JPH0870196A - Electromagnetic wave shielding box - Google Patents

Abstract

PURPOSE: To make quite equal the positions of the magnetic shielding surfaces of an electromagnetic wave shielding box to those of the electrostatic shielding plates of the shielding box by a method wherein the shielding of an electromagnetic wave is broken down into a magnetic field shielding and an electric field shielding and the shielding effect in the respective single states of the magnetic field and electric field shieldings is analyzed. CONSTITUTION: The framework of a box is constituted of conductor rods 1, which respectively constitute a plane-shaped conductor loop, and a plurality of conductor rods having the same cut section as that of the rods 1. As magnetic shielding surfaces, which fulfill the most magnetic shielding effect, of the box are formed between the surfaces 40 on the outside of the framework of the box and a virtual surface surrounded with a group of straight lines, which pass through the centers of gravity of the cut surfaces of all the conductor rods, the fact that electrostatic shielding plates of the box are installed at the positions of the magnetic shielding surfaces is a characteristic, which is hitherto never contrived. Accordingly, the box has the characteristic of such an visual appearance as to say that the central parts, which are apart from the conductor rods of the framework, of the shielding plates are more recessed than parts, which are mounted to the framework by screws, of the shielding plates. By these means, the mulfunction of an equipment due to noise radio waves, which intrude into an equipment storing container, can be prevented from being generated.

Description

Detailed Description of the Invention

[0001]

[Industrial field of application] Normal electronic equipment storage containers, electronic control equipment storage containers, aircraft navigation-related electronic equipment storage containers, power equipment control circuit storage containers, etc.

[0002]

2. Description of the Related Art A box frame of a device storage container is mainly composed of a chevron-shaped steel or aluminum conductor bar, and an electronic device or the like is placed inside a box in which a copper plate or an aluminum plate is installed outside the frame. Stored in a single layer, or more devices are stored in multiple stages in a box, mechanically held and stored by a frame that remains in conduction with the box framework and its outer plates. ．

The energy of electromagnetic waves is divided into two energies, electric field and magnetic field. Therefore, in order to shield the electromagnetic waves, it is obvious that the invasion of both types of energy must be blocked.

Regarding the shielding of the electric field, if the outer side of the box is entirely covered with a steel plate or an aluminum plate as described above, the relaxation time at that time is extremely short, so that an electric field close to 100% is reached until an extremely high frequency is reached. A shielding effect can be expected.

On the other hand, with respect to the shielding of the magnetic field, since there is a minute gap between the conductor rod forming the frame of the box and the steel plate or the aluminum plate installed on the outside of the frame, the magnetic field that leaks and intrudes from there is present. It is not very well known that it must be blocked by current flowing in a loop of conductor rods made of a box framework.

The most lagging point in the prior art is that we do not understand the physical phenomenon in which there is a magnetic shielding surface that most effectively blocks the magnetic flux that enters the box due to the current flowing through the conductor loops of the framework. This is to allow the existence of essential defects in the structure of the electromagnetic shielding box made by the technology.
That is, these boxes have a structure in which the magnetic shield surface and the electrostatic shield surface, which effectively act, are present at positions separated from each other.

The energy of electromagnetic waves is always divided into electric field energy and magnetic field energy. If one of them decays, the energy is replenished from the other and the energies of both are immediately equalized. Due to the existence of such a physical phenomenon, the above-mentioned structure in which the two surfaces are separated is a defective structure, and the creation of a breakthrough technique for matching the two surfaces is straddling.

The effect of shielding electromagnetic waves by the prior art will be described with reference to examples. Electromagnetic waves try to enter the electromagnetic shielding box. Then, first, even if 100% electric field energy disappears on the external electrostatic shield surface, the magnetic field energy is preserved as it is, so the energy is equally divided inside the box and 1 / An electric field and a magnetic field have four energies. If the electromagnetic wave advances a little, it will reach the position where the magnetic shielding surface exists. Therefore, assuming that the magnetic field is attenuated to 1/10, the energy of the magnetic field after passing there is (1/4) × (1/100)
However, since the electric field energy does not decrease at all, the energy of both after passing there is 0.1 of the energy penetrating from the outside.
2625 times each, and the electric field and magnetic field inside the box are both attenuated by about -6 dB.

