JPH11261286A - Radio wave shield region in building - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shield radio wave regardless of moisture adhering to sash, or the like, by applying the surface of a sash in the radio wave shield region within a building in parallel with a planar radio wave shielding body comprising conductive elements having length in two axial directions shorter than one half of the wavelength of a radio wave to be shielded. SOLUTION: A radio wave shield region 15 in a building has floor, ceiling and wall surrounding a window 1 in a conductive sash 3 entirely formed of a radio wave shielding barrier wall 2. A planar radio wave shielding body 4 is formed by arranging conductive elements having length in the biaxial direction on a specified orthogonal coordinate system shorter than one half of the wavelength of a radio wave 14 to be shielded on the entire surface along two axes at an interval shorter than one half of the wavelength. The body 4 is disposed in parallel with the plane of the sash 3 and the air gap therebetween is set in the range of 1/30-1/2 of the wavelength in order to shield the radio wave while resonating at the frequency thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave shielding area in a building, and more particularly to security for preventing wiretapping, interference, and intrusion of communication information due to leakage of radio waves between indoor and outdoor in radio communication in an indoor space. Also, the present invention relates to a radio wave shielding area for effective use of a carrier wave indoors which is not affected by an outdoor call in an indoor simple portable telephone system (Personal Handyphone System, PHS).

[0002]

2. Description of the Related Art With the advance of information technology, the number of intelligent buildings equipped with radio wave communication functions has increased, and furthermore, with the spread of digital information communication and PHS, confidentiality protection, interference prevention, and efficient use of radio waves have been improved. Opportunities to provide electromagnetic shielding space inside buildings are increasing. In electromagnetic shielding space, ceiling surface,
Although it is indispensable to electromagnetically shield the entire floor surface and the entire peripheral surface of the side surface, windows are also indispensable in a building due to requirements for livability.

FIG. 1 shows an example of the configuration of a PHS in a company or indoors. Partition wall 2 with electromagnetic shielding function (floor surface 2f, ceiling surface 2c,
The radio wave shielding area 15 is defined by the surrounding wall 2w), and the base station 5 is attached to, for example, the ceiling of the radio wave shielding area 15, and the base station 5
The intra-area mobile telephones 6 that communicate with each other at 14 are appropriately dispersed and arranged in the shielded area 15. If there is radio wave leakage in the window 1 of the surrounding wall 2w,
There is a risk of eavesdropping, intrusion, interference, and obstruction by the outdoor out-of-bounds mobile phone 7.

In the PHS, a frequency group including a fixed number of carrier frequencies is allocated to the time division multiplexing / time division simultaneous transmission / reception system. It is also anticipated that the carrier frequency that is desired to be
The situation for indoor use is broken, and the risk of the line being busy inside the house increases.

To solve these problems, electromagnetic shielding may be considered by covering the window with a conductive material or the like. However, the conductive material is poor in optical transparency, so that it is capable of daylighting and maintaining the function of viewing the external scenery. Had a problem. As a transparent electromagnetic shielding means, it has been proposed to provide a radio-shielding sheet (FSS) having a conductive element dispersed type and frequency selectivity on a glass surface as shown in FIG. 2D (Techniques for Analyzing Frequency).
Selective Surfaces ―A Review, by RAJ MITTRA et a
l, Proceedings of IEEE, December 1988).

The sheet-like body FSS is formed, for example, on a surface of a window glass 1a (see FIG. 7) by regularly arranging small metal pieces (metallized pieces).
ic patch) consists of elements 10 (hereinafter sometimes referred to as isotropic conductive elements) or regularly arranged small aperture elements on a metal screen, and the total reflection near the resonance point specific to those elements. Or total propagation (total
transmission). The principle is the receiving operation of a half-wave dipole antenna.

In FIG. 5A, when a dipole half-wave antenna 11 having a reception resistor R receives an electromagnetic wave arriving at a power density P, the power induced in the reception resistor R is represented by a conductor constituting the antenna. It is known that energy (= P × A) existing in an area A much larger than the area A is absorbed. The area A is approximately A ≒ 0.13λ
² (λ is the wavelength). On the other hand, the receiving resistance R is
When a short circuit occurs as shown in (B), the received power is reflected in the opposite phase, but the reflection area A _S (scientific name is the scattering cross section) is approximately given by A _S ≒ 0.52λ ² (λ is the wavelength). Larger than the area A of absorption.

