JPH0517845Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic field generating device that uses a plurality of ring-shaped yokes each having a plurality of through holes into which cylindrical permanent magnets are inserted. The present invention is suitable for use in a computerized tomography (NMR-CT) device that utilizes nuclear magnetic resonance.

[Prior Art] The sharpness of an image of an NMR-CT device is greatly affected by the uniformity of the device's magnetic field. For this reason, NMR
- In CT equipment, it is extremely important to obtain a uniform magnetic field over as wide a range as possible.

As a device for obtaining a uniform magnetic field over a wide range, there is a device that generates a magnetic field by arranging multiple anisotropic trapezoidal segment magnets in a ring shape to form a dipole ring magnet, and using multiple dipole ring magnets. Are known.

However, since such a magnetic field generating device uses a trapezoidal segment magnet, there is a problem in that the device becomes larger and its weight increases, and the manufacturing cost increases. Furthermore, there was also the problem that adjustment to obtain a uniform magnetic field was not easy. Furthermore, the shape and magnetization direction of the trapezoidal segment magnets are complicated, making it difficult to manufacture them.

[Objective of the Invention] The objective of the present invention is to provide a magnetic field generating device which is characterized by being small, lightweight, and low manufacturing cost, and further which is extremely easy to adjust.

[Means and effects for solving the problem] The present invention provides first and second ring-shaped yokes each having a plurality of through holes extending in the central axis direction and arranged at approximately equal intervals around the central axis. and; a plurality of third ring-shaped yokes each having a plurality of through holes around the central axis that extend in the direction of the central axis and are arranged at approximately equal intervals; 2 and a plurality of cylindrical permanent magnets inserted into each of the plurality of third through holes; the first, second and plurality of third ring-shaped yokes each have a central axis that The plurality of third ring-shaped yokes are arranged so as to be substantially in a straight line, and are arranged adjacent to each other so that the plurality of third ring-shaped yokes are located between the first and second ring-shaped yokes. This is a magnetic field generator.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view of a ring-shaped yoke used in the magnetic field generator according to the present invention.

In FIG. 1, a ring-shaped yoke 10 has a plurality of through holes 14 provided in its thick portion 12 parallel to the central axis of the yoke (the Z axis perpendicular to the X axis and the Y axis) and at approximately equal intervals. have In addition, the ring-shaped yoke 10
is preferably a soft magnetic material.

In the embodiment shown in FIG. 1, there are 16 through holes 14. In order to obtain a highly uniform magnetic field, it is better to have as many through holes as possible, but in reality, 16 or twice as many as 32 through holes are used.
It is enough.

A cylindrical permanent magnet 16 magnetized in advance in a specific direction is arranged in each of the plurality of through holes 14 so that the magnetization direction is as shown in FIG. Cylindrical permanent magnet 1
6 is rotatably inserted into the through hole 14 to adjust the magnetization direction, so it is extremely easy to set the magnetization direction as shown in FIG. One of the features of the present invention is that the magnetization direction can be easily adjusted in this way. Note that in order to make the cylindrical permanent magnet 16 rotatable within the through hole 14 for adjustment, the through hole 14
It is desirable to provide a spacer or the like between the inner wall of the magnet and the surface of the cylindrical magnet (not shown).

In order to obtain a uniform magnetic field over a wide range, magnets (e.g. trapezoidal permanent magnets) are arranged in a cylindrical shape,
A dipole ring in which the magnetization direction of each magnet is as shown in FIG. 1 is known. Therefore, a detailed explanation of the dipole ring itself will be omitted.

FIG. 2 is a schematic side view of the device according to the invention. In the embodiment shown in FIG. 2, five ring-shaped yokes 10, 22, 24, 26 and 28 are provided. As shown in FIG. 1, each ring-shaped yoke has cylindrical permanent magnets (indicated by 16, 32, 34, 36, and 38) in through holes provided at equal intervals in its thick wall. Reference number 40, 42, 44, 4
Reference numeral 6 denotes a thin disc-shaped spacer provided between each ring-shaped yoke.

As is clear from Fig. 2, the ring-shaped yoke 1
0, 22, 24, 26, 28 are the respective central axes (Z
The ring-shaped yokes 22, 24, 26 are arranged adjacent to each other so as to be located between the other ring-shaped yokes 10, 28. Furthermore, since the uniformity of the magnetic field at the ends of a plurality of ring-shaped yokes arranged in a cylindrical shape as a whole is not as good as that at the center, the diameter of the cylindrical permanent magnet provided in the ring-shaped yokes arranged at the ends is , is larger than the diameter of the cylindrical permanent magnet provided in the central yoke. Furthermore,
In order to generate a uniform magnetic field, the inner diameter of each ring-shaped yoke is approximately equal.

In the embodiment described above, two types of ring-shaped yokes are used, but if necessary, another ring-shaped yoke having the same inner diameter as the ring-shaped yokes 22, 24, or 26 and having a thinner wall thickness can be used. It may be provided in the center of the

[Effects of the Invention] As explained above, the present invention has the advantage of being smaller, lighter, and lower in manufacturing cost than the conventional example. Furthermore, the present invention has the remarkable effect that since the cylindrical permanent magnet can be easily rotated, it is extremely easy to adjust the uniformity of the generated magnetic field.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a ring-shaped yoke according to the present invention, and FIG. 2 is a schematic side view of the device according to the present invention. In the figure, 10, 22, 24, 26, and 28 are ring-shaped yokes, 14 is a through hole provided in the ring-shaped yoke, and 16, 32, 34, 36, and 38 are cylindrical permanent magnets, respectively.

Claims (1)

[Claims for Utility Model Registration] (1) First and second ring-shaped yokes each having a plurality of through holes extending in the direction of the central axis and arranged at approximately equal intervals around the central axis; and a central axis. a plurality of third ring-shaped yokes each having a plurality of through holes around the central axis extending in the direction and arranged at approximately equal intervals; a plurality of cylindrical permanent magnets inserted into each of the third through holes, the first, second, and plurality of third ring-shaped yokes each have a central axis that is substantially in a straight line. and the plurality of third ring-shaped yokes are arranged adjacent to each other so as to be located between the first and second ring-shaped yokes. Device. (2) The first, second, and third cylindrical permanent magnets are each adjustable in position by rotation within the inserted through hole. Device. (3) at least one fourth ring-shaped yoke extending in the direction of the central axis and having a plurality of through holes arranged at approximately equal intervals around the central axis; The device according to claim 1, further comprising: a plurality of cylindrical permanent magnets inserted into each of the through holes of the device. (4) The device according to claim 3, wherein the position of each of the fourth cylindrical permanent magnets can be adjusted by rotation within the inserted through hole.