If the positions of the magnetic shield surface and the electrostatic shield surface are selected at the same position using the same box, the value is about -20 dB.
It is obvious that there is a lot of room for improvement in the conventional technology because of the attenuation of.

Under the condition that an electromagnetic field outside the box penetrates into the box, the inside of the box holds a storage device, or the inside of the box is braced for the purpose of holding the mechanical strength of the box.
If you use structures that use conductive materials, such as stanchions or housings for equipment, without being electrically insulated from the metal conductors that make up the box, the electric current that should flow through the conductor loops will be shunted to those structures, and magnetic shielding will occur. Produces a negative effect that greatly reduces the effect of. With respect to this point as well, no consideration is given to the related art.

[0011]

At the time of a lightning strike, an electric computer, terminal equipment therefor, work equipment such as an electronically controlled robot, navigation-related equipment for aircraft, control circuits for electric power equipment, etc.
Although all devices have been stored and used in metal boxes for some time, malfunctions or damage to the devices often occur due to noise signals from the outside.

Since there are many reports of accidents when military aircraft and civilian aircraft are attempting to take off and land in a heavy thunderstorm, navigation-related equipment may malfunction due to noise when the aircraft is hit by lightning. it is conceivable that.

The above-mentioned accident caused by noise enters the inside of the box because the electric signal used in the high-speed processing and multifunctional electronic circuit is small and the technical level of the electromagnetic shielding box is low. The cause is that the noise signal that is generated is larger than the electrical signal.

If the noise signal entering the inside of the electromagnetic wave shielding box can be further reduced and the malfunction of the device can be prevented, it can greatly contribute to the industrial world. Achieving this goal is the task to be solved.

[0015]

[Means for Solving the Problems] Since the electric field vector in the electromagnetic wave can be made perpendicular to the conductor surface, the phenomenon that the electric field does not leak or penetrate from the gap where the conductors are superposed does not occur.

On the other hand, since the magnetic field vector can be made parallel to the conductor surface, from the minute gap in which the conductors are superposed,
It leaks or intrudes.

Therefore, as a means for shielding electromagnetic waves, an electrostatic shield surface is formed on the outer plate of the box, and a magnetic shield surface is formed by the conductor loop of the frame of the box.

It is necessary to solve the differential equation in order to clarify the physical phenomenon that enables magnetic shielding by the conductor loop.

The alternating magnetic field that is about to enter from the outside into a conductor loop whose area is s, the electric resistance of the loop is R, and the inductance of the same loop is L is H = H ₀ si
First, the current flowing through the conductor loop when nωt is calculated. Where ω is the angular frequency. The interlinkage magnetic flux with the loop is φ ₀ (t) = μSH ₀ sin ωt. In the formula, μ is the magnetic permeability.

If the electromotive force of the loop is V (t), the following differential equation holds for the current i flowing through the conductor loop. Becomes. By rewriting this formula, the following formula is obtained. By solving (Equation 2), setting i = 0 at t = 0, and showing the steady-state solution after the transient state has passed, the following equation is obtained.

By multiplying (Equation 3) by the inductance L of the loop, a magnetic flux can be obtained and represented by φ ′ (t) = Li, which φ ′ (t) is the magnetic flux due to the loop current. Therefore, φ ″ (t) = Li + φ ₀ (t) cannot be prevented from interlinking in the loop, and becomes a magnetic flux penetrating into the inside of the box. Since its value is φ ₀ = μsH ₀ , Becomes.

In order to find the maximum and minimum values of (Equation 4) by setting ωt = θ in (Equation 4), the modified equation of (Equation 4) with ωt = θ is differentiated by θ and rearranged. Then, the following formula is obtained. − (R / L) cos θ = ω sin θ (Equation 5) From this (Equation 5), − (R / L) × (1 / ω) = tan θ (Equation 6) and θ = tan ⁻¹ {−R / ( Lω)} ± 180 °
Xn (Equation 7) is obtained. In the formula, n is an integer.

