present invention, FIG. 2 is a bottom view of FIG. This figure is a plan view showing a magnetic field generating ring in an example of the device according to the present invention, and FIG. 5 is a plan view showing a conventional uniform magnetic field generating device. 16: Block, 17: Magnetic field generation ring, 18: Permanent magnet section, 19: High magnetic permeability material section. Patent applicant: Asahi Kasei Industries Co., Ltd. Representative: Takuo Kusano 1 Figure t3 Figure ↓ or 4 z

Claims (1)

[Claims] (1) A plurality of magnetic field generating rings are arranged offset in the axial direction with respect to the same axis, making the ring as a whole approximately cylindrical, and generating a uniform magnetic field approximately perpendicular to the axis within the cylindrical part. In the uniform magnetic field generator, each magnetic field generating ring is composed of at least two blocks divided in the circumferential direction, and the inner circumferential side of the ring of each block is a permanent magnet part, and the outer circumferential side is a high-temperature magnet part. a permeable material part, and the permanent magnet part of each block is magnetized in the radial direction of the ring constituted by the block,
A uniform magnetic field generator characterized in that the direction of magnetization is inward in one half of the ring and outward in the other half.