JP2002216179A - Radio wave absorbing structure and automatic fare collecting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide radio wave absorption structure which can sufficiently absorb a radio wave radiated from a radio source for a wide range and an automatic rate collecting system by using it. SOLUTION: In radio wave absorbing structure, a plurality of sheet-like wave absorbers 1 are arranged in parallel in an inclined state with respect to a reference plane 2a. Since the sheet-like wave absorbers 1 are arranged in parallel in a state where they are inclined with respect to the reference plane 2a, the incident angles of the radio waves with respect to the respective surfaces of a plurality of sheet-like wave absorbers 1 become small even if the incident angle of the radio wave with respect to the reference plane 2a when the radio wave radiated from the prescribed radio source is made incident on the radio absorbing structure 10. Thus, the radio wave which is made incident from the radio source can sufficiently be absorbed for the wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorbing structure which absorbs unnecessary radio waves output from electronic equipment such as a computer, and suppresses unnecessary reflection of radio waves output from an antenna and a radar. The present invention relates to an automatic toll collection system that uses a system.

[0002]

2. Description of the Related Art A radio wave absorber absorbs unnecessary radio waves that cause radio wave interference, and is attached to a housing of an electronic device such as a computer so that a high-frequency pulse generated from the inside of the electronic device is transmitted outside the device. In order to prevent leakage from the antenna or radar, or to prevent the radio waves radiated from the antenna or radar from being reflected by the structure when attached to the surface of a structure around the antenna or radar. It is used.

As such a radio wave absorber, a so-called flat-plate type radio wave absorber has been conventionally known. This flat-plate-type radio wave absorber is generally composed of a flat metal layer and at least one flat radio wave absorber layer laminated on its surface. In such a radio wave absorber,
After the radio wave incident from the atmosphere to the radio wave absorber layer is gradually absorbed by the radio wave absorber layer and passed through and reflected by the metal layer, the reflected radio wave is again absorbed by the radio wave absorber layer Has become.

[0004]

However, the above-mentioned conventional flat plate type electromagnetic wave absorber has the following problems.

That is, in the above-mentioned conventional flat plate type electromagnetic wave absorber, the amount of electromagnetic wave absorption (dB) is generally shown in FIG. 4 with respect to the incident angle θ of the electromagnetic wave with respect to the normal direction of the surface of the electromagnetic wave absorber layer. Have a relationship. That is, the radio wave absorption amount (d
B) is sufficiently large when the incident angle θ is small,
Becomes larger and becomes lower at a certain value (generally about 40 °). Therefore, when a radio wave is incident from a certain radio wave source to the flat-plate type radio wave absorber, the amount of radio wave incident near the radio wave source is increased, but the radio wave incident far from the radio wave source is absorbed. The amount may be small, and radio waves radiated from a certain radio source cannot be sufficiently absorbed over a wide range.

The present invention has been made in view of the above circumstances, and provides a radio wave absorbing structure capable of sufficiently absorbing a radio wave radiated from a radio wave source over a wide range, and an automatic toll collection system using the same. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention provides a radio wave absorber comprising a plurality of sheet-shaped radio wave absorbers arranged in a state inclined with respect to a reference plane. It is a structure.

According to the present invention, since the sheet-shaped radio wave absorbers are arranged side by side with respect to the reference plane,
When a radio wave radiated from a certain radio wave source is incident on the radio wave absorbing structure of the present invention, even if the angle of incidence of the radio wave with respect to the reference plane is large, the radio wave on each surface of the plurality of sheet-shaped radio wave absorbers is not affected. The incident angle can be reduced. Therefore, radio waves radiated from the radio wave source can be sufficiently absorbed over a wide range.

Further, the automatic toll collection system of the present invention comprises:
A radio wave is emitted from the roadside antenna installed at or near the ceiling of the tollgate toward the communication area on the lane, and the vehicle-mounted device receives the radio wave when the vehicle equipped with the vehicle-mounted device enters the communication area. An automatic toll collection system that automatically collects tolls by transmitting radio waves from the vehicle-mounted device, wherein the radio wave absorption structure is installed on the ceiling of the tollgate and absorbs radio waves reflected by the communication area. The radio wave absorbing structure is a radio wave absorbing structure described above.

