JP3417048B2 - Radio wave absorber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin wave absorber capable of effectively suppressing reflection even with respect to obliquely incident waves, and in particular, has developed a 1/4 wavelength resistance film absorber type wave absorber. The present invention relates to a thin electromagnetic wave absorber.

[0002]

2. Description of the Related Art In recent years, as the use of radio waves has progressed, problems such as radio interference and malfunctions due to radio waves have arisen, and it is effective to use a thin radio wave absorber as a countermeasure.

The most common type of thin electromagnetic wave absorber has a structure in which a mixture layer 250 of ferrite powder or carbon powder and rubber is laminated on the front surface of an electromagnetic wave reflector 251, as shown in the sectional view of FIG. It is a thing.

Further, as a thin wave absorber of the 1/4 wavelength resistive film absorber type, as shown in FIG. 26 (a sectional view taken along the line AA of FIG. 27) and FIG. 27 (a perspective view), the thickness is about λ _g / 4 (λ
_(g is the wavelength of the radio wave in the dielectric) The radio wave reflector 261 is provided on the back surface of the dielectric layer 260, and the front surface of this dielectric layer 260 is arranged in a grid pattern with equal vertical and horizontal intervals. There is known a radio wave absorber which is mainly composed of the fiber 262a and has a resistance film 262 having a surface resistance of about 377 Ω / □ in all directions (Japanese Patent Publication No. 2-5879).
No. 6).

[0005]

Unwanted reflected waves from an object such as a structure are not only generated by a radio wave vertically incident on the object but also an electromagnetic wave obliquely incident on the object. Therefore, a radio wave reflector having excellent absorption characteristics for such obliquely incident radio waves is required. However, since any of the above-mentioned radio wave absorbers is designed for vertical incidence, the radio wave absorption performance is deteriorated with respect to obliquely incident radio waves, and it is difficult to obtain a sufficient reflection suppressing effect.

Further, as shown in FIG. 28, the electromagnetic wave absorber 2
When a radio wave is perpendicularly incident on the surface of 80, the electric field E _i and the magnetic field H _i of the incident radio wave must be the radio wave absorber 2.
Although parallel to the surface of 80, such a situation does not occur with obliquely incident radio waves. That is, in the obliquely incident radio wave, as shown in FIG. 29, the electric field E _i of the incident radio wave is incident on the incident surface (the surface perpendicular to the surface of the radio wave absorber and including the traveling directions of the incident radio wave and the reflected radio wave) 281. When vertical (TE wave),
As shown in FIG. 30, the magnetic field H _{i of the} incident radio wave is applied to the incident surface 281.
And (TM wave) are present. Since such various linearly polarized waves and circularly polarized waves are used as radio waves, they are effective for both TE wave and TM wave polarization and have no polarization dependence, and can be used for any polarized wave. A radio wave absorber having a reflection suppressing effect is desired.

In the conventional electromagnetic wave absorber shown in FIG. 25, it is currently the case to design the electromagnetic wave absorber for oblique incidence by adjusting the thickness, dielectric constant and magnetic permeability of the mixture layer 250. Although quite difficult, it is possible by repeating cut and try. However, it is extremely difficult to design and realize a thin electromagnetic wave absorber that operates at an arbitrary incident angle and an arbitrary frequency without having polarization dependency.

In the conventional 1/4 wavelength type electromagnetic wave absorber shown in FIGS. 26 and 27, the surface resistance of the resistance film 262 is changed from 377 Ω / □ and the thickness of the dielectric layer 260 is adjusted. Thus, it is possible to design an electromagnetic wave absorber for oblique incidence. However, in this case as well,
It is effective only for one polarized wave, and a sufficient reflection suppressing effect could not be expected for polarized waves and circular polarized waves different from this.

Therefore, the present invention provides a thin electromagnetic wave absorber that does not have polarization dependence, is easy to design and manufacture, and can effectively suppress reflection even for oblique incident waves. is there.

[0010]

According to the present invention, a dielectric layer, a radio wave reflector layer laminated on one surface of the dielectric layer, and a radio wave reflector layer laminated on the other surface of the dielectric layer. The present invention relates to a radio wave absorber including a resistance film layer. According to the invention,
Particularly, the resistance film layer is configured such that the surface resistance in the first direction in the layer plane of the resistance film layer and the surface resistance in the second direction in the layer plane intersecting the first direction are different from each other. Has been done.

