KR20220060016A - Electromagnetic waves absorber comprising porous barium titanate foam and manufacture method thereof - Google Patents

Abstract

The present invention relates to an electromagnetic wave absorber comprising a porous barium titanate foam and a manufacturing method thereof. According to the composition, the electromagnetic wave absorber provided by the present invention has great radar absorption performance without additional radar absorption materials and has an advantage that the absorber can be used even at a high-temperature or high-pressure environment.

Description

Electromagnetic waves absorber comprising porous barium titanate foam and manufacture method thereof

The present invention relates to an electromagnetic wave absorber including a porous barium titanate foam and a method for manufacturing the same.

One of the various methods to have stealth performance applied to fighters or naval ships is to use a material that absorbs electromagnetic waves emitted from radar (hereinafter referred to as 'radar absorption material'). A radar-absorbing material refers to a material that converts light incident electromagnetic waves into heat and absorbs them so that weapons such as ships and vehicles are not detected by enemy radars. In general, radar absorbing materials are intentionally designed to absorb incident radar waves in as many directions of incidence as possible. For decades, radar-absorbing materials have received special attention because of their properties, particularly their stealth properties, and have been utilized in military applications such as fighters and naval vessels.

In the case of a conventional radar absorption material, it refers to an absorption material coated with a radar absorption material based on a polymer substrate, which is a lightweight material but has problems of thermal deformation and deterioration of properties at high temperatures due to the unique characteristics of the polymer material. A porous ceramic coated with a radar absorbing material has been proposed as a substitute for such a polymer material, but a lot of research has not been done yet.

According to the previous studies of the present inventors, for radar absorption properties of porous alumina and mullite, they have low dielectric constant values of 11.3 at 24 GHz and 1.66 at 10 GHz, respectively. Therefore, in the case of porous ceramics, the conductivity was improved by coating a radar absorbing material. By coating carbon and cobalt with high conductivity on the open pore structure porous ceramics, porous having high electromagnetic wave absorption characteristics of radar in the X-band band. I have done research on ceramics.

However, there are many difficulties in manufacturing the porous ceramics coated with the radar absorbing material. First, when manufacturing porous ceramics with an open pore structure using the replication template method, porous ceramics with an open pore structure can be manufactured by impregnating a polyurethane template with a ceramic slurry and then performing a sintering process. After sintering, the slurry of the radar absorbent material It cannot be compressed to remove excess slurry in the coating step. Therefore, in order to facilitate the coating of the radar absorbing material, porous ceramics having a low pore density should be prepared. However, in the case of porous ceramics having a low pore density value, there are many difficulties in practical handling and application due to various factors such as high porosity, large pore size, small number of partition walls per unit area, and inherent brittleness of ceramics.

As a background art of the present invention, Japanese Patent Laid-Open No. 2015-536295 describes a lightweight carbon foam as an electromagnetic interference shielding material and a heat conductive material.

An object of the present invention is to provide a porous ceramic foam for electromagnetic wave absorption having excellent electromagnetic wave absorption performance without an additional radar absorption material.

Another object of the present invention is to provide an electromagnetic wave absorber including a porous ceramic foam having excellent electromagnetic wave absorption performance that can be used even in high temperature and high pressure environments.

Another object of the present invention is to provide a method for manufacturing a highly efficient electromagnetic wave absorber having excellent electromagnetic wave absorption performance that can be used even in high temperature and high pressure environments.

According to one aspect, an electromagnetic wave absorber comprising a porous barium titanate foam and absorbing electromagnetic waves of an X-band band is provided.

According to one embodiment, the porous barium titanate foam may be greater than 10 PPI and less than or equal to 60 PPI.

According to one embodiment, the porous barium titanate foam may have a porosity of 80% or more.

According to an embodiment, the electromagnetic wave absorber may have a dielectric constant of 7 ε' or more in a frequency range of 8.2 to 12.4 GHz.

According to an embodiment, the electromagnetic wave absorber may have a return loss value of -3 dB or less in a frequency range of 8.2 to 12.4 GHz.

According to an embodiment, the electromagnetic wave absorber may have a compressive strength of 0.5 MPa or more.

According to an embodiment, the electromagnetic wave absorber may have a thickness of 1.5 to 10 mm.