In the automatic toll collection system, a radio wave is emitted from a roadside antenna toward a communication area, and a vehicle entering the communication area receives a radio wave by an onboard device mounted on the communication area, and sends back the radio wave to collect a toll. Receipt is performed. In this case, after the radio wave emitted from the roadside antenna is reflected on the road surface of the communication area or the roof of another vehicle and then reflected on the ceiling of the toll gate, if the radio wave emitted by the Outside reception and transmission,
Fees may not be properly received. Therefore, in the present invention, a radio wave absorbing structure is installed on the ceiling of a tollgate, and the above-described radio wave absorbing structure is used as the radio wave absorbing structure. By doing so, radio waves incident on the ceiling at a large incident angle are incident on each of a plurality of sheet-shaped radio wave absorber surfaces of the radio wave absorbing structure at a small incident angle, and Even if the radio wave emitted from the antenna is reflected in the communication area and then enters the ceiling of the tollgate, the radio wave can be sufficiently absorbed over a wide range. For this reason, outside the communication area, the reception of the radio wave by the vehicle is sufficiently prevented, and the situation where the fee is not properly collected is prevented.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

FIG. 1 is a perspective view showing one embodiment of the radio wave absorbing structure of the present invention. As shown in FIG. 1, the radio wave absorbing structure 10 includes a plurality of sheet-shaped radio wave absorbers 1 and a support member 2 that supports the plurality of sheet-shaped radio wave absorbers 1.

The support member 2 has a shape obtained by, for example, forming a plurality of wedge-shaped notch grooves 3 on one surface of a flat plate-like member, and the plurality of notch grooves 3 are arranged side by side. . By forming the plurality of notches 3 in the support member 2 in this manner, the support member 2 is provided with a plurality of inclined bases 4.
Is formed. Therefore, these inclined tables 4 are also provided side by side, and each of the inclined tables 4 has a flat inclined surface 4a inclined at a fixed angle with respect to the flat bottom surface (reference plane) 2a of the support member 2. ing. The sheet-shaped radio wave absorber 1 is bonded and fixed to each of the inclined surfaces 4a.

The material of the support member 2 is not particularly limited, and may be, for example, plastic, concrete, metal, or the like. However, plastic is preferable from the viewpoint of ease of manufacture and lightness.

The inclined surface 4a with respect to the bottom surface 2a of the support member 2
Is not particularly limited as long as it is an acute angle.
The angle is preferably from 60 to 60 °, and more preferably 45 °. When the inclination angle is less than 30 °, in FIG. 2, for a large φ, θ also becomes considerably large, and a large amount of radio wave absorption tends to not be obtained. When the inclination angle exceeds 60 °, conversely, for a small φ, Θ becomes considerably large, and a sufficient radio wave absorption amount cannot be obtained.

It is preferable that the inclined bases 4 of the support member 2 are juxtaposed at an arrangement pitch P which is at least の times the wavelength of the radio wave to be absorbed. In this case, the sheet-shaped radio wave absorbers 1 are arranged at the same pitch as the arrangement pitch P of the inclined bases 4, and the pitch of the inclined bases 4 is one of the wavelengths of the radio waves to be absorbed.
If the ratio is less than / 4, the sheet-shaped radio wave absorber 1 of the radio wave absorbing structure 10 is not covered by the bottom surface 2
will function as being parallel to a,
This is because there is a tendency that the object of the present invention is not sufficiently achieved.

On the other hand, the sheet-shaped radio wave absorber 1 is generally formed by laminating a flat metal layer 5 and a flat radio wave absorber layer 6.

The metal layer 5 is not particularly limited as long as it can reflect an incident radio wave. Examples of the metal layer 5 include aluminum, copper, iron and alloys thereof. Of these, aluminum is preferably used because of its high reflectance and light weight.

Although the thickness of the metal layer 5 is not particularly limited,
Usually, it is 0.01 to 5 mm, and from the viewpoint of simplification of processing and weight reduction of the sheet-shaped electromagnetic wave absorber 1, 0.01 to 5 mm.
Preferably, it is 1.5 mm.

The radio wave absorbing material of the radio wave absorbing material layer 6 is, for example, a nonwoven fabric made by mixing short metal fibers with glass fiber or polyester fiber, foamed polyethylene containing carbon powder, synthetic rubber containing ferrite, carbonyl. A known radio wave absorbing material such as a resin containing iron is used.

The radio wave absorbing material layer 6 has a substantially constant thickness, usually 0.3 to 100 mm. ~
It is preferably 30 mm.

Next, the operation of the above-described radio wave absorbing structure 10 will be described.