When (Equation 7) is established, the second term in (Equation 4) becomes 0, and the maximum and minimum values of φ ″ (t), φ ″, can be expressed by the following equation. φ ″ = φ ₀ sin (θ ± 180 ° × n) (Equation 8)

The relationship between φ ₀ (t) and φ ″ (t) is
Fig. 1 shows a diagram drawn under the condition that magnetic shielding is poor so that the fluctuation of φ "(t) becomes large. Rough condition is R / L = 3000, f = 1kc, tan.
⁻¹ {R / (Lω)} = − 25.5227 ± 180 ° ×
It is a condition of n.

2 shows the absolute value of the ratio of φ ″ and φ _{0 on} the vertical axis and the value of R / (Lω) on the horizontal axis. In the example shown in FIG. R / (Lω) = 0.4
It was 7746. As a result of trial manufacture of a planar conductor loop using a rectangular tubular conductor, the R / L ratio was 4
Since it has been confirmed that it is possible to make up to 00, if the case of using this conductor loop is considered, the ratio of R / (Lω) becomes 0.06366 even at the same frequency, and from FIG. It can be seen that the value of becomes 0.06353, which is much smaller than that in the case of FIG.

Mathematical analysis for considering the magnetic shielding from (Equation 1) to (Equation 8) shows that the current shown in (Equation 1) uniformly flows in the rod-shaped conductor forming the planar conductor loop. Since this is a premise, all the magnetic flux due to the loop current passes through a plane surrounded by a group of straight lines passing through the center of gravity of the cut surface of the conductor. Therefore, it is clear that this surface exerts the best magnetic shielding effect.

If the cut surfaces of the rod-shaped conductors forming the planar conductor loop have different shapes, a group of straight lines passing through the respective centers of gravity and parallel to the rods cannot exist on the same plane. Of course, it is not possible to create a magnetically shielded surface that best exhibits.

To shield the electromagnetic waves, it is clear that the advancing electric field and magnetic field should be blocked at the same surface position, so that the position of the surface where the magnetic shielding effect is best exerted can be clearly defined. It is also clear that the problem of the present application can be solved if the electric field can be shielded at the same plane position.

FIG. 3 shows a conceptual diagram of an embodiment of the present invention. The figure shows how the entire box is covered with an electrostatic shield. In the figure, 10 is an electrostatic shield.

For the purpose of including a target space requiring electromagnetic wave shielding, the box has an end portion and an end portion of each of a plurality of linear conductor rods of the same material having the same cutting surface cut into an appropriate length. First, a framework of a polyhedral box, which is mechanically and electrically connected and consists of a plurality of planar conductor loops, is constructed.

To ensure magnetic shielding, conductor rods are shared between adjacent planar conductor loops. In other words, the ridgeline of the box framework consists of a single Todong Bar.

When it is necessary to increase the mechanical strength of the frame of the box or the area of the planar conductor loop becomes too large, a plurality of planar conductor loops are formed in order to subdivide one planar conductor loop. Partition.

From the outside of the framework of the polyhedron box, an electrostatic shield having an outside surface thereof, a surface parallel to the symbol 40, is provided inside the conductor loop whose outside surface is removed from the conductor rod of the framework. Between the outer surface of the frame, the position of the symbol 40, the center of gravity of the cut surface of each conductor rod of the frame, the virtual plane surrounded by a plurality of straight lines passing through the symbol 20, and the position of the symbol 30,
It is installed with the conductor loop and the electrostatic shield plate electrically connected.

The appearance of the box shown in FIG. 3 is characterized in that the electrostatic shield plate has a recess inside the conductor rod surrounded by the frame of the box.

FIG. 4 shows a cross section of FIG. 3 taken along the alternate long and short dash line and seen in the direction of the arrow. In the figure, 1 is a conductor rod which constitutes a planar conductor loop, and the cut surfaces of all the conductor rods are the same rectangular pipes. 10 in the figure
Is an electrostatic shielding plate, and shows an example in which the plate has a certain thickness so that the box has mechanical strength. The symbol 40 in the figure indicates the outer surface of the framework.

