JP2001358491A - Shield for radio waves or magnetic waves - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shield for radio waves or magnetic waves, in which the reflection of the radio waves or the magnetic waves is smaller that in conventional cases, whose absorption performance of the radio waves or the magnetic waves is high, which is thin and whose weatherability is high. SOLUTION: A carbon thin layer 20 which is composed of a carbon fiber sheet and the like is formed on the surface of a metal foil 11 composed of a metal foil or a metal sheet. The layer 20 is constituted in such a way that the carbon concentration of the layer 20 becomes high as it is approached to the metal foil 11. Another metal foil 12 is formed on the side opposite to the layer 20 in the metal foil 11. A cavity-containing material thin layer 13 which is composed of a material containing cavities is interposed between the metal foils 11, 12 as a pair in a state that it insulates the equivalents 11, 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield for radio waves or magnetic waves (electromagnetic wave shield) and a shield structure for an end thereof.

[0002]

2. Description of the Related Art Conventionally, there has been a demand for a thin radio wave or magnetic wave shielding material having high performance. And the inventor, as seen in WO 00/1792,
By providing an insulating layer including a cavity between the aluminum layers, a thin and flexible radio wave or magnetic wave shield with high performance was proposed.

However, since a thin aluminum foil or the like is used as a material, it is easily corroded, for example, outdoors or in a chemical factory, and it has been desired to improve weather resistance and nonflammability. Also, the number c
In electronic devices and the like having a small surface area of m square, there are reflections from the aluminum surface and electromagnetic waves which are re-emitted without being absorbed in the shield. Although it has been considered to make the aluminum foil on the electromagnetic wave generation side low in purity, there is still a problem of reflection, and it is not desirable from the viewpoint of the performance of the shield.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional situation, the present invention provides a thin and highly weather-resistant radio wave or magnetic wave which reflects less radio wave or magnetic wave and has higher radio wave or magnetic wave absorption performance than before. The purpose is to provide a shield.

[0005]

In order to achieve the above object, a feature of the present invention is that a radio wave or a magnetic wave shield is characterized in that a carbon thin film made of a material containing carbon is formed on a surface of a metal foil such as a metal foil or a metal sheet. That is, a layer is provided.

[0006] The thin carbon layer may be configured such that the carbon concentration of the thin carbon layer becomes higher as the carbon layer approaches the metal foil or the like.

[0007] The carbon thin layer can be constituted as a fiber to which carbon powder is adhered or a sheet made of carbon fiber. Further, the carbon element may be laminated on the surface of the metal foil or the like to form the carbon thin layer.

On the other hand, in order to further improve the radio wave shielding effect, another metal foil or the like is provided on the side of the metal foil or the like opposite to the side facing the carbon thin layer, and a cavity is provided between the pair of metal foils or the like. It is preferable to interpose a thin layer of a cavity-containing material made of a material containing the metal foil or the like in a state of insulating these metal foils and the like. The cavity-containing material thin layer may be configured as a composite of a film made of an insulating material and a carbon thin layer containing a cavity.

The thin layer containing the hollow material may be a nonwoven fabric, a woven fabric,
It may be paper, mesh or porous material or a combination thereof. Further, as the metal foil or the like, for example, an aluminum foil can be used.

Furthermore, it is desirable that the metal foil and the like and the carbon thin layer are configured to be able to take the ground. According to such a configuration, the apparent thickness of the metal foil or the like or the carbon thin layer is increased, and the shielding effect is enhanced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, referring to the attached drawings,
The present invention will be described in more detail. FIG. 1 is a sectional view showing an example of a radio wave or magnetic wave shield 1a according to the present invention. The radio wave or magnetic wave shield 1a includes a metal foil shield layer 10 and a thin carbon layer 20.

The metal foil shield layer 10 includes a pair of aluminum foils 11 and 12 as an example of a metal foil and the like, and further includes a hollow insulating layer 13 between the pair of aluminum foils 11 and 12 to form a shield 1a. are doing. Metal foil 1
As 1 and 12, there is a possibility that, besides aluminum foil, commonly used metal foils such as copper, steel, zinc or nickel, and vapor-deposited films using these metals may be used.