It is preferable that the angle at which the first direction and the second direction described above intersect is substantially a right angle.

It is preferable that the product of the surface resistance in the first direction and the surface resistance in the second direction is approximately equal to the square of the characteristic impedance of the free space.

In this case, when θ is the incident angle of the incident radio wave to be absorbed, the surface resistance in the first direction is approximately 120π /
cos θ (Ω / □), and the surface resistance in the second direction may be approximately 120π · cos θ (Ω / □).

When a radio wave is incident on a radio wave reflector such as a metal at an incident angle θ, a standing wave is generated on the front surface of the radio wave reflector.
The input impedance when the radio wave reflector is viewed from the incident side of radio waves repeats zero and infinity periodically along the normal direction of the radio wave reflector, but at a position d ₀ away from the reflector surface. , As shown in FIG. 2A, it becomes infinite without depending on the polarization. Here, d ₀ is given by the following equation, where λ is the wavelength of the incident radio wave. d ₀ = λ / {4√ (1-sin ² θ)}

When a resistance film having a surface resistance R _s is arranged at the position of this distance d ₀ , the input impedance Z _in at that position in consideration of this resistance film is as shown _in FIG. 2B.
Since the surface resistance R _s of the resistance film and the infinite impedance are equivalently connected in parallel, Z _in = R _{s holds} . Therefore, the reflection coefficient S in this case is represented by the following equation according to each polarization. However, Z ₀ represents the characteristic impedance of free space (Z ₀ = 120πΩ). In case of TE wave S = (R _s −Z ₀ / cos θ) / (R _s
+ Z ₀ / cos θ) In the case of TM wave S = (R _s −Z ₀ · cos θ) / (R _s
+ Z ₀ · cos θ)

Therefore, for TE waves, the surface resistance R _s of the resistance film is set to R _s = Z ₀ / cos θ. For TM waves, the surface resistance R _s of the resistance film is set to R _s = Z ₀ · cos θ. Thus, the reflection coefficient S can be made zero.

As shown in FIG. 29 and FIG. 30, the TE wave and the TM wave have the electric fields of the incident electric waves which are orthogonal to each other, and therefore the direction of the electric current generated on the resistance film surface is also TE.
The wave and the TM wave are orthogonal to each other. Therefore, the surface resistance of the resistance film is adjusted by adjusting the surface resistance for TE wave and TM wave by giving directionality to the surface resistance of the resistance film, that is, the surface resistance of the resistance film layer in the first direction and the first direction. By making the surface resistance in the second direction in the layer plane intersecting the direction of 1 and 2 different from each other, good electromagnetic wave absorption characteristics without polarization dependence can be obtained.

Further, in the radio wave absorber of the present invention, if the wavelength and incident angle of the target radio wave and the dielectric constant of the dielectric material are determined, the thickness of the dielectric material and the surface resistance in each direction of the resistance film are unique. Therefore, the design and manufacturing are very easy.

Surface resistance R _{s in} the first direction for the TE wave
= Z ₀ / cos θ and the surface resistance R _s = Z ₀ · cos θ for the TM wave in the second direction, the product R _s · R _s is calculated from the above equation as R _s · R _s = (Z ₀ / cos θ ) (Z ₀ · cos θ) =
Z ₀ ^{2, that} is, equal to the square of the characteristic impedance of free space.

The current generated on the resistance film surface is TE wave and TM.
It is most preferable that the crossing angle between the first direction and the second direction is a right angle, since they are orthogonal to each other with respect to waves, but if it is only desired to suppress the reflection coefficient to a certain value other than zero or less. The angle may deviate from the right angle to some extent. Further, the surface resistance in each direction of the resistance film may be slightly deviated from the above value as long as it is desired to suppress the reflection coefficient to a certain value other than zero. For example, oblique incidence angle θ = 60 °
In, in the reflection coefficient S = 0.1 or less, by adjusting the surface resistance R _s with respect to the TE wave R _s = 617~922Ω, the surface resistance R _s for the TM wave between R _s = 154~230Ω It becomes possible with.

When a space between the resistance film layer and the radio wave reflector layer is constituted by a dielectric layer having a relative permittivity ε _r , the thickness d of this dielectric layer is d = λ / {4√ ( By setting ε _r −sin ² θ)}, it is possible to obtain the same radio wave absorption characteristics as in the above case.

