JP2003152380A - Magnetic shielding case - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light and inexpensive magnetic shielding case having excellent shielding performance. SOLUTION: While openings 22 of a first case section made of a soft magnetic material and a second case section 21 made of a conductive material and electrically integrated communicate each other, either of the first case section and second case section 21 covers the other. When an AC magnetic field 23 is applied from a direction where a flux goes toward the opening 22, a laminar eddy current 24 to the opening 22 is induced at the second case section 21. The direction of a secondary magnetic field 25 generated by the eddy current 24 is opposite to that of the magnetic field 23, thus effectively canceling the magnetic field 23 inside the magnetic shielding case.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield case for enclosing a device to be magnetically shielded.

[0002]

2. Description of the Related Art When a device using an electron beam such as a cathode ray tube is exposed to an unnecessary magnetic field from the outside, a Lorentz force is applied to the electron beam and the beam trajectory deviates from a regular trajectory. When the unnecessary magnetic field from the outside is an AC magnetic field, a disturbance such as image shake occurs. Further, in an electronic device or the like that handles a minute signal, induction noise induced by an unnecessary external magnetic field may be a problem. Therefore,
In order to avoid these obstacles, a magnetic shield case surrounding a target device has been conventionally used.

11 (a) and 11 (b) show a conventional example of such a magnetic shield case. This magnetic shielding case 1
1 is made of a material having a high magnetic permeability such as iron, silicon steel, permalloy, and amorphous metal, that is, a soft magnetic material,
The cathode ray tube 12 and various electronic devices 13 shown in FIG. 11C are inserted into the magnetic shield case 11. In order to operate the switches and knobs of the cathode ray tube 12 and the electronic device 13 and to visually check the display surface of the cathode ray tube 12 and the display panel portion of the electronic device 13, at least one of the pair of opposing surfaces of the magnetic shielding case 11 is to be seen. One is the opening 14,
As shown in FIGS. 11 (a) and 11 (b), the magnetic shielding case 11 is a four-sided or five-sided case.

Since the magnetic resistance of the soft magnetic material forming the magnetic shield case 11 is low, the magnetic shield case 11 becomes the magnetic circuit 15 when a magnetic field is applied to the magnetic shield case 11 from the outside. Then, as shown in FIG. 12A, when a magnetic field is applied from the direction in which the magnetic flux 16 strikes the wall surface of the magnetic shield case 11, most of the magnetic flux 16 passes through the thickness of the magnetic shield case 11. . As a result, the applied magnetic field is weakened inside the magnetic shield case 11, and the cathode ray tube 12
The electronic device 13 is less affected by the applied magnetic field.

However, as shown in FIG. 12B, when a magnetic field is applied from the direction of the magnetic flux 16 toward the opening 14, the opening 14 becomes a gap of the magnetic circuit 15 and the magnetic circuit 15 is formed. Increase the magnetic resistance of. As a result, the magnetic flux 16 easily enters the inside of the magnetic shielding case 11, and the cathode ray tube 12 and the electronic device 13 are greatly affected by the applied magnetic field. In other words, in the magnetic shield case 11, the applied magnetic field inside is not effectively weakened and the shield performance is not high, especially when the magnetic field is applied from the direction in which the magnetic flux 16 is directed to the opening 14.

On the other hand, in recent years, the resolution and size of color television receivers and color monitor devices in which the cathode ray tube 12 is used have been increasing, and electronic devices 1
Higher accuracy of 3 is also progressing. Therefore, the cathode ray tube 12 and the electronic device 13 are more sensitive to magnetism, and the magnetic shielding case 11 is also required to have higher shielding performance. On the other hand, the only way to improve the shielding performance of the magnetic shielding case 11 is to increase the thickness of the magnetic shielding case 11.

[0007]

However, as mentioned above,
Since the opening 14 serves as a gap of the magnetic circuit 15 to increase the magnetic resistance of the magnetic circuit 15, it is difficult to effectively enhance the shielding performance. In such a case, in order to obtain the required shielding performance, the required thickness of the magnetic shielding case 11 is considerably increased, and the required amount of the soft magnetic material is also increased. As a result, the weight of the magnetic shielding case 11 becomes heavy and the price also increases. Therefore, an object of the present invention is to provide a magnetic shielding case which has high shielding performance, is lightweight, and is inexpensive.

