JP5665293B2 - Translucent wave absorber - Google Patents

Description

  The present invention relates to a radio wave absorber that absorbs radio waves without obstructing optical information.

  With the widespread use of ETC devices based on electromagnetic wave communication technology using circularly polarized wave transmitting / receiving antennas, there is an increasing demand for installing multiple lanes instead of single gates. As a risk in parallel lanes, in the transmission and reception, a failure due to radio wave interference is likely to occur in adjacent lanes due to reflection from a vehicle, particularly a large vehicle, and an interference-preventing radio wave absorption wall is required between the lanes to prevent the failure. This interference-preventing radio wave absorbing wall is premised on ensuring a field of view where a parallel running partner can be seen as a risk of parallel merging.

  When a consumer ETC device based on electromagnetic wave communication technology using a circularly polarized wave transmitting / receiving antenna is realized in a drive-through or a semi-underground parking lot, an interference preventing radio wave absorbing wall is required. According to the present invention, it is possible to secure a field of view for preventing the effects of radio wave interference and preventing danger due to parallel merging by automatic toll collection at the parallel gate. Further, since light is transmitted, sunlight can be taken into the room when the present invention is used as a roof.

  Conventionally, in response to this requirement, transparent special electromagnetic wave absorbing material, one having a transparent plate and a conductive resistance film to ensure translucency, or using a carbon material or a ferrite material to form a lattice or net structure Constituent materials such as these have been proposed.

For example, Patent Document 1 discloses that a resin sheet is sandwiched between two glass plates as a transparent shielding / absorbing material used for a toll island partition in a toll gate on a highway, and the glass plate and the resin sheet are in contact with each other. A radio wave absorber having a structure formed of a transparent conductive film is disclosed on the surface.

In addition, the radio wave absorber of Patent Document 2 is made of a radio wave shielding function material (for example, a stainless steel wire mesh) that prevents incoming radio waves from passing to the non-arrival side. It is characterized by being sandwiched by the formed absorbent main body (for example, glass fiber reinforced plastic).

On the other hand, as a high-frequency electromagnetic wave shielding body that shields electromagnetic waves from inside and outside at an opening in a building in order to prevent electromagnetic interference, Patent Document 3 describes that water or a substance containing water as a main component between two transparent plates. Is disclosed, and an electromagnetic wave shielding transparent body in which an electromagnetic wave shielding transparent conductive film is provided on the transparent plate is disclosed.
JP 2008-182045 A JP 2007-067766 JP JP 05-037178 A

In order to obtain highly reliable communication, the radio wave absorber is required to have a capability of stably absorbing radio waves of a target frequency with high efficiency. Conventionally, most of the materials are colored materials and special materials such as ferrite and carbon, and high-precision processing and special equipment for that purpose are required to match the radio wave absorption performance to the radio wave band. Furthermore, there is a concern that the conductive film as described above may be peeled off by wind or the like when installed on an ETC island. Also in Patent Documents 1 and 2, there is a problem that the cost of special materials and conductive resistive films is generally high. In addition, the grating shape and the lattice wall in Patent Document 2 have restrictions on the shape for securing the absorption characteristics, and the blind spots on the field of view cannot be avoided. Further, such a solid wave absorber requires a rigorous design according to the frequency of the radio wave to be absorbed, and it is difficult to adjust the frequency band.

In Patent Document 3, there is a function of a window through which solar radiation or the like enters, and electromagnetic waves such as various radio waves entering from the outside are reflected and shielded by a transparent conductive film, and the reflected electromagnetic waves are absorbed by water or the like. This is based on the knowledge that the transmission loss of radio waves due to water is high, and the air between window glass plates is made into water, and the performance value for absorbing specific radio waves has not been clarified. In addition, if the sealed liquid leaks, changes or deteriorates, the light transmission and electromagnetic wave absorption performance will be affected. Since the characteristics of radio wave absorption change significantly due to changes in temperature, material deformation, etc., the performance of radio wave absorbers in ETC systems based on electromagnetic wave communication technology using circularly polarized wave transmission / reception antennas does not change throughout the seasons. Or it can be tuned for optimum performance.

The present invention has been made in view of such circumstances, and in a parallel lane of an ETC system, it has translucency for preventing radio wave interference, even if the frequency characteristics change due to changes in the external natural environment. An electromagnetic wave absorber that can be used is provided. In addition, since the present invention can be a translucent radio wave absorber with reduced material cost, it is not limited to an ETC system based on an electromagnetic wave communication technology using a circularly polarized wave transmitting / receiving antenna, and the radio wave absorber and radio wave for uniform polarization It can be used in a wide range of applications besides dark rooms.