In the present embodiment, as the hollow insulating layer 13, a nonwoven fabric, a woven fabric, a net, Japanese paper, Western paper, a porous material sheet, a combination thereof, or the like can be used. As the hollow insulating layer 13, a natural material such as cotton, hemp, rayon, or cellulose is most desirable. Inorganic material fibers such as class fibers and asbestos can also be used. As the porous material, an inorganic material such as ceramics, which includes independent small cavities or continuous small cavities, can be used. The cavity may contain nitrogen or carbon dioxide gas in addition to air. The “combination of these” in the hollow insulating layer is, for example, a material obtained by laminating two or more material layers such as laminating a nonwoven fabric sheet and a net,
It includes both a mixture of two or more kinds of materials such as a mixture of a porous material and a nonwoven material to form a sheet.

The thin carbon layer 20 is formed of the metal foil shield layer 1
The surface is provided on the surface of the aluminum foil 11 on the electromagnetic wave intrusion side. In the present embodiment, the carbon thin layer 20 is formed by sequentially stacking three first to third carbon fiber sheets 21 a to 21 c having different carbon contents set so that the carbon concentration becomes higher as approaching the aluminum foil 11. Glued. These first to third carbon fiber sheets 21a to 21c
Is paper or nonwoven fabric made of synthetic or natural fibers to which carbon powder is attached. For the first to third carbon fiber sheets 21a to 21c, paper or non-woven fabric made of carbon fiber composed of carbon up to the center may be used. When carbon fibers are used for the carbon thin layer 20 and the below-described hollow carbon layer 17, not only the weather resistance of the shield 1a but also its noncombustibility can be improved.

Next, the above-mentioned radio wave or magnetic wave shield 1a
The operation in is described. Aluminum foil 1
1, 12, the carbon thin layer 20 is connected to the ground E via a ground wire 100. Although a specific method of connecting to the ground E will be described in the second and subsequent embodiments, it is desirable to take the ground E for at least the aluminum foil 11 and the thin carbon layer 20.

Electromagnetic waves N1 to N generated from connected electronic devices
4 reaches the main shield 1a from the carbon thin layer 20 side, a part of the electromagnetic waves N1 to N3 is applied to each of the first to third carbon fiber sheets 21a constituting the carbon thin layer 20.
~ C flow as a high frequency current. In addition, a part of the electromagnetic wave N4 reaching the aluminum foil 11 similarly flows in the aluminum foil 11 and its surface as a high-frequency current. The flow as the high-frequency current flows through the aluminum foil 1
1. If generated in the thin carbon layer 20, the electric current is converted into thermal energy as Joule heat, and as a result, the electromagnetic wave is attenuated.

When the electromagnetic wave reaches the metal foil, it is converted into Joule heat by a slight eddy current, but generally the flow as the high-frequency current described above is small and most is reflected. However, when the ground E is provided, the high-frequency current becomes smoother toward the ground E,
The reflection of electromagnetic waves is reduced. By this operation, each layer is connected to the ground E, so that the aluminum foils 11 and 1 of each layer are connected.
2. The apparent thickness of the carbon thin layer 20 is increased, and the electromagnetic wave absorbing ability is improved.

In general, when a carbon layer is used, it is necessary to provide an air layer of urethane or the like having a thickness of at least １ ／ of the wavelength in addition to the carbon layer in order to absorb an electric field. ing. However, it has been clarified that by taking the ground E, it is possible to absorb electromagnetic waves up to a low frequency band having a long wavelength with a very thin layer, even if the microwave is not a short wavelength microwave.

In general, higher-frequency electromagnetic waves gather on the surface of the conductor, and lower-frequency electromagnetic waves penetrate deeper into the conductor. Therefore, the first to third carbon fiber sheets 21a
In (c), by increasing the carbon concentration closer to the aluminum foil 11, a high frequency component of the electromagnetic wave is absorbed on the surface side, and a lower frequency component is absorbed at a position closer to the aluminum foil 11. are doing. In order to change the carbon concentration, the porosity may be changed by compressing the carbon fiber more, and the amount of carbon powder adhering to the fiber or the like may be increased or decreased.