FIG. 2 is a side view schematically showing the positional relationship between the radio wave absorbing structure 10 and the radio wave source. As shown in FIG. 2, in the radio wave absorbing structure 10, a plurality of sheet-shaped radio wave absorbers 1 are arranged side by side with respect to a virtual reference plane 7. In FIG. 2, the symbol φ indicates the angle of incidence with respect to the reference plane 7, and the symbol θ indicates the angle of incidence with respect to the surface of the sheet-shaped electromagnetic wave absorber 1.

When a radio wave is radiated from the radio wave source 8, the radio wave enters each of the plurality of radio wave absorbers 1 of the radio wave absorbing structure 10. At this time, at a position close to the radio wave source 8, the incident angle φ with respect to the reference plane 7 is small, and the incident angle θ with respect to the surface of the sheet-shaped radio wave absorber 1 is also small. on the other hand,
At a position far from the radio wave source 8, the incident angle φ with respect to the reference plane 7 is large, but the incident angle θ with respect to the surface of the sheet-shaped radio wave absorber 1 is small. Here, the sheet-like radio wave absorber 1
In general, as shown in FIG. 4, when the incident angle is small, the amount of radio wave absorption is large, while the incident angle is large and about 4
When it exceeds 0 °, it has a characteristic that the radio wave absorption decreases. Therefore, by reducing the incident angle of the radio wave on each of the plurality of sheet-shaped radio wave absorbers 1, the radio wave source 8
Can be sufficiently absorbed over a wide range.

In the above embodiment, the sheet-shaped radio wave absorber 1 is composed of the flat metal layer 5 and the flat radio wave absorber layer 6, but the material of the support member 2 is the metal layer. 5
If it is the same as above, the sheet-shaped radio wave absorber used in the present invention may be constituted only by the radio wave absorber layer.

Next, an embodiment of the automatic toll collection system of the present invention will be described.

FIG. 3 is a side view schematically showing an embodiment of the automatic toll collection system of the present invention. As shown in FIG. 3, the automatic toll collection system 20 has a ceiling 23 on a lane 22 into which a vehicle 21 enters, and a communication area A is provided below the ceiling 23 in the lane 22. On the ceiling 23, a roadside antenna 24 is installed on the traveling side of the vehicle 21, and the roadside antenna 24 emits a radio wave toward the communication area A.

In such an automatic toll collection system 20, radio waves are originally emitted from the roadside antenna 24 toward the communication area A, and the vehicle 21 that has entered the communication area A
Is received by the on-vehicle device 25 mounted thereon, and the radio wave is also emitted from the on-vehicle device 25 to collect the fee.

However, even when the vehicle 21 has not reached the communication area A, the radio wave emitted from the roadside antenna 24 may be reflected on the ceiling 23 after being reflected on the communication area A. In this case, the unstable reception of the radio wave by the vehicle-mounted device 25 is performed outside the communication area A. As a result, the system may malfunction and the fee may not be collected properly.

Therefore, in the automatic toll collection system 20, the above-described radio wave absorbing structure 10 is installed on the ceiling 23.

Here, in the radio wave absorbing structure 10,
It is preferable to arrange the plurality of sheet-shaped radio wave absorbers 1 so as to face the communication area A. Further, it is preferable that the arrangement pitch P of the sheet-like radio wave absorbers 1 is at least １ ／ times the wavelength of radio waves emitted from the roadside antenna 24 (see FIG. 1). Arrangement pitch P of sheet-like radio wave absorber 1
When the wavelength is less than 1/4 of the wavelength of the radio wave, the sheet-shaped radio wave absorber 1 of the radio wave absorbing structure 10 functions as a parallel to the ceiling surface with respect to the target radio wave. This is because there is a tendency that the purpose is not sufficiently fulfilled. The upper limit of the pitch P of the inclined base 4 of the support member 2 varies depending on the wavelength of the radio wave, but is usually three times the wavelength, and preferably one to two times the wavelength.

Specifically, in the automatic toll collection system 20, as a radio wave, usually 5.8 GHz (wavelength 5.2)
cm). Therefore, the radio wave absorbing structure 1
At 0, the pitch P of the inclined table 4 may be 1.3 cm or more.

Next, the aforementioned automatic toll collection system 20
The operation of will be described.