FIG. 5 shows a conceptual diagram of an embodiment in which an electrostatic shield plate is installed on one planar conductor loop which constitutes an electromagnetic wave shield box. In the figure, 1 is a straight conductor rod. In the example of the figure, the shape of the loop formed by the conductor rod is rectangular, but the result of the mathematical analysis shown so far is that if it is composed of linear conductor rods and exists on the same plane, Of course, the present invention can be applied to all polygons having multiple sides.

FIGS. 6, 7, and 8 are cross-sectional views of FIG. 5 taken along the alternate long and short dash line and seen in the direction of the arrow.
In each figure, the symbol 20 indicates the center of gravity of the cut surface of the conductor rod, and the dashed-dotted line symbol 30 passing through the point indicates the position of the virtual plane when it is considered that current flows only in the conductor rod.
The condition that the position of the surface is the same as the position of the shielding surface when the magnetic shielding effect is most exerted is limited to the case where an extremely thin metal foil or metal vapor deposition film is used as the magnetic shielding plate.

When the mechanical strength of the electromagnetic wave shielding box is to be shared by the magnetic shielding plate to some extent, it is also necessary to use a thick metal plate as the electrostatic shielding plate. In such a case, the electromagnetic induction current that flows through the electrostatic shield plate equivalently flows around the plate, that is, near the conductor rods that form the framework of the box, so that the magnetic shield that maximizes the magnetic shield effect is obtained. The position of the shielding surface is from the position 30 of the virtual surface to the surface 40 outside the framework.
Move in the direction of.

However, the magnetic shielding surface does not extend outside the surface symbol 40 outside the frame.

The difference between the figures is that FIG. 6 is a combination of a rectangular tubular conductor rod and a thin electrostatic shield plate, FIG. 7 is a combination of a rectangular tubular conductor rod and a relatively thick electrostatic shield plate, and FIG. The difference is the combination of the mountain-shaped conductor rod and the relatively thick electrostatic shield plate.

Although only the examples of using the tubular or mountain-shaped conductor rods have been shown so far as the conceptual diagrams of the embodiments, it goes without saying that the conductor rods may have solid cut surfaces. The only problem is that the weight increases when the outer dimensions are the same.

Under the condition that the value of R / (Lω) exceeds 0.1, the magnetic field penetrates into the box at a rate of 1/10 or more. Therefore, the structure inside the box, such as braces, columns and pedestals. , A conductor loop is formed between all the structures that make up the outside of the box, the conductor rod of the frame, and the electrostatic shield. Since a current flows through the conductor loop, the current flowing through the conductor loop that forms the framework of the box is reduced, and the effect of magnetic shielding is reduced. In that case, the metal inside the box, such as the braces, columns, and pedestals, must be electrically insulated from the metal that forms the outside of the box.

[0043]

As shown in FIG. 2, the effect of magnetic shielding is a combination of the electric resistance R of the planar conductor loop, the inductance L of the same loop, and the angular frequency ω of the electric signal penetrating from the outside. The value of R / (Lω) is determined. Moreover, it was possible to clarify the position of the magnetic shield surface that maximizes the effect of magnetic shield. The position of the magnetic shield surface,
It was also clarified that the position of the electrostatic shield surface can be made exactly the same, that is, the invention of the present application can be embodied.

In the prior art, the position of the electrostatic shield surface is the surface of the box, and the magnetic shield surface is located closer to the inside of the box away from the surface and is a surface for blocking the magnetic field. Blocked only the magnetic field, and blocked the electric field only at the electric field shielding surface located away from it.

In other words, in the prior art, for example, 100
When an electrostatic shield surface that can shield only a percent electric field and a magnetic shield surface that can also shield a 100 percent magnetic field are present at a distance, no matter which surface is exposed to the electromagnetic waves of intruding noise, The energy of 0.5 × 0.5 = 0.25 of the original electromagnetic wave energy penetrates inside the box. Half of them 0.12
5 is the energy of the electric field. If this value is doubled and the square root is calculated, it will be 0.5, so the attenuation in the box will be -6 dB if expressed in dB.