Since the carbon fibers are randomly combined and have a very large surface area, the amount of heat energy converted by the flow of a high-frequency current on the fiber surface is very large. Further, since the surfaces of the first to third carbon fiber sheets 21a to 21c are random, eddy currents are easily generated by receiving electromagnetic waves entering from various angles, and eddy currents are easily generated even if there is a gap. As a result, conversion to Joule heat is likely to occur as a whole, the ability to absorb electromagnetic waves is improved, and irregular reflection of electromagnetic waves is less likely to occur.

On the other hand, in the metal foil shield layer 10,
The electromagnetic wave that has reached the aluminum foil 11 flows through the surface of the aluminum foil 11 as a high-frequency current and penetrates the aluminum foil 11. However, when the aluminum foil 11 and the aluminum foil 12 are brought very close to each other,
In this way, multiple reflection of the electromagnetic wave N5 occurs between the aluminum foil 11 and the aluminum foil 12. The electromagnetic wave is further absorbed and attenuated by the multiple reflection of the electromagnetic wave N5.

By the way, the low frequency wave among the multiple reflection waves of the electromagnetic wave N5 may pass through the aluminum foil 11 and be emitted again to the electromagnetic wave incident side. In addition, an electric field is generated on the carbon thin layer 20 side of the aluminum foil 11 by a high-frequency current appearing on the side of the aluminum foil 12 of the aluminum foil 11 due to the multiple reflection electromagnetic wave N5 and the like, and the electromagnetic wave is emitted to the incident side of the electromagnetic wave. It may be done.
However, by providing the thin carbon layer 20 on the surface of the aluminum foil 11, the multiple reflection wave N5 can be absorbed so as not to be emitted again to the incident side of the electromagnetic wave. A synergistic effect can be obtained.

In the present invention, the same applies to the following embodiments, but a foil or film is used for each layer. The means used for lamination is not particularly limited according to the material of each layer to be used, but generally, a lamination method using an adhesive or a pressure-sensitive adhesive can be used. In the case of using the base material for forming each layer or a material obtained by processing the surface of the base material with a fusible resin, a lamination method by thermocompression bonding can be used. In the present embodiment, for example, a polyester-isocyanate cross-linking adhesive is used as an adhesive for each layer, but other adhesives and pressure-sensitive adhesives that can be used for this lamination include acrylic, ester, epoxy, and urethane-based adhesives. Silicone, rubber, olefin, amide, melamine, vinyl ether or even natural product starch, casein, glue and the like may be used.

Next, another embodiment of the present invention will be described below. Unless otherwise specified, the same components as those in the above embodiment are denoted by the same reference numerals. In the shield 1b according to the second embodiment shown in FIG. 2, an example of the shield 1b that can be used as a building material or the like is shown.
In this shield 1b, the metal foil shield layer 10 is constituted by one piece of aluminum foil 11, and the first to
A thin carbon layer 20 composed of third carbon fiber sheets 21a to 21c is provided. Further, a PET (polyethylene terephthalate) film 16 is formed on the surface of the carbon thin layer 20.
, The surface of the carbon thin layer 20 is protected and decorated. Also, considering the coloring and adhesive properties,
It is preferable to use a white PET film 16 or a mat-shaped PET film. Note that a further electromagnetic wave absorbing effect can be obtained by attaching a PET film on which the above-described metal film is deposited to the surface of the thin carbon layer 20 with the deposited film facing outside, or by attaching a conductive film.

On the other hand, an adhesive layer 41 and a release layer 42 are sequentially provided on the other side of the aluminum foil 11, and the release layer 42 is peeled off so that the shield 1b can be adhered to a wall surface as a building material or the like. . The adhesive layer 41 can be generally made of an acrylic, urethane, polyester, silicone, or rubber adhesive. The release layer 42 includes the adhesive layer 41
Is used until it is used, and a polyolefin film or release paper can be used.