In the radio wave absorber of the present invention, the resistive film layer is a woven fabric in which an insulating fiber and a conductive fiber or a metal wire having a predetermined line resistance are woven, or a predetermined film is formed on the insulating film. It is preferable to use a film in which a conductive film having the above surface resistance is arranged in a predetermined pattern.

The radio wave absorber of the present invention preferably further comprises a protective film layer laminated on the surface of the resistance film layer opposite to the dielectric layer.

[0024]

The present invention will be described in detail with reference to the following examples.

FIG. 1 is a perspective view schematically showing the structure of a radio wave absorber in one embodiment of the present invention, FIG. 3 is a sectional view taken along the line BB of FIG. 1, and FIG. 4 is a resistance film in the embodiment of FIG. It is a top view which shows the structure of a layer schematically.

In these figures, 10 is a dielectric layer having a predetermined thickness, 11 is a radio wave reflector layer laminated on the back surface of the dielectric layer 10, and 12 is a resistive film layer laminated on the front surface of the dielectric layer 10. Shown respectively.

The dielectric layer 10 includes (1) a foam material such as polyethylene, polystyrene, polyurethane or silicon,
(2) Organic resin such as vinyl chloride, acrylic, polycarbonate or Teflon, (3) wood, (4) glass,
(5) Ceramic, (6) Rubber, (7) Paper, and (8)
The dielectric material is any one of air and the like and is formed in a flat plate shape. The thickness d of the dielectric layer 10 is such that θ is the incident angle of the incident radio wave to be absorbed, λ is the wavelength of the incident radio wave, and ε _r
Is defined as the relative permittivity of the dielectric layer 10, d = λ / {4√ (ε _r −sin ² θ)} is set.

The radio wave reflector layer 11 includes (1) a metal plate made of aluminum, iron, copper or stainless steel, a metal foil made of copper, aluminum or iron, (3) a metal wire in a grid pattern,
It is made of any material of (4) carbon fiber cloth, (5) metal plated cloth, and (6) metal fiber cloth such as stainless steel.

In this embodiment, the resistance film layer 12 is made of a woven cloth in which insulating fibers and resistance wires (conductive fibers or metal wires) 13 and 14 having a predetermined line resistance are woven, and The lines are woven in a grid as shown in FIGS. In this case, by appropriately selecting the type of material and diameter of the resistance wire 13 woven in the vertical direction and the resistance wire 14 woven in the horizontal direction and the number (interval) per unit length of the resistance film layer 12, The surface resistance R _{sl in the} vertical direction and the surface resistance R _{st in the} horizontal direction are set so that R _sl = Z ₀ / cos θ R _st = Z ₀ · cos θ. Here, θ is the incident angle of the incident radio wave to be absorbed, and Z ₀ is the characteristic impedance of the free space (Z ₀ = 120πΩ). By installing such a radio wave absorber in an appropriate direction, as described above, T
Both the reflection coefficient S of the E wave and the TM wave can be made zero.

Since the electric currents generated on the surface of the resistance film 12 are orthogonal to each other in the TE wave and the TM wave, the angle formed by the resistance wire 13 woven in the vertical direction and the resistance wire 14 woven in the horizontal direction is a right angle. However, the angle may deviate from a right angle to some extent as long as it is desired to suppress the reflection coefficient to a certain value other than zero. Further, the surface resistance of the resistance film 12 in each direction may be slightly deviated from the above value as long as it is desired to suppress the reflection coefficient to a certain value other than zero. For example, in order to make the reflection coefficient S = 0.1 or less at the oblique incident angle θ = 60 °, the surface resistance R _s for the TE wave is R _s = 617 to 922Ω, and the surface resistance R _s for the TM wave is R _s = It becomes possible by adjusting between 154 and 230Ω.

The resistance wires 13 and 14 are made of conductive fibers or metal wires. As the conductive fiber, for example, copper sulfide (CuS) or other conductive layer adhered and formed on the surface of synthetic fiber such as acrylic by a dyeing technique, carbon fiber or silicon carbide fiber is formed.