According to another aspect, i) preparing a porous polymer template; ii) coating the porous polymer template by impregnating the slurry containing barium titanate; iii) drying the porous polymer template coated with the barium titanate; and iv) sintering the barium titanate-coated porous polymer template to form a porous barium titanate foam from which the porous polymer template is removed. A manufacturing method is provided.

According to one embodiment, the porous polymer template in step i) may be a polyurethane foam.

According to one embodiment, the porous polymer template in step i) may have a pore density of greater than 10 PPI and less than or equal to 60 PPI.

According to one embodiment, the porous polymer template in step i) may have a porosity of 80% or more.

According to one embodiment, the slurry including barium titanate in step ii) may have a viscosity of 0.1 to 10 Pa·s or less.

According to an embodiment, the slurry containing barium titanate in step ii) may include at least one of an organic binder, an inorganic binder, and a dispersant.

According to an embodiment, in step iii), it may include burning out the organic binder.

According to one embodiment, the step of milling the slurry containing barium titanate in step iii) may include.

According to an embodiment, sintering may be performed at 1100 to 1400° C. in step iv).

According to an embodiment, the method may further include optimizing the thickness of the electromagnetic wave absorber according to the pore density of the porous barium titanate foam.

According to one embodiment, it is possible to provide a porous ceramic foam for electromagnetic wave absorption having excellent electromagnetic wave absorption performance without an additional radar absorption material.

According to one embodiment, it is possible to provide an electromagnetic wave absorber including a porous ceramic foam for electromagnetic wave absorption having excellent electromagnetic wave absorption performance that can be used even in high temperature and high pressure environments.

According to an embodiment, a highly efficient electromagnetic wave absorber having excellent electromagnetic wave absorption performance that can be used even in high temperature and high pressure environments can be efficiently manufactured.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

FIG. 1 a is an optical photograph of a commercial polyurethane foam having a pore density of 45 PPI, and FIG. 1 b is an optical photograph of a porous barium titanate foam manufactured through a replication template method using a commercial polyurethane foam.
Figure 2a is a graph showing the optimized viscosity characteristics of alumina and barium titanate slurry, Figure 2b is as the pore density increases, barium titanate sintered at 1250 ℃ and alumina sintered at 1600 ℃ is a graph showing the density value of, c of FIG. 2 shows the pore size distribution of porous barium titanate and porous alumina, and d of FIG. 2 is porous barium titanate when the pore density is 10, 25, 45 PPI It is a graph comparing the compressive strength values of porous alumina and porous alumina.
3 a, c, and e show images obtained by reconstructing a cross-sectional image of the porous barium titanate foam into a three-dimensional shape, and b, d, and f of FIG. 3 show a cross-section of a tomography image.
Figure 4a is a photograph showing the microstructure of the polyurethane foam, Figure 4b is a photograph showing the microstructure of the porous barium titanate foam sintered at 1250 ℃.
5 is a graph showing the change value of the permittivity of the porous barium titanate foam with an open pore structure measured in the X-Band band according to frequency. will be.
6a is a graph showing the return loss value according to the pore density according to the frequency when the thickness of the electromagnetic wave absorber is 2.08 mm, and FIG. 6b is a graph showing the optimum thickness value according to the pore density through computational simulation. , FIG. 6 c is a graph showing the calculated return loss value of the barium titanate foam according to an embodiment of the present invention in comparison with the comparative example.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention.

The singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present application, terms such as 'comprise' or 'have' are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, and one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In the present application, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated. In addition, throughout the specification, "on" means to be located above or below the target part, and does not necessarily mean to be located above the direction of gravity based on the direction of gravity.

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, and in the description with reference to the accompanying drawings, the same or corresponding components are given the same reference numerals, and the overlapping description thereof will be omitted. do.

The present inventors prepared porous ceramics with an open pore structure through a replication template method using barium titanate having a high dielectric constant value, so that a porous ceramic foam exhibiting high absorption properties for electromagnetic waves without coating a radar absorbing material was prepared to complete the present invention.

Accordingly, according to one aspect, an electromagnetic wave absorber comprising a porous barium titanate foam and absorbing electromagnetic waves of an X-band band is provided.

