JP7531990B2 - Cable penetration structure of shielding material - Google Patents

Description

The present invention relates to a cable penetration structure of a shielding member that prevents electromagnetic wave leakage caused by a non-conductive cable such as an optical cable penetrating a shielding wall of an electromagnetic wave shielding room, etc.

Generally, a space that shields against electromagnetic waves (hereinafter, shielded space) is covered with a member (hereinafter, shielding member) made of a material that blocks electromagnetic waves, such as a metal plate, but due to the needs of the equipment, such as piping, it is often installed by penetrating the shielding member. Recently, there have been cases where non-conductive cables such as optical cables are drawn into shielded rooms. In such cases, preventing electromagnetic wave leakage from the cable penetration points of optical cables, etc. is extremely important in order to ensure the shielding performance of the shielded space.

In the above-mentioned penetration, if the metal tube through which the cable is inserted is completely earthed and attached to the shielding surface, then according to the "waveguide principle," if the inner diameter of the metal tube is less than half the wavelength of the electromagnetic waves to be shielded, and the length required for attenuation exceeds six times the inner diameter of the tube, then electromagnetic waves of that wavelength cannot pass through. For example, since the wavelength of a 10 GHz electromagnetic wave is 30 mm, a high shielding effect can be achieved by using a metal tube with an inner diameter of less than 15 mm.

However, when the frequency reaches 40 GHz, the inner diameter needs to be less than 4 mm, and it takes a lot of work to manufacture a penetration hardware by brazing such an extremely thin metal tube. Furthermore, if a large number of cables are to be wired, this poses an even greater problem of enormous effort, time, and cost.

As an example of prior art related to preventing electromagnetic wave leakage at cable penetration parts of shielding members such as those described above, there is Patent Document 1. Patent Document 1 discloses an electromagnetic wave leakage prevention structure in which a cylindrical metal tube is inserted and fixed into a penetration hole provided in a partition wall of a shielded room, a shielded cable covered with a shielding layer is inserted into the metal tube, and the gap between the shielded cable and the inner surface of the metal tube is filled with metal fibers.

The cable core of the shielded cable is an electrical conductor, and experimental results have shown that when the shielding layer is partially removed and the exposed cable core is electrically shorted to the inner surface of the metal tube by filling it with metal fibers, it exhibits an attenuation rate of 75 dB or more (leakage can be prevented) for electromagnetic waves of 10 KHz to 1000 KHz (1 MHz).

Japanese Patent Application Publication No. 08-274487

However, the performance verification experiment of the electromagnetic wave leakage prevention structure disclosed in Patent Document 1 only provides limited results in the low frequency range of 10KHz to 1000KHz (1MHz) electromagnetic wave frequency range that is the object of shielding, and the specifications of the electromagnetic wave shielding material are not specified. As a result, it is difficult for even an engineer in this field to estimate the effect in the high frequency range of up to 40GHz that is the object of this invention by so-called "extrapolation" in the range above 1GHz, where there is no experimental data. Furthermore, there is no suggestion of a method for ensuring shielding performance in the high frequency range above 1GHz, and the present invention is intended for non-conductive cables.

The present invention provides a cable penetration structure for a shielding member that is highly effective in preventing leakage of electromagnetic waves in the high frequency band up to 40 GHz at a penetration part where a non-conductive optical cable or the like penetrates a shielding member that covers a shielded space, and that is easy to manufacture.

The means of the present invention to solve the above problem is a cable penetration structure for a shielding member, which is constructed as follows:

The cable penetration structure of the shielding member according to the present invention is characterized in that at least one core wire (hereinafter simply referred to as the core wire) of a non-conductive cable such as an optical cable is inserted into an insertion hole formed in a metal through-hole panel having a hole diameter less than 1/2 the wavelength of the electromagnetic wave to be shielded and a thickness at least six times the hole diameter , both sides of the through-hole panel are covered with protective covers that protect the core wire, one protective cover being a cable holding panel that holds the cable and the other protective cover being a connector installation panel in which a connector that holds the core wire is installed . The number of the core wire inserted into the insertion hole may be one, or multiple core wires as long as they can be inserted into the insertion hole.

The through-hole panel may be a single plate or two or more laminated thin plates, so long as it has a thickness that is at least six times the required thickness of the hole diameter. In the case of laminated plates, it is easy to drill very thin holes because each plate is thin.

The connectors for connecting the core wires inside and outside the cable penetration box may be provided for each of the core wires, or may be installed in two or more locations according to the number of bundles in which the core wires are bundled together.

With the cable penetration structure described above, the high-frequency electromagnetic waves to be shielded are blocked by the extremely fine hole portion of the penetration panel through which the core wire is inserted, and the core wire is protected by the cable holding panel and connector installation panel.

