KR20040089283A - Microwave absorber with improved microwave absorption rate by forming impedance resistance film on the surface - Google Patents

Abstract

PURPOSE: A conductive thin film type microwave absorber is provided to reduce the thickness of the microwave absorber by using, as a microwave absorbing layer, a metallic magnet having a high magnetic permeability and dielectric constant or a ceramic ferroelectric substance having a high dielectric constant. CONSTITUTION: A conductive thin film type microwave absorber comprises a microwave absorbing layer(1) having a thickness 1/4 of the incident electromagnetic wave length; a resistance film(2) formed on the electromagnetic wave incident surface of the microwave absorbing layer, and which has a surface resistance of 377±20 §Ù/sq so as to induce an impedance matching; and a conductor layer(3) formed at the surface opposite from the surface of the microwave absorbing layer on which the resistance film is formed.

Description

MICROWAVE ABSORBER WITH IMPROVED MICROWAVE ABSORPTION RATE BY FORMING IMPEDANCE RESISTANCE FILM ON THE SURFACE}

The present invention relates to a conductive thin film type wave absorber having an impedance resistance film formed thereon to improve radio wave absorption. More specifically, the magnetic wave absorber layer has a magnetic permeability and a high dielectric constant or a dielectric having a high dielectric constant, and at the same time reduces the thickness thereof. The present invention relates to a conductive thin film type wave absorber having an improved resistance to radio wave absorption by forming an impedance resistance film having a function of inducing impedance matching to a resistance film.

Recently, markets such as digital home appliances such as mobile communication terminals and notebook PCs are rapidly growing quantitatively and qualitatively. However, as the problem that the electromagnetic waves emitted from these devices may be harmful to the human body has been raised, not only domestic but also the whole world are trying to study the human impact of electromagnetic waves and prepare countermeasures. To date, no definite human hazard has been identified, but countries are strengthening their regulations by promulgating human protection standards.

One of the measures to prevent the leakage of electromagnetic waves and to minimize the harmful effects of human body in these devices is the use of radio absorbers. In the case of mobile phones currently on the market, the inside of the case is coated with a metal coating to minimize the leakage of radio waves. However, since the reflected radio waves can cause electromagnetic interference between internal circuits or components, they have radio wave attenuation functions rather than electromagnetic wave shielding materials. The absorber is more effective.

The most important characteristic required as an electromagnetic wave absorber for electromagnetic wave attenuation in a mobile communication terminal is that the electromagnetic wave absorption rate must be large at the communication frequency (cellular phone: 0.8 ㎓, PCS: 1.8 I, IMT-2000: 2.2 ㎓), and, of course, the thickness of the It must be thin.

However, when the absorber is composed of the existing ferrite magnetic material or carbon powder, since the thickness reaches 5 to 10 mm in the frequency band, the use of a new material required for thinning and a new type of radio absorber should be considered.

Impedance matching type radio absorber attaches a conductor plate to the back of dielectric or magnetic material of specific thickness where impedance matching occurs, and multi-reflects the radio wave inside the material.This matching thickness minimizes the reflectance and maximizes the absorption rate. Inversely proportional to the square root of permeability and permittivity.

For example, in order to reduce the thickness of the absorber to 1 mm or less based on the PCS frequency band of 1.8 GHz, the relative permeability or dielectric constant must be 1,700 or more. In the case of spinel ferrite magnetic materials, the permeability decreases rapidly beyond the Snoek limit frequency and is only 2 to 3 at 1 kHz or more. Even in the case of hexagonal ferrite, which is used as an absorber for high frequency band, the permeability is only about 10-20 at 1㎓ or more. Therefore, it is fundamentally impossible to manufacture a thin wave absorber for a mobile communication frequency band using a ferrite magnetic material.

Recently, a method of constructing a thin wave absorber using the high permeability characteristics of the plate-shaped soft magnetic metal has been proposed, but the absorption capacity is maintained at a maximum of 80% because the impedance matching is not completely satisfied.

In order to solve the above problems of the prior art, the present invention uses a magnetic material having a high permeability and a high dielectric constant or a dielectric having a high dielectric constant as a spacer to reduce the thickness of the radio wave absorber, and induces impedance matching to the surface resistive film. The purpose of the present invention is to provide a conductive thin film type wave absorber having an absorption rate of 99% or more and a thickness of 0.1 to 3 mm in the 0.8 to 2.2 GHz frequency band, thereby improving the wave absorption rate.