That value is the limit that can be reached by the prior art. Even in the case of plated copper mesh, since the mesh is knitted, both the magnetic shield surface and the electrostatic shield surface formed by the mesh are along the mesh, but both are wavy or uneven. It is hard to say that the magnetic shield surface and the electrostatic shield surface are in the same position.

In the present application, the position of the magnetic shield surface is clarified, and the electrostatic shield surface is installed at the same position, and it is easy to embody. The electrostatic shield attached to the outside of the frame of the box need only be screwed, and therefore the contents of the box can be easily repaired and taken out.

According to the present application, if an electromagnetic wave is to be shielded,
As shown below, it is clear that the shielding effect is much superior to that of the conventional technique. First, regarding magnetic shielding, it is assumed that R / (Lω) is 1/10, and then the effect of electrostatic shielding is 97%. Since the magnetic shield surface and the electrostatic shield surface are at the same position, the energy of the magnetic field passing through that position is 1/100, and the electric field energy is (3/100) ² = 9 × 10 ⁻⁴ . The values obtained by adding the two and dividing by 2 are the magnetic field energy and electric field energy, respectively, which are entered in the box.
If the square root of twice that value is obtained, it means that the values of the magnetic field and electric field have decreased to 0.104403 times as compared with the outside of the box. If the reduction is expressed in dB, it will be approximately -19 dB.

As can be seen from the above description, the invention of the present application is an excellent invention that far exceeds the prior art.

[0050]

FIG. 3 is a conceptual diagram of an embodiment of the present invention. In the figure, 1 is a conductor rod forming a planar conductor loop, and a box frame is constituted by a plurality of conductor rods having the same cross section. Since the magnetic shield surface that exerts the most magnetic shield effect can be formed between the outer surface of the frame of the box, the symbol 40 and the temporary surface surrounded by the straight line group passing through the centers of gravity of the cut surfaces of all the conductor rods,
One of the unique features is that the electrostatic shield is installed at the position of the magnetic shield. Therefore, in the central portion of the frame of the electrostatic shield away from the conductor rod, the electrostatic shield has the appearance feature that it is recessed from the portion attached to the frame with a screw. The appearance is shown in Fig. 3.

As a conductor rod, a rectangular tubular conductor rod, FIGS. 6 and 7, is superior to the mountain-shaped conductor rod in FIG. 8 from the viewpoint of electromagnetic wave shielding. The reason is that in both FIGS. 6 and 7, the position of the center of gravity is inside the rectangular tubular conductor rod, and no electric field is generated at that position, whereas in the case of the mountain-shaped conductor rod, the center of gravity of the cut surface is Because it is not surrounded by a conductor, it is possible to generate an electric field. Therefore, the effect of electric field shielding is slightly inferior.

As a rectangular tubular conductor rod, the cut surface is 2 cm ×
Using a copper rod having a wall thickness of 2 mm and a tube thickness of 2 mm, a flat conductor loop having a side length of 1 m was manufactured as a prototype, and the R / L value was measured to be 400. Using this value, the invention of the present application is embodied, and it is as follows if the noise radio wave is reduced at the peak 500 cycles of the noise frequency at the time of lightning strike to ground.

First, R / (Lω) is calculated to be 0.12
73. Next, assuming that the effect of electrostatic shielding is 0.95, the magnetic field and electric field are about -17 dB inside the box.

If the same box is examined at 10 kc, R
Since the value of / (Lω) is 0.006366619, and the effect of electrostatic shielding does not change with frequency, the effect of reducing the magnetic field and electric field inside the box is approximately -26 dB.

Due to the ventilation window for releasing the heat generated by the equipment installed inside the box and the electrical connection with the outside, the effect of electrostatic shielding is not 100%. Considering the area ratio, the limit is considered to be 97 to 95%.