That is, the periphery of the half-wave antenna 11 operates as if it were a transparent reflector. This is the principle of the FSS, and a resonance element corresponding to a state in which the antenna terminating resistor is short-circuited acts as a reflector having an area corresponding to the reflection area in a surrounding electromagnetic field. As a matter of course, radio waves having a frequency that does not resonate are transmitted without being reflected, and thus do not impede the application of electromagnetic waves other than the resonance frequency.

In the FSS, the surface on which reflection is actually performed is not a surface having a small thickness, but is a half-wavelength antenna 11, that is, a spheroid having an element as an axis. It also has shielding performance for the gap s (see FIG. 1) between the frame metal and the radio wave shielding sheet. In practice,
In many cases, the radio wave shielding sheet FSS is composed of a plurality of elements in multiple directions so as to function on the polarization plane of an arbitrary radio wave.

[0010]

However, the conventional radio wave shielding sheet provided on the glass surface has the following disadvantages.

(1) The resonance of the conductive element 10 of the FSS, and thus the FSS
The overall resonance frequency is greatly affected by the dielectric constant of the dielectric substance close to the conductive element 10, but when glass is the base, the dielectric constant to affect depends on the type and thickness of the glass, It also depends on the presence or absence of glass surface treatment for ultraviolet rays, infrared rays, etc. For this reason, adapting to a wide variety of various commercially available glasses complicates the problem and makes it difficult to solve it industrially.

(2) The window glass is exposed to the outside air, and raindrops and water droplets due to dew condensation adhere to the surface thereof on a daily basis. While the relative dielectric constant of glass is 3 to 7, the relative dielectric constant of water is about 80, and the resonance point of FSS fluctuates due to the attachment of water droplets, and the effect of electromagnetic shielding becomes unstable.

(3) An indoor-installed base station 5 is indispensable for a PHS dedicated to indoor use. Base stations and outdoor mobile phones for security purposes to prevent information in the indoor PHS from leaking to the outside, and to prevent indoor carriers from being used outdoors and reduce the frequency of indoor busy. It is conceivable to suppress the connection with the telephone 7. It is considered as a rough guide to avoid the direct coupling between the outdoor mobile phone 7 and the indoor base station 5 whose distance d from the indoor base station 5 is 10 meters. The output power of the base station is legally required to be 10 mW, the electric field strength of the radio wave transmitted by the base station antenna is about 110 dBμV / m, and the propagation loss in 10 m of free space is expected to be about 58 dB (frequency about 2 GHz). Since the minimum receiving sensitivity of the mobile phone 7 is about 10 dBμV / m,
Approximately 40 dB (110-58-1
0) is assumed. However, if the cross-shaped conductive elements 10 shown in FIG.
20dB attenuation is the limit.

Accordingly, an object of the present invention is to provide a radio wave shielding area in a building surrounded by a radio wave shielding wall having a high attenuation rate which is not affected by a change in the dielectric constant of the surface of a window glass.

[0015]

In order to achieve the above object, the present inventor has determined that a conventional FSS conductive element has an isotropic shape in the sense that it has the same shape in two axial directions of a rectangular coordinate system. Or, it is a simple linear dipole shape, and the spacing c between the elements to improve the attenuation factor (see FIG. 2D)
It has been noted that if the distance is narrowed, interference occurs between the elements, so that the attenuation rate cannot be increased beyond a certain limit. If the conductive element has an anisotropic shape having different shapes in the biaxial directions of the predetermined orthogonal coordinate system, it is possible to avoid interference between the elements and obtain a high attenuation rate even when the interval c between the elements is narrowed. Found experimentally. In addition, a gap s (see Fig. 1) from the window glass surface to FSS
The FSS function is not strongly affected by the dew condensation on the glass surface.