  According to the first aspect of the present invention, a translucent liquid or a sol-like substance is sealed between two transparent plates facing each other at an interval equal to or greater than the radio wave penetration depth. Alternatively, double-sided absorption that absorbs radio waves incident on one transparent plate and absorbs radio waves incident on the other transparent plate by matching or close to each other so that the radio wave impedances of the sol-like materials cancel each other. It is set as the translucent electromagnetic wave absorber characterized by having performance.

The invention according to claim 2 is provided with a radio wave reflecting material having translucency in the liquid or sol-like substance when the radio wave absorbing substance layer thickness of the liquid or sol-like substance is less than the radio wave penetration depth, This radio wave reflector is used to control the phase and amplitude of the reflected wave from the transparent plate and the front surface of the liquid or sol-like substance so that the radio wave impedance matches or approaches it. A translucent radio wave absorber characterized by being provided so as to be movable.

  The invention according to claim 3 is the net according to claim 2, wherein the radio wave reflecting material is a net having radio wave reflectivity.

According to a fourth aspect of the present invention, in any one of the first to third aspects, an external connection port that allows the liquid or sol-like substance to enter and exit is provided.

When absorbing high-frequency radio waves of a specific frequency such as ETC radio waves, the radio wave absorber may be affected by external changes such as temperature and humidity, and the radio wave absorption performance may change. I couldn't make that adjustment, and I had to replace it if it went crazy. However, the translucent radio wave absorber according to claim 1 is hardly affected by the radio wave absorption performance due to temperature change or the like by using an absorption layer having a radio wave penetration depth or more.

The invention described in claim 2
(1) When absorbing high-frequency radio waves of a specific frequency such as ETC radio waves, the radio wave absorber is affected by external changes such as temperature and humidity, and the radio wave absorption performance changes and adjustment is required. In this case, adjustment is performed by changing the distance between the radio wave reflecting material and the transparent plate, and stable radio wave absorption performance can be obtained.
(2) The radio wave absorption characteristic is to work to cancel the phase and amplitude with the reflected wave from the surface material of the absorber and the reflected wave from the inside, and changes with the distance between the transparent plate where the radio wave enters and the radio wave reflecting material Therefore, by controlling the distance, stable radio wave absorption performance can be obtained in response to radio wave adjustment in the optimum frequency band for changes in the natural environment.

  The translucent radio wave absorber according to claims 1 to 3 can be configured without using a special material, and the material cost can be suppressed. In particular, the first aspect of the present invention has a simple structure of a transparent plate and a liquid or sol-like substance, and there is nothing that obstructs light transmission inside, so that the visibility is excellent.

The translucent wave absorber according to claim 4 is:
(1) When the radio wave absorber is affected by external changes such as temperature, and the radio wave absorption performance changes, it is connected to the external unit and the liquid or sol-like substance that is the internal component Stable radio wave absorption performance can be obtained by controlling temperature, solution concentration, and the like.
(2) In addition, when the liquid or sol-like substance is altered or deteriorated and its translucency or radio wave absorption is affected, stable radio wave absorption performance can be obtained by maintenance such as replacement. .
(3) By replacing the liquid or sol-like substance, the radio wave absorption characteristics can be changed, and radio wave absorption can be performed in accordance with the radio wave of the frequency to be absorbed at high frequencies.

Sectional drawing of the translucent electromagnetic wave absorber in connection with embodiment of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention The graph which showed the electromagnetic wave absorption characteristic of one Example of invention

  A translucent wave absorber according to the present invention will be described with reference to the cross-sectional view of FIG.

The transparent plate 10 is a hard transparent plate such as an inorganic plate glass or an organic glass plate (polycarbonate plate, acrylic plate, etc.), and a transparent film or film is formed on the surface to prevent scattering, or the film or film is sandwiched. It may be sandwiched between transparent plates.

The liquid or sol-like substance 11 enclosed between the two transparent plates 10 is water or a solution dissolved in water, a transparent organic liquid or a solution dissolved therein, an inorganic transparent liquid or a solution dissolved therein, and a mixture thereof. It is a liquid. Specifically, the solution is based on water, electrolytes with high solubility such as sodium chloride, potassium chloride, calcium chloride, sodium sulfate, potassium sulfate, etc., solutions of sugars such as glucose, fructose, sucrose, lactose, citric acid A solution of an organic acid such as ascorbic acid or acetic acid, a simple substance or a diluted liquid of alcohols such as methyl alcohol, propylene glycol, glycerin, ethylene glycol or ethyl alcohol, or a simple substance or a mixed liquid thereof. To the sol-like substance, a polymer material such as starch paste, carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol or the like is added to the above solution to stabilize the solution and the mixed solution while ensuring fluidity. The radio wave can be attenuated by the liquid or sol-like substance 11 having a high radio wave transmission loss at a high frequency.