Among various ceramics, barium titanate is a material with a high dielectric constant value (1 × 10 ³ at 10 GHz), and is one of the most widely known electronic ceramics materials. However, when the porous ceramics with an open pore structure are manufactured using barium titanate, the effective dielectric constant value compared to the dense structure decreases to about 1 × 10 ² at 10 GHz. This can be judged as a result of the reduction of the effective area due to the open pore structure and the high porosity. Also, the thickness of the maximum return loss factor is inversely proportional to the square root of the dielectric constant, and this value is determined by the wavelength equation. Therefore, if the dielectric constant is high, the thickness of the maximum return loss factor can be minimized.

Although many studies have been reported on applying barium titanate to multilayer ceramic capacitors, studies on other applications such as microfibers or nanostructures have not been conducted much. In addition, studies using barium titanate as a radar absorbing material have rarely been reported.

In particular, the barium titanate foam of the present application is an open pore structure porous ceramic having a three-dimensional network structure, and has an advantage in that materials can freely pass due to high porosity and excellent pore connectivity.

The electromagnetic wave absorber using the barium titanate foam of the present application has a reticulated porous ceramic structure manufactured using barium titanate having a high dielectric constant, and thus does not require an additional radar absorber coating.

Therefore, according to the present application, when coating a radar absorption material to improve radar absorption characteristics, it is not necessary to consider the following factors to be considered.

(1) The higher the pore connectivity, the larger the range of reflection and scattering for the incident electromagnetic wave.

(2) In the case of porous alumina coated with carbon or cobalt particles, a part of the incident electromagnetic wave is absorbed by the conduction properties of carbon and cobalt particles on the surface, and propagates through the porous alumina with lower intensity as it progresses to the inside.

(3) Incident electromagnetic waves may be reflected from the surface of the radio wave absorbing material, which may rather be a major cause of lowering the stealth performance.

In the case of coating radar absorbing materials such as carbon and cobalt, the above various factors do not only have a positive effect.

Quantitatively, the return loss (RL) of 2.08 mm thick reticulated porous barium titanate was close to -16 dB at 16 dB (radar absorption of 97.49%). On the other hand, the return loss (RL) of the prepared 2.50 mm thick reticulated porous barium titanate was close to -21 dB at 9.2 dB (radar absorption of 99.21%).

The porous material of the present disclosure is advantageous for reducing the weight of the radar absorbing material, particularly when applied to a fighter aircraft. Porous materials are composed of solids and pores, but if the pore size is much smaller than the incident wavelength, the incident wavelength is not sensitive to the pores. X-band radar (8.2-12.4 GHz) operates at wavelengths between 2.5 and 4 cm, but pores are less than a millimeter in size.

According to the known Maxwell-Garnett equation, it is effective if the porosity of the reticulated porous barium titanate is 80-90% (typically between 70-95% porosity of the reticular porous ceramic due to the limitation of the replication method using the sacrificial polymer template). The dielectric constant is determined to be about 1 × 10 ² at 10 GHz.

The thickness of the maximum return loss (RL) is inversely proportional to the square root of the dielectric constant and can be determined by the ¼ wavelength equation. If the dielectric constant is high enough, the maximum RL thickness can be minimized, and then the weight can be minimized since both the weight and the thickness of the radar absorbing material are very important. Therefore, the reticulated porous barium titanate foam can be effectively utilized in military applications, especially for fighters.

Although not limited thereto, the porous barium titanate foam may be greater than 10 PPI and less than or equal to 60 PPI. A porous barium titanate foam having a PPI in the above range may be suitable in terms of radar absorption and compressive strength.

Although not limited thereto, the porous barium titanate foam may have a porosity of 80% or more. Porous barium titanate foam having a porosity in the above range may be suitable in terms of radar absorption and compressive strength.

Although not limited thereto, it was found that the electromagnetic wave absorber of the present application has an excellent dielectric constant of 7 ε' or more in a frequency range of 8.2 to 12.4 GHz.

Although not limited thereto, the electromagnetic wave absorber of the present application exhibits excellent return loss values of -3 dB or less in a frequency range of 8.2 to 12.4 GHz.

Although not limited thereto, it was found that the electromagnetic wave absorber of the present application has excellent compressive strength of 0.5 MPa or more.