1 is a schematic diagram and an equivalent circuit diagram of a radio wave absorber according to the present invention;

2 is a graph showing the complex permeability and the dielectric constant of the soft magnetic metal powder-organic polymer composite material applied to the magnetic composite of the present invention;

3 is a graph showing the complex dielectric constant of a ceramic ferroelectric-organic polymer composite material applied to the magnetic composite of the present invention;

4 is a graph showing radio wave absorption characteristics of a first embodiment of the present invention;

5 is a graph showing radio wave absorption characteristics of a second embodiment of the present invention;

6 is a graph showing radio wave absorption characteristics of a third embodiment of the present invention;

7 is a graph showing radio wave absorption characteristics of a fourth embodiment of the present invention;

8 is a graph showing radio wave absorption characteristics according to a fifth embodiment of the present invention.

♣ Explanation of symbols for main part of drawing ♣

1: Radio wave absorption layer 2: Resistance film 3: Conductor layer

In order to achieve the above object, the present invention is a radio wave absorption layer having a thickness of 1/4 of the incident electromagnetic wave wavelength (λ); A resistive film formed on the electromagnetic wave incident surface of the electromagnetic wave absorbing layer and having a sheet resistance of 377 ± 20 mA / sq to induce impedance matching; An impedance resistive film is formed, comprising a conductor layer formed on an opposite surface of the radio wave absorption layer on which the resistance film is formed, thereby providing a conductive thin film wave absorber having improved radio wave absorption rate.

In addition, the present invention provides a conductive thin film wave absorber having an improved electromagnetic wave absorption rate by forming an impedance resistive film is characterized in that the electromagnetic wave absorbing layer is a composite material incorporating a soft magnetic metal powder into an organic polymer matrix, or a ceramic ferroelectric.

In addition, the present invention provides a conductive thin film type wave absorber having an improved resistance to absorption by forming an impedance resistive film, wherein the resistive film has a sheet resistance of 377 Ω / sq.

In the present invention, the soft magnetic metal powder constituting the electromagnetic wave absorbing layer is selected from pure iron, carbonyl iron, sand dust and permalloy, silicon steel, the ceramic ferroelectric is selected from BaTiO ₃ , PMN-based relaxed ferroelectric Characterized by the impedance resistance film is formed to provide a conductive thin film type wave absorber with improved radio wave absorption rate.

On the other hand, the resistive film constituting the present invention is formed with an impedance resistive film, characterized in that selected from the conductive paste, the conductive polymer and the conductive oxide thin film to provide a conductive thin film type wave absorber with improved radio wave absorption.

In the present invention, the conductive paste constituting the resistive film is selected from metal-carbon powder, metal-silver powder, metal-copper powder and metal-nickel powder, and the conductive polymer is selected from polyacetylene, polyaniline (PANI) and polypyrrole (PPy). The conductive oxide thin film is selected from an indium tin-based and semiconducting oxide to form an impedance resistive film to provide a conductive thin film type wave absorber having improved radio wave absorption.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration of the present invention.

1 is a schematic diagram and an equivalent circuit diagram of a radio wave absorber according to the present invention.

In the electromagnetic wave absorber according to the present invention, as shown in FIG. 1A, a radio wave absorbing layer composed of a magnetic composite material or a pure ceramic ferroelectric in which a rear surface is short-circuited with a conductor 3 and a magnetic material is incorporated into an organic polymer matrix. (1) and a resistive film 2 having a function of inducing impedance matching to a surface on which electromagnetic waves are incident.

The electromagnetic wave absorber according to the present invention as described above may be represented by a transmission line as shown in FIG. 1 (B), and the input impedance Zin of the surface of the absorption layer and the resistance film at a distance of λ / 4 from the short-circuit transmission line. Sheet resistance (R) can be interpreted as a circuit connected in parallel, Zin in the short transmission line is given by the following equation (1).

Where Z ₀ is the free impedance wave impedance (= 377Ω), j = where λ ₀ is the wavelength in free space, d is the thickness of the dielectric or magnetic material, μ _r is the complex permeability (= μ _r '-j μ _r "), and ε _r is the complex dielectric constant (= ε _r ' -jε _r "). . When d = λ / 4, Z _in = ∞, so the synthetic impedance on the surface of the absorber becomes equal to the sheet resistance R of the thin film as shown in Equation 2 below.