[0008]

In a magnetic shielding case (FIG. 1) according to claim 1, a first case portion (not shown) made of a soft magnetic material and a second case portion 2 made of a conductive material.
One of the first case portion 21 and the second case portion 21 covers the other in a state in which the opening portions 22 and 1 communicate with each other. Therefore, even if the device to be magnetically shielded is surrounded by the magnetic shield case, the target device can be operated and viewed through the opening 22 of the first case part 21 and the second case part 21. , Do not hinder the use of the target device.

Since the second case portion 21 is electrically integrated, a layered electric closed circuit is formed with respect to the opening portion 22. Therefore, when an alternating magnetic field 23 is applied from the direction in which the magnetic flux is directed to the opening 22, a layered eddy current 24 is induced in the opening 22 by electromagnetic induction. Secondary magnetic field 2 generated by this eddy current 24
Since the direction of 5 is opposite to that of the applied magnetic field 23,
Even if the thickness of the magnetic shield case is not increased, the applied magnetic field 23 is effectively canceled inside the magnetic shield case particularly when the magnetic field 23 is applied from the direction of the magnetic flux toward the opening 22. .

Moreover, since the conductive material forming the second case portion 21 is generally cheaper than the soft magnetic material forming the first case portion, the material of the magnetic shield case is used. The cost is low. Further, if the second case portion 21 is used as a reinforcing material for maintaining the shape of the first case portion, the magnetic permeability of the first case portion is lowered by the internal stress due to the own weight of the first case portion itself. This can be prevented, and the applied magnetic field inside the magnetic shield case can be more effectively canceled.

There may be a gap between the first case portion and the second case portion 21 in a state where one covers the other. Further, the length of the second case portion 21 does not need to be the same as the length of the first case portion in the direction of penetrating the opening portion 22, and for example, the plurality of annular second case portions 21 may be the same as those described above. They may be sequentially arranged in the direction. Further, as the soft magnetic material, amorphous metal, permalloy, silicon steel, iron and a composite material in which these are combined are suitable, and as the conductive material, aluminum, aluminum alloy, copper, copper alloy and the like are suitable.

In the magnetic shielding case according to claim 2 (FIG. 2), at least a part of the pair of facing parts of the second case part 26 facing the opening 27 is the blocking part 2.
It is 8. Therefore, at least one of the openings 2
When an AC magnetic field 31 is applied from the direction in which the magnetic flux abuts a portion other than the pair of facing portions which are 7 in FIG. 7, an eddy current 32 is induced in the electrically closed circuit including the above-mentioned blocking portion 28 by electromagnetic induction. To be done. The direction of the secondary magnetic field 33 generated by the eddy current 32 is opposite to the direction of the applied magnetic field 31.

As a result, the magnetic field 31 is applied not only when the magnetic field is applied from the direction toward the opening 27 but also from the direction in which the magnetic flux strikes a portion other than the pair of facing portions, at least one of which is the opening 27. Is also applied, the applied magnetic field 31 is effectively canceled inside the magnetic shield case.

There may be a gap between the first case portion and the second case portion 26 in a state where one covers the other. Further, among the pair of facing portions of the second case portion 26, at least a portion of the portion facing the opening portion 27 may be the closing portion 28, so that a portion of this portion is the opening portion. May be. Further, as the soft magnetic material, amorphous metal, permalloy, silicon steel, iron and a composite material in which these are combined are suitable, and as the conductive material, aluminum, aluminum alloy, copper, copper alloy and the like are suitable.

In the magnetic shield case according to claim 3 (FIG. 3), the peripheral edge portion 3 of the opening 35 in the second case portion 34 is
The thickness of 6 is thicker than the thickness of the portion other than the peripheral portion 36. Therefore, the peripheral portion 36 has a large cross-sectional area and low electric resistance, and a large amount of eddy current 38 is induced in the peripheral portion 36 by electromagnetic induction by the applied magnetic field 37. As a result, the secondary magnetic field 41 generated by the eddy current 38 also increases, and the applied magnetic field 37 is effectively canceled inside the magnetic shield case near the opening 35.

