JPH02139903A - Magnetic-field generation apparatus - Google Patents

Abstract

PURPOSE:To make the magnetic-field distribution uniform by causing a pair of yokes to be saturated magnetically. CONSTITUTION:A pair of pole pieces 2, 2 are mounted on the surface oppositely facing a pair of magnets 1, 1 which are disposed at diametrically opposed positions via space 5, and a pair of yokes 3, 3 are disposed across the section between the opposed sides. A human body is housed in the space 5. Magnetic fluxes generated by the magnets 1, 1 are magnetically short-circuited by the yokes 3, 3. The dimensions and quality of the yoke 3, 3 are selected so that the magnetic fluxes passing through the yokes 3, 3 are magnetically saturated. The rear surfaces of the magnets 1, 1 are magnetically saturated by a back yoke 4. Thus, magnetic-field distribution non-umiformality at both sides of the pole piece is suppressed. Much more of the magnetic fluxes pass through the space 5 and the intensity of the magnetic-field is intensified, the magnetic- field distribution being uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic field generator, and particularly to a magnetic field generator used in a medical nuclear magnetic resonance tomography apparatus.

[Prior Art] In a medical nuclear magnetic resonance tomography apparatus, it is necessary to generate a strong magnetic field of several thousand G at several 1 OCIII (Jll! Therefore, in addition to improving the magnet itself, various proposals have been made regarding the shape and arrangement method of the magnet and pole piece.6 Such a conventional technique is disclosed, for example, in Japanese Patent Application Laid-open No. 102544/1982. As shown in FIG. 7, there is a magnetic field generator for a nuclear magnetic resonance tomography apparatus in which a permanent magnet 1.1 forming an air gap 7 generates a static magnetic field in the air gap 7. This is a magnetic field generating device in which an annular magnetic body 6 in contact with a permanent magnet 1.1 is arranged within a generating area.

[Problems to be Solved by the Invention] In the magnetic field generating device described above, there are no special regulations regarding the magnetic properties of the annular magnetic body 6, and most of the magnetic flux generated by the permanent magnet 1.1 is caused by the annular magnetic body. 6, and there was a fear that a magnetic field of the required strength could not be obtained in a space that requires a strong magnetic field, that is, a space 5 that accommodates a human body.

In addition, medical nuclear magnetic resonance tomography devices require a strong and uniform magnetic field, but it is difficult to form a strong magnetic field uniformly, that is, uniformly both in field strength and magnetic field direction. Even if a magnetic field is designed, it is difficult to obtain a magnetic field with sufficient precision unless on-site adjustments are made after manufacturing and installation.

In particular, when a magnetic field is created using permanent magnets, it is almost impossible to create a strong magnetic field over a wide range using a single permanent magnet, so each block must be constructed as a combination of several blocks. Differences in characteristics between block magnet lofts and individual differences in the same lot cannot be avoided, so it is desirable to provide an adjustment mechanism after manufacturing and installation.

Therefore, an object of the present invention is to provide a magnetic field generating device that can provide a required magnetic field to a space that requires a uniform and strong magnetic field, and also allows fine adjustment of the magnetic field distribution.

[Means for Solving the Problems] The present invention has been made to solve the above problems, that is, a pair of pole pieces are attached to the opposing surfaces of a pair of magnets that are arranged opposite to each other with a space between them. 4. A magnetic field generating device in which a pair of yokes are spanned between opposing both sides of a pole piece to form a magnetic short circuit surrounding the space, the magnetic field generating device magnetically saturating the pair of yokes. In other words, the pole piece and the yoke can be formed integrally.

In addition, the yoke can be arranged replaceably or movably, or the yoke can be formed of a fixed part and a movable part,
Regarding the latter, it is possible to form a thin part, hole, or gap in the fixed part, and form the movable part in a shape that compensates for this.6 [Function] Since the magnetic flux generated by the magnet passes through the pole piece and the yoke, The edge effect that occurs when a yoke is not provided can be suppressed.6 Also, in the present invention, the magnetic flux passing through the yoke is formed so as to be magnetically saturated, so the magnetic flux generated by the magnet is distributed between the pole piece and the yoke. The magnetic field distribution in the space becomes uniform due to the influence of the leakage magnetic flux from the yoke part.