In addition, the reflectance of the electromagnetic wave on the surface of the absorber is proportional to the difference between the synthetic impedance (Z) and the characteristic impedance (Z ₀ ) of the free space, as shown in Equation 3 below, so that the sheet resistance of the absorber surface is equal to the characteristic impedance of the free space. When set to sq, an anti-reflective absorber can be formed by impedance matching (Z ₀ = R = 377Ω).

In addition, since the wavelength λ in the magnetic composite material 1 applied in the present invention decreases as the permeability and permittivity increase as in Equation 4, in order to construct a thin conductive film type wave absorber, the permeability and the dielectric constant in the frequency band used are The synthesis of large materials is important.

Where λ ₀ is the wavelength in free space.

Therefore, the present invention makes the radio wave absorption ratio maximum by configuring the thickness of the magnetic complex 1 to 1/4 lambda for the wavelength? In the various magnetic complexes 1 to be applied.

As described above, when the radio wave absorber according to the present invention is applied as a radio wave absorber for a mobile communication portable terminal, the magnetic composite material constituting the radio wave absorption layer 1 has a product of permeability and permittivity in the frequency band of 1.8 GHz or more. It is preferable to adopt the material to be made.

This condition is because the thickness of the absorber can be reduced to 1 mm or less only when the product of the permeability and the permittivity of the radio wave absorber 1 at 1.8 kW is 1700 or more.

Table 1 below shows the soft magnetic metal powder milled for 4 hours using an Attrition Mill to flatten the shape of the powder, and then mixes the powder and the silicone rubber in a weight ratio of 16: 1. It is the complex permeability and permittivity measured at 1.8 ㎓ and the λ / 4 value calculated from each material.

The complex permeability and dielectric constant values vary depending on the shape of the soft magnetic powder, the type of material used as the binder, and the mixing ratio. When the conductive thin film type electromagnetic wave absorber is formed by using the materials of the composite magnetic material 1 of Table 1, the thickness of the absorber 1 should be equal to the calculated λ / 4 to obtain the maximum absorption effect.

In addition, in the case of constructing a radio wave absorber to be used at different frequencies using these materials, a conductive thin film wave absorber should be manufactured after calculating the λ / 4 value by measuring the complex permeability and permittivity at the frequency of use.

The soft magnetic metal compact, which is a magnetic material that satisfies the above conditions, is a composite material prepared by incorporating into an organic polymer matrix, and is applied to the radio wave absorption layer 1, and the ceramic ferroelectric material is a pure material, not a composite material. Applies to

In addition, the soft magnetic metal compact may be applied to pure iron, carbonyl iron, sand dust and permalloy, silicon steel having a predetermined permeability and dielectric constant, and the ceramic ferroelectric has a predetermined dielectric constant of BaTiO ₃ (abbreviated BT), PMN-based relaxed ferroelectric (PMN-PT or PMN-PZN) can be selected and applied.

FIG. 2 is a graph showing the complex permeability and the complex dielectric constant of the composite material of the soft magnetic metal powder-organic polymer applied to the electromagnetic wave absorbing layer 1 constituting the electromagnetic wave absorber of the present invention, and FIG. It is a graph showing the complex dielectric constant of the ceramic ferroelectric-organic polymer composite material applied to the composite.

FIG. 2 is a graph illustrating the complex permeability and the complex dielectric constant of the electromagnetic wave absorbing layer (1) made of soft magnetic metal powder-silicon rubber applied to the present invention, and μ _r '= 3.7, μ _r "at a frequency of 1.8 kHz. Λ / 4 = 1 mm calculated by Equation 4 above by showing = 4.4, ε _r '= 380, ε _r "= 165.

3 is a complex measured by applying a ferroelectric having a composition of 0.9 Pb (Mg _⅓ Nb _⅔ ) O ₃ -0.1 PbTiO ₃ (abbreviated 0.9PMN-0.1PZN) to the radio wave absorbing layer 1 constituting the radio wave absorber of the present invention. As permittivity, λ / 4 = 2.5 mm calculated by Equation 4 by showing ε _r '= 225 and ε _r "= 150 at a frequency of 2 kHz.

The rear part of each of the electromagnetic wave absorbing layers 1 manufactured as described above, that is, the rear part where the electromagnetic wave is incident, is shorted by fixing the conductor 3,

The opposite surface of the back surface to which the conductor 3 is fixed, that is, the incident surface to which the electronic plate is incident, forms a resistive film 2 having a predetermined sheet resistance to induce impedance matching.