As a modification of the resistance film layer, there is also a structure as shown in FIG. That is, a woven cloth (or a film in which the resistance lines 53 are attached in parallel in the longitudinal direction) 55 in which the resistance lines 53 are woven in parallel in the longitudinal direction as shown in FIG. Woven fabric in which the resistance wires 54 are woven in parallel in the horizontal direction (or a film in which the resistance wires 54 are attached in parallel in the longitudinal direction) 56
And are superposed on each other as shown in FIG.
2 may be configured. The angle between the vertical resistance line 53 and the horizontal resistance line 54 and the surface resistance in each direction are the same as in the embodiment of FIG.

FIG. 6 is a sectional view schematically showing the structure of a radio wave absorber according to another embodiment of the present invention.

In the figure, 60 is a dielectric layer having a predetermined thickness,
61 is a radio wave reflector layer laminated on the back surface of the dielectric layer 60,
62 is a resistance film layer laminated on the front surface of the dielectric layer 60;
Indicates the protective film layers laminated on the surface of the resistive film layer 62, respectively. The structures and functions of the dielectric layer 60, the radio wave reflector layer 61, and the resistance film layer 62 are exactly the same as in the embodiment of FIG.

The protective film layer 63 is applied to improve the durability of the resistive film layer 62, and is (1) a film or paint of organic resin such as polyurethane, fluorine series or silicon series, (2) It is made of a material having excellent durability such as glass, (3) ceramic, and (4) rubber.

FIG. 7 is a plan view schematically showing the structure of the resistance film layer in still another embodiment of the present invention.

The resistance film layer 72 in this embodiment is composed of a conductive film having a predetermined surface resistance or a conductive paint having a predetermined pattern formed on an insulating film, and the pattern is shown in FIG. Thus, the conductive pattern portion is formed in a grid pattern. In this case, the surface resistance R _{sl in} the vertical direction and the surface resistance R _{st in the} horizontal direction of the resistance film layer 72 are selected by appropriately selecting the width and the distance between the conductive strip 73 in the vertical direction and the conductive strip 74 in the horizontal direction. Is set to be R _sl = Z ₀ / cos θ R _st = Z ₀ · cos θ. Here, θ is the incident angle of the incident radio wave to be absorbed, and Z ₀ is the characteristic impedance of the free space (Z ₀ = 120πΩ). In the example of FIG. 7, the width of the conductive strips 73 in the vertical direction is 0.6 mm and the intervals are 3.
4 mm, the lateral conductive strips 74 have a width of 1.2 mm and a spacing of 2.8 mm. By installing such a radio wave absorber in an appropriate direction, it becomes possible to make both the reflection coefficient S of TE waves and TM waves zero, as described above. When the surface resistance in each direction is set according to the pattern as in this embodiment, the resistance value can be adjusted very easily.

Since the currents generated on the surface of the resistance film 72 are orthogonal to each other for the TE wave and the TM wave, the angle formed by the vertical conductive strip 73 and the horizontal conductive strip 74 may be a right angle. Most preferably, the angle may deviate from a right angle to some extent as long as it is desired to keep the reflection coefficient below a certain value other than zero. In addition, the resistance film 72
The surface resistance in each direction may be slightly deviated from the above value as long as it is desired to suppress the reflection coefficient to a certain value other than zero. For example, in order to make the reflection coefficient S = 0.1 or less at the oblique incident angle θ = 60 °, the surface resistance R to the TE wave is
The _s R _s = _617~922Ω, the surface resistance R _s for the TM wave becomes possible by adjusting between R _s = 154~230Ω.

The conductive pattern portion is insulated by evaporating or coating a thin film of (1) metal oxide such as indium tin oxide (ITO), tin oxide or zinc oxide, or (2) metal nitride such as titanium nitride. It is laminated on the conductive film and formed into a predetermined pattern by an etching process, or is formed by printing a conductive paint, which is formed by adding carbon to a resin, on the insulating film in a predetermined pattern.

The conductive pattern is not limited to the grid pattern shown in FIG. 7, but may have various shapes as long as the vertical surface resistance and the horizontal surface resistance of the resistance film layer can be set as described above. Is applicable. For example, as shown in FIG. 8, it may be a resistive film layer 82 having a conductive pattern 84 formed of an elliptical punched pattern 83.