The core wire is inserted through a hole that is much smaller than the diameter of the hole through which the cable is inserted, but since it is only necessary to drill the required number of holes in a relatively thin metal plate, this method is much easier to manufacture than the conventional method of attaching extremely thin metal tubes that match the diameter of the core wire one by one.

The present invention, which is based on the above-mentioned means, has the following effects.
(1) The cable penetration structure of the present invention is effective in blocking electromagnetic waves in the high frequency range up to 40 GHz on walls made of shielding materials through which cables such as optical cables pass.
(2) Such a high-performance cable penetration can be produced easily and at low cost.
(3) The thickness of the through-hole panel, which is made of a metal plate through which the core wire passes, is only about six times the diameter of the insertion hole of the extremely thin core wire, so it can be thin and can be stored compactly even when the cable holding panel and connector installation panel are attached.

1 is a cross-sectional view of a cable penetration box according to a first embodiment of the present invention, in which an optical cable penetrates a shielding member. FIG. 2 is a cross-sectional view taken along line I-I of FIG. 1, showing a cable holding panel that holds an optical cable in a cable penetration box. This is a cross-sectional view taken along line R-R of Figure 1, and is a metal through-hole panel having holes through which the core wires are inserted one by one. This is a cross-sectional view of the cable in Figure 1, which shows a connector installation panel that connects the inside and outside of the cable penetration box one by one. FIG. 11 is a cross-sectional view of a cable penetration box according to a second embodiment of the present invention, in which an optical cable penetrates a shielding member. This is a cross-sectional view of Figure 5, which shows a connector installation panel that connects the core wires inside and outside the cable penetration box, where (a) shows an example where all the core wires are grouped together in one location, and (b) shows an example where the core wires are grouped together in two locations. 1 is a cross-sectional view of a shielded building showing an example in which a cable penetration box according to the present invention is installed in a shielded wall of a shielded room.

A first embodiment of the present invention will be described with reference to Figs. 1 to 4. Fig. 1 is a cross-sectional view of a cable penetration box 2 in which an optical cable 6 penetrates a shielding member 1. The box is made up of a cable holding panel 3 that holds the optical cable 6 with a protective coating in the cable penetration box 2, a metal through-hole panel 4 with insertion holes 4a, 4a, ... through which the core wires 6a, 6a, ... are inserted one by one, and a connector installation panel 5 on which connectors 5a, 5a, ... are installed to connect the core wires 6a, 6a, ... inside and outside the cable penetration box 2, and the through-hole panel 4 is fixed in an electrically conductive state to the shielding member 1 of the shielding wall.

The through holes 4a, 4a, ... opened in the through hole panel 4 have a hole diameter less than 1/2 the wavelength of the electromagnetic wave to be shielded, and the thickness of the through hole panel 4 must be six times or more the hole diameter of the through holes 4a, 4a, ... For example, when the frequency is 40 GHz, the inner diameter of the hole must be less than 1/2 the wavelength, 3.75 mm, and the hole length must be six times that, or 22.5 mm, or more, so the thickness of the through hole panel 4 must be 23 mm or more.

For example, if the diameter of the core wires 6a, 6a, ... is 1 mm, then a hole with an inner diameter of about 1.5 mm will be sufficient for insertion, and holes of less than 3.75 mm will need to be drilled for each core wire 6a, 6a, ... that will penetrate the 23 mm thick metal plate. If the optical cable 6 is a bundle of 100 cores, then 100 holes will need to be drilled.

To drill extremely fine holes in metal plates, the diameter of the drill teeth becomes thin, but if the plate is thick, the drill teeth are more likely to break. Therefore, if the through-hole panel 4 is not made of a single sheet, but is made of multiple overlapping thin plates and holes are drilled individually, damage to the drill teeth can be avoided. However, it is necessary to seal the gaps around the entire periphery of the overlapping thin plates by welding or other measures to prevent leakage of electromagnetic waves.

In addition, as long as the diameter of the insertion holes 4a, 4a, ... is less than 1/2 the wavelength of the electromagnetic waves to be shielded and the thickness of the through-hole panel 4 is at least six times the diameter of the insertion holes 4a, 4a, ..., the diameter of the insertion holes 4a, 4a, ... can be made larger, and in that case, even with the 100-core cable, the number of holes to be drilled can be reduced to less than 100, and the diameter of the drill teeth can also be increased, reducing damage caused by drilling.

If, based on conventional thinking, a 100-core optical cable 6 is passed directly through the shielding material 1, the hole diameter is large, so in order to ensure the same electromagnetic shielding effect for 40 GHz as that obtained by a through-hole panel 4 with insertion holes 4a, 4a, ..., it would be necessary to pass the cable through a fairly long metal through-pipe, which would make it difficult to secure a place to install it.