Metal foil shield layer 10 and carbon thin layer 20
And an adhesive layer (not shown) is interposed therebetween. When this adhesive layer is made of a conductive adhesive, the metal foil shield layer 10
It is enough to take earth E from only. However, in this embodiment, since the metal foil shield layer 10 and the carbon thin layer 20 are insulated, the ground piece 30 is straddled over the ends of the metal foil shield layer 10 and the carbon thin layer 20, At the joints 31, 31 and the grounding piece 30, the contact 3
In step 2, the metal foil shield layer 10, the thin carbon layer 20, and the ground piece 30 are brought into conductive contact. Then, the ground piece 30 is connected to the ground E via the ground wire 100.

The shield 1 according to the third embodiment shown in FIG.
c, a plurality of metal foil shield layers 10, a carbon thin layer 20 made of a carbon fiber sheet 22 having a carbon concentration substantially uniform in the thickness direction, and a carbon thin layer 20.
And a decorative layer 16 on the surface.

The aluminum foils 11 and 12 are bonded to PET films 14 and 15 which are examples of insulating layers, respectively, so that the aluminum foils 11 and 12 have good workability for bonding with the hollow carbon layer 17 and high bonding strength. The hollow carbon layer 17, which is a thin layer of a hollow material, is made of the same material as the first to third carbon fiber sheets 21a to 21c and the carbon fiber sheet 22. The hollow carbon layer 17 itself has conductivity. Have. However, the insulation between the aluminum foils 11 and 12 is maintained by interposing the insulating layer on at least one surface or both surfaces of the hollow carbon layer 17. Note that, as the insulating layer, a film using a material such as rubber, plastic, or ceramic or a coating film obtained from a paint can be used instead of the PET film.

By the way, the high-frequency current flows more easily in the PET films 14 and 15 than in the hollow insulating layer 13.
Therefore, since the hollow carbon layer 17 has conductivity, it may seem at first glance that a high-frequency current flows between the aluminum foils 11 and 12. However, when a high-frequency current flows through the hollow carbon layer 17, eddy current is likely to be generated due to the presence of the cavity, and the loss due to the eddy current is large. Can be prevented.

The metal foil shield layer 10 and the carbon thin layer 20
A non-overlapping portion is provided between the aluminum foil 11 and the decorative layer 16, and the grounding piece 30 is straddled between the aluminum foils 11 and 12 and is brought into contact with the aluminum foil 11 and the carbon thin layer 20. The thin carbon layer 20 is connected to the ground E. The previous embodiment is similar,
Aluminum foils 11, 1 superimposed on each other
2. The metal foil shield layer 1 is formed by straddling the ground piece 30 along the entire edge of the end of the carbon thin layer 20.
0. Leakage of electromagnetic waves from the end of the thin carbon layer 20 can be prevented. Of course, for the purpose of connecting to the ground E only, it is sufficient to provide the ground piece 30 locally instead of providing it around the entire edge.

In this embodiment, the ground piece 30 is connected to the ground E
The shield wire 101 is used for connection to the terminal. The core wire 102 of the shield wire 101 is used for connection, and the outer wire 10
The shield at 3 prevents leakage of electromagnetic waves from the ground wire 100.

The cavity-containing insulating layer 13 and the cavity-containing carbon layer 17
Thickness should be as thin as possible with sufficient shielding.
And the thickness is preferably 1 mm or less, more preferably
Is suitably less than 500 microns. In addition, including
The thickness of the cavity insulating layer 13 and the thickness of the cavity-containing carbon layer 17
Should be finite, but preferably 30 microns or more
Is appropriate. Examples of the cavity-containing insulating layer 13 include:
For example, 10 to 100 g / m ^TwoUse Japanese paper or non-woven fabric
be able to. In addition, for example, aluminum foils 11 and 1
2 is about 15-20 microns thick, and PET is 2
The thickness of each of these layers is about 0 to 25 microns.
It is not limited to the value of and can be changed as appropriate.