As a modification of the resistive film layer, FIG.
There is also a configuration as shown in. That is, as shown in FIG. 7B, the conductive strips 93 extending in the longitudinal direction in parallel with each other.
A patterned film 95 and a film 96, which is formed by patterning conductive strips 94 extending in parallel to each other in the lateral direction as shown in FIG. 9A, are superposed as shown in FIG. Layer 92 may be constructed. For the material and forming method of the conductive pattern, the angle between the vertical conductive strip 93 and the horizontal conductive strip 94, and the surface resistance in each direction, see FIG.
Since it is exactly the same as the case of the above embodiment, the description thereof will be omitted.

As another modification of the resistance film layer, there is a structure as shown in FIG. That is, as shown in FIG. 1B, a woven fabric in which the resistance wires 103 are woven in parallel in the longitudinal direction (or a film in which the resistance wires 103 are attached in parallel in the longitudinal direction) 1
05 and a film 106 formed by patterning conductive strips 104 that extend in parallel to each other in the lateral direction as shown in FIG. 11A are superposed as shown in FIG. You may. It goes without saying that the vertical and horizontal configurations described above may be reversed, and the resistance lines and those of other conductive patterns may be combined. Regarding the material and forming method of the resistance wire and the conductive pattern,
Vertical resistance lines 103 and horizontal conductive strips 10
The angle formed by 4 and the surface resistance in each direction are the same as in the embodiment of FIGS.

An actual configuration example of the electromagnetic wave absorber and its electromagnetic wave absorption characteristics will be described below.

Structural Example 1 Resistive film layer: A woven fabric in which conductive fibers having a linear resistance of 42 KΩ / m and polyester fibers are woven so that the conductive fibers form a lattice, and the woven fabric has a thickness of about 200 μm and is conductive. The diameter of the fiber is about 100 μm, and the weaving interval of the conductive fiber is 18 mm for the longitudinal conductive fiber and 4.5 for the lateral conductive fiber.
mm, which makes the surface resistance of the resistive film layer 754 in the vertical direction.
Ω / □, adjusted to 189Ω / □ in the lateral direction, Dielectric layer: 48.1 mm thick foamed polyethylene sheet, Radio wave reflector layer: 30 μm thick aluminum foil. An absorber was formed.
FIG. 11 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by a radio wave with an oblique incident angle of 60 °. From the figure, at a frequency of 3 GHz, TE wave and T wave
It can be seen that good absorption characteristics are obtained for both M waves.

Structural Example 2 Resistive film layer: A woven fabric in which conductive fibers having a linear resistance of 42 KΩ / m and polyester fibers are woven so that the conductive fibers form a lattice, and the woven fabric has a thickness of about 200 μm and is conductive. The diameter of the fiber is about 100 μm, and the weaving interval of the conductive fiber is 12.8 mm for the longitudinal conductive fiber and 6.4 mm for the lateral conductive fiber, which makes the surface resistance of the resistive film layer 533 Ω / in the longitudinal direction. □, adjusted to 267 Ω / □ in the lateral direction Dielectric layer: 34.7 mm thick foamed polyethylene sheet, radio wave reflector layer: 30 μm thick aluminum foil, using a wave absorber of the structure as shown in FIG. Formed.
FIG. 12 shows the result of measuring the radio wave absorption characteristics of the radio wave absorber with a radio wave having an oblique incident angle of 45 °. From the figure, at a frequency of 3 GHz, TE wave and T wave
It can be seen that good absorption characteristics are obtained for both M waves.

The surface resistances in the vertical and horizontal directions of the resistive film layer are not such that the effect cannot be obtained at all unless the resistance values of the above-mentioned constitutional examples are exactly matched, and the values deviate from this value to some extent. However, a sufficient radio wave absorption effect can be obtained. Hereinafter, this point will be described using the measurement results. However, in the following example, the configuration is exactly the same as in the configuration example 2 except that the weaving interval of the conductive fibers is changed.

[Example 1 of changing surface resistance value] 42 KΩ line resistance
/ M conductive fiber weaving spacing is 10.5 mm in the longitudinal conductive fiber and 5.5 mm in the lateral direction, and the surface resistance of the resistive film layer is 441 Ω / □ in the longitudinal direction and in the lateral conductive fiber. In the case of 231 Ω / □, as shown in FIG. 13, a return loss of 20 dB was obtained at a frequency of 3 GHz.