[0056]

The physical contents of the prior art are

In addition, the technical limit resulting therefrom is 004.
I explained in 5.

The summary of the physical contents which is the characteristic of the present application is 0
The invention of the present application is an excellent invention that greatly contributes to the industry, as indicated by the specific numerical values 0048 and 0052, 0053, 0054, which show the contents of the new technology far exceeding the conventional technology as shown in 047.

[Brief description of drawings]

FIG. 1 is a graph in which the vertical axis represents φ ₀ (t) and φ ″.
(T) is a diagram showing θ = ωt on the horizontal axis.

FIG. 2 is a diagram showing the absolute value of the ratio of φ ″ / φ ₀ on the vertical axis and R / (Lω) on the horizontal axis.

FIG. 3 is a conceptual diagram of an embodiment of the present invention.

FIG. 4 is a cross-sectional view of FIG. 3 taken along the alternate long and short dash line and seen in the direction of the arrow.

FIG. 5 is a conceptual diagram of an embodiment in which an electrostatic shielding plate is installed on one planar conductor loop which constitutes an electromagnetic wave shielding box.

FIG. 6 is a cross-sectional view of FIG. 5 taken along the chain line and seen in the direction of the arrow. This is an example in which a thin electrostatic shield is installed on a rectangular tubular conductor rod.

FIG. 7 is a sectional view at the same position as in FIG. This is an example in which a thick electrostatic shield is installed on a rectangular tubular conductor rod.

FIG. 8 is a sectional view at the same position as in FIG. This is an example in which a thick electrostatic shield is installed on a mountain-shaped conductor rod.

[Explanation of symbols]

Symbol 1 is a linear conductor rod that constitutes the framework of the planar conductor loop and the box. Symbol 10 is an electrostatic shield plate installed on the outside of the box. Symbol 20 is the center of gravity of the cut surface of the conductor rod. The symbol 30 indicates the position of the temporary surface surrounded by the straight line passing through the center of gravity of the cut surface of the conductor rod. The symbol 40 indicates the position of the outer surface of the box framework, which is composed of a plurality of conductor rods.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 594164209 Kurashita Kurashita 2-1-26 Shimonagaya, Konan-ku, Yokohama-shi, Kanagawa Prefecture Arcadia No. 304 Shimonagaya Shimonagaya (72) Inventor Shuichiro Kawamata 7-29-15 (72) Ryoke, Urawa City, Saitama Prefecture ) Inventor Jun Kawamata 1 at 82 Inari, Susono City, Shizuoka Prefecture (72) Inventor Ken Kawamata 7-29-15 Ryoke, Urawa City Saitama Prefecture (72) Inventor Yoji Nagai 1-17-10 Higashi Nakahara, Hiratsuka City, Kanagawa Prefecture Bill 305 (72) Inventor Hiroshi Kurata 2-1-26 Shimonagaya, Konan-ku, Yokohama-shi, Kanagawa Arcadia Shimonagaya 304

Claims (1)

[Claims] 1. An end portion and an end portion of each of a plurality of conductor rods of the same material having the same cut surface cut into an appropriate length according to the purpose of including a target space requiring electromagnetic wave shielding are machined. Electrically and electrically connected to form a planar conductor loop, and if necessary, a planar conductor loop partitioned into a plurality of planes by the conductor rod, and a conductor rod between adjacent planar conductor loops. A plurality of planar conductor loop surfaces that are shared to form a framework of a box of a polyhedron, on each planar conductor loop surface that is a framework, from the outside of the box, of an electrostatic shield plate parallel to that surface, On the inside of the conductor loop whose outer surface is dislocated from the conductor rods that form the framework, use a straight line that passes through the center of gravity of the cut surface of each conductor rod that forms the planar conductor loop from a position that matches the surface of the frame. To the position of the enclosed virtual plane Between the conductor loop and the electrostatic shield plate are electrically connected to each other, and the electrostatic shield plate is installed on each face of the polyhedron at the position of the magnetic shield face that maximizes the magnetic shield effect. Electromagnetic wave shielding box characterized by