The resistive film 2 formed to induce the impedance matching is a kind of coating layer, and may be formed by applying various kinds of conductive materials in the form of paste or paint, or using other coating equipment (sputter or the like).

Experimental results show that the range of the resistive film 2 applied to the present invention is very narrow. In the present invention, when the sheet resistance value of the resistive film is within the range of 377 ± 20 μs / sq, high radio wave absorption is obtained.

In particular, in the present invention, when the resistive film 2 having a sheet resistance of 377 kW / sq was formed on the incident surface of the magnetic composite body 1, it was found that it exhibited the highest radio wave absorption rate.

Therefore, in the present invention, all conductive materials satisfying the above sheet resistance are available, but in the present invention, the conductive paste, the conductive polymer, and the conductive oxide thin film are selected and applied.

In particular, the conductive paste was selected from metal-carbon powder, metal-silver powder, metal-copper powder and metal-nickel powder.

The conductive polymer was selected from polyacetylene, polyaniline (PANI) and polypyrrole (PPy).

The conductive oxide thin film was selected from indium tin-based and semiconducting oxides and used as the material of the resistive film 2.

Hereinafter, the action will be described in detail by the preferred embodiment of the present invention.

Example 1

Magnetic composite material prepared by mixing pure iron powder produced by milling pure iron powder with an average particle size of 70 μm in an Attrition Mill for 4 hours and silicon rubber applied as an organic polymer matrix material in a weight ratio of 16: 1. It is shown by measuring the complex permeability and the complex dielectric constant of the equation, by the equation (4) by showing μ _r '= 3.7, μ _r "= 4.4, ε _r ' = 380, ε _r " = 165 at a frequency of 1.8 kHz Calculated λ / 4 = 1 mm.

As described above, the pure iron compact and the organic polymer silicone rubber were kneaded and compressed to prepare a magnetic composite material having a thickness of 1 mm and applied as a radio wave absorbing layer (1). The rear portion thereof was made of silver or gold having excellent conductivity. After the short-circuit with the conductive plate 3, a mixed paste, which is a conductive paste, was applied to the incident surface to which electromagnetic waves were incident to a thickness of 0.1 mm using a bar coating method.

The manufacturing method of the conductive paste is as follows. A soft magnetic metal powder powder composed of a plated silver (Ag) powder, silicon (Si) 9.0 to 9.6 wt.%, Aluminum (Al) 5.2 to 5.8 wt. Powder = 20: 30) and remixed with a high molecular binder (polyvinyl, polyester, etc.) to prepare a paste having a sheet resistance of 377 ± 20 μs / sq using a three-bone roll.

Figure 4 shows the result of measuring the return loss of the radio wave absorber according to the present invention manufactured as described above with a network analyzer.

That is, it was investigated that the maximum reflection loss (power absorption rate = 99%) of -20 Hz at the frequency of 1.8 kHz, and -3 kHz (about 50% of the case where the resistive film 2 according to the present invention is not applied). Compared to the power absorption rate, the radio wave absorption ability was remarkably improved.

Example 2

In Example 2, the green compact was milled for 3 hours using an Attrition Mill of a soft magnetic metal powder composed of Si 9.0 to 9.6 wt.%, Al 5.2 to 5.8 wt.%, And a residual amount of Fe. After manufacturing, the green compact and polyethylene chloride (CPE) were uniformly mixed in a weight ratio of 8: 1, and then made of a magnetic composite material having a thickness of 2 mm having a lambda / 4 thickness using a double roll to absorb a radio wave. It applied to (1).

In order to form a conductive film having a sheet resistance of 377 Ω / sq as the electromagnetic wave incident surface of the electromagnetic wave absorbing layer 1 composed of the magnetic composite material, polyaniline (PANI), polyethylenedioxythiophene (PEDOT), polypyrrole (Ppy), etc. After application to a thickness of 탆, the back surface was shorted with a conductor plate 3.

5 is a result of measuring the return loss of the radio wave absorber manufactured by the above method with a network analyzer.

When the resistive film of 377Ω / sq is not applied, the return loss of -6.5㏈ (approximately 50% power absorption) is shown, while the maximum return loss of -18㏈ (power absorption rate = 90%) at the frequency of 1.8 ~ 2GHz It was found that the radio wave absorbing ability was significantly improved, and it was found that there was no difference according to the kind of the conductive polymer constituting the resistive film 2.

