JPS63127746A - Magnetic field generator for magnetic resonance diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a magnetic field generating device used to generate a static magnetic field in a magnetic resonance diagnostic apparatus or the like.

(Prior Art) Generally, this type of magnetic field generating device consists of permanent magnets 1, 1 arranged opposite to each other as shown in FIG.
．． 1 and the permanent magnet 1.
．． 1 and a yoke 3 that magnetically couples the magnetic pole plates 2 and 2 to form a magnetic circuit, and generates a magnetic field between the magnetic pole plates 2 and 2.

In this type of device, it is necessary to make the magnetic field in the air gap 4 between the upper and lower magnetic pole plates 2°2 uniform, so conventionally the magnetic poles are arranged as shown in Fig. 2 or 3. The peripheral edge 2A of the facing surface of the plate 2 is raised to make the magnetic field distribution uniform.

(Problem to be Solved by the Invention) However, when the peripheral edge 862A of the facing surface of the magnetic pole plate 2 is raised as described above, the thickness increases by the raised area compared to the central part, and the permanent magnet The magnetic flux from the magnetic flux cannot reach the gap 4 unless it passes further from the center by this increased amount, and as a result, the magnetic flux 1 in the area corresponding to the peripheral edge 2A in the gap 4 decreases. There is a problem with putting it away.

To solve this problem, the peripheral edge 2 that extends into the cavity 4 must be
It is conceivable to increase the amount of permanent magnet 1 so that the required magnetic field strength can also be obtained for the part corresponding to A, but
In this case there are legal issues.

In other words, all of the magnetic flux needs to pass through the magnetic circuit described above, but since magnetic flux has the property of passing easily through magnetic bodies and having difficulty passing through non-magnetic bodies (magnetic resistance is large), the magnetic field is limited to the strength of the permanent magnet. Instead, it is greatly influenced by the yoke placed around the permanent magnet, the a-pole plate, etc. Therefore, the magnetic flux from the opposing magnets 1 is directed toward the yoke 3 located closer, as shown by arrow F in FIG. 2, than toward the other magnet 1 via the gap 4. The magnetic strength actually generated in the gap 4 is only about 30 to 40% of the magnetic field strength of the magnet 1. Therefore, if the resistance of the permanent magnet 1 is increased to obtain the required magnetic field strength in the air gap 4, the magnetic field loss will be extremely large, and the amount of permanent magnets will be 1.7 to 1.6 times the target. The problem arises that it is necessary to provide a

An object of the present invention is to solve the above-mentioned problems in the conventional device and to make the magnetic field distribution in the gap even more uniform.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention has a structure in which the peripheral edge of the facing surface of the permanent magnet is raised from the center.

(for production) Since the present invention has the above configuration, it operates as follows.

In other words, even when the periphery of the opposing surface of the magnetic pole plate is raised, the periphery of the opposing surface of the permanent magnet is raised, and as a result, the thickness of the magnetic pole plate is made more uniform than in the past. becomes. Therefore, the magnetic flux from the permanent magnet reaches the gap after passing the same distance at the periphery of the magnetic pole plate as it does at the center, so the magnetic intensity in the gap corresponding to the periphery decreases as in the conventional case. Thereby, the magnetic field can be made uniform.

Furthermore, by raising the peripheral edge of the facing surface of the permanent fa 15, the peripheral edge of the facing surface of the permanent magnet is moved away from the yoke, so that magnetic loss is reduced compared to the conventional case.

Therefore, according to the present invention, it is possible to efficiently obtain a uniform magnetic field distribution without increasing the strength of the permanent magnet.

(Example) The illustrated embodiment will be described below.

Figure 1 is for a magnetic resonance diagnostic device according to the present invention! FIG. 2 is a schematic front view showing one embodiment of the i-magnetic field generating device, in which the same parts as in the conventional device shown in FIG. 2 are designated by the same reference numerals. That is, 3 is a yoke similar to the conventional one.

5.5 is a permanent magnet, and the corresponding surface periphery 5A.

5A is raised, and the bottom peripheral edge is also inclined accordingly so that the thickness is the same overall.

6.6 is a magnetic pole plate, and its opposing peripheral edge 6A.

6A is raised along the permanent magnet, so that the overall shape is similar to that of the permanent magnet.

Furthermore, the illustrated permanent magnet 5.5 has its peripheral edge 7 cut out in an annular shape at the joint with the yoke 3, so a yoke material (or permanent magnet material) is applied to the cut portion.
It is filled with an annular member made of the same material.

The magnetic field generating device as described above has the following effects.

■ Even if the periphery 6A of the facing surface of the magnetic pole plate 6.6 is raised as shown in the figure, the periphery 5A of the facing surface of the permanent magnets 5, 5 is raised, so as a result, the thickness of the magnetic pole plate 6 is Equalized compared to before. Therefore, the magnetic flux from the permanent magnet 5 reaches the gap 4 if it passes the same distance at the peripheral edge 6A of the magnetic pole plate 6 as it does at the center.
The magnetic strength of the portion corresponding to the peripheral edge of the magnetic field does not decrease, thereby making the magnetic field uniform.

■ By raising the peripheral edge 5A of the facing surface of the permanent magnet, as a result, the peripheral edge 5A of the facing surface of the permanent magnet is raised to the yoke 3.
Therefore, the magnetic loss is reduced compared to the conventional case. In other words, the distance between the peripheral edges 5A of the facing surfaces of the permanent magnets becomes shorter than in the past, and at the same time the distance from the peripheral edge 5A to the yoke 3 increases, so the magnetic loss is significantly reduced compared to the conventional.

(2) Therefore, according to this embodiment, it is possible to efficiently obtain a uniform magnetic field distribution without increasing the strength of the permanent magnet.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above embodiment, and can be modified as appropriate within the scope of the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to efficiently obtain a uniform magnetic field distribution without increasing the strength of the permanent magnet.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view showing an embodiment of a magnetic field generating device for a magnetic resonance diagnostic apparatus according to the present invention, FIG. 2 is a schematic front view of a conventional device, and FIG. 3 is a partial front view of another conventional example. be. 3...Yoke, 4...Gap, 5...Permanent magnet,
5A... Permanent magnet periphery, 6... ra magnetic pole plate 6A.
...periphery of magnetic pole plate.

Claims (1)

[Claims] A magnetic field generating device that generates a magnetic field between the magnetic pole plates, comprising permanent magnets arranged opposite to each other, magnetic pole plates provided on opposing surfaces of these permanent magnets, and a yoke that magnetically couples the permanent magnets. . A magnetic field generating device for a magnetic resonance diagnostic apparatus, characterized in that a peripheral edge portion of the facing surface of the permanent magnet is raised from a central portion.