A second embodiment of the present invention is shown in Figures 5 and 6. Figure 5 is a cross-sectional view of a cable penetration box 2 in which an optical cable 6 penetrates a shielding member 1. The cable holding panel 3 that holds the optical cable 6 with a protective coating, shown in the cross-sectional view along the line E-I of Figure 5, and the metal through-hole panel 4 with insertion holes 4a, 4a, ... through which the core wires 6a, 6a, ... are inserted one by one, shown in the cross-sectional view along the line R-R of Figure 5, are the same as those in the first embodiment.

In the second embodiment, as shown in Figures 6(a) and (b), which are cross-sectional views taken along the line H-H in Figure 5, the number of connectors 5a connecting the core wires 6a, 6a, ... inside and outside the cable penetration box 2 is set to match the number of bundles of core wires 6a that are bundled together. Figure 6(a) shows the case where all of the core wires 6a, 6a, ... are bundled together in one location, and Figure 6(b) shows the case where the core wires 6a, 6a, ... are bundled together in two locations. It goes without saying that they may be bundled together in three or more locations if necessary.

Figure 7 shows an example of installing the cable penetration box 2 described above in a building with a shielded room. Figure 7 shows the situation where an optical cable 6 is pulled from a work room without shielding measures into shielded rooms A and B on both sides. In the work room, the optical cable 6 is still covered with a protective covering that bundles all the core wires, and both ends are inserted into the cable insertion holes 3a, 3a of the cable holding panels 3, 3 of the cable penetration boxes 2, 2. In the cable holding panels 3, 3, as shown in Figure 1, the core wires 6a, 6a, ... are separated, and each one is inserted into the insertion holes 4a, 4a, ... of the metal through-hole panel 4. In the shielded room A, the core wires 6a, 6a, ... are connected to the core wires 6a, 6a, ... outside the cable penetration box 2 (inside the shielded room A) by the connectors 5a, 5a, ... of the connector installation panel 5 (corresponding to the first embodiment).

In addition, in the shielded room B, the core wires 6a, 6a, ... that were separated into individual wires inside the cable penetration box 2 are collected in three locations by three connectors 5a, 5a, ... installed on the connector installation panel 5, and are connected to the optical cables 6, 6, ... outside the cable penetration box 2 (inside the shielded room B) (corresponding to the second embodiment).

Therefore, at the cable penetration section of the shielding member (wall) required for the optical cable 6 that is pulled in from the unshielded workroom to the shielded rooms A and B on both sides, electromagnetic waves cannot pass through the insertion holes 4a, 4a, ... of the metal penetration panel 4 installed in the cable penetration box 2, so leakage of electromagnetic waves is prevented.

As described above, by separating the optical cable 6, which is made up of multiple bundled core wires and protectively covered, into the core wires 6a, 6a, ... and inserting each of these into the extremely thin insertion holes 4a, 4a, ... in the metal through-hole panel 4, it is possible to obtain high shielding performance even against high-frequency electromagnetic waves such as 40 GHz.

In addition, if the through holes 4a, 4a, ... have a hole diameter less than 1/2 the wavelength of the electromagnetic wave to be shielded and are opened in a metal through-hole panel with a thickness of at least 6 times the hole diameter, the electromagnetic wave shielding effect will not change even if multiple core wires 6a are inserted into the through holes 4a, 4a, ..., so the present invention is not limited to a single wire as in the above embodiment.

The method of drilling extremely thin insertion holes 4a, 4a, ... for inserting the core wires 6a, 6a, ... in a metal through-hole panel 4 as in the present invention has a great electromagnetic wave shielding effect at high frequencies, and also makes it possible to form a cable penetration part of the shielding member that is extremely compact and easy to manufacture, compared to the conventional method of inserting the optical cable 6 itself into a long penetration tube (including a honeycomb tube).

The present invention provides high electromagnetic shielding performance at the cable penetration section of the shielding material of a shielded room with a compact, easy-to-manufacture structure, and will contribute greatly to improving electromagnetic shielding technology in higher frequency bands up to 40 GHz, in response to needs that are expected to increase in the future, such as cases in which non-conductive cables such as optical cables are pulled into a shielded room.

1: Shielding material 2: Cable penetration box 3: Cable holding panel 3a: Cable insertion hole 4: Penetration hole panel 4a: Insertion hole 5: Connector installation panel 5a: Connector 6: Optical cable 6a: Core wire

Claims (2)

A cable penetration structure of a shielding member according to the present invention, characterized in that at least one core wire of a non-conductive cable is inserted into an insertion hole formed in a metal through-hole panel having a hole diameter less than 1/2 the wavelength of the electromagnetic wave to be shielded and a thickness at least 6 times the hole diameter , both sides of the through-hole panel are covered with protective covers that protect the core wire, one protective cover is a cable holding panel that holds the cable, and the other protective cover is a connector installation panel in which a connector that holds the core wire is installed . The cable penetration structure of the shielding member according to claim 1, characterized in that the through hole panel is a single plate or a multi-ply plate having a thickness six times or more than the hole diameter.

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