A shield 1d according to a fourth embodiment of the present invention
As shown in FIG. 4, the chassis 1
10 is attached. In this embodiment, the chassis 1
10 is made of metal or conductive material, or
At least the contact portions 32 of the ground piece 30 and the aluminum foil 12 have conductivity, and the surface of the chassis 110 to which the shield 1d is attached corresponds to the inner surface of the electronic device.

The metal foil shield layer 10 has substantially the same configuration as the metal foil shield layer 10 of the shield 1c according to the third embodiment, except that the carbon-containing carbon layer 17 is a cavity-containing insulating layer 13. The adhesive layer 41 is made of aluminum foil 1
A part of the coating is refrained from the edge of the second portion 2 and directly contacts the chassis 110 at the contact portion 32. In addition, carbon thin layer 2
0, the aluminum foil 11 is sequentially stacked with their edges shifted in steps, and the grounding piece 30 contacts the carbon thin layer 20, the aluminum foil 11 and the chassis 110 to make them conductive with each other. Is earth E. By providing the ground piece 30 along the entire edge of the shield 1d, it is possible to prevent the electromagnetic wave from leaking from the edge of the shield 1d.

In the shield 1e according to the fifth embodiment of the present invention shown in FIGS. 5 and 6, the shield 1e is connected to the ground E by a small piece of ground piece 33. Metal foil shield layer 1
0, the laminate of the aluminum foil 11 and the PET film 14 and the laminate of the aluminum foil 12 and the PET film 15
And the PET film 14 are bonded so as to face each other. The carbon thin layer 20, the aluminum foils 11, 12
The edges are shifted one by one like a step,
The ground piece 33 contacts the carbon thin layer 20, the aluminum foils 11, 12 and the chassis 110 to make them conductive with each other. The ground piece 33
A ferrite layer 34 is provided on a contact surface between the ferrite layer 34 and the shield 1e, and the ferrite layer 34 is configured to further absorb high frequencies. The grounding piece 33 is fixed by a slightly larger adhesive tape 35.

The above-mentioned radio wave or magnetic wave shields 1a to 1e
In measuring the shielding effect of the above, a radio wave and a magnetic wave are generated by changing the frequency from the transmitting side antenna by the tracking generator. The transmitted signal received by the receiving antenna through the shield to be measured was amplified by the preamplifier, and the shielding effect was measured for each frequency by the spectrum analyzer.

In the radio wave or magnetic wave shields 1c to 1e shown in the third to fifth embodiments described above, the radio wave shielding effect is superior to the aluminum plate having a thickness of 3 mm, exceeding the measurement limit of the measuring device, and is 0.1 MHz. It is presumed that a shielding effect of 30 to 40 dB or more is obtained over the entire band from to 3 GHz. As for the magnetic wave shielding effect, a shielding effect close to that of an aluminum plate having a thickness of 3 mm was obtained.

Finally, the possibilities of other embodiments of the present invention will be listed. In each of the above embodiments, the ground E can be obtained by shifting the edges of the thin carbon layer 20 and the aluminum foils 11 and 12 in advance in a step-like manner and overlapping them sequentially, or by partially holding down the adhesive layer 41 at the edge of the shield. Had a configuration. However, although the edges of the thin carbon layer 20, the aluminum foils 11, 12 and the like are almost aligned, the configuration can be such that the ground E can be obtained also by making them peelable from each other.

In the above-described embodiment, only one metal foil shield layer 10 is provided. However, two or more metal foil shield layers may be provided, and may be appropriately changed depending on required performance. Also,
The material constituting each layer is not limited to the above-mentioned materials.

In the above embodiment, the number of the carbon fiber sheets 21a to 21c is not limited to three, and may be appropriately stacked. Also, the carbon fiber sheet indicated by reference numeral 22 may be used singly or as an arbitrary plural number.

In the above embodiment, a carbon fiber sheet was used as the hollow carbon layer 17 and the carbon thin layer 20. However, the carbon thin layer may be formed by laminating a carbon element on the surface of a metal foil or the like. For example, in the CVD (chemical vapor debodying) method, methane gas is
(Carbon) and H (hydrogen) are separated, and a film-like carbon film is formed on the surface of an aluminum foil or the like. In each case of stacking once, twice, and three times, the carbon density of each layer can be changed by changing conditions such as potential, voltage, and characteristic speed.