Although not limited thereto, the electromagnetic wave absorber may have a thickness of 1.5 to 10 mm. Therefore, the reticulated porous barium titanate foam can be effectively utilized in military applications, especially for fighters.

According to another aspect, i) preparing a porous polymer template; ii) coating the porous polymer template by impregnating the slurry containing barium titanate; iii) drying the porous polymer template coated with the barium titanate; and iv) sintering the barium titanate-coated porous polymer template to form a porous barium titanate foam from which the porous polymer template is removed. A manufacturing method is provided.

Although not limited thereto, if the porous polymer template in step i) is polyurethane foam, it may be suitable in terms of workability and radar absorption and compressive strength of the prepared electromagnetic wave absorber when manufacturing the electromagnetic wave absorber.

Although not limited thereto, when the pore density of the porous polymer template in step i) is greater than 10 PPI and less than or equal to 60 PPI, it may be suitable in terms of workability and radar absorption and compressive strength of the prepared electromagnetic wave absorber, 45 Below PPI may be more suitable.

Although not limited thereto, when the porosity of the porous polymer template in step i) is 80% or more, it may be suitable in terms of workability and radar absorption efficiency and compressive strength of the prepared electromagnetic wave absorber when manufacturing the electromagnetic wave absorber.

Although not limited thereto, when the slurry containing barium titanate in step ii) has a viscosity of 0.1 to 10 Pa·s or less, in terms of workability and radar absorption efficiency and compressive strength of the prepared electromagnetic wave absorber in manufacturing the electromagnetic wave absorber may be suitable.

The most important step in manufacturing porous ceramics using the replication template method is the coating step. In the coating step, the prepared ceramic slurry should be able to impregnate the inside of the polyurethane template. In the step of removing the excess slurry, it does not flow down to the partition wall of the polyurethane foam, forms a sufficient coating layer, and has a slurry viscosity characteristic with fluidity enough to prevent clogging of pores to form a uniform coating layer. Since the uniform coating layer significantly affects the mechanical properties of the porous ceramics after sintering, the formation of a uniform coating layer is very important.

Although not limited thereto, the slurry including barium titanate in step ii) may include at least one of an organic binder, an inorganic binder, and a dispersant. The organic binder, the inorganic binder, and the dispersing agent may use a known commercially available material, in the embodiment of the present application, polyvinyl alcohol and methyl cellulose are used as the organic binder, Ludox HS-40 is used as the inorganic binder, and a dispersant is used. As a DAVAN C-N was used.

Although not limited thereto, it may include burning out the organic binder in step iii). The radar absorption efficiency and compressive strength of the electromagnetic wave absorber may be improved by the above steps.

Although not limited thereto, it may include milling the slurry containing barium titanate in step iii). By the above step, the coating efficiency can be improved by uniformly mixing the slurry containing barium titanate.

Although not limited thereto, the case of sintering at 1100 to 1400° C. in step iv) may be suitable in terms of workability and radar absorption efficiency and compressive strength of the manufactured electromagnetic wave absorber when manufacturing the electromagnetic wave absorber.

Although not limited thereto, the method may further include optimizing the thickness of the electromagnetic wave absorber according to the pore density of the porous barium titanate foam. According to the above configuration, when applying the electromagnetic wave absorber, it is possible to optimize the weight reduction, radar absorption efficiency and compressive strength.

[ Example ]

Example . porous barium titanate Foam manufacturing

As a sacrificial polymer template, a commercial polyurethane foam manufactured by SKB Tech with pore densities of 10, 25, and 45 PPI was used, and the polyurethane foam was cut to a certain size (5 cm x 5 cm x 1 cm).

For the raw material composition ratio of the ceramic slurry to be coated on the polyurethane foam, 200 g of barium titanate powder is weighed and mixed with 120 ml of distilled water. Then, as an organic binder, polyvinyl alcohol (average molecular weight (Mn)~500, Junsei chemical , Japan) and 3 g of methyl cellulose (methyl cellulose, average molecular weight (Mn) ~ 40,000, Sigma-Aldrich, USA) were mixed. In addition, 15 ml of Ludox HS-40 (Sigma-Aldrich, USA) was added as an inorganic binder. was used. In addition, 4 g of DARVAN C-N was mixed as a dispersant for uniform dispersion of the ceramic slurry.

