JP4771851B2 - Magnetic shield device - Google Patents

Description

  The present invention relates to a magnetic shield device, and more specifically to a magnetic shield device having an opening for a door or a window.

  For example, an apparatus using a strong magnetic field such as an MRI apparatus or an apparatus using a large current is used with a magnetic shield so as not to leak the generated magnetic field to the outside. In addition, there is a need for a magnetic shield in order to avoid the influence of a precision measuring device or the like due to a magnetic field entering from the outside. Conventionally, in order to reliably perform magnetic shielding, a structure in which a magnetic field generation source or a portion where an external magnetic field is to be shielded is sealed with a magnetic material such as a steel plate has been employed. However, the sealed structure has a problem regarding heat dissipation or maintenance. In addition, when a shield room such as an MRI room in a hospital has a sealed structure, there is a case where a person entering the room is given a feeling of pressure. In recent years, there has been a proposal of an open type magnetic shield device that does not have a sealed structure but magnetically shields magnetic bodies by arranging them in a comb shape (see Patent Document 1).

However, a door that can be opened and closed by providing an opening in a magnetically shielded room, whether it is a sealed structure or an open structure, for the entry and exit of people and things, as well as for monitoring and maintenance. Or it is necessary to provide a window. In this case, since there is an air gap between the door and the device, the magnetic resistance to the magnetic flux flowing through the magnetic shield device increases, which may hinder the flow of magnetic flux and increase the leakage magnetic flux. Therefore, there is a need for a door or window having a structure that generates as little leakage flux as possible. However, the conventionally proposed door for magnetic shielding has a complicated structure and has not been a structure for mass production (see Patent Documents 2 and 3).
JP 2002-164686 A JP-A-8-78878 Japanese Patent Laid-Open No. 6-21680

  In view of the above problems, an object of the present invention is to provide a magnetic shield device that prevents a decrease in shielding performance due to an opening while having a simple structure.

In order to achieve the above object, a magnetic shield device according to the present invention is provided with a main body composed of a first magnetic shield member made of a grain-oriented electrical steel sheet configured in an interdigital shape, and provided in the main body . An opening portion surrounded by a mounting frame to which an end of the grain-oriented electrical steel sheet configured in the interdigital shape of the magnetic shield member is fixed, and the grain- oriented electrical steel sheet configured in an interdigital shape that magnetically shields the opening portion A second magnetic shield member that can be opened and closed, and the mounting frame is made of an electromagnetic steel plate having a laminated surface parallel to the opening surface of the opening, and is shaped like the interdigital transducer of the first magnetic shield member. the Rukoto to have a size capable of circulating the magnetic flux flowing from the end of the configured oriented electrical steel sheet caught and characterized.

  Further, the electrical steel sheet constituting the mounting frame may be a directional electrical steel sheet, and an easy axis of magnetization of at least a part of the electrical steel sheet may be in a direction around the opening. May be arranged in the direction of turning around.

  Furthermore, the openable / closable second magnetic shield member disposed in the opening can be a door or a window.

  For example, when a door is provided in the magnetic shield device, the magnetic flux flowing into the door can be captured and circulated by reducing the leakage magnetic flux by configuring the mounting portion surrounding the opening where the door is disposed as described above. Can be made. In particular, it is possible to further reduce the leakage magnetic flux by aligning the easy magnetization axis of the grain-oriented electrical steel sheet with the direction of circling the door.

  Hereinafter, embodiments of the present invention will be described by analysis by simulation with reference to the drawings. FIG. 1 shows an analysis model for analyzing the shield of the door 20 of the open type magnetic shield apparatus 10. The body of the magnetic shield device 10 as an analysis model is a cube having a side of 900 mm, and an opening of 200 mm in width and 300 mm in length is provided in the center of one surface at a place 200 mm from the bottom, and the mounting frame 11 is provided around the opening. The door 2 is attached to the attachment frame 11 so that it can be opened and closed. Further, all the faces of the hexahedron are configured in a comb shape or a blind shape by arranging a large number of grain-oriented electrical steel sheets at intervals. The analysis region was a quarter S of the device surrounded by the alternate long and short dash line.

  FIG. 2 shows an open type magnetic shield device 10 of FIG. 1 cut out by a one-dot chain line. As shown in FIG. 2, the magnetic shield device 10 shields a magnetic field from a magnetic field generator modeled by a coil 14 having an iron core 13. This analysis model assumes, for example, a shield room in a hospital where an MRI apparatus is arranged. In this example, the longitudinal directions of a number of grain-oriented electrical steel sheets are arranged so as to be aligned with the easy axis direction and coincide with the direction of the magnetic field generated by the coil 15.