[Example 2 of changing surface resistance value] Line resistance 42 KΩ
/ M of the conductive fibers is 15 mm in the vertical conductive fibers and 7.5 mm in the horizontal conductive fibers, and the surface resistance of the resistance film layer is 630 Ω / □ in the vertical direction and 3 in the horizontal direction.
In the case of 15Ω / □, as shown in FIG. 14, a return loss of 20 dB was obtained at a frequency of 3 GHz.

[Example 3 of changing surface resistance value] Line resistance 42 KΩ
The interweaving distance of the conductive fibers of 9 m / m is 9 mm for the longitudinal conductive fibers and 4.5 mm for the lateral conductive fibers, and the surface resistance of the resistance film layer is 378 Ω / □ in the longitudinal direction and 18 in the lateral direction.
When 9Ω / □, as shown in FIG.
At GHz, a return loss of 15 dB was obtained.

[Modification Example 4 of Surface Resistance Value] Line Resistance 42 KΩ
/ M of the conductive fibers is 18 mm in the vertical direction and 9 mm in the horizontal direction, and the surface resistance of the resistance film layer is 756 Ω / □ in the vertical direction and 378 in the horizontal direction.
If Ω / □, as shown in Fig. 16, frequency 3G
At Hz, a return loss of 15 dB was obtained.

Structural Example 3 Resistive film layer: an indium tin oxide (ITO) film having a surface resistance of 80 Ω / □ laminated on a polyethylene terephthalate film having a thickness of 75 μm, which was etched to form a grid-like conductive pattern, and an ITO film. The conductive pattern is set so that the width and the interval between the vertical strip and the horizontal strip are as shown in FIG. As a result, the surface resistance of the resistive film layer is 533Ω / □ in the vertical direction and 2 in the horizontal direction.
Adjusted to 67Ω / □, a dielectric layer: a foamed polyethylene sheet having a thickness of 34.7 mm, a radio wave reflector layer: an aluminum foil having a thickness of 30 μm, and a radio wave absorber having a structure as shown in FIG. 7 was formed.
FIG. 17 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by a radio wave with an oblique incident angle of 45 °. From the figure, at a frequency of 3 GHz, TE wave and T wave
It can be seen that good absorption characteristics are obtained for both M waves.

Structure 4 Resistive film layer: IT having a surface resistance of 80 Ω / □ laminated on a polyethylene terephthalate film having a thickness of 75 μm.
A film obtained by etching the O film into a grid-shaped conductive pattern,
The conductive pattern of the ITO film is set such that the vertical strips and the horizontal strips have widths and intervals as shown in FIG. By doing this, the surface resistance of the resistive film layer is adjusted to 533Ω / □ in the vertical direction and 267Ω / □ in the horizontal direction, dielectric layer: foamed polyethylene sheet with a thickness of 10.8 mm, radio wave reflector layer: aluminum foil with a thickness of 30 μm , Was used to form a radio wave absorber having a structure as shown in FIG.
FIG. 18 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by a radio wave with an oblique incident angle of 45 °. From the figure, it can be seen that good absorption characteristics are obtained for both TE and TM waves at a frequency of 9.4 GHz.

Structure 5 Resistive film layer: IT having a surface resistance of 80 Ω / □ laminated on a polyethylene terephthalate film having a thickness of 75 μm.
A film obtained by etching the O film into a grid-shaped conductive pattern,
The conductive pattern of the ITO film is set such that the vertical strips and the horizontal strips have widths and intervals as shown in FIG. By doing this, the surface resistance of the resistive film layer is adjusted to 533Ω / □ in the vertical direction and 267Ω / □ in the horizontal direction. Dielectric layer: foamed polyethylene sheet with a thickness of 34.7 mm, radio wave reflector layer: aluminum foil with a thickness of 30 μm Protective film layer: A radio wave absorber having a structure as shown in FIG. 6 was formed using a fluororesin film having a thickness of 50 μm.
FIG. 19 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber with a radio wave having an oblique incident angle of 45 °. From the figure, at a frequency of 3 GHz, TE wave and T wave
It can be seen that good absorption characteristics are obtained for both M waves.