The translucent radio wave reflecting material 12 disposed in the liquid or sol-like substance 11 is formed by forming a transparent conductive film on a transparent substrate such as glass, a film, a sheet, and the like. Any material that reflects radio waves may be used to shield radio waves. The transparent conductive film contains a metal oxide such as ITO as a main component. The radio wave reflecting material 12 is provided in parallel to the transparent plate and is movable in a direction in which the distance from the transparent plate is changed. The film-shaped or sheet-shaped radio wave reflecting material 12 may be spread and fixed to a frame body or an X-shaped frame that can hold the four corners. Further, it is desirable that the radio wave reflecting material 12 has a large surface so that the radio wave reflecting material 12 can move in a liquid or sol-like substance. Alternatively, the radio wave reflector 12 may have a hole having a diameter of a quarter wavelength or less of the radio frequency.

Further, the radio wave reflecting material 12 having translucency may be a net having radio wave reflectivity that is structurally translucent. The net having radio wave reflectivity may be a net and a material that does not transmit radio waves, such as metal, conductive carbon, and conductive plastic. The mesh may be equal to or less than a quarter wavelength of the radio frequency. If the ETC radio wave is in the 5.8 GHz band, the mesh is 12.9 mm or less. The thinner the wire diameter of the net, the more advantageous it is for light transmission.

For example, if the radio wave reflecting material 12 having translucency is configured by forming the radio wave reflecting material 12 on a hard substrate such as glass, one or a plurality of legs are provided on the substrate in a direction perpendicular to the glass surface. The distance of the radio wave reflecting material 12 from the transparent plate 10 can be moved by providing and extending the outside of the transparent plate 10 and moving its legs back and forth.

The film-like or sheet-like radio wave reflector 12 is provided with, for example, one or more legs at right angles to the corners of the frame that supports the radio wave reflector 12, and extends to the outside of the transparent plate 10, and the legs are moved back and forth. By changing the distance, the distance of the radio wave reflecting material 12 from the transparent plate 10 can be moved. The legs can be fixed with a cylinder, connected to the cylinder with a hose from the outside, and the distance can be adjusted by adjusting the pressure in the cylinder. In this case, the pressure adjusting liquid may not be the liquid of the absorber. The translucent radio wave absorber of the present invention has the same radio wave absorption performance for radio waves from either direction of the two transparent plates, and there are a plurality of radio wave reflectors 12 as well as single. Also good. In this case, a transparent plate or the like unrelated to radio wave absorption can be provided in the middle of the plurality of radio wave reflectors 12, and the transparent plate can be fixed with legs or cylinders that can move the distance of the radio wave reflector 12 respectively. .

The external connection port is for allowing the liquid or the sol-like substance 11 inside the translucent radio wave absorber to enter and exit, and is preferably formed on a transparent plate. It becomes possible to control deterioration and temperature change. The number of external connection ports is not limited to one, and a plurality of external connection ports may be provided for circulation. Moreover, you may connect to an external pump unit etc. as needed instead of connecting to the exterior as a water stop cock.

In particular, when it is necessary to use the radio wave absorber according to the present invention for an island of an ETC facility based on electromagnetic wave communication technology using a circularly polarized wave transmitting / receiving antenna, it is necessary to absorb radio waves from both lanes. It is also possible to provide two translucent radio wave reflectors 12 in the liquid or sol-like substance 11 of the translucent radio wave absorber according to the invention so that the distance from each transparent plate 10 can be adjusted. Alternatively, the two radio wave reflecting materials 12 may not be provided in the liquid or sol-like substance 11 and may be installed back to back.

  Since radio wave absorption depends on the dielectric properties, magnetic properties, and conductive properties of the material, the radio wave absorption properties are determined by the material and thickness of the transparent plate 10 and the type and thickness of the liquid or sol-like material 11. come. The example at the time of implementing as a translucent electromagnetic wave absorber is shown below. It is evaluated by measurement using a circularly polarized wave transmitting / receiving antenna.

Figure 5 shows the oblique incidence characteristics of a translucent wave absorber with a mixed solution layer of 5% potassium chloride and 10% methanol filled with a 5mm thick float glass plate and a mixed solution layer thickness of 15mm. 2 is a graph of 2. Measurement was performed by attaching a circularly polarized wave transmitting / receiving antenna to an arch type measuring instrument, changing the incident angle every 10 degrees from 10 degrees to 60 degrees, and measuring the reflection characteristics of radio waves from 4.5 to 8 GHz with a network analyzer. . Regardless of the angle change, there is very little deviation in the characteristic change. From this data, the impedance of the float glass plate and the impedance of the mixed liquid almost coincide .