  In FIG. 3, the door part contained in an analysis area is expanded and shown. A mounting frame 11 is provided around the opening of the magnetic shield device 10 in which a large number of grain-oriented electrical steel sheets 17 are formed in a comb shape. A door 20 including a door frame 21 and a door interior 22 is attached to the mounting frame 11 and disposed in the opening. An interdigital magnetic steel plate 17 is fixed to the side plate 111 of the mounting frame 11. Magnetic flux from the magnetic field generator (coil 14) circulates in the interdigital magnetic steel sheet 17 and flows into the mounting frame 11 from the side plate 111. Here, the gap existing between the mounting frame 11 and the door frame 21 is set to 1 mm. For the actual door opening and closing, the gap between the mounting frame 11 and the door frame 21 needs to be at least 1.7 mm. However, for the analysis, it is sufficient to have a gap, and the gap is set to 1 mm.

  FIG. 4 shows a dimensional relationship between the mounting frame 11 and the door 20 in the analysis region. The mounting frame 11 has a width of 25 mm and a thickness of 6 mm. The door frame 21 of the door 20 has a width of 25 mm and a thickness of 6 mm corresponding to the mounting frame 11, and a gap between the mounting frame 11 and the door frame 21 is 1 mm. Nine directional electromagnetic steel plates 23 are arranged on the door frame 21 with an interval of 24 mm to form a door interior 22. The grain-oriented electrical steel sheet 23 is 1 mm thick.

  FIG. 5 is a diagram for explaining the grain-oriented electrical steel sheet used in the present embodiment. A grain-oriented electrical steel sheet is obtained by laminating a plurality of thin sheets 31 of a magnetic steel sheet having a reduced thickness and improved magnetism, and having directionality, and each thin plate 31 is provided with an insulating film 33 for performing interlayer insulation. Has been. The grain-oriented electrical steel sheet of the present embodiment is obtained by laminating thin plates 31 having an insulating film 33. Hereinafter, as shown in the figure, the lamination direction is Lami, the easy magnetization axis direction is L, the direction perpendicular to the easy magnetization axis in the plane of the steel sheet, that is, the hard magnetization axis is indicated by C, and the surface on which the insulating film is applied is laminated. It is called a surface.

  As described above, the present invention is based on the knowledge that the magnetic field that is not captured by the magnetic shield device leaks to the outside of the shield device. The inflowing magnetic flux is caused to flow around the opening as much as possible. In the magnetic shield device 10 shown in FIGS. 1 and 2, the magnetic flux flowing into the door 20 is captured by the mounting frame 11 and is caused to circulate around the door portion. In the present embodiment, the mounting frame 11 and the door frame 21 are formed of directional electromagnetic steel plates, and the respective directional electromagnetic steel plates are arranged as in a pattern A shown in FIG.

  In the pattern A, the laminating direction Lami of the directional electromagnetic steel sheets used for the mounting frame is a direction orthogonal to the wall surface, that is, the opening plane on which the door is arranged, in other words, the laminated surface of the directional electromagnetic steel sheets is parallel to the opening surface. It is arranged to be. Moreover, it is comprised so that the magnetization easy axis | shaft L of a grain-oriented electrical steel plate may come to the longitudinal direction of the attachment frame 11. FIG. This arrangement is expected to improve the trapping property of the magnetic flux from the interdigital magnetic steel sheet of the magnetic shield device by the mounting frame and to allow the mounting frame 11 to circulate the magnetic flux.

  In order to confirm this, as a comparative example, analysis was performed together with patterns B and C shown in FIGS. In FIG. 6, only the side plate 111 and the upper plate 112 are shown for the mounting frame 11, but the right side plate in the drawing (not shown) is the same as the side plate 111, and the lower plate (not shown) is the same as the upper plate 112. .

  The attachment frame 11 of the pattern B is the same as the pattern A in that the easy magnetization axis L of the directional electromagnetic steel sheet is arranged in the longitudinal direction of the attachment frame 11. Therefore, the improvement of the circulation property of the magnetic flux captured by the mounting frame can be expected. However, the laminating direction Lami of the grain-oriented electrical steel sheets is the vertical direction in the upper and lower portions of the mounting frame 21 and is in the left-right direction in the left and right portions of the mounting frame 21. That is, the laminated surface of the grain-oriented electrical steel sheets used is orthogonal to the opening plane.

