JPH04152606A - Magnetic field generating device - Google Patents

Abstract

PURPOSE:To facilitate the manufacture of the title magnetic field generating device, to effectively concentrate magnetic flux in the vicinity of the center of the air gap and the generate a high strength magnetic field uniformly without increasing magnetic material by a method wherein the circumferential part of a permanent magnet part is formed thicker than the center part. CONSTITUTION:A magnetic circuit is composed of a pair of permanent magnet part 1, on which air gap 5 is formed, and a structure formed in such a manner that a pair of magnetic field adjusting pole pieces, which are fixed to the permanent magnet part 1 are, magnetically coupled by a tabular yoke 3 and a support pole 4. At this point, the thickness t2 pf the circumferential part 12 of the permanent magnet part 1 is constructed so as to become thicker than the thickness t1 of the center part 11. Concretely, first, a disc-shaped permanent magnet part of thickness t1 is formed, and then the circumferential part of thickness t2 is formed by increasing the magnet on the outside part only. Also, the piece 2 can be manufactured by a simple method in which only a tabular pure iron is cut and surface-process is conducted. Using the same quantity of magnet material as before, a high strength and uniform magnetic field can be generated from the part in the vicinity of the air gap center, and the magnetic circuit of the structure which is formed by the technique easier than that heretofore in use, can be obtained.

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 MHI devices: permanent magnet method, normal conductive magnet method, and superconducting magnet method. Among these, the permanent magnet method is the most effective because it does not involve the consumption of electric power or helium. Most economical. Furthermore, in recent years, with the advent of rare earth magnets with strong magnetic force and improvements in the performance of signal detection devices and imaging technology, the possibility of permanent magnet type MR processing devices has increased.

In an MHI device, the strength and uniformity of the static magnetic field affect the quality of the captured image, so a high intensity and uniform magnetic field with an accuracy of 10-' or less is required near the center of the gap into which the subject is inserted. In order to meet this strict condition, conventionally, in the basic magnetic circuit shown in Fig. 2,
As disclosed in No. 6, a pair of upper and lower permanent magnet portions made of rare earth magnets are arranged so that opposing surfaces form concave curved surfaces with respect to the air gap, thereby generating a high-intensity magnetic field near the center of the air gap. Ta. Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 83-241905, a part of the pole piece has a laminated structure of magnetic plates that are laminated substantially perpendicularly to the side surface of the pole piece to generate a high-intensity uniform magnetic field near the center of the gap. Ta.

[Problems to be Solved by the Invention] However, as in the prior art described above, forming a permanent magnet in a concave curved shape or forming a magnetic plate in a laminated structure is difficult to manufacture, and has a negative impact on assembly accuracy. There is a great possibility of giving.

Therefore, an object of the present invention is to create a magnetic circuit that can generate a uniform magnetic field of high intensity near the center of the gap using the same amount of magnet material as conventional techniques, and that is easier to manufacture than conventional techniques. It is to propose.

[Means for Solving the Problems] The magnetic field generating device of the present invention magnetically couples a pair of permanent magnet parts facing each other with a gap formed therebetween and a pair of pole pieces fixed to the permanent magnet parts using a yoke and a support. In the magnetic field generating device that generates a magnetic field in the air gap with this structure, the permanent magnet portion is characterized in that the peripheral portion is thicker than the central portion.

Embodiment FIG. 1 is an explanatory diagram showing a magnetic circuit used in a magnetic field generating device in an embodiment of the present invention. The magnetic circuit has a structure in which a pair of permanent magnet parts 1 facing each other with an air gap 5 formed therein, and a pair of magnetic field adjustment pole pieces 2 fixed to the permanent magnet parts 1 are magnetically coupled by a plate-shaped yoke 3 and a support column 4. Become. Here, the permanent magnet part 1 is assembled so that the thickness t2 of the peripheral edge part 12 is thicker than the thickness tl of the central part 11. Specifically, first, a disk-shaped permanent magnet portion with a thickness of tl was constructed, and then the number of magnets was increased only in the outer portion to construct a peripheral portion with a thickness of t2. Further, the pole piece 2 is manufactured by a simple method of cutting and surface-processing a plate-shaped pure iron.

