JPH05335832A - Radio wave absorbing body - Google Patents

Abstract

PURPOSE:To obtain an optically transparent radio wave absorbing body. CONSTITUTION:The absorbing body is provided with a radio wave reflection body 11, a dielectric 12 whose thickness is nearly lambdag/4 (lambdag is a wavelength of a radio wave in a dielectric body) arranged on the body 11 and a resistance film 13 arranged on the body 12. A transparent film made by a metal oxide, a metal niteride or their mixture with the ion plating, vapor deposition or sputtering or the like is arranged as a resistance film 13 in a radio wave arrival direction and the dielectric 12 whose thickness is nearly lambdag/4 (lambdag is a wavelength of a radio wave in a dielectric body) is arranged on the rear side. Furthermore, the radio wave reflecting body 11 transmitting a light is arranged on the rear side of the dielectric body 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent electromagnetic wave absorber used for preventing radar ghost (prevention of false images) and reflection such as scattering of electromagnetic waves from a reflector.

[0002]

2. Description of the Related Art In recent years, as the use of radio waves has progressed, problems such as radio wave interference and malfunctions have occurred. As one of the countermeasures against these problems, a radio wave absorber is used and has a great effect.

The electromagnetic wave absorber is generally constructed by mixing a loss material such as ferrite or carbon with a holding material such as rubber or resin. Therefore, the conventional radio wave absorber does not transmit light and does not have transparency.

Recently, the use of radio waves is wide-ranging, and therefore the demand for transparent wave absorbers is increasing.

[0005]

However, as described above, since the conventional radio wave absorber is not transparent, it is impossible to install the radio wave absorber at a location where transparency is required.

The present invention is intended to solve these problems, and an object thereof is to provide a transparent electromagnetic wave absorber.

[0007]

In order to solve the above-mentioned problems, the present invention serves as a radio wave absorber in the direction of arrival of radio waves.
A resistive film with a surface resistance of 7Ω (radio frequency characteristic impedance in free space) is placed, and the back surface of the film is λ _g / 4 (where λ _g is the wavelength of the radio wave in the dielectric). The structure in which the dielectric is arranged, that is, λ / 4
Type electromagnetic wave absorber, and each member is optically transparent.

Preferably, a metal oxide is used as the resistance film,
A transparent foil film made of metal nitride or a mixture thereof by ion plating, vapor deposition, sputtering or the like is used.

Further, transparent glass, resin or air is used as the dielectric.

A metal wire grating or a transparent metal foil film is used as the radio wave reflector.

[0011]

[Operation] When a radio wave is vertically incident on the metal surface, a large standing wave is generated. The load impedance periodically repeats zero and infinity, but from the metal plate it is a quarter of λ (λ / 4).
At remote locations the impedance is infinite. FIG. 9 shows this as a model. Therefore, as shown in FIG. 10, when a thin resistance film (surface resistance is R _s ) is placed at that position, the load impedance Z at that position in anticipation of the resistance film is parallel to the surface resistance R _s of the resistance film and the infinite impedance. Therefore, it becomes the surface resistance itself. Therefore, the reflection coefficient S in this case is expressed by the following equation.

[Equation 1] Therefore, if the surface resistance R _s of the resistive film is set to the radio wave characteristic impedance (= 377Ω) in free space, the reflection coefficient becomes S = 0.
Becomes That is, the impedances are perfectly matched. Therefore, if the dielectric thickness and the resistance film are designed so as to satisfy this condition, a λ / 4 type electromagnetic wave absorber can be realized.

[0012]

Example 1 A transparent acrylic resin plate having a thickness of 5 mm (dielectric 1
2) is a metal wire grid (grid spacing 5 mm) (radio wave reflector 11)
125 μm thick, lined with metal oxide attached
A transparent PET (polyethylene terephthalate) film (resistive film 13) was attached to the surface of an acrylic resin plate with a transparent adhesive to prepare a radio wave absorber.

As a method of measuring the electromagnetic wave absorption characteristics of this electromagnetic wave absorber, the reflected power method was used for the measurement. The measuring system is shown in FIG.