After mixing, the polyurethane template was impregnated in the prepared ceramic slurry after ball milling for 24 hours. In order to prepare the reticulated porous barium titanate by the replica method, a commercial polyurethane foam was immersed until the strut wall of the barium titanate coating slurry was completely coated with barium titanate particles. . Thereafter, the polyurethane foam impregnated with barium titanate was pressed by hand, and excess barium titanate slurry was removed to form a thin barium titanate coating layer on the strut wall of the polyurethane foam.

After impregnation, the specimen dried at room temperature for 24 hours was burn-out with an organic binder at 400° C. for 1 hour, and then sintered at 1250° C. for 1 hour. Through this process, an open-pore structure porous barium titanate foam having the same specifications and PPI as the polyurethane foam template was prepared.

comparative example 1 and 2. Preparation of carbon and cobalt coated alumina foam

For comparative data of the porous barium titanate foam, a porous alumina foam coated with carbon and cobalt was prepared, and characteristics were evaluated.

First, surface treatment was performed with 3-aminopropyltrimethoxysilane (APTMS) to increase the adhesion between alumina foam and carbon before coating. The carbon used as the radar absorbent material was Ketjen Black (EC-300j, AkzoNobel, Netherlands), and the batch of carbon slurry was adjusted to 3 - 10 g. 100 ml of distilled water was used as a solvent in each carbon slurry, 10 g of polyvinylpyrrolidone (Sigma-Aldrich, USA) was added as an organic binder, and sodium dodecylbenzene sulfonate (SDBS, Sigma-Aldrich, USA) 1 g After adding the dispersant, the mixture was stirred for 10 minutes and ultrasonically dispersed for 10 minutes to prepare a carbon slurry. Then, it was dip-coated on reticulated porous alumina, and completely dried at 25°C for 24 hours.

In addition, reticulated porous alumina was prepared for coating the cobalt radar absorbent material. Samples were pretreated with APTMS prior to coating as with carbon coating. The cobalt slurry is a radar absorbing material, containing 30-40 wt % of cobalt powder (R125, AOMETAL, Republic of Korea), 54-63 wt % of an epoxy resin (YD128, Kukdo Chemical, Republic of Korea), and 6-7 wt % of a curing agent ( KBH1089, Kukdo Chemical, Republic of Korea). The cobalt slurry was coated on reticulated porous alumina and dried completely at room temperature for 24 hours.

[ Experimental example ]

The microstructure was observed using a scanning electron microscope (SEM, JSM-5800, JEOL, Japna), and porous barium tie was performed using micro X-ray computed tomography (μ-CT, XTH-160, Nikon, Japen) technology. The three-dimensional open pore network structure of the tanate foam was observed. The compressive strength of the porous barium titanate foam was measured using a universal testing machine (instron 5982, U.S.A). The prepared specimen was measured using an Agilent N53230A analyzer (PNA-L Vector Network Analyzer) to measure the radio wave absorption characteristics of the open pore structure, and the measurement frequency band was 8.2 - 12.4 GHz.

FIG. 1 a is an optical photograph of a commercial polyurethane foam having a pore density of 45 PPI, and FIG. 1 b is an optical photograph of a porous barium titanate foam manufactured through a replication template method using a commercial polyurethane foam.

It can be seen that an open-pore structure porous barium titanate foam having the same specifications and PPI as the polyurethane foam template was manufactured.

The most important step in manufacturing porous ceramics using the replication template method is the coating step. In the coating step, the prepared ceramic slurry should be able to impregnate the inside of the polyurethane template. In the step of removing the excess slurry, it does not flow down to the partition wall of the polyurethane foam, forms a sufficient coating layer, and has a slurry viscosity characteristic with fluidity enough to prevent clogging of pores to form a uniform coating layer. Since the uniform coating layer significantly affects the mechanical properties of the porous ceramics after sintering, the formation of a uniform coating layer is very important.

Figure 2a is a graph showing the optimized viscosity characteristics of alumina and barium titanate slurry, Figure 2b is as the pore density increases, barium titanate sintered at 1250 ℃ and alumina sintered at 1600 ℃ is a graph showing the density value of, c of FIG. 2 shows the pore size distribution of porous barium titanate and porous alumina, and d of FIG. 2 is when the pore density is 10, 25, 45 PPI, porous barium titanate It is a graph comparing the compressive strength values of porous alumina and porous alumina.