When all or part of the yoke is made movable, the amount of saturation magnetic flux passing through the yoke and the leakage magnetic flux from the yoke can be changed to finely adjust the magnetic field distribution in the space.

“Embodiments” Examples of the present invention will be explained based on the attached drawings.
The figure is a sectional view of one embodiment of a magnetic field generating device according to the present invention.

In the figure, a pair of magnets 1 are placed opposite each other with a space 5 in between.
．． A pair of pole pieces 2.2 are attached to the opposing surfaces of the pole piece 2.2, and a pair of yokes 3.3 are spanned between the opposing sides of the pole piece 2.2. The space 5 is surrounded in the longitudinal direction (direction perpendicular to the paper plane of FIG. 1) by the pole piece 2.2 and the yoke 3.3. A human body is housed in the space 5 when the present magnetic field generating device is used as a medical nuclear magnetic resonance tomography device.

The magnetic flux generated by the magnet 1.1 is magnetically short-circuited by the yoke 3.3, but the magnetic flux of the yoke as shown in FIG. The dimensions and material of the yoke 3.3 are selected so that the characteristics fall within the range B or B' in the figure. However, the two curves in the figure represent two types of yokes with different magnetic saturation characteristics. The back side of the magnet 1.1 is magnetically short-circuited by the back yoke 4.

The present embodiment is constructed as described above, and the magnetic flux generated by the magnet 1.1 is transmitted to the pole piece 2.2 and the yoke 3.
3, and the edge effect that occurs when no yoke is provided, that is, the non-uniformity of the magnetic field distribution on both sides of the pole piece, is suppressed. In addition, the dimensions and material of the yoke 3.3 are selected so that the magnetic flux passing through the yoke is magnetically saturated, so compared to when the yoke's magnetic properties are non-saturated, the magnetic flux generated by the magnet is The magnetic flux passes through the space 5 more, increasing the magnetic field strength in the space 5, and is influenced by the leakage magnetic flux from the yoke, so that the magnetic field distribution in the space 1 m5 becomes uniform.

In the above description, the magnet 1.1 can be formed by an electromagnet, but it is preferable to form it by a permanent magnet because additional equipment can be omitted.

The material of the permanent magnet used in this magnetic field generator is not particularly limited, and Nd-Fe-B electromagnets, S+-Co magnets, ferrite magnets, alnico magnets, etc. can be used, among which Nd-Fe - B-based magnets are particularly preferable because they have a large maximum magnetic force, and the pole piece 2.2 and yoke 3.3 may be integrated or separate;
Regarding its shape, the cross section of the space 5 surrounded by the pole piece and the yoke may be formed not only square but also circular, elliptical, etc.

Next, if the pole pieces 2, 2 and the yoke 3.3 are formed separately and the yoke 3.3 is formed to be replaceable, the change from B to B' or from B' to B in FIG. 2 can be made by replacing the yoke. The magnetic field distribution within the space 5 can be adjusted by changing the amount of saturation magnetic flux of the yoke and the leakage magnetic flux from the yoke. In other words, the yoke that makes the actual magnetic field distribution within the space 5 most uniform can be adjusted. The dimensions and material can be determined 6. Also, the yoke 3.3 is placed on both sides of the pole piece, that is, the first
If the yoke is formed to be movable in the direction of the arrow in the figure, the magnetic field distribution within the space 5 can be adjusted by moving the yoke, that is, the position of the yoke can be determined to make the actual magnetic field distribution within the space 5 most uniform. can.

Next, as shown in FIG.
, 3a and movable parts 3b and 3b arranged to be freely attachable and detachable, the amount of saturation magnetic flux passing through the entire yoke and the leakage magnetic flux can be changed by attaching and detaching or replacing the movable parts, and the magnetic field distribution in the space 5 can be changed. In other words, it is possible to determine the dimensions and materials of the movable parts 3b, 3b that make the actual magnetic field distribution within the space 5 most uniform. Furthermore, if the yoke 3.3 is formed of fixed parts 3a, 3a and movable parts 3b, 3b disposed so as to be movable, the amount of saturation magnetic flux passing through the entire yoke and the leakage magnetic flux can be changed by the movement of the movable parts. The magnetic field distribution in the space 5 can be adjusted, ie the position of the movable parts 3b, 3b can be determined which makes the actual magnetic field distribution in the space 5 most uniform.