Structural Example 6 Resistive film layer: IT having a surface resistance of 80 Ω / □ laminated on a polyethylene terephthalate film having a thickness of 75 μm
A film obtained by etching the O film into a grid-shaped conductive pattern,
The conductive pattern of the ITO film is set such that the vertical strips and the horizontal strips have widths and intervals as shown in FIG. By this, the surface resistance of the resistive film layer is adjusted to 533Ω / □ in the vertical direction and 267Ω / □ in the horizontal direction, dielectric layer: a polycarbonate sheet with a thickness of 5.3 mm, radio wave reflector layer: an aluminum foil with a thickness of 30 μm, Was used to form a radio wave absorber having a structure as shown in FIG.
FIG. 20 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by a radio wave with an oblique incident angle of 45 °. From the figure, it can be seen that good absorption characteristics are obtained for both TE and TM waves at a frequency of 9.4 GHz.

Conventional Example 1 for comparison : Resistive film layer: Surface resistance of 380 Ω / laminated on the entire surface of a polyethylene terephthalate film having a thickness of 75 μm.
Using the ITO film of □, the dielectric layer: a foamed polyethylene sheet having a thickness of 7.8 mm, the radio wave reflector layer: an aluminum foil having a thickness of 30 μm, a radio wave absorber having a structure as shown in FIG. 26 was formed. FIG. 21 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by radio waves having an oblique incident angle of 45 °, and FIG. 22 shows the radio wave absorption characteristics by vertically incident radio waves.
In the case of vertical incidence, good absorption characteristics are obtained at a frequency of 9.4 GHz, but in the case of oblique incidence, both TE waves and TM waves have poor absorption characteristics, so satisfactory characteristics cannot be obtained.

Conventional Example 2 for Comparison, Resistive Film Layer: Surface resistance laminated on the entire surface of a polyethylene terephthalate film having a thickness of 75 μm is 267 Ω /
Using the ITO film of □, the dielectric layer: a foamed polyethylene sheet having a thickness of 10.8 mm, and the radio wave reflector layer: an aluminum foil having a thickness of 30 μm, a radio wave absorber having a structure as shown in FIG. 26 was formed. FIG. 23 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by a radio wave with an oblique incident angle of 45 °. At the frequency of 9.4 GHz, good absorption characteristics of TM waves are obtained, but satisfactory absorption characteristics of TE waves are not obtained.

Conventional Example 3 mixture layer for comparison : Chloroprene rubber having an average particle size of 3 μm
Thickness of 2.5% ferrite powder of 30% by volume
A composite wave sheet having a thickness of 30 mm and a radio wave reflector layer: an aluminum foil having a thickness of 30 μm were used to form a radio wave absorber having a structure as shown in FIG. FIG. 24 shows the result of measuring the radio wave absorption characteristics of this radio wave absorber by a radio wave having an oblique incident angle of 45 °. At the frequency of 9.4 GHz, good absorption characteristics of TM waves are obtained, but satisfactory absorption characteristics of TE waves are not obtained.

As described above, the electromagnetic wave absorber of the present invention has a very excellent oblique incident electromagnetic wave absorption property regardless of the polarization of the electromagnetic wave. Therefore, not only the vertically polarized wave but also the circularly polarized wave can effectively suppress the unnecessary reflected wave that is obliquely incident, and since the design and the manufacturing are easy, the manufacturing can be performed at low cost.

The embodiments described above are merely illustrative of the present invention and are not restrictive, and the present invention can be implemented in various other modifications and alterations. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

[0060]

As described above in detail, according to the present invention, the resistive film layer is formed in the first plane in the layer plane of the resistive film layer.
Since the surface resistance in the direction of and the surface resistance in the second direction in the layer plane intersecting the first direction are different from each other, it is possible to obtain a very excellent electromagnetic wave absorption characteristic without polarization dependence. have. Therefore, not only the vertically polarized wave but also the circularly polarized wave can suppress the unnecessary reflected wave that is obliquely incident very effectively. Further, since the design and manufacture are easy, it is possible to manufacture at low cost.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a configuration of a radio wave absorber according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of radio wave absorption in the present invention.

FIG. 3 is a sectional view taken along line BB of FIG.

FIG. 4 is a plan view schematically showing the configuration of a resistive film layer in the embodiment of FIG.

FIG. 5 is a perspective view schematically showing the configuration of a modification of the resistance film layer.

FIG. 6 is a sectional view schematically showing a configuration of a radio wave absorber according to another embodiment of the present invention.

