JPH04186805A - Magnetic field generator - Google Patents

Abstract

PURPOSE:To obtain the title magnetic field generator capable of easily adjusting the evenness of the central magnetic field intensity by a method wherein an adjusting mechanism vertically shifting the magnetic pole pieces in the central part is provided in the central part of the magnetic pole pieces structured so as to wrap the magnetic pole pieces in the central part. CONSTITUTION:Within the title magnetic field generating device having opposite magnetic pole pieces 2, 3 forming a cavity 5 upward and downward so as to generate a magnetic field in the cavity 5, an adjusting mechanism 6 for vertically shifting the second shims 2 is provided on the central part of the magnetic pole pieces 3 (the first shim) structured as if wrapping the magnetic pole piece in the central part (the second shims)2. For example, respective four each of permanent magnet blocks 1 are coupled with one another on the side surface parts of the opposite one pair of the first shims 3 while respective yokes 4 couple the upper and lower pairs of permanent magnets to make a magnetic circuit further to form a cavity between upper and lower magnetic pieces 2. On the other hand, the interval between the cavities of the second shims 2 is made adjustable by turning the adjusting bolt 6 to move the second shims 2. Besides, the permanent blocks 1 are to be made of rare earth magnet.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a high-strength and This invention relates to a magnetic field generator that generates a highly accurate and uniform static magnetic field.

[Prior art] There are three methods for generating magnetic fields in MR engineering wave equipment: permanent magnet method, normal conductive magnet method, and superconducting magnet method. Among these, the permanent magnet method involves the consumption of electric power and helium. It was said to be the most economical because there was no However, this permanent magnet method was not put into practical use because the magnetic field generated in the air gap was weak because the magnetic energy of the permanent magnet was small, and it was difficult to reduce the weight. Under these circumstances, rare earth permanent magnets with strong magnetic force have been developed in recent years, and as a result, permanent magnet type MHI devices are becoming popular. FIG. 3 shows a conventional magnetic field generating device, which is integrally molded with yokes 4 arranged on the upper, lower, left and right sides. A magnetic circuit was formed by the magnetic pole pieces 7, and a strong magnetic field was generated in the air gap 5.

[Problem to be solved by the invention] However, since conventional MHI devices do not have a mechanism for adjusting the magnetic pole pieces, if the calculation data before the prototype does not match the central magnetic field strength uniformity of the prototype, it is difficult to make the prototype. Must be repeated. Furthermore, the structure of the conventional magnetic field generator has the problem that it is difficult to adjust the uniformity of the central magnetic field. 1
In a magnetic circuit used in an MHI device that requires a uniform magnetic field of 0-' or less, finishing accuracy and assembly accuracy of each component become a problem. Among these, the shape of the magnetic pole piece has a particularly large effect on the uniformity of the magnetic field. However, in the prior art described above, since the magnetic pole piece is integrally molded, it is extremely difficult to change the shape of the magnetic pole piece after assembly. SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems, and its purpose is to propose a structure of a magnetic field generating device that can easily adjust the uniformity of the central magnetic field strength.

[Means for Solving the Problems] A magnetic field generating device of the present invention has magnetic pole pieces facing each other with an air gap formed above and below, and generates a magnetic field in the air gap. (hereinafter referred to as the second sim)
(hereinafter referred to as the first shim)
It is characterized in that an adjustment mechanism for moving the second shim up and down is provided in the center of the shim.

[Example] FIG. 1 is a sectional view showing an embodiment of the present invention.

1 is a permanent magnet block, 2 is a second shim of the magnetic pole piece, 3 is a first shim that wraps around the second shim, 4 is a yoke, 5 is
is a gap, and 6 is an adjustment bolt provided at the center of the first shim. By turning the adjustment bolt 6, the second shim can be moved and the gap distance of the second shim can be adjusted. FIG. 2 is a perspective view showing a configuration example according to the present invention, in which four permanent magnet blocks are respectively coupled to the side surfaces of a pair of opposing first shims. Each yoke 4 connects a pair of upper and lower permanent magnets to form a magnetic circuit, and further forms a gap between the upper and lower magnetic pole pieces 2.