In the embodiment shown in FIG. 1, the radio wave shielding area 15 in the building according to the present invention is a radio wave shielding area in a building in which the floor and the ceiling surface and the surrounding wall with the conductive window frame 3 are all partitions 2 having electromagnetic shielding ability. In the area 15, the length a ₁ in the biaxial direction of the predetermined rectangular coordinate system,
b ₁ (see FIG. 2 (A)) is a conductive element 9 (see FIG. 2, hereinafter sometimes referred to as an anisotropic conductive element) having a half wavelength or less of a radio wave of a frequency to be shielded. A radio wave shielding sheet 4 spread over the entire predetermined surface along the two axes at an interval c.
And the gap s between the window frame 3 and the plane defined by the window frame 3 and the plane body 4 is set to a size of one third to one half of the wavelength. It becomes as. Preferably, the inter-element interval c is set to one-tenth or less of the wavelength of the frequency radio wave to be shielded.

The lengths a ₁ and b ₁ of the conductive element 9 in the biaxial direction of the predetermined rectangular coordinate system are set to be equal to or less than a half wavelength of the radio wave of the frequency to be shielded in order to resonate and shield the radio wave of the frequency. It is. The interval c between the adjacent conductive elements 9 is set to be equal to or less than a half wavelength of the frequency, and preferably equal to or less than one-tenth wavelength in order to obtain high attenuation at the frequency. When the gap s between the window frame 3 and the plane defined by the window frame 3 and the radio wave shielding sheet 4 is set to have a size in the range of one third to one half of the wavelength, when the width is smaller than this range, The performance of the radio wave shielding sheet 4 is degraded by the influence of moisture that may adhere to the window frame 3 and the surface defined by the window frame 3, and if it is wider than this range, the radio wave shielding in this gap s decreases. is there.

Preferably, the conductive element 9 is an anisotropic conductive element having different shapes in two axial directions of a predetermined rectangular coordinate system. Further, the radio wave shielding sheet 4 can be formed by mounting the conductive element 9 on a transparent non-conductive film.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As is clear from the embodiment shown in FIG. 1, the radio wave shielding area 15 according to the present invention is composed of a floor surface 2f, a ceiling surface 2c and a peripheral wall 2w with a conductive window frame 3 having electromagnetic shielding ability. Since it is surrounded by the partition wall 2, except for the inner window 1 of the conductive window frame 3, the ingress and egress of radio waves are suppressed to the extent necessary for radio wave shielding. The radio wave shielding planar body 4 covering the window 1 has lengths a ₁ and b ₁ in two axial directions such as an x-axis and a y-axis in a predetermined rectangular coordinate system (FIG. 2).
(A)), an FSS formed by laying a conductive element 9 having a frequency to be shielded, for example, a half wavelength or less of a radio wave of 1.9 MHz, on the entire surface along the two axes at an element interval c of the half wavelength or less.
In addition, since the gap s between the window frame 3 and the surface defined by the window frame 3 and the radio wave shielding sheet 4 is set to a size of one third to one half of the wavelength, the radio wave in the window 1 Attenuation is also maintained to the extent required for radio wave shielding.

As a whole, the radio wave shielding area 15 is completely surrounded by a partition having a necessary radio wave shielding ability, so that radio wave propagation inside and outside the shielding area 15 can be suppressed to a required limit or less. Moreover, there is a gap between the window 1 and the window frame 3 and the radio wave shielding sheet 4.
s, so even if water drops on window 1 or window frame 3 (not shown)
Even if there is such adhesion, the radio wave shielding performance of the radio wave shielding planar body 4 does not directly decrease due to the dielectric constant of the water droplet.

Thus, the object of the present invention is to provide "a radio wave shielding area in a building surrounded by a radio wave shielding wall having a high attenuation rate which is not affected by a change in the dielectric constant of the window glass surface".

As shown in FIG. 2A, if the conductive element 9 is formed into an anisotropic shape having different shapes in two axial directions such as an x-axis and a y-axis in a predetermined orthogonal coordinate system, for example, a Y-shaped element is used. Even if the interval c is reduced, the effective parallel length between the adjacent elements 9 can be suppressed, and interference between elements can be avoided. Therefore, FIG.
2 (A) and FIG. 2 (C) can be achieved by the radio wave shielding sheet 4 including the conductive elements 9 shown in FIG. 2 (B). It has been experimentally confirmed that this can be achieved. Table 1 shows the element dimensions a and b and the element spacing c of these examples together with the conventional example shown in FIG.