Here, a radio wave whose frequency is swept by a sweeper is emitted from the transmitting antenna, and the sample is placed 3 m from the antenna. The receiving antenna is also placed 3 m from the sample, and the reflection of the radio wave by the sample is analyzed by the network analyzer connected to the receiving antenna via the amplifier.

FIG. 1 is a block diagram of the radio wave absorber.
The result of the radio wave absorption characteristics at that time is shown in FIG.

[0016]

[Embodiment 2] The thickness of the transparent PET film (radio wave reflector 21) having a thickness of 125 μm, which is vapor-deposited with gold, is 5 mm.
The transparent acrylic resin plate (dielectric 22) of No. 1 is lined, and a 125 μm-thick transparent PET film (resistive film 23) on which the metal oxide is mounted is mounted on the surface of the acrylic resin plate with a transparent adhesive and the radio wave is applied. An absorber was created.

A block diagram is shown in FIG. The result of the radio wave absorption characteristics at that time is shown in FIG.

[0018]

[Example 3] Thickness 0.5 mm with metal oxide attached
Transparent PVC plate (resistive film 33) and a transparent acrylic resin plate (radio wave reflector 31) with a metal wire grid (lattice spacing 5 mm) mounted on one side, leaving a gap (10 mm) (dielectric 32) We made the electromagnetic wave absorber by facing each other.

The block diagram is shown in FIG. The result of the radio wave absorption characteristics at that time is shown in FIG.

[0020]

[Embodiment 4] A transparent glass (dielectric 42) having a thickness of 8 mm on which a metal oxide (resistive film 43) is mounted is lined with a metal wire lattice (lattice spacing 5 mm) (radio wave reflector 41), An absorber was created. The block diagram is shown in FIG. The result of the radio wave absorption characteristics at that time is shown in FIG.

[0021]

As described above, the present invention has transparency in the electromagnetic wave absorber, and thus can be used in a place where transparency is required, for example, a window glass.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a radio wave absorber according to an embodiment (1) of the present invention.

FIG. 2 is a diagram showing a configuration of a radio wave absorber of an embodiment (2) of the present invention.

FIG. 3 is a diagram showing a configuration of a radio wave absorber according to an embodiment (3) of the present invention.

FIG. 4 is a diagram showing a configuration of a radio wave absorber of an embodiment (4) of the present invention.

FIG. 5 is a diagram showing a radio wave absorption characteristic of an embodiment (1) of the present invention.

FIG. 6 is a diagram showing a radio wave absorption characteristic of an embodiment (2) of the present invention.

FIG. 7 is a diagram showing radio wave absorption characteristics of an embodiment (3) of the present invention.

FIG. 8 is a diagram showing a radio wave absorption characteristic of an embodiment (4) of the present invention.

FIG. 9 is a diagram showing a principle of operation of the present invention.

FIG. 10 is a diagram showing a principle of operation of the present invention.

FIG. 11 is a diagram showing a radio wave absorption characteristic measuring system of a radio wave absorber according to an example of the present invention.

[Explanation of symbols]

 11, 21, 31, 41 Radio wave reflector 12, 22, 32, 42 Dielectric 13, 23, 33, 43 Resistive film

Claims (4)

[Claims] 1. A radio wave having a radio wave reflector, a dielectric having a thickness of about λ _g / 4 (λ _g is a wavelength of a radio wave in a dielectric body) provided thereon, and a resistive film provided thereon. In the absorber, a transparent foil film made by metal plating, metal nitride or a mixture thereof by ion plating, vapor deposition, sputtering or the like is arranged as a resistance film in the radio wave arrival direction,
A transparent dielectric with a thickness of about λ _g / 4 (where λ _g represents the wavelength of radio waves in the dielectric) is placed on the back surface, and a radio wave reflector that transmits light is placed on the back surface of the dielectric. An electromagnetic wave absorber characterized by being arranged. 2. The radio wave absorber according to claim 1, wherein the resistance film is selected from ITO (indium oxide / tin oxide), tin oxide, zinc oxide, and titanium nitride. 3. The radio wave absorber according to claim 1, wherein the transparent dielectric is selected from air, glass, and transparent organic polymers. 4. The radio wave absorber according to claim 1, wherein the radio wave reflector is selected from a metal wire grating or a transparent metal foil film.