JP4570064B2 - Radio wave absorption road - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave absorbing road, and more particularly, to a radio wave absorbing road that can prevent transmission errors caused by reflection on the road surface of radio waves used in communication between roads and vehicles or between vehicles and vehicles.
[0002]
[Prior art]
Intelligent transportation systems (ITS) that include people, roads, and vehicles in an integrated system have been built using state-of-the-art information and communication technologies. Since this ITS includes mobile objects, it communicates wirelessly and uses signals in the GHz band to several tens of GHz band. That is, the 2.5GHz band for the road traffic information communication system VICS, the 5.8GHz band for the automatic toll storage system ETC, the 36-38GHz band for the road-to-vehicle communication system, the 60GHz band for the inter-vehicle communication system, the 76GHz band for the automotive radar system, etc. is there.
[0003]
At such a frequency of 1 GHz band or higher, radio waves are likely to be reflected on the road surface (road surface) and cause a multipath failure. Therefore, it is necessary to reduce this road surface reflection.
[0004]
An example of a conventional method for preventing road surface reflection is proposed in Japanese Patent Publication No. 60-003106. In this method, on the one hand, load resistance and abrasion resistance necessary for roads are ensured by asphalt pavement, and on the other hand, in order to suppress radio wave reflection, the asphalt composition used for the pavement is made of an inorganic dielectric such as ferrite. Filled with filler. Further, the normalized input impedance Z with respect to the jamming radio waves of the asphalt pavement as seen from the surface is adjusted to be approximately 1. In this case, since the normalized input impedance of air is selected as 1, the reflectance of the radio wave incident on the asphalt pavement in which Z is adjusted to approximately 1 from the air can be kept low.
[0005]
The reason why the input impedance Z of the asphalt pavement can be adjusted as described above is as follows. That is, the normalized input impedance Z of asphalt pavement is given by the following formula (1), but its complex relative permeability μ _r is 1, so that the complex relative permittivity ε _r is adjusted by the component composition and its thickness By adjusting t, the value of Z for the frequency of the specific wavelength can be made close to 1. In equation (1), μ _r is the complex relative permeability of the asphalt pavement, ε _r is its complex relative permittivity, λ is the wavelength of the radio wave to be reflected in free space, and t is the thickness of the asphalt pavement.
[0006]
[Expression 1]
Z = (μ _r / ε _r ) tanh j {(2π / λ) t (μ _r / ε _r ) ^1/2 } (1)
[0007]
[Problems to be solved by the invention]
However, the conventional method has a problem that the reflected wave cannot be sufficiently weakened because there is a relatively high limit in suppressing the reflection of radio waves.
[0008]
As expected from the above asphalt pavement, in order to reduce the reflection of radio waves on the road surface, it is necessary that the material of the road surface has a radio wave refractive index close to 1 at the interface with air. . A desirable material in terms of the refractive index of the radio wave is a foam containing a lot of air and cannot be applied to roads that require load resistance and wear resistance. A high-density inorganic material having load resistance and wear resistance has a limit in bringing the refractive index of the radio wave closer to 1, and thus has a limit on the effect of suppressing radio wave reflection.
[0009]
In addition, when the road surface is covered with water due to rain, water spray, etc., the radio waves are easily reflected. It is required to improve drainage at the time of rainfall and to prevent the road surface from being covered with water simultaneously with suppression of radio wave reflection.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a radio wave absorbing road in which radio wave reflection on the road surface is reduced and reflected waves are scattered to suppress the influence of reflection.
[0011]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventor has provided unevenness on the road surface to scatter reflected radio waves to reduce the influence of reflection, and at the same time improve drainage to reflect the radio waves during raining and watering. We paid attention to the fact that it can be reduced.
[0012]
Referring to FIG. 1, a radio wave absorbing road according to the present invention is a road having a roadbed 3, a base layer 2 and a surface layer 1, and is made of a material having a lower dielectric constant and higher load resistance and wear resistance than the base layer 2. 2 is provided with a drainable surface layer 1 and the surface of the surface layer 1 is compacted, bonded, embedded, etc. with a granular material 4 having a representative length of 1/10 or more of the wavelength of the reflected radio wave and a low dielectric constant. Unevenness is formed, and the reflected radio wave from the surface of the surface layer 1 is scattered by the unevenness. Here, the representative length of the granular material 4 is a spherical equivalent diameter. For example, a spherical equivalent diameter d of a particle having a volume V is d = (6V / π) ^1/3. Is the diameter d.