  FIG. 3 is a graph showing the performance at 5.8 GHz, which is an ETC communication radio wave, in the oblique incidence characteristic measurement data of the previous paragraph. Performances of -31 to -47 dB were exhibited at angles from 10 to 50 degrees.

  It is a translucent wave absorber composed of a 5mm thick metal net filled with ethylene glycol between 5mm thick acrylic plates, and 4.5-8GHz by changing the position of the metal net from the acrylic plate. The graph of FIG. 4 shows the radio wave absorption characteristics reflected between the two. The measuring apparatus uses an arch type measuring instrument with a radius of 1.5 meters and measures reflection characteristics with an incident angle of 10 degrees, a network analyzer, and a circularly polarized wave transmitting / receiving antenna. As a result of changing the distance from the acrylic plate to the metal net from 4.5 to 2.5 mm, there is -10 dB in almost the whole band, and when the ethylene glycol thickness is 2.5 mm, a reflection peak near -45 dB is shown near 6.3 GHz, An ultra-wideband characteristic of -35 dB was exhibited at 6.5 to 8.0 GHz.

  It is a translucent wave absorber composed of a 5mm thick metal net filled with water between 5mm thick float glass plates. The position of the metal net from the float glass plate is changed to 4.5 ～ The graph of Fig. 5 shows the radio wave absorption characteristics reflected between 8GHz. The thickness of the water layer up to the metal net is around 4.0 mm and 3.5 mm, and the peak of reflection (absorption peak) has two peaks (bimodal).

  FIG. 6 is a graph showing the result of measurement in the same manner as the translucent radio wave absorber in which the water in the previous paragraph is a mixed solution of water and 20% propylene glycol. When the thickness of the liquid layer up to the metal net was 4.25 mm, a reflection performance peak of −40 dB was observed at around 5.5 GHz.

  FIG. 7 is a graph showing the result of measurement in the same manner for a translucent radio wave absorber in which the water in the previous paragraph was a 5% saline solution. This characteristic hardly changes even when the thickness of the liquid layer up to the metal net changes, has an absorption peak around 5.6 to 5.9 GHz, and around 5.9 GHz at a liquid layer thickness of 4.75 mm to the metal net. It showed a reflection characteristic of -40dB.

  Fig. 8 shows the results of the measurement of oblique incidence characteristics in ETC by the electromagnetic wave communication technology using a circularly polarized wave transmitting / receiving antenna, which is a translucent wave absorber in which the 5% saline solution in the previous paragraph is made 5% potassium chloride water. It is a graph of. The reflection characteristics were measured by changing the incident angle from 10 to 60 degrees, and the graph is data representing the oblique incident performance picked up at a reference frequency of 5.8 GHz and expressed for each angle. As a result of selecting a more appropriate liquid layer thickness in consideration of characteristics that are difficult to change due to a change in incident angle, a performance of -32 to -42 dB was shown.

Filled with 5% saline solution between 5mm thick float glass plates, is a translucent wave absorber composed of a metal net of 5mm with a wire diameter of 0.2Φ, and from the float glass by changing the position of the metal net Figure 9 shows the radio wave reflection characteristics when the thickness of the liquid layer up to the metal net is changed from 3 mm to 7 mm. When the liquid layer thickness is 4 mm or more, the radio wave reflection characteristics do not change greatly. This indicates that a metal net is not required when the thickness of the radio wave absorber layer is greater than the radio wave penetration depth.

10 .... Transparent plate, 11 .... Liquid or sol-like substance, 12 .... Radio wave reflecting material

Claims (4)

A translucent liquid or sol-shaped wave absorbing material is sealed between two transparent plates facing each other at an interval greater than the radio wave penetration depth, and the radio wave impedance of the transparent plate and the radio wave of the liquid or sol-shaped material By matching the impedance, the reflected wave from the transparent plate and the reflected wave from the inside cancel the phase and amplitude , absorb the radio wave incident on one transparent plate, and enter the other transparent plate A translucent radio wave absorber characterized by having a double-sided absorption capability that also absorbs radio waves.
In a radio wave absorber in which a translucent liquid or sol-like radio wave absorber is enclosed between two transparent plates facing each other with a distance less than the radio wave penetration depth, the translucent liquid or sol substance is translucent. A translucent radio wave absorber characterized in that a radio wave reflecting material having a property is provided and the radio wave reflecting material is movable. The translucent radio wave absorber according to claim 2, wherein the radio wave reflecting material is a net having radio wave reflectivity.
The translucent radio wave absorber according to claim 1, further comprising an external connection port through which the liquid or sol-like substance can enter and exit.

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