  With respect to the mounting frame 11 of the pattern C, any part of the mounting frame 11 on the top, bottom, left and right is composed of a magnetic steel sheet having a stacking direction in the vertical direction. That is, the laminated surface is horizontal and is therefore orthogonal to the opening surface. Looking at the left and right portions of the mounting frame 11 connected to the interdigital magnetic steel sheet of the magnetic shield device, the easy magnetization axis L is horizontal, and in the same direction as the easy magnetization axis L of the interdigital magnetic steel sheet of the magnetic shield device. It has become. This is expected to satisfactorily capture the magnetic flux flowing from the interdigital magnetic steel sheet of the magnetic shield device in the mounting frame.

  The door frame 21 is common to the patterns A to C because the door frame 21 is arranged through the gap from the mounting frame 11 and is considered to contribute less to capturing the magnetic flux. Specifically, like the pattern C, any part of the door frame 21 is composed of a grain-oriented electrical steel sheet having a horizontal laminated surface.

  FIG. 7 is a plan view showing a calculation region K for analysis of the magnetic shield device 10, and the calculation region K is set so as to include the analysis region S of the magnetic shield device 10. As shown in the figure, the x axis and the y axis are set, and (x, y) = (0, 0) is set at the center of the magnetic shield device. The calculation of the leakage magnetic field distribution is as follows: (1) y-axis (x = 0), magnetic field relative to the distance from the door 20, (2) x-axis (y = 0), wall surface (the magnetic field generator inside the apparatus is an MRI apparatus) If so, the magnetic field with respect to the distance from the gantry direction wall), (3) the point P on the road passing through the points P, Q, and R in the figure separated from the apparatus wall surface in the analysis region 7 by a predetermined distance (100 mm). Magnetic field with respect to distance from.

  8 to 10 show the analysis results. FIG. 8 shows a case where the magnetic flux density with respect to the distance from the door wall surface is plotted when x = 0 in the case of (1) above. Here, when the attachment portion and the door frame are set to the pattern A, the thick solid line is used, the pattern B is the one-dot chain line, and the pattern C is the two-dot chain line. Furthermore, as Reference Example 1, the leakage magnetic field distribution of a magnetic shield device in which both the mounting frame 11 and the door frame 12 are formed of solid iron SS400 is indicated by a broken line, and as Reference Example 2, the leakage of a magnetic shield device having no opening is shown. The magnetic field distribution is shown by a thin solid line.

  As apparent from the figure, the leakage magnetic field of the pattern A shows a low value that does not change from that without the opening, and the magnetic shielding device has a very high magnetic field shielding capability. On the other hand, the patterns B and C are worse than Reference Example 1 in which no electromagnetic steel sheet is used.

  FIG. 9 shows the magnetic flux density plotted against the distance from the wall surface when y = 0 in the case of (2) above. Also in this case, the same result as in FIG. 8 is shown, and the leakage magnetic field adopting the pattern A is the same as that without the opening.

  FIG. 10 is the case of (3) above, and the magnetic flux density is plotted along the path of P → Q → R. Also in this case, the same results as in FIGS. 8 and 9 are shown, and the superiority of the magnetic shield of the pattern A door portion can be seen.

  According to this analysis result, the magnetic shielding effect differs greatly depending on how the laminated surfaces of the electromagnetic steel sheets are arranged with respect to the flowing magnetic flux. In the pattern B, the side plate 111 of the mounting frame 11 against which the interdigital magnetic steel plate of the magnetic shield device abuts is laminated so that the magnetic steel plate constituting the side plate 111 is orthogonal to the direction in which the magnetic flux flows. That is, the laminated surface of the side plate 111 is orthogonal to the flow of magnetic flux, and hinders the flow of magnetic flux. Therefore, the magnetic flux cannot flow into the mounting frame 11, and the leakage magnetic field increases.

  Further, in the pattern C, unlike the pattern B, the magnetic flux easily flows into the side plate 111 of the mounting frame 11, but the laminated surface is arranged so as to prevent the flow of magnetic flux in the vertical direction passing through the side plate 111. Therefore, the magnetic flux that has flowed in cannot flow around the mounting frame 11, and the leakage magnetic field also increases.

  In the pattern A according to the present embodiment, the laminated surface is arranged in parallel to the opening surface and does not hinder the flow of magnetic flux. Therefore, the magnetic flux easily flows and further circulates around the mounting frame 11. Flowing.