[0013]
The reason why the representative length of the granular material 4 for forming irregularities is 1/10 or more of the wavelength of the reflected radio wave is that the radio wave reflection from the irregularities cannot be suppressed when the material particles are smaller than that. (Katsuyoshi Sato, Satoshi Liang, Masayuki Fujise, “Reflection characteristics of various asphalt road surfaces in the millimeter wave band”, Proceedings of the IEICE Conference, Society B1, p. 10, 1998). In addition , by making the surface layer drainage, it is possible to prevent a puddle from being generated and radio waves reflected from the puddle water surface during rainfall or watering.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a radio wave absorbing road according to the present invention. In this embodiment, a base layer 2 made of asphalt or concrete pavement is provided on the roadbed 3. Furthermore, in order to reduce the radio wave reflection on the surface of the surface layer 1, the surface layer 1 is formed by laying and compacting a material having high load resistance and wear resistance and a low dielectric constant.
[0015]
Further, a granular material 4 having a representative length of 1/10 or more of the wavelength of the reflected radio wave and having a small dielectric constant is compacted on the surface of the surface layer 1, and the compacting pressure is appropriately adjusted to adjust the surface layer 1's surface. Unevenness is formed on the surface. Moreover, the unevenness | corrugation by the granular material 4 may be formed by adhesion | attachment, embedding, etc., and you may form combining suitably methods, such as compaction, adhesion | attachment, embedding. The reflected radio wave from the surface of the surface layer 1 is scattered by the unevenness to reduce the influence of reflection. As the granular material 4, aggregates such as crushed stones and ball gravel, artificial or natural resins, rubbers and the like can be used.
[0016]
Furthermore, the surface layer 1 can be made drainable in order to prevent the occurrence of water accumulation on the surface layer 1 and the reflection of radio waves from the surface of the water during raining or watering.
[0017]
Thus, it is possible to achieve the object of the present invention, that is, “a radio wave absorbing road in which the reflection of radio waves on the road surface is reduced and the reflected waves are scattered to suppress the influence of reflection”.
[0018]
【Example】
When the base layer 2 is made asphalt or concrete pavement when the radio wave reflector is intentionally or accidentally formed on the roadbed 3 by using a steel floor board or steel material, the base layer 2 asphalt or concrete absorbs radio waves. In order to provide performance, a material (high dielectric constant material) 5 that increases the dielectric constant can be mixed as shown in FIG. The reason for using the high dielectric constant material 5 is that the radio wave used in ITS has a high frequency of 1 GHz band or higher, and it is particularly necessary to prevent radio wave reflection from the road surface. This is because the radio wave absorption effect of 5 can be expected.
[0019]
For this purpose, the high dielectric constant material 5 includes a metal or oxide thereof, iron oxide or dust thereof, carbon, inorganic powder or particles such as alumina sintered body, and a material containing carbon fiber or carbon, such as rubber. The powder and particle | grains of a carbon containing material can be mentioned. Furthermore, for example, a tire which is a rubber containing carbon contains about 25% of carbon, and may be mixed with asphalt as chips or powder. Use of waste tires is preferable in terms of resource saving. Further, it is also expected that reflection on the road surface can be reduced by using cancellation due to phase inversion between the reflected radio wave at the reflector and the reflected radio wave at the surface layer 1.
[0020]
FIG. 3 shows a book in which a surface layer 1 having a thickness of 50 mm is formed by drainage asphalt on a base layer 2 having a thickness of 50 mm made of radio wave absorbing asphalt, and irregularities are provided on the surface of the surface layer 1 by crushed stones 4 having a particle diameter of 20 mm. The test body of the radio wave absorption road structure of the invention is shown. Aggregates having a particle size of 10 to 15 mm were used for the drainage asphalt of the surface layer 1. In addition, as the radio wave absorbing asphalt of the base layer 2, an aggregate having a particle size of 10 mm or less and iron oxide dust having a weight ratio of 10% with respect to the total amount of the asphalt pavement was mixed as a high dielectric constant material.