It is preferable that the thickness of the peripheral edge portion 36 of the opening 35 in the second case portion 34 is twice or more than the thickness of the portion other than the peripheral edge portion 36. Further, in order to increase the thickness of the peripheral edge portion 36, the thickness of the second case portion 34 itself may be increased, or a member other than the second case portion 34 may be attached.

In the magnetic shielding case according to claim 4 (FIG. 4), the second case portion 42 made of a conductive material has a first case portion 43 made of a soft magnetic material and a third case portion (not shown). ) And is sandwiched between. Therefore, as shown in FIG. 4A, an AC magnetic field 44 parallel to the wall surface of the magnetic shield case is applied from the outside, and is generated by the magnetic field 45 from the magnetized wall surface of the first case portion 43. An eddy current is induced in the second case portion 42 by electromagnetic induction, and the applied magnetic field 44
Even if a magnetic field 46 in the same direction as is generated by the eddy current, this magnetic field 46 is shielded by the third case portion, and the magnetic field 46 generated due to the applied magnetic field 44 is further generated inside the magnetic shield case. Effectively canceled.

As shown in FIGS. 4 (b) and 4 (c), when an AC magnetic field 47 perpendicular to the wall surface of the magnetic shield case is externally applied, the second case portion is caused by electromagnetic induction. An eddy current 48 is induced in 42, and the direction of the secondary magnetic field 51 generated by this eddy current 48 is opposite to the direction of the applied magnetic field 47. Moreover, the secondary magnetic field 51 also magnetizes the first case portion 43, and the magnetic field 5 caused by this magnetization is generated.
The direction of 2 is also opposite to the direction of the applied magnetic field 47. Therefore, in this case, the applied magnetic field 47 is canceled in the magnetic shield case only in the first case part 43 and the second case part 42, but there is no problem even if the third case part is provided. Does not happen.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, first to third embodiments of the invention of the present application applied to a magnetic shield case for a 32-inch wide television receiver and conventional examples for comparison with these embodiments will be described. , 5 to 10 and FIG. 13. FIG. 13 shows a conventional example for comparison. The conventional magnetic shield case 11 is a four-sided case formed of a sheet having a thickness of 3 mm and made of an amorphous alloy which is a soft magnetic material. In both the conventional magnetic shield case 11 and the magnetic shield cases of the first to third embodiments described later, the width W is 880 mm and the height H is 580 mm.
mm, depth D is 600 mm.

FIG. 5 shows a first embodiment. In the magnetic shield case 53 of the first embodiment, a thickness of 4 mm made of aluminum which is a conductive material is provided inside a case portion 54 similar to the magnetic shield case 11 shown in FIG.
The four-sided case portion 55 formed from the sheet is inserted. Since the processing from the sheet to the four surfaces for forming the case portion 55 is performed by welding, the case portion 5
5 is electrically integrated. FIG. 6 shows a second embodiment. In the magnetic shield case 56 of the second embodiment, a case portion 58 formed by welding a back plate 57 made of aluminum and having a thickness of 4 mm to the case portion 55 shown in FIG.
Is inserted inside the case portion 54.

FIG. 7 shows an evaluation device for the magnetic shield cases 53 and 56 of the first and second embodiments. In this evaluation device 61, three Helmholtz coils 62 each composed of a square coil of 2 m square are arranged in a cubic frame shape, and a 32 type wide television receiver 63 in which magnetic shielding cases 53 and 56 are mounted is provided. It is arranged at the center of the evaluation device 61.

Table 1 below is measured at the centers of the magnetic shield cases 53 and 56 when an AC magnetic field having a magnetic flux density of 3 μT and a frequency of 50 Hz is separately applied to the Helmholtz coil 62 in the front-rear direction, the left-right direction and the up-down direction. Shows the magnetic flux density. From this Table 1, the magnetic shielding case 1 of the conventional example
It can be seen that the magnetic shielding case 53 of the first embodiment is improved in the shielding performance particularly in the front-back direction as compared with 1.
It can be seen that the magnetic shielding case 56 of the second embodiment has improved shielding performance in all directions.