[0023]

[Table 1] Table 1 (unit cm) Drawing number abc 2 (A) 0.236 (width w = 0.02) 0.272 0.003 2 (B) 0.306 0.353 0.003 2 (C) 0.433 0.375 0.003 2 (D) 0.5 0.5 0.5

The function of the conductive element 9 having an anisotropic shape will be described. The antenna and the conductive element 9 of the FSS which operates in a similar manner generate a standing wave at a resonance frequency as is widely known. The curve V in FIG. 3 shows that the voltage is high at the tip of the antenna or the conductive element 9 (open end and the impedance is extremely high), while the standing wave voltage is almost zero at the center thereof (the impedance is extremely low). Indicates that

In a conventional linear element, as shown in FIG. 3A, a high standing wave voltage and a high impedance at an end facilitate coupling between adjacent elements at the end.
In the figure, the distance c between the elements at
_{As shown} in Fig. ₄ , it must be kept at about a half wavelength of the resonance frequency. On the other hand, in the conductive element 9 having, for example, a Y-shaped anisotropic shape, as shown in FIG. 3B, the adjacent conductive element 9 is always brought close only to the central portion having low impedance and the end portion having high impedance. It becomes possible.

The limitation of the distance c between adjacent conductive elements causes a phenomenon as shown in FIG. That is, for example, in the case of the cross-shaped isotropic conductive element 10, the inter-element spacing c must be increased, so that the reflection area A _S of each element 10 in FIG. A gap is formed as in (). On the other hand,
For example, in the conductive element 9 having a Y-shaped anisotropic shape, the distance c between the elements can be reduced, so that the adjacent conductive element 9 shown in FIG.
The reflecting surface of the superposition above a certain reflection level as shown in FIG. 4 (B) the reflection area A _S due can be continuously formed. In short, the inter-element spacing c
, The element density (proportional to the reflection attenuation) is increased, and the radio wave shielding sheet 4 having a high attenuation can be provided.

FIG. 6 shows that the attenuation factor of the FSS using the conventional isotropically shaped conductive element 10 is less than about 20 dB as indicated by the dotted line, whereas the anisotropically shaped conductive element 9 of the present invention is used. Used
The FSS shows that a high attenuation rate of 40 dB or more can be obtained as shown by the solid line. In the case of the conductive element 10 having an isotropic shape, since radio waves leak from the gap between the elements, the conductive element 10
Even if the resistance value itself is reduced, the shielding attenuation is not improved beyond a certain limit.

Furthermore, according to the present invention, the radio wave shielding sheet 4
Is provided away from the window frame 3 and the window 1, so that the window glass 1a
(FIG. 7), the structure of the window frame 3 and the physical properties of the material are not affected, and a change or the like that can flexibly adapt to the change of the communication system can be easily performed.

[0029]

FIG. 7A shows an embodiment in which a higher shielding attenuation is provided by arranging the radio wave shielding planes 4 in a double manner. FIG. 7B shows an embodiment in which a heat-reflective transparent metal film 8 is disposed between the window glass 1a and the radio wave shielding sheet 4 to further enhance the shielding attenuation by a synergistic effect of the two.

FIG. 8A shows a composite anisotropic element 19 in which a Y-shaped anisotropic conductive element 9b is arranged inside a triangular anisotropic conductive element 9a. An example in which the conductive elements 19 are spread to form the radio wave shielding sheet 4 will be described. In this case, the shielding function is exhibited at a plurality of resonance frequencies. FIG. 8 (B)
This is an embodiment in which a triangular anisotropic conductive element 9d is arranged between adjacent Y-shaped anisotropic conductive elements 9b, and a shielding function is similarly exhibited at a plurality of resonance frequencies.

In the above description, a PHS using a carrier wave in the 1,900 MHz band is assumed. However, similar effects and applications exist in a wireless LAN in the 2,450 MHz band. Further, it will be apparent to those skilled in the art that various modifications can be made to the above-mentioned radio wave shielding area in the building within the technical scope of the present invention.

[0032]

As described above in detail, the radio wave shielding area in a building according to the present invention is provided with a gap between the radio wave shielding sheet and the window, and more preferably a radio wave shielding made of an anisotropic conductive element. The use of the planar body has the following remarkable effects.