In the magnetic circuit described above, the basic composition is Pr17 atomic %.
-Fe76.5 at% -B5 at% -Cu1.5 at%
A rare earth magnet manufactured by hot/rolling has a maximum energy product of 26.2 megagauss-ersted (M
When the magnetic field strength at the center of the gap was 1875G, a uniform magnetic field of 40 ppm or less was obtained within 300 DSV.

FIG. 2 is an explanatory longitudinal cross-sectional view showing a basic magnetic circuit used in a conventional magnetic field generating device. The magnetic circuit has a structure in which a pair of upper and lower permanent magnet parts 1 and a pair of pole pieces 2 fixed to the permanent magnet part 1 are magnetically coupled by a yoke 3 and a support 4, and the permanent magnet part 1 is It has a plate shape and has a constant wall thickness. In this magnetic circuit, Pr having the same magnetic properties as the permanent magnet used in the magnetic circuit of the present invention is used.
-Using a Fe-B magnet, the effective gap length L is 500
In order, when the magnet weight was 1.4 tons, the magnetic field strength at the center of the gap was 1764 G, and the uniformity within 300 DSV was 40 ppm.

FIG. 3 is an explanatory diagram of a pole piece used in a conventional magnetic field generator. A high magnetic permeability member 6 made of a silicon copper plate or the like and a nonmagnetic material 7 are arranged around the outer periphery of the pole piece 2 so as to form a laminated structure in a substantially perpendicular direction.

FIG. 4 is an explanatory diagram showing a conventional magnetic circuit.

The permanent magnet portion 1 is arranged so as to form a concave curved surface with respect to the air gap 5, and a high-intensity magnetic field is generated in the air gap 5.

Even with the conventional technology shown in FIGS. 3 and 4, the air gap 5
Although it is possible to generate a high-intensity magnetic field, it is difficult to manufacture due to its complicated structure, and there is a strong possibility that assembly accuracy will be adversely affected. In comparison, the magnetic circuit according to the embodiment of the present invention shown in FIG. 1 is relatively simple to manufacture and can generate a stronger magnetic field in the air gap 5 than the basic magnetic circuit shown in FIG. It is.

Furthermore, in order to avoid an increase in the weight of the magnetic circuit, the permanent magnet used in the magnetic field generator of the present invention has a maximum energy product of 25
(MGOe) or higher Nd-Fe-B system or Pr
A rare earth magnet such as -Fe-B is desirable.

[Effects of the Invention] As described above, according to the present invention, a pair of permanent magnet parts facing each other with a gap formed therein and a pair of pole pieces fixed to the permanent magnet parts are magnetically coupled by a yoke and a support, In the magnetic field generating device that generates a magnetic field in the air gap with this structure, the permanent magnet part is constructed so that the peripheral part is thicker than the central part, which is easier to manufacture than the conventional technology. It is now possible to effectively concentrate the magnetic field near the center of the gap, making it possible to generate a more intense uniform magnetic field without increasing the amount of magnet material.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the basic structure of a magnetic circuit of a magnetic field generating device in an embodiment of the present invention. FIG. 2 is an explanatory diagram showing the basic magnetic circuit of the magnetic field generator. FIG. 3 is an explanatory diagram showing a pole piece used in a conventional magnetic circuit. FIG. 4 is an explanatory diagram showing a conventional magnetic circuit. 1... Permanent magnet part, 11... Permanent magnet center part, 12
...Permanent magnet periphery, 2...Pole piece, 3...
・Yoke, 4... Support, 5... Gap, 6...
High magnetic permeability member, 7...Non-magnetic material Figure jI3 Figure 4

Claims (1)

[Claims] A magnetic field generating device in which a pair of permanent magnet parts facing each other with a gap formed therein and a pair of pole pieces fixed to the permanent magnet parts are magnetically coupled by a yoke and a column, and a magnetic field is generated in the gap with this structure. A magnetic field generating device characterized in that the permanent magnet portion is formed thicker at the peripheral portion than at the center portion.