Example 3

Example 3 was used as _{PMN-PZN (0.8Pb (Mg ⅓} Nb ⅔) O 3 -0.2Pb (Zn ⅓ Nb ⅔) O 3) electric wave absorbing layer (1) of a ferroelectric composition.

The powder used for preparing PMN-PZN specimens was first synthesized by mixing MgO and Nb ₂ O ₅ to synthesize a MgNb ₂ O ₆ Columbite phase, and then mixing ZnO and Nb ₂ O ₅ to synthesize a ZnNb ₂ O ₆ Columbite phase. At this time, 3wt.% Excess MgO was added to promote the formation of the Columbite phase.

MgNb ₂ O ₆ Columbite phase and ZnNb ₂ O ₆ Columbite phase were synthesized by mixing in a ball mill and calcining at 750 ° C. for 2 hours.

MgNb ₂ O ₆ Columbite, ZnNb ₂ O ₆ Columbite, and PbO (excess 1 wt.%) Powder were mixed in a ball mill and calcined at 900 ° C. for 2 hours to prepare PMN-PZN powder. The molded body was kept at 500 ° C. for 2 hours to remove the PVA binder, after which the temperature was raised to 5 ° C./min and sintered at 1000 ° C. for 3 hours.

Then, a thickness of 2.5 mm was processed and sputter-coated an ITO thin film having a sheet resistance of 377 3 / sq on the surface as the resistive film 2, the back surface was short-circuited with the conductor plate 3, and then the reflection loss was measured and shown in FIG. Shown.

That is, before the coating of the ITO thin film with the resistive film 2, the reflection loss of about -2 손실 was measured. However, in the case of the radio wave absorber coated with the resistive film 2, the frequency absorber was -20 at the frequency of 2 ㏈. It can be seen that the radio wave absorption ability is remarkably improved as the reflection loss of power (power absorption rate = 99%).

Example 4

In Example 4, BaTiO ₃ (abbreviated BT), which is a ceramic ferroelectric, was applied as the material for the electromagnetic wave absorbing layer 1 constituting the present invention.

That is, the raw material powder for preparing BT was BaCO ₃ and TiO ₂ of the reagent grade, and the powder mixed by wet mixing for 24 hours in a ball mill at a molar ratio of 1: 1 was calcined at 1100 ° C. for 2 hours.

After adding 0.5wt.% Of PVA binder to the calcined powder, a molded article of Toroidal form (inner diameter 3mm, outer diameter 9mm) was prepared, and the PVA binder was removed at 500 ° C for 2 hours, and then at 1300 ° C for 2 hours. Sintered, and the ITO thin film was coated on the incident surface of the prepared specimen using an RF sputtering device.

The reflection loss of the radio wave absorber according to the present invention manufactured as described above is shown in FIG.

As shown in FIG. 7, when the ITO resistive film 2 is not applied, the return loss of -4.5 ㏈ (about 70% power absorption) is shown, while the ITO resistive film 2 is 2.4 when the ITO resistive film 2 is shown. It was found that the maximum return loss (power absorption rate = 99%) of -20 Hz at the frequency of kHz was found to be a significant improvement in the radio absorption capability.

Example 5

In Example 5, 0.9 Pb (Mg _⅓ Nb _⅔ ) O ₃ -0.1 PbTiO ₃ (abbreviated PMN-PT), which is a ceramic ferroelectric, was applied as a material for the radio wave absorption layer (1).

In other words, the raw material powder used for the production of PMN-PT specimens was PbO, MgO, Nb ₂ O ₅ , TiO ₂ of the reagent grade, first MgO and Nb ₂ O ₅ was mixed to form a MgNb ₂ O ₆ Columbite phase. At this time, in the case of MgO 3wt.% Was added in an excess to promote the formation of the Columbite phase.

The mixed powder was calcined at 750 ° C. for 4 hours to synthesize a MgNb ₂ O ₆ Columbite phase. MgNb ₂ O ₆ Columbite, PbO (excess 1 wt.%) And TiO ₂ powder were weighed and wet mixed for another 24 hours.

The mixed powder was calcined at 900 ° C. for 2 hours, and the calcined powder was pulverized again by a wet method and dried, and the molding of the powder was the same as in the preparation of the BT specimen.

The molded article molded as described above was maintained at 500 ° C. for 2 hours to remove the PVA binder, and was prepared by sintering at 1200 ° C. for 2 hours.

