JPH01109290A - Magnetic shield apparatus - Google Patents

Abstract

PURPOSE: To reduce the weight of an entire device by providing a magnetic shielding member made of a ferromagnetic body in parallel with the direction of magnetic field and by surrounding the periphery of a magnetic field to be shielded and providing a plane coil vertical to the direction of magnetic field and at both edges of the magnetic field to be shielded. CONSTITUTION: A plane coil 3 is arranged within a plane that is vertical to the axial core of electromagnets 1A and 1B at the upper and lower parts of the electromagnets 1A and 1B. A current for forming a magnetic field for canceling a magnetic field that is formed at the upper and lower parts of the electromagnets 1A and 1B by the electromagnets 1A and 1B is allowed to flow to the coil 3, thus shielding the leaked magnetic field at the upper and lower parts of the electromagnets 1A and 1B. Also, the coil 3 forms a magnetic field that is in parallel with the magnetic shield member 2B near the coil 3. The magnetic field increases the number of magnetic force lines passing through the inside of the member 2B and further increases magnetic shielding effect.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a device (: for example) for effectively blocking leakage magnetic fields in a magnetic field utilization device such as a nuclear magnetic resonance diagnostic device using an air-core electromagnet.

Conventional technology, for example, a normal conducting nuclear magnetic resonance diagnostic apparatus uses an air-core normal conducting magnet to obtain the static magnetic field necessary for imaging.

An air-core normally conducting magnet forms a magnetic field at its center and at the same time forms a magnetic field (hereinafter referred to as a leakage magnetic field) around the center. Leakage magnetic fields may have an adverse effect on certain devices around nuclear magnetic resonance diagnostic equipment, causing peripheral equipment to malfunction or stop working.For example, if a pacemaker is placed in a strong magnetic field, its functions may be affected. Therefore, the normal conduction type nuclear magnetic resonance diagnostic apparatus requires a shield function to block the leakage magnetic field.

In Fig. D, air-core electromagnets rA and IB of a nuclear magnetic resonance diagnostic apparatus are disposed facing each other with a predetermined interval above and below C; about their common axis. Related devices such as gradient magnetic field generating means and high frequency signal transmitting/receiving means are omitted and not shown. Magnetic shield members 2A and 2B made of a ferromagnetic material such as iron are provided to surround the entire device including electromagnets IA and 1B.

Problems to be Solved by the Invention In Figure C, the lines of magnetic force outside the electromagnets form a curved line centered around the axes of the electromagnets IA and IB. Specifically, there are few lines of magnetic force in the direction perpendicular to the axis, that is, on the left and right sides of the two lateral magnetic shield members, and leakage magnetic fields are blocked. On the other hand, lines of magnetic force tend to remain in the direction parallel to the axis, that is, in the vertical direction of the two upper and lower magnetic shield members, and these lines of magnetic force are projected almost perpendicularly to the upper and lower magnetic shield members 2Bζ. Therefore, it is difficult to be blocked by these, and it is difficult to weaken the leakage magnetic field to a predetermined level (1. However, the increase in the weight of the magnetic shielding member is small, but the increase in the magnetic shielding effect is small (for example, even if the thickness is doubled, the magnetic shielding effect will not be doubled.) This may lead to an increase in overall weight, such as in hospitals (
;It may become a major obstacle during installation.

Means for Solving the Problems The present invention provides a magnetic shield member made of a ferromagnetic material that is provided parallel to the direction of the magnetic field (and surrounding the magnetic field to be shielded), and a planar coil that is perpendicular to the direction of the magnetic field and that surrounds the magnetic field to be shielded. This is a magnetic shielding device characterized in that it is disposed at both ends of a magnetic field to be generated.

A ferromagnetic material is a material that has a strong property of becoming magnetized when placed in a magnetic field, and is, for example, an iron-based material.