FIG. 7 is a plan view schematically showing the structure of a resistance film layer in still another embodiment of the present invention.

FIG. 8 is a perspective view schematically showing the configuration of a modification of the conductive pattern.

FIG. 9 is a perspective view schematically showing the configuration of another modification of the resistive film layer.

FIG. 10 is a perspective view schematically showing the configuration of still another modification of the resistive film layer.

11 is a diagram illustrating a radio wave absorption characteristic of Configuration Example 1. FIG.

FIG. 12 is a diagram illustrating a radio wave absorption characteristic of configuration example 2;

FIG. 13 is a diagram showing a radio wave absorption characteristic of a surface resistance changing example 1;

FIG. 14 is a diagram showing a radio wave absorption characteristic of a second modification example of the surface resistance value.

FIG. 15 is a diagram showing a radio wave absorption characteristic of a surface resistance value changing example 3;

FIG. 16 is a diagram showing a radio wave absorption characteristic of Modification Example 4 of the surface resistance value.

FIG. 17 is a diagram showing a radio wave absorption characteristic of Configuration Example 3;

FIG. 18 is a diagram illustrating a radio wave absorption characteristic of configuration example 4;

FIG. 19 is a diagram illustrating a radio wave absorption characteristic of configuration example 5;

FIG. 20 is a diagram illustrating a radio wave absorption characteristic of configuration example 6;

FIG. 21 is a diagram showing a radio wave absorption characteristic of oblique incidence in Conventional Example 1 for comparison.

FIG. 22 is a diagram showing a vertically incident radio wave absorption characteristic of Conventional Example 1 for comparison.

FIG. 23 is a diagram showing a radio wave absorption characteristic of Conventional Example 2 for comparison.

FIG. 24 is a diagram illustrating a radio wave absorption characteristic of Conventional Example 3 for comparison.

FIG. 25 is a cross-sectional view showing an example of a conventional thin electromagnetic wave absorber.

26 is a cross-sectional view taken along the line AA of FIG.

FIG. 27 is a perspective view showing another example of a conventional thin electromagnetic wave absorber.

FIG. 28 is a diagram illustrating directions of an electric field E _i and a magnetic field H _i of a vertically incident radio wave.

FIG. 29 is a diagram illustrating directions of an electric field E _i and a magnetic field H _i of TE waves that are obliquely incident.

FIG. 30 is a diagram illustrating the directions of an electric field E _i and a magnetic field H _i of TM waves that are obliquely incident.

[Explanation of symbols]

10, 60 Dielectric layer 11, 61 Radio wave reflector layer 12, 52, 62, 72, 82, 92, 102 Resistive film layer 13, 14, 53, 54, 103 Resistive wire 63 Protective film layer 73, 74, 93, 94, 104 Conductive strip

Continuation of the front page (56) References Japanese Patent Laid-Open No. 2-107000 (JP, A) Japanese Patent Laid-Open No. 2-184098 (JP, A) Japanese Patent Laid-Open No. 6-85532 (JP, A) Japanese Patent Laid-Open No. 63-283195 (JP , A) JP 2-12896 (JP, A) JP 58-210696 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05K 9/00 H01Q 17/00

Claims (6)

(57) [Claims] 1. A radio wave absorber provided with a dielectric layer, a radio wave reflector layer laminated on one surface of the dielectric layer, and a resistance film layer laminated on the other surface of the dielectric layer. The resistance film layer has a surface resistance in a first direction in a layer plane of the resistance film layer and a surface resistance in a second direction in the layer plane intersecting the first direction. A radio wave absorber, which is configured to be different from each other. 2. The radio wave absorber according to claim 1, wherein an angle at which the first direction and the second direction intersect is substantially a right angle. 3. The product of the surface resistance in the first direction and the surface resistance in the second direction is substantially equal to the square of the characteristic impedance of free space.
The electromagnetic wave absorber described in. 4. The resistance film layer is a woven fabric obtained by weaving insulating fibers and conductive fibers or metal wires having a predetermined line resistance. The electromagnetic wave absorber according to the item. 5. The resistance film layer comprises a film in which a conductive film having a predetermined surface resistance is arranged in a predetermined pattern on an insulating film. The radio wave absorber described. 6. The protective film layer laminated on the surface of the resistance film layer opposite to the dielectric layer, further comprising a protective film layer. Radio wave absorber.