[0023]

[Table 1]

By the way, as shown in FIG. 8, in the cathode ray tube 12 which is a kind of equipment to be magnetically shielded by the magnetic shield case 11, the flight distance of the electron beam 64 when scanning the central portion of the display surface. The flight distance of the electron beam 65 when scanning the edge of the display surface is longer than that. For this reason,
Magnetic shielding case 1 even if the magnetic field applied from the outside is uniform
The shielding performance in the vicinity 66 of the peripheral edge of the opening 14 on the front side of 1 greatly affects the obstacle of the cathode ray tube 12.

FIG. 9 shows a third embodiment for alleviating this obstacle. Magnetic shielding case 6 of the third embodiment
In FIG. 7, a case 71 formed by welding a 4 mm-thick rear plate 68 made of aluminum to the case 55 shown in FIG. 5 is inserted inside the case 54. However, in order to dissipate heat from the cathode ray tube 12, the lower and upper sides of the back plate 68 have openings 7 having a height of 150 mm and 100 mm, respectively.
It is 2.

The cathode ray tube 12 of the television receiver
In particular, an obstacle is liable to occur especially in the vertical magnetic field applied from the outside, but if an opening is provided for heat dissipation of the cathode ray tube 12, the left side and the right side of the back plate are more open. Also, when the lower side and the upper side of the back plate 68 are the openings 72, a horizontal current effective for shielding the vertical magnetic field is sufficiently induced in the back plate 68.

Further, in the magnetic shield case 67, a four-sided case portion 73 having a depth of 100 mm and formed of a sheet made of aluminum and having a thickness of 10 mm is attached inside the opening portion on the front surface side of the case portion 71. . Therefore,
The thickness of the peripheral portion of the opening on the front surface side of the case portion 71 is substantially thicker than the thickness of the portion other than the peripheral portion by 10 mm, and a large amount of eddy current is induced in the peripheral portion by electromagnetic induction. Furthermore, the thickness of the amorphous alloy is 3 mm
A four-sided case portion 74 having a depth of 200 mm formed from the sheet is inserted inside the opening on the front surface side of the case portion 73.

FIG. 10 shows the magnetic shield case 56 of the second embodiment shown in FIG. 6 and the magnetic shield case 67 of the third embodiment shown in FIG. The magnetic flux density measured in the horizontal cross section at the center in the height direction of the magnetic shielding cases 56 and 67 when applied in the vertical direction by the coil is shown. From FIG. 10, the opening 7 on the front side of the magnetic shielding case 67 is compared with the peripheral portion 76 of the opening 75 on the front side of the magnetic shielding case 56.
It can be seen that the shielding performance in the peripheral edge portion 78 of 7 is improved.

In any of the above first to third embodiments, the magnetic shielding cases 53, 56, 67 have a rectangular tubular shape or one of the openings is closed. The magnetic shielding case may have a shape different from the above shape, for example, a cylindrical shape, a truncated pyramid cylinder shape, a truncated cone cylinder shape, or a shape in which one of the openings is closed.

[0030]

In the magnetic shield case according to the first aspect of the present invention, even if the magnetic field is not thickened, especially when the magnetic field is applied from the direction of the magnetic flux toward the opening, the applied magnetic field shields the magnetic field. It is effectively canceled inside the case, and the material cost of the magnetic shield case may be low. Therefore, it has high shielding performance, is lightweight, and is inexpensive.

In the magnetic shield case according to the second aspect, not only when the magnetic field is applied from the direction toward the opening, but also in the part other than the pair of facing parts where at least one of the openings is the opening, Even when a magnetic field is applied from the abutting direction, the applied magnetic field inside the magnetic shield case is effectively canceled. Therefore, the shielding performance is higher.

In the magnetic shield case according to the third aspect, the applied magnetic field is canceled particularly effectively inside the magnetic shield case near the opening. Therefore, the shielding performance is higher.