The magnetic shielding member, which is provided parallel to the axial direction of the working electromagnets IA and IB, has its longitudinal direction parallel to the lines of magnetic force over a long section, so that the magnetic field l: effectively reduces the leakage magnetic field in the perpendicular direction. cut off. On the other hand, the two planar coils provided perpendicularly to the direction of the magnetic field cancel out the leakage magnetic field in the direction parallel to the magnetic field, thereby blocking the leakage magnetic field.

Example ■ Fig. 7 e: Example shown: In the case of the title magnet IA,
Magnetic shielding member 2B installed above and below IB
Although it has a disk-like shape, it may also have a donut-like shape with a hole in the center.

The main determining factor for this geometry is, for example in the case of a nuclear magnetic resonance diagnostic apparatus, the required magnetic field homogeneity inside the electromagnets IA, IB. The planar coil 3 is located above and below the electromagnets IA and IB.

The axis 1 of 1B is arranged in two perpendicular planes. It is desirable that the shape of the planar coil 3 match the shape of the magnetic shielding member 2B, but there is no problem even if the shape is slightly deviated.

Planar coil 36: is electromagnet IA.

A current is applied to create a magnetic field that cancels the magnetic field created by IB above and below it.

By doing this, leakage magnetic fields above and below the electromagnets IA and IB are blocked.Furthermore, the planar coil 3 forms a magnetic field parallel to the magnetic shielding member 2B in its vicinity.

This magnetic field increases the number of lines of magnetic force passing through the inside of the magnetic shielding member 2B, further increasing the magnetic shielding effect.

■ Fig. 2 shows an example. The planar coil 3 is arranged on the electromagnet IA, IB side of the magnetic shielding member 2B, that is, on the inside 4:. The current flowing through the planar coil 3 is in the opposite direction (magnetic flow) to that in the case (■). This direction is the direction that increases the number of magnetic lines of force inside the magnetic shielding member 2B as in the case (■). Similarly, it is possible to increase the number of magnetic lines of force passing through the inside, and as a result, increase the magnetic shielding effect and block the leakage magnetic field.However, the planar coil 3 alone is located above the axis of the electromagnet IA%IB: Since the formed magnetic field is in the same direction as the leakage magnetic field of the electromagnets IA and IB, there is no effect of canceling the magnetic field, and therefore the obtained magnetic shielding effect is inferior to the case (2).

■ Fig. 3 shows an example. The planar coil 3 is arranged in the same manner as in ■■. The shape is preferably an annular shape, but it does not necessarily have to be an annular shape; for example, the shape of the two magnetic shielding members may be matched to the shape seen from the axial direction of the electromagnets IA and IB. 4: Let a magnetic current flow through the planar coil 3 in the same way as in ■. By doing this 42, the electromagnet IA,
The leakage fields above and below the IB are canceled out.

Effect The present invention has a cooperative effect (
Therefore, the magnetic shielding effect is remarkable, and for example, in nuclear magnetic resonance diagnostic equipment, leakage magnetic fields can be effectively blocked. Therefore, the negative effects of leakage magnetic fields outside the system can be significantly reduced, and the overall weight of the equipment can be reduced, making it suitable for hospitals. This has the effect of reducing the burden placed on the constituent materials of buildings such as.

[Brief explanation of the drawing]

FIG. 7 is a schematic sectional view of an embodiment of the present invention, FIG. 2 is a schematic sectional view of another embodiment, FIG. 3 is yet another schematic sectional view, and FIG.
The figure is a schematic cross-sectional view showing an example of a conventional magnetic shielding device. 1-...Electromagnet, 2...Magnetic shielding member, 3...
Planar coil patent applicant Asahi Kasei Industries, Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A magnetic shielding member made of a ferromagnetic material is provided parallel to the direction of the magnetic field and surrounding the magnetic field to be shielded,
A magnetic shielding device characterized in that planar coils are arranged perpendicular to the direction of the magnetic field and at both ends of the magnetic field to be shielded.