JPH0421107Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial field of application This invention is a permanent magnet used in medical nuclear magnetic resonance tomography (hereinafter referred to as NMR-CT), which can obtain cross-sectional images of objects and depict the properties of tissues. Regarding a magnetic field generator using
The present invention relates to a magnetic field generating device that generates a strong, highly accurate, and uniform static magnetic field in a required space at the center of a large air gap, and particularly to a magnetic field generating device that can correct partial magnetic field uniformity in the required space.

BACKGROUND ART
In order to obtain the desired tomographic image by inserting the device into an air gap that generates a strong magnetic field of 10 KG, this magnetic field must be strong, uniform, and stable with an accuracy of 10 ^-4 or less. Known magnetic field generators include normal conducting magnets made of conductive wire made of copper or aluminum wrapped in a cylindrical shape, and superconducting magnets that use special conducting wire cooled to a temperature close to absolute zero. .

The former is structurally inexpensive, but it requires a huge amount of electricity and cooling water to generate a sufficiently strong magnetic field, resulting in high running costs, and the leakage magnetic field created by the coil can be a negative factor depending on the application. On the other hand, the latter type of superconducting magnet has the advantage of consuming less power and being small and generating a strong magnetic field, but it requires the use of expensive liquid helium or the like as a coolant. There is a problem that the running cost as well as the so-called initial cost is extremely high, so it has not been widely used.

The present applicant has previously proposed a magnetic circuit for NMR-CT that uses permanent magnets with a magnetic field strength equal to or higher than that of the above-mentioned normal conduction magnets, consumes no power, and has a small leakage magnetic field. A magnetic field generating device for magnetically coupling a magnetic pole piece and at least one permanent magnet with a yoke to generate a magnetic field in the air gap, characterized in that an annular protrusion is provided on each opposing surface of the magnetic pole piece. Proposed a generator (patent application 1982-
No. 196785).

With the above magnetic field generating device, it was possible to significantly improve the uniformity accuracy of the magnetic field generated in the air gap. However, when designing the above magnetic field generator,
The most efficient magnetic circuit is designed through analysis based on the magnetic properties of permanent magnets and the shapes of various component parts, but due to variations in magnetic properties and dimensional accuracy of each component, it is difficult to increase the magnetic field as designed. It is difficult to obtain accuracy, and in terms of maintenance management,
There is a problem in that it is difficult to maintain the magnetic field as designed, and it is necessary to adjust the magnetic field during or after assembly of the magnetic field generator.

Purpose of the invention In view of the current situation, this invention has been developed to obtain a highly accurate, uniform and stable magnetic field in the required space in the center of the air gap of a magnetic field generator using permanent magnets that can obtain a strong magnetic field, and to facilitate maintenance and management. In order to obtain a uniform and stable magnetic field, the present invention also aims at a magnetic field generating device having a magnetic circuit capable of adjusting the magnetic field.

Structure and effect of the invention That is, this invention magnetically couples a pair of magnetic pole pieces facing each other with an air gap and at least one permanent magnet using a yoke, and provides a high degree of uniformity in the required space at the center of the air gap. A magnetic field generating device that generates a static magnetic field is characterized in that magnetic paint is applied to required locations on opposing surfaces of a pair of magnetic pole pieces in order to correct partial magnetic field uniformity in a required space at the center of the air gap. It is a magnetic field generator.

In this invention, the magnetic paint is applied to the opposing surfaces of a pair of magnetic pole pieces in order to finely adjust the magnetic field in the required space at the center of the gap in ppm units, and is not necessarily applied to the entire surface of the opposing surfaces of the pair of magnetic pole pieces. There is no need to apply it, just apply an appropriate amount to the areas required to adjust the magnetic field according to the individual magnetic circuit.
Magnetic field adjustment can be easily performed.

As the magnetic paint, any of the known magnetic paints can be used, such as magnetite, maghemite, chromium dioxide, cobalt-based iron oxide, and metal magnetic powder, which are used for magnetic recording media and are manufactured by dispersing magnetic particles in a binder solution. can.