In these cases, compared to the case where the entire yoke is formed to be replaceable or movable, it is sufficient to form a portion that can compensate for errors in design and manufacturing as a movable part and to be detachable or movable. The attachment/detachment mechanism or movement mechanism of the movable parts 3b, 3b can be made smaller. Furthermore, the fixed parts 3a, 3a of the yoke can be formed integrally with the pole piece 2.2.

Next, other embodiments in which the yoke 3.3 is formed by fixed parts 3a, 3a and movable parts 3b, 3b arranged movably are shown in FIGS. 4 to 6. A thin wall portion 3C is formed in the longitudinal direction of the center of the portion 3a, and the movable portion 3b is formed into a plate shape that fits into the thin wall portion 3c, thereby making it movable. Note that the shape of the thin wall portion and the movable portion is not limited to a rectangular shape, but may also be a wedge shape, a semicircle, or the like.

In FIG. 5, a plurality of tapped holes 3d are arranged in a row in the longitudinal direction of the center of the fixed portion 3a, and a plurality of screws are screwed into the movable portion 3b into the screw holes 3d. In this case, the tapped holes and screws must be arranged densely in the longitudinal direction so as not to impair the uniformity of the magnetic field distribution in the longitudinal direction. Alternatively, instead of using threaded holes and screws, a square hole, circular hole, etc. may be formed in the fixed part, and the movable part may be formed in a prismatic or cylindrical shape that fits into the square hole, circular hole, etc. so that it can move forward and backward. good.

In FIG. 6, a gap B3e is formed in the longitudinal direction at the center of the fixed part 3a, and the movable part 3b is formed into a plate shape that fits into the gap 3e so as to be able to move forward and backward. Also in the embodiments shown in FIGS. 4 to 6 above, the amount of saturation magnetic flux passing through the entire yoke and the leakage magnetic flux are changed by moving the movable parts 3b and 3b, and the magnetic field distribution in the space 5 is adjusted. That is, it is possible to determine the position of the movable parts 3b, 3b that makes the actual magnetic field distribution in the space 5 most uniform.

[Effects of the Invention] Since the present invention is a magnetic field generating device in which the yoke is magnetically saturated, it is possible to provide a required magnetic field to a space that requires a uniform and strong magnetic field. When formed to be replaceable, detachable, or movable, the magnetic field distribution can be finely adjusted.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the magnetic field generator according to the present invention, FIG. 2 is an explanatory diagram showing the relationship between the amount of magnetic flux generated by the magnet and the amount of magnetic flux passing through the yoke, and FIG. 3 is the invention according to the present invention. FIGS. 4 to 6 are sectional views of essential parts of still other embodiments, and FIG. 7 is a sectional view of a conventional example. 1... Magnet 2... Pole piece 3...
Yoke 3a... Fixed part 3b... Movable part 4... Back yoke 5... Space Figure 4 Figure 6 Figure 5 Figure 7

Claims (5)

[Claims] (1) A pair of pole pieces are attached to the opposing surfaces of a pair of magnets that are arranged opposite to each other with a space in between, and a pair of yokes are spanned between the opposing sides of the pole pieces to form a magnetic short circuit that surrounds the space. A magnetic field generating device, characterized in that the pair of yokes are magnetically saturated. (2) The magnetic field generating device according to claim 1, wherein the pair of pole pieces and the pair of yokes are integrally formed. (3) Claim 1, wherein the pair of yokes are arranged exchangeably or movably, so that the magnetic field distribution in the space can be adjusted.
The magnetic field generator described. (4) The magnetic field generating device according to claim 1 or 2, wherein the pair of yokes are formed by a fixed part and a movable part arranged to be detachable or movable, so that the magnetic field distribution in the space can be adjusted. (5) The magnetic field generating device according to claim 4, wherein a thin wall portion, a hole, or a gap is formed in the fixed portion of the pair of yokes, and the movable portion is formed in a shape that compensates for the thin wall portion, hole, or gap.