The radio wave or magnetic wave shield according to the present invention can be used as a base building material or the like to be attached to a wall or structure of a medical institution or the like. In addition, this shield,
It is also possible to generate a large amount of high-frequency digital noise and to use it as a shield for computers, electronic devices, and the like to be protected from digital noise. This shield is also suitable for covering electric wires and the like that dislike high-frequency noise.

The present invention can be implemented by appropriately combining the components shown in the first to fifth embodiments and the like.

[0044]

As described above, according to the characteristics of the radio wave or magnetic wave shield according to the present invention, the reflection of the radio wave or the magnetic wave is smaller than before and the radio wave or the magnetic wave absorption performance is higher, and
It has become possible to provide a thin and highly weather-resistant shield.

It should be noted that the reference numerals in the claims are merely for convenience of comparison with the drawings, and the present invention is not limited to the configuration of the accompanying drawings by the description. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a radio wave or magnetic wave shield according to the present invention.

FIG. 2 is a cross-sectional view showing a second embodiment of a radio wave or magnetic wave shield according to the present invention.

FIG. 3 is a cross-sectional view showing a third embodiment of the shield for radio waves or magnetic waves according to the present invention.

FIG. 4 is a cross-sectional view showing a fourth embodiment of a radio wave or magnetic wave shield according to the present invention.

FIG. 5 is a plan view showing a fifth embodiment of the shield for radio waves or magnetic waves according to the present invention.

FIG. 6 is a sectional view taken along line AA of FIG. 5;

[Explanation of symbols]

 1a-d Shield of radio wave or magnetic wave 10 Metal foil shield layer 11, 12 Aluminum foil (metal foil etc.) 13 Cavity-containing insulating layer 14, 15 PET film (insulating layer) 16 Decorative layer 17 Cavity-containing carbon layer 20 Carbon thin layer 21a -C first-third carbon fiber sheet 22 carbon fiber sheet 30 grounding piece 31 joining part 32 contacting part 33 grounding piece 34 ferrite layer 35 adhesive tape 41 adhesive layer 42 peeling layer 100 ground wire 101 shield wire 102 core wire 103 outer net wire 110 Chassis E Ground

Claims (8)

[Claims] A radio wave or magnetic wave shield comprising a thin metal layer (20) made of a material containing carbon provided on the surface of a metal foil (11) made of a metal foil or a metal sheet. 2. The radio wave according to claim 1, wherein the thin carbon layer (20) is configured so that the carbon concentration of the thin carbon layer (20) increases as the metal foil or the like (11) approaches. Or a shield of magnetic waves. 3. The radio wave or magnetic wave shield according to claim 1, wherein the carbon thin layer (20) is a sheet made of fibers or carbon fibers to which carbon powder is adhered. 4. The radio wave or magnetic wave shield according to claim 1, wherein the thin carbon layer (20) is formed by laminating a carbon element on the surface of the metal foil or the like (11). 5. A metal foil or the like (11) on the side opposite to the carbon thin layer (20) facing side of the metal foil or the like (11).
2), and a thin layer of hollow material (13, 17) of a material containing a cavity is interposed between the pair of metal foils (11, 12) in a state where these metal foils (11, 12) are insulated. The radio wave or magnetic wave shield according to claim 1, wherein the radio wave or the magnetic wave is shielded. 6. A film (14, 15) in which the thin layer of hollow material is made of an insulating material and a thin carbon layer (17) containing voids.
The radio wave or magnetic wave shield according to claim 5, which is a complex with the above. 7. A radio or magnetic wave shield according to claim 5, wherein the thin layer of hollow material (13, 17) comprises a nonwoven, woven, paper, mesh or porous material or a combination thereof. 8. The radio wave or magnetic wave shield according to claim 1, wherein said metal foil or the like (11, 12) is an aluminum foil.