First, a radio wave emitted from the roadside antenna 24 is reflected at the communication area A, and this reflected wave is
Is incident on the radio wave absorbing structure 10 installed in the device. At this time, in the radio wave absorbing structure 10, radio waves can be incident on the surface of the sheet-shaped radio wave absorber 1 at a small incident angle regardless of the position near or far from the communication area A. Therefore, even if the radio wave enters the ceiling 23 at a large incident angle, the radio wave absorbing structure 10 sufficiently absorbs the radio wave. Therefore, the radio wave emitted from the roadside antenna 24 is sufficiently prevented from being received outside the communication area A, and the situation in which the system malfunctions is sufficiently prevented.

In the above embodiment, an example of an automatic road toll collection system for a car has been described as an application of the radio wave absorption structure of the present invention. However, the radio wave absorption structure of the present invention is applied to an automatic road toll collection system. DS using wireless communication technology
The present invention can also be applied to an RC (Dedicated Short Range Communications) system, for example, a parking fee system, a fee settlement system at a gas station, a drive-through system, and the like.

The radio wave absorbing structure of the present invention can be applied to an intelligent transportation system other than the automatic toll collection system. For example, the radio wave absorbing structure of the present invention is installed over a wide area along side walls (for example, sound insulation walls) provided on both sides of a road, and an antenna for transmitting and receiving traffic information and the like is provided along each of the side walls on both sides or on the road. In a system arranged at appropriate intervals along the path, radio waves transmitted from the antenna are sufficiently absorbed by the radio wave absorbing structure of the present invention, so that communication errors due to unnecessary reflection of radio waves can be prevented.

[0037]

As described above, according to the radio wave absorbing structure of the present invention, the radio wave which should be incident on the reference plane at a large incident angle is small on the surface of the sheet-shaped radio wave absorber. Since the light is incident at the incident angle, the radio waves incident on the radio wave absorbing structure over a wide range can be sufficiently absorbed.

According to the automatic toll collection system of the present invention, unnecessary radio waves that are reflected in the communication area and then reflected on the roof of the toll booth and can be received by the on-vehicle device of the vehicle are transmitted by the radio wave absorber. Since it is sufficiently absorbed over a wide range, it is possible to sufficiently prevent situations such as double collection of fees.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a radio wave absorber of the present invention.

FIG. 2 is a side view showing a positional relationship between a radio wave source and a radio wave absorbing structure.

FIG. 3 is a side view schematically showing an embodiment of the automatic toll collection system of the present invention.

FIG. 4 is a graph schematically showing the incident angle dependence of the amount of absorption in a sheet-shaped electromagnetic wave absorber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sheet-shaped radio wave absorber, 2 ... Support member, 2a ... Bottom (reference plane), 4 ... Slope table, 4a ... Slope surface, 7 ... Reference plane, 8 ... Radio source, 10 ... Radio wave absorption structure, 20 ... Automatic toll collection system, 21: vehicle, 22: lane, 23: roof, 24: roadside antenna, A: communication area, 25: vehicle-mounted device.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor ▲ Yoshi ▼ Sawato 2-12-12 Nishikawadaminami, Utsunomiya-shi, Tochigi Kanto Kogyo Line Co., Ltd. (72) Inventor Shigeo Matsufuji 2-Nishikawadanami, Utsunomiya-city, Tochigi No. 5-12 Kanto Steel Wire Co., Ltd. F term (reference) 3E027 EA01 EB02 EC07 5E321 AA41 AA50 GG11 5J020 EA04 EA07 EA09

Claims (4)

[Claims] 1. A radio wave absorbing structure comprising a plurality of sheet-shaped radio wave absorbers arranged side by side in a state inclined with respect to a reference plane. 2. The radio wave absorbing structure according to claim 1, wherein an inclination angle of each of the plurality of sheet-shaped radio wave absorbers with respect to the reference plane is 30 to 60 °. 3. The radio wave according to claim 1, wherein the plurality of sheet-shaped radio wave absorbers are arranged side by side at an arrangement pitch of at least の times the wavelength of the radio wave to be absorbed. Absorbing structure. 4. A vehicle-mounted device which emits radio waves from a roadside antenna installed at or near a ceiling of a tollgate toward a communication area on a lane and enters the communication area when a vehicle equipped with the vehicle-mounted device enters the communication area. An automatic toll collection system that receives the radio wave and automatically collects a toll by emitting a radio wave from the in-vehicle device toward the roadside antenna, wherein the system is installed on the ceiling of the tollgate, It has a radio wave absorbing structure that absorbs radio waves reflected in the communication area,
An automatic toll collection system, wherein the radio wave absorbing structure is the radio wave absorbing structure according to claim 1.