Referring to FIG. 2 a, the viscosity of the alumina slurry was found to be significantly lower than that of the barium titanate slurry, suggesting that it could more easily penetrate into an overly narrow cell. This offers significant advantages for preparing reticulated porous ceramics, especially when the PPI of the sacrificial polymer template is greater than 60. Moreover, it is important to consider the initial motivation to use reticulated porous barium without additional radar absorbing material. This is because the need to improve the compressive strength of reticulated porous barium titanate with high PPI is high. Through preliminary experiments, the mixing ratio of the barium titanate slurry was determined in consideration of the weight ratio effect of the organic binder (PVA) and the barium titanate particles.

Referring to b of FIG. 2 , as the pore density increases, it can be seen that the density values of barium titanate sintered at 1250° C. and alumina sintered at 1600° C. increase with a similar width.

2c shows the pore size distribution of porous barium titanate and porous alumina. The pore size of about 50 - 100 μm can be determined due to voids formed by heat treatment of the polyurethane foam, as shown in FIG. 4 b. As the pore sizes other than that were not measured, it can be concluded that in the case of porous barium titanate and porous alumina, a dense structure within the partition wall was formed due to the optimized sintering temperature.

2d is a graph comparing the compressive strength values of porous barium titanate and porous alumina when the pore density is 10, 25, and 45 PPI. Regardless of the type of ceramics, the compressive strength value increases as the pore density value increases. This is because in the case of porous ceramics manufactured using the replication template method, the overall mechanical properties of the barrier ribs are not inherent structural properties of the raw material. It can be seen that there is a large influence on the number of Through this, it was possible to prepare porous barium titanate having mechanical properties similar to that of porous alumina, which proved its applicability as a radio wave absorbing material.

In the case of a porous ceramic foam using the replication template method, the thickness and connectivity of the skeleton formed inside the foam affect overall mechanical properties. This was observed using , and the results are shown in FIG. 3 .

That is, a, c, and e of FIG. 3 show images obtained by reconstructing a cross-sectional image of a porous barium titanate foam into a three-dimensional shape, and b, d, and f of FIG. 3 show a cross-section of a tomography image.

Through the tomography image and the image reconstructed into a three-dimensional shape, it can be confirmed that the internal structure of the porous barium titanate foam has excellent pore connectivity without clogging pores.

Figure 4a is a photograph showing the microstructure of the polyurethane foam, Figure 4b is a photograph showing the microstructure of the porous barium titanate foam sintered at 1250 ℃.

In the case of porous ceramics using the replication template method, as shown in FIG. 4B , it has a microstructure in which triangular macrovoids are formed at the site removed after thermal decomposition of the polymer template. Therefore, the size of the voids formed at this time and the defects in the skeleton affect the overall mechanical properties of the porous ceramic foam, which causes a decrease in the operating life in the application field.

In general, electromagnetic properties of porous ceramics (especially radar absorption properties) can be expressed by permittivity and permeability.

5 is a graph showing the change in permittivity of the porous barium titanate foam with an open pore structure measured in the X-Band band according to frequency. will be.

Referring to FIG. 5 , the pore density having the maximum permittivity of the porous barium titanate foam was adjusted to 10, 25, and 45 PPI, showing that the permittivity increases as the pore density increases. However, when the pore density value is increased to 45 PPI or more, the high dielectric constant does not match the wave impedance of the free space on the surface, so the reflectance of electromagnetic waves becomes very large, resulting in a decrease in absorption.

The electromagnetic wave absorption characteristics of the radar of the porous barium titanate foam prepared in the present invention were measured without coating with a radar absorption material such as carbon because it has a high dielectric constant unlike conventional ceramics such as porous alumina and porous mullite.

According to the present application, when a radar absorption material is coated to improve radar absorption characteristics, it is not necessary to consider factors to be considered.

6a is a graph showing the return loss value according to the pore density according to the frequency when the thickness of the electromagnetic wave absorber is 2.08 mm, and FIG. 6b is a graph showing the optimum thickness value according to the pore density through computational simulation. , FIG. 6 c is a graph showing the calculated return loss value of the barium titanate foam according to an embodiment of the present invention in comparison with the comparative example.