In the magnetic shielding case according to the fourth aspect, even if an alternating magnetic field parallel to the wall surface is applied from the outside, the magnetic field generated due to the applied magnetic field is more effectively canceled inside the magnetic shielding case. Be done. Therefore, the shielding performance is higher.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a main part of a magnetic shielding case corresponding to claim 1 of the present invention.

FIG. 2 is a partially cutaway perspective view of a main part of a magnetic shielding case corresponding to claim 2 of the present invention.

FIG. 3 is a partially cutaway perspective view of an essential part of a magnetic shielding case corresponding to claim 3 of the present invention.

FIG. 4 shows an essential part of a magnetic shield case corresponding to claim 4 of the present invention, in which (a) is a cross-sectional view when a magnetic field parallel to the wall surface of the magnetic shield case is applied from the outside,
(B) is a perspective view when a magnetic field perpendicular to the wall surface of the magnetic shield case is applied from the outside, and (c) is a sectional view taken along the line cc in (b).

FIG. 5 is a perspective view of the first embodiment of the present invention.

FIG. 6 is a partially cutaway perspective view of a second embodiment of the present invention.

FIG. 7 is a perspective view of an evaluation device for a magnetic shielding case.

FIG. 8 is a cross-sectional view for explaining a problem when the device to be magnetically shielded is a cathode ray tube.

FIG. 9 is a partially cutaway perspective view of a third embodiment of the present invention.

FIG. 10 is a cross-sectional view showing the distribution of the magnetic flux density inside the magnetic shielding case, (a) in the case of the second embodiment of the present invention, and (b) in the case of the third embodiment of the present invention. Is.

FIG. 11 shows a conventional example of the invention of the present application, (a)
Is a partially cutaway perspective view of a four-sided magnetic shielding case, (b) is 5
FIG. 3C is a partially cutaway perspective view of the magnetic shielding case on the surface, and FIG.

FIG. 12 is a cross-sectional view for explaining the problem in one conventional example of the invention of the present application, where (a) is a case where a magnetic field is applied from the direction in which magnetic flux strikes the wall surface of the magnetic shielding case, and (b) is a diagram. This is the case where the magnetic field is applied from the direction in which the magnetic flux goes toward the opening.

FIG. 13 is a perspective view of a conventional example of the present invention.

[Explanation of symbols]

21 ... Case part (second case part), 22 ... Opening part, 2
6 ... Case part (second case part), 27 ... Opening part, 28
... Blocking portion, 34 ... Case portion (second case portion), 35 ...
Opening part, 36 ... Peripheral part, 42 ... Case part (second case part), 43 ... Case part (first case part), 53 ... Magnetic shielding case, 54 ... Case part (first case part), 55
... Case part (second case part), 56 ... Magnetic shield case, 57 ... Back plate (closed part), 58 ... Case part (second case part), 67 ... Magnetic shield case, 68 ... Back plate (closed) Part), 71 ... case part (second case part), 73 ... case part (peripheral part), 74 ... case part (third case part), 75, 77 ... opening part

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Claims (4)

[Claims] 1. A first case portion made of a soft magnetic material in which at least one of a pair of facing portions is an opening, and both a pair of facing portions are made of a conductive material. And an electrically integrated second case portion, and the first case portion and the opening portion of the first case portion and the second case portion are in communication with each other. A magnetic shielding case in which one side of the second case portion covers the other. 2. A first case portion made of a soft magnetic material in which at least one of a pair of facing portions is an opening, and one of the pair of facing portions is an opening and at least a part of the other is closed. And a second case part which is made of a conductive material and is electrically integrated with each other, and the openings of the first case part and the second case part communicate with each other. The magnetic shield case in which one of the first case portion and the second case portion covers the other in the state of being opened. 3. The magnetic shielding case according to claim 1, wherein a thickness of a peripheral portion of the opening in the second case portion is larger than a thickness of a portion other than the peripheral portion. 4. A third case part made of a soft magnetic material is provided, wherein at least one of the pair of facing parts is an opening part, and the first case part covers the second case part. The second case part covers the third case part in a state where the openings of the first, second and third case parts communicate with each other. The magnetic shielding case according to any one of items.