(A) Electromagnetic shielding can be performed without being affected by moisture that can adhere to window glasses and window frames. (B) A radio wave shielding area having a high degree of radio wave shielding can be provided by using a radio wave shielding planar body in which the distance between the conductive elements is reduced. (C) It is possible to easily cope with a change of a carrier wave frequency in a wireless communication system such as a PHS by replacing a radio wave shielding sheet. (D) If a transparent conductive element is used, it is possible to shield radio waves without impairing the lighting properties of the window glass and observing the external scenery. (E) It can be easily adapted to windows of existing buildings.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a radio wave shielding area in a building according to the present invention.

FIG. 2 is a diagram showing a structural example of a conductive element for a radio wave shielding sheet.

FIG. 3 is a diagram showing a voltage distribution in a conductive element.

FIG. 4 is a diagram showing a distribution of an equivalent radio wave reflection surface around a conductive element in a radio wave shielding plane.

FIG. 5 is a diagram showing a distribution of an equivalent radio wave reflection surface around a conductive element alone.

FIG. 6 is a graph showing a comparison of radio wave shielding performance between an isotropic conductive element and an anisotropic conductive element.

FIG. 7 is an explanatory diagram of another embodiment relating to radio wave shielding of a window.

FIG. 8 is a diagram showing a composite arrangement of conductive elements having different shapes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Window 2 ... Partition wall 3 ... Window frame 4 ... Radio wave shielding sheet | seat 5 ... Base station 6 ... In-area mobile phone 7 ... Out-of-area mobile phone 8 ... Transparent metal film 9 ... Anisotropic conductive element 10 ... Isotropic Conductive element 11 ... Half-wave antenna 14 ... Radio wave 15 ... Shielding area of radio wave 19 ... Composite anisotropic conductive element

Claims (12)

[Claims] In a radio wave shielding area in a building, in which a floor / ceiling surface and a surrounding wall with a conductive window frame are all partitions having an electromagnetic shielding ability, a frequency to be shielded in a biaxial direction of a predetermined orthogonal coordinate system. A radio wave shielding planar body in which conductive elements having a wavelength equal to or less than a half wavelength of the radio wave are spread over the entire predetermined surface along the two axes at an interval between the elements equal to or less than the half wavelength, stretched in parallel with a surface determined by the window frame, and A radio wave shielding area in a building in which a window frame and a gap between a plane defined by the window frame and the planar body have a size of one third to one half of the wavelength. 2. A radio wave shielding area in a building according to claim 1, wherein said conductive element is an anisotropic conductive element having different shapes in two axial directions of said predetermined orthogonal coordinate system. 3. A radio wave shielding area in a building according to claim 1, wherein an element interval between said conductive elements is set to one tenth or less of said radio wave wavelength. 4. A radio wave shielding area in a building, wherein the radio wave shielding planar body is formed by laying over the entire surface of a transparent resin thin film in the above-mentioned mode in the radio wave shielding area according to any one of claims 1 to 3. 5. A radio wave shielding area in a building, wherein the radio wave shielding area according to any one of claims 1 to 4, further comprising the planar body provided on a side of the planar body opposite to the window frame. 6. A window glass is attached to the window frame in any of the radio wave shielding areas according to any one of claims 1 to 5, and a gap between the window frame and the window glass and the planar body is set to be 30 minutes of the wavelength. A radio wave shielding area inside a building that has a size of one to one half. 7. The radio wave shielding area in a building, wherein the radio wave shielding plane is provided on the side of the window glass on the side of the radio wave shielding area in the building. 8. The radio wave shielding area in a building according to claim 6, wherein a transparent metal film is provided in a gap between said window glass and said planar body. 9. A radio wave shielding area in a building, wherein each of the conductive elements of the radio wave shielding planar body has a Y-shape in the radio wave shielding area according to any one of claims 1 to 8. 10. A radio wave shielding area in a building, wherein each of the conductive elements of the radio wave shielding planar body has a triangular shape in the radio wave shielding area according to any one of claims 1 to 8. 11. In the radio wave shielding area according to any one of claims 1 to 8, each conductive element of the radio wave shielding plane is formed by a hollow triangular wire member and a Y-shaped member provided in the hollow portion. A radio wave shielding area inside the building that is formed as a composite anisotropic conductive element. 12. A radio wave shielding area in a building according to any one of claims 1 to 11, wherein said partition wall is used as a vehicle structural member.