Referring to FIG. 6 a, the pore density value is 45 PPI, and when the thickness of the barium titanate foam is 2.08 mm, it shows a value of -16 dB (radio absorption rate 97.49%) at 9.2 GHz. In addition, since the absorption rate increases as the pore density value increases from 10 PPI to 45 PPI, it can be seen that the absorption characteristics can be improved without coating the radio wave absorbing material. In addition, since the reflection loss value changes sensitively according to the thickness of the specimen, it will show a higher absorption capacity if it has an optimized thickness.

However, in the case of porous ceramics with an open pore structure using the replication template method, it is impossible to control and measure the thickness of the specimen because it is manufactured using a commercially available urethane foam. Therefore, a method was used to obtain the optimum thickness by computationally simulating a specimen having a thickness of 2.08 mm using the parameters obtained by actually measuring it.

That is, referring to the b of FIG. 6 , it can be confirmed that the value of the optimum thickness according to the pore density is shown by computational simulation, and the return loss value is maintained near -17 dB over the entire area, which is about 98 % of the absorption capacity. In addition, as the pore density value increased, the optimal thickness of the porous barium titanate decreased, which had a thinner open pore structure through control of the pore density when the absorption capacity was at a similar level. It has an important meaning that it is possible. Recalling that it is advantageous to have the thinnest possible thickness of the radio wave absorbing material, it was confirmed that the radio wave absorbing material has good radio wave absorption properties as the pore density value increases.

In the above, although an embodiment of the present invention has been described, those of ordinary skill in the art can add, change, delete or Various modifications and variations of the present invention may be made by addition, etc., and this will also be included within the scope of the present invention.

Claims (17)

Including porous barium titanate foam,
An electromagnetic wave absorber that absorbs electromagnetic waves in the X-band band. According to claim 1,
The porous barium titanate foam is an electromagnetic wave absorber of greater than 10 PPI and less than or equal to 60 PPI. The method of claim 1,
The porous barium titanate foam has a porosity of 80% or more, an electromagnetic wave absorber. According to claim 1,
The electromagnetic wave absorber has a dielectric constant of 7 ε' or more in a frequency range of 8.2 to 12.4 GHz. According to claim 1,
The electromagnetic wave absorber has a return loss value of -3 dB or less in a frequency range of 8.2 to 12.4 GHz. According to claim 1,
The electromagnetic wave absorber has a compressive strength of 0.5 MPa or more. According to claim 1,
The electromagnetic wave absorber has a thickness of 1.5 to 10 mm. i) preparing a porous polymer template;
ii) coating the porous polymer template by impregnating the slurry containing barium titanate;
iii) drying the porous polymer template coated with the barium titanate; and
iv) sintering the barium titanate-coated porous polymer template to form a porous barium titanate foam from which the porous polymer template is removed; Way. 9. The method of claim 8,
In step i), the porous polymer template is a polyurethane foam, a method for producing an electromagnetic wave absorber comprising a porous barium titanate foam. 9. The method of claim 8,
In step i), the porous polymer template has a pore density of more than 10 PPI and less than or equal to 60 PPI, a method for producing an electromagnetic wave absorber comprising a porous barium titanate foam. 9. The method of claim 8,
In step i), the porous polymer template has a porosity of 80% or more, a method of manufacturing an electromagnetic wave absorber comprising a porous barium titanate foam. 9. The method of claim 8,
In step ii), the slurry containing barium titanate has a viscosity of 0.1 to 10 Pa·s or less, a method for producing an electromagnetic wave absorber including a porous barium titanate foam. 9. The method of claim 8,
In step ii), the slurry containing barium titanate includes at least one of an organic binder, an inorganic binder, and a dispersant. 14. The method of claim 13,
A method of manufacturing an electromagnetic wave absorber comprising a porous barium titanate foam, comprising the step of burning out the organic binder in step iii). 14. The method of claim 13,
A method of manufacturing an electromagnetic wave absorber comprising a porous barium titanate foam comprising milling the slurry containing barium titanate in step iii). 9. The method of claim 8,
Sintering at 1100 to 1400 °C in step iv), a method for producing an electromagnetic wave absorber comprising a