The ITO thin film was coated on the incident surface of the prepared PMN-PT specimen using an RF Magnetron Co-Sputtering apparatus, and the reflection loss of the radio wave absorber according to the present invention was measured and shown in FIG. 8.

As shown in Fig. 8, when the ITO resistive film 2 is not applied, the return loss of -1㏈ (approximately 20% power absorption) is shown, whereas when the ITO resistive film 2 is shown, 2 is shown. The maximum return loss (power absorption rate = 99.5%) of -25 Hz at the frequency of kHz was investigated, indicating that the radio absorption ability was remarkably improved.

In addition, as can be seen in Figures 6 to 8, it can be seen that the radio wave absorption capacity is very sensitive to change according to the sheet resistance of the ITO thin film applied to the resistive film (2).

In other words, as the sheet resistance of the thin film of ITO was close to 377Ω / sq, the radio wave absorbing capacity increased significantly to -20㏈ level, and the radio wave absorbing capacity decreased rapidly as it escaped from 377Ω / sq. In the case of the thin film wave absorber, the surface resistivity of the surface resistive film has the effect of absorbing radio waves within the range of 377 ± 20 Ω / sq.

As described above, according to the present invention, a radio wave absorber of 99% in the mobile communication frequency band and a thickness of 0.1 to 3 mm in thickness can be manufactured.

Therefore, by using a magnetic magnetic material having a high permeability and a high dielectric constant or a ceramic ferroelectric having a high dielectric constant as a radio wave absorbing layer of the radio wave absorber, the thickness of the radio wave absorber of the present invention could be reduced to a level of 0.1 to 3 mm, and the sheet resistance of 377 ± 20 μs / sq, In particular, by using a metal paste, a conductive polymer or a thin film-type resistive film having a sheet resistance of 377 Ω / sq for impedance matching, the radio wave absorption rate could be increased to 90% or more.

Such a thin, lightweight radio wave absorber has an industrially useful effect that can be effectively used to prevent human harm from electromagnetic leakage or electromagnetic interference due to radiation noise, which may be a problem in a mobile communication terminal.

Claims (9)

In the conductive thin film wave absorber, An electromagnetic wave absorbing layer 1 having a thickness equal to 1/4 of the incident electromagnetic wave wavelength? A resistive film (2) formed on the electromagnetic wave incident surface of the electromagnetic wave absorbing layer (1) and having a sheet resistance of 377 ± 20 mA / sq to induce impedance matching; A conductive thin film type electromagnetic wave absorber having an impedance resistive film formed thereon, comprising a conductor layer (3) formed on the opposite side of the electromagnetic wave absorbing layer (1) on which the resistance film (2) is formed. The method according to claim 1, The electromagnetic wave absorbing layer (1) is a composite material obtained by incorporating a soft magnetic metal powder into an organic polymer matrix or a ceramic ferroelectric. The method according to claim 1, The resistive film (2) is formed of an impedance resistive film, characterized in that having a sheet resistance of 377 Ω / sq, conductive wave type radio wave absorber with improved radio wave absorption rate. The method according to claim 1 or 2, The soft magnetic metal compact comprising the radio wave absorbing layer (1) is formed of an impedance resistive film, characterized in that selected from pure iron, carbonyl iron, sand dust, permalloy, and silicon steel. The method according to claim 1 or 2, The ceramic ferroelectric constituting the electromagnetic wave absorbing layer (1) is a conductive thin film type electromagnetic wave absorber having an impedance resistance film is formed, characterized in that selected from BaTiO 3, PMN-based relaxed ferroelectric. The method according to claim 1 or 3, The resistive film (2) is an electrically conductive thin film type wave absorber having an impedance resistive film is formed, characterized in that selected from a conductive paste, a conductive polymer and a conductive oxide thin film is improved. The method according to claim 1 or 3, The conductive paste constituting the resistive film 2 is formed of a metal-carbon powder, a metal-silver powder, a metal-copper powder, and a metal-nickel powder. Absorber. The method according to claim 1 or 3, The conductive polymer constituting the resistive film (2) is an electrically conductive thin film-type radio wave absorber having an impedance resistance film is formed, characterized in that selected from among polyacetylene, Polyaniline (PANI) and Polypyrrole (PPy). The method according to claim 1 or 3, The conductive oxide thin film constituting the resistive film (2) is formed of an impedance resistive film, characterized in that selected from indium-tin-based and semiconducting oxide is a conductive thin film type radio wave absorber with improved radio wave absorption rate.