  FIG. 11 is a diagram showing an outline of the magnetic characteristics of the material used for the magnetic shield. In the figure, B-H curves are shown for L, C, Lami and solid iron Fe of grain-oriented electrical steel sheets. As can be seen from the figure, even with the hard-to-magnetize axis C of the grain-oriented electrical steel sheet, the magnetic properties are better than the solid iron Fe. Although it is L, the directionality electrical steel plate which changed the direction of C and L so that the longitudinal direction may be set to C about the part, for example, the side plate 111 may be used. Furthermore, the magnetization difficult axis C of all the attachment frames 11 may be oriented in the circumferential direction of the attachment frame 11. Further, the mounting frame 11 may be made of a non-oriented electrical steel sheet instead of the directional electrical steel sheet. However, the laminated surface of the non-oriented electrical steel sheet needs to be arranged in parallel to the opening surface.

  The mounting frame 11 is preferably configured to allow all the magnetic flux flowing into the mounting frame 11 to flow so that there is no leakage magnetic field. In other words, the mounting frame 11 has a size that can secure a passage that allows a magnetic flux flowing through a portion corresponding to the opening to flow in a state where there is no opening in which the door is disposed. In the case of the present embodiment, referring to FIG. 3, the magnetic flux flowing into the mounting frame 11 is 13 sheets of 1 mm thick electromagnetic steel plates 17 constituting the magnetic shield device, that is, 13 mm. On the other hand, since the thicknesses of the upper plate and the lower plate of the attachment frame 11 are 6 mm each, the total is 12 mm, and almost all the magnetic flux flowing into the attachment frame 11 can be captured and circulated by the attachment frame 11. It was a size. Here, if the thicknesses of the upper plate and the lower plate of the mounting frame 11 are 6.5 mm or more, a better magnetic shield can be achieved.

  In the present embodiment, an open type magnetic field shield device using an interdigital magnetic steel sheet is adopted, but it is needless to say that it can be applied to a closed type magnetic field shield device.

It is a figure which shows schematic shape of the magnetic shielding apparatus of this embodiment. It is a figure which notches and shows a part of magnetic shield apparatus of FIG. It is a figure which expands and shows the door vicinity of a magnetic shielding apparatus. It is a figure which shows the analysis object part of the attaching part and door of a magnetic shield apparatus. It is a figure explaining a grain-oriented electrical steel sheet. (A) is a figure which shows the attachment frame which is embodiment of this invention, (b), (c) is a figure which shows the attachment frame which is a comparative example. It is a top view which shows the area | region which calculates a leakage magnetic field. It is a graph (the 1) which shows the calculation result of a leakage magnetic field. It is a graph (the 2) which shows the calculation result of a leakage magnetic field. It is a graph (the 2) which shows the calculation result of a leakage magnetic field. It is the schematic which shows the magnetic characteristic of a magnetic shielding material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Magnetic shield apparatus 11 (Door) attachment part 111 Side plate of attachment part 112 Upper plate of attachment part 13 Iron core 14 Coil 17 Directional electrical steel sheet of shield device 20 Door 21 Door frame 22 Inside door 23 Directional electrical steel sheet 31 inside door Laminated thin plate of grain-oriented electrical steel sheets 32 Insulating film S Analysis area K Calculation area

Claims (6)

Interdigital to provided in the body and body made of a first magnetic shielding member made of a configured oriented electrical steel sheet, the edge of the interdigital the configured oriented electrical steel sheet of the first magnetic shield member An opening surrounded by a mounting frame with a fixed part;
A magnetic shield for the opening, and a second magnetic shield member that is openable and closable made of a grain-oriented electrical steel sheet ,
The mounting frame is made of an electromagnetic steel plate having a laminated surface parallel to the opening surface of the opening, and receives a magnetic flux flowing from an end portion of the grain-oriented electrical steel plate formed in the interdigital shape of the first magnetic shield member. magnetic shield and wherein the Rukoto to have a size capable of circulating caught and.   The magnetic shield device according to claim 1, wherein the electrical steel sheet constituting the mounting frame is a grain-oriented electrical steel sheet.   3. The magnetic shield device according to claim 2, wherein an easy magnetization axis of at least a part of the electromagnetic steel sheets constituting the mounting frame is in a direction around the opening. The magnetic shield device according to claim 3 , wherein easy axes of magnetization of the electrical steel sheets constituting the mounting frame are aligned in a direction around the opening. The magnetic shield device according to any one of claims 1 to 4 , wherein the second magnetic shield member that can be opened and closed arranged in the opening is a door. Said opening is disposed on the openable and closable a second magnetic shield member, the magnetic shielding apparatus according to any one of claims 1 to 4, characterized in that a window.

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