[0021]
Using the specimen shown in Fig. 3, the return loss for the radio wave with a frequency of 5.8GHz used in the automatic charge storage system ETC was measured. In general, the reflection attenuation amount is expressed by how much the reflectance is attenuated compared to the complete reflection of the aluminum plate, which uses an aluminum plate that almost completely reflects radio waves as a reference. In this measurement, a transmission / reception double rigid guide antenna is placed at a position where the incident angle and the reflection angle are both 5 degrees with respect to the surface of the measurement object, and the electric field strength of the incident wave and the reflected wave is measured by a network analyzer. The reflectance was determined. The reflection loss was calculated by comparing the reflectance when the measurement object was a reference aluminum plate with a thickness of 3 mm and the reflectance when the measurement object was the test specimen. An example of the measurement result is shown in FIG. In the figure, the return loss of the aluminum plate is 0 dB (reference value).
[0022]
As shown in the figure, the return loss of this test specimen with respect to radio waves having a frequency of 5.8 GHz was about 20 dB. The conventional general asphalt paved road has a return loss of 3 to 4 dB at a frequency of 5.8 GHz. The general target value of the return loss of the TV wave absorbing wall is 14 dB. Compared to these conventional radio wave return loss for structures such as asphalt, the return loss of about 20 dB at a frequency of 5.8 GHz of the road structure test specimen of the present invention in FIG. It can be expected to contribute to the suppression of obstacles. In addition, when the surface of the road is filled with water, the above-mentioned radio wave reflection attenuation amount becomes 0 dB. Therefore, in order to maintain the radio wave reflection attenuation and suppress the reflection radio wave disturbance even during rain, the surface layer 1 is drained. It is necessary to.
[0023]
【The invention's effect】
As described above, the radio wave absorption road of the present invention is a granular material having a low dielectric constant on the surface of the surface layer of the road structure, such as a pavement made of a material having a low dielectric constant and a high load resistance and wear resistance. Concavities and convexities are formed by compaction and the like, and the reflected radio waves are scattered by the irregularities to suppress the influence of the reflected radio waves.
[0024]
(A) The influence of reflection can be effectively suppressed by a combination of reducing radio wave reflection on the road surface and scattering the reflected wave due to unevenness on the road surface.
(B) By making the road surface layer drainable, it is possible to drain the road surface during raining or watering, prevent water from accumulating, and prevent radio wave reflection from the surface of the water pool.
(C) By combining antireflection on the road surface layer and radio wave absorption performance on the underlying layer, the influence of radio wave reflection from the road surface can be comprehensively suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of one embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing another embodiment of the present invention.
FIG. 3 is an explanatory view of a test body of a radio wave absorption road structure according to the present invention.
FIG. 4 is a graph showing the measurement results of the return loss of the test specimen shown in FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Surface layer 2 ... Base layer 3 ... Roadbed 4 ... Granular material 5 ... High dielectric constant material

Claims (6)

In roads with roadbed, base layer, and surface layer, by providing a drainage surface layer on the base layer with a material having a low dielectric constant and high load resistance and wear resistance compared to the base layer, radio wave reflection from the surface layer is suppressed, A radio wave absorbing road having irregularities formed by a granular material having a representative length of 1/10 or more of the wavelength of the reflected radio wave and a low dielectric constant on the surface of the surface layer. The radio wave absorption road according to claim 1 , wherein the base layer is made of asphalt or concrete having radio wave absorption performance. The radio wave absorbing road according to claim 1 or 2 , wherein the granular material for forming irregularities is one or more selected from the group consisting of aggregate, resin, and rubber. The radio wave absorbing road according to claim 2 , wherein powder or particles made of an inorganic substance and / or a carbon-containing substance are mixed into asphalt or concrete as a base layer. 5. The radio wave absorbing road according to claim 2, wherein rubber chips or powder containing carbon are mixed in asphalt or concrete as a base layer. 6. The radio wave absorbing road according to claim 1 , wherein a radio wave reflector is provided between the roadbed and the base layer.

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