Any configuration can be used for the magnetic circuit as long as at least one permanent magnet is used and magnetic pole pieces that are opposed to each other with an air gap are magnetically coupled with a yoke. It is desirable to appropriately select the shape of the magnetic pole piece depending on the size and size of the required air gap.

It is also good to have a magnetic circuit with an annular protrusion on one side of the magnetic poles facing each other with an air gap in between.Protrusions of various shapes, such as protrusions with a triangular or trapezoidal cross section, can be used on the periphery of the plane of the magnetic pole face or at any desired location. It is also possible to provide convex protrusions in the center of the annular protrusion, either continuously or discontinuously.

The magnetic field generating device according to this invention is a device that can generate a strong magnetic field of 1 to 5 kg by using the following permanent magnet, and weighs less than 10 tons.
100ton of magnetic field generator using ferrite magnet
Compared to the above, a significant reduction in size and weight can be achieved.

Permanent magnet used in the invention The permanent magnet used in the magnetic field generator of this invention is
Ferrite magnets, alnico magnets, and rare earth cobalt magnets can be used, but the applicant has previously proposed a new high-performance permanent magnet that does not contain expensive Sm or Co. At least one rare earth element) permanent magnet (JP-A-Sho
No. 57-145072) not only has a large maximum energy product, but also has temperature characteristics with a temperature coefficient of residual magnetic flux density (Br) of -0.07%/℃ to -0.15%/℃. By applying the above NMR-CT, the device can be made smaller.
Excellent performance can be obtained, and furthermore, the magnetic properties of this permanent magnet, especially when used after being cooled to below 0° C., can be effectively used to obtain a significantly high maximum energy product.

The above Fe-BR-based permanent magnet has R (where R is at least one kind of rare earth elements including Y) 8 at% to 30 at%, B2 at% to 28 at%, Fe42 at% to 90 at%. It is a permanent magnet whose main phase is a tetragonal phase, and R is a light rare earth that is abundant in resources, mainly Nd and Pr.
It is an excellent permanent magnet that exhibits an extremely high energy product of over 25NGOe with

Disclosure of the invention based on drawings FIG. 1 is a longitudinal sectional front view of a magnetic circuit used in NMR-CT according to this invention.

The magnetic circuit shown in Figure 1 consists of a pair of Fe-B-R
A magnetic pole piece 2 is fixed to one end of each of the system permanent magnets 1, 1 and opposed to each other, and the other end of the permanent magnet 1 is connected to a yoke 3 having a cylindrical shape with a part of its circumference open. The pair of magnetic pole pieces 2, 2 have a predetermined magnetic field inside the periphery of their opposing surfaces. Fe-B-
The R-based permanent magnets 1, 1 are magnetized in the same direction.

In the above configuration, for example, if the magnetic paint 6 is applied to the central concave portion of the magnetic pole piece 2 having the annular protrusion 5 at a location and thickness necessary for magnetic field adjustment, a static magnetic field with extremely high uniformity can be obtained within the air gap 4. .

In the drawings, for ease of illustration, an example is shown in which the entire central concave portion of the magnetic pole piece 2 is coated thickly, but various magnetic paints may be selected depending on the required magnetic field adjustment.
The magnetic field can be easily adjusted by applying it at the required location and thickness.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view of a magnetic circuit used in a magnetic field generating device according to this invention. 1... Fe-BR-based permanent magnet, 2... Magnetic pole piece,
3...Yoke, 4...Gap, 5...Annular protrusion, 6...
...Magnetic paint.

Claims (1)

[Scope of utility model registration request] A magnetic field generating device that magnetically couples a pair of magnetic pole pieces facing each other with an air gap and at least one permanent magnet using a yoke to generate a highly uniform static magnetic field in a required space in the center of the air gap, A magnetic field generating device characterized in that a magnetic paint is applied to required locations on opposing surfaces of a pair of magnetic pole pieces in order to correct partial magnetic field uniformity in a required space at the center of the air gap.