The width X of the permanent magnet block 1 is 23 cm, and the height y is 23 cm.
5 cm, and the length Z is a rectangular parallelepiped of 50 cm. The radius of the second shim 2 of the magnetic pole piece is 30 cm, the wall thickness is 28 cm, and they are provided vertically facing each other, and the gap distance between the magnetic pole pieces 2 is 52 cm.
It is m.

The first shim 3 and the yoke 4 are made of iron-based material with high magnetic permeability. The permanent magnet block 1 is made of a rare earth magnet, and has a basic composition of 17 atomic percent Pr and 76.5 atomic percent Fe.
5.0 atom % of B, and 1.5 atom % of Cu.

The permanent magnet in this example uses a mechanical force Oersted (MGOe) with a maximum energy product of 27,
The magnet weight is approximately 1.5 tons. Although the permanent magnet block 1 was magnetized this time before assembly, it is also possible to magnetize it even after assembly in the magnetic circuit configured as shown in this embodiment.

The magnetic field generating device of this embodiment has a magnetic flux density of 0.0 at the center of the air gap 5. 2 Tesla (T), uniformity of void center is 220pp
m was obtained. By moving the second shim using the adjustment bolt 6 and adjusting the gap distance, it is possible to change the central magnetic field strength uniformity. In this example, by lowering the upper second shim by 1 mm and raising the lower second shim by 1 mm to shorten the air gap distance, the magnetic field strength at 15 cm vertically from the center increases by 0°5 Gauss, and the radius from the center increases. 10 in the direction
The magnetic field strength at 0 m drops by 0.3 Gauss. When the upper second shim is raised and the lower second shim is lowered to extend the gap distance, the tendency is opposite to that described above. By moving the second shims and changing the gap distance in this way, the magnetic field strength and magnetic field strength distribution at the center of the upper and lower second shims can be adjusted.

Therefore, a desired magnetic field can be easily obtained.

Although the present invention has been described in detail above, the materials, dimensions, magnetic properties, etc. are not limited to the examples shown in the text.

For example, in magnets, ferrite, alnico,
It is also possible to use other high magnetic performance magnets. Furthermore, although the case in which there are four pairs of magnets has been described in this embodiment, it is possible to achieve a high-performance magnetic circuit even if the number of poles is changed. In terms of size, magnetic circuits from several centimeters to several meters can also produce the same effects as the present invention.

[Effects of the Invention] As described above, the present invention has the following effects. The magnetic field generating device of the present invention is provided with an adjustment mechanism that can move the second shim and change the gap distance, so that it is possible to adjust the gap distance by moving the upper and lower second shims, and it is possible to adjust the gap distance by moving the upper and lower second shims. magnetic field strength and magnetic field uniformity can be easily obtained. Therefore, this magnetic field generating device does not require much precision in parts processing. In addition, since it is not necessary to recreate the shim because magnetic field strength and magnetic field uniformity cannot be obtained, it has the effect of being inexpensive and having excellent productivity.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the present invention. FIG. 2 is a perspective view of the present invention. FIG. 3 is a sectional view of the prior art. 1... Permanent magnet 2... Second shim of the magnetic pole piece 3... First shim of the magnetic pole piece 4... Yoke 5... Air gap 6... Adjustment bolt 7... Pole piece applicant Seiko Epson Corporation Figure 1

Claims (1)

[Claims] In a magnetic field generating device that has magnetic pole pieces facing each other with an air gap formed above and below and generates a magnetic field in the air gap, a magnetic pole piece (hereinafter referred to as a second shim) configured to wrap around a central magnetic pole piece (hereinafter referred to as a second shim) is used. , a magnetic field generating device characterized in that an adjustment mechanism for moving a second shim up and down is provided in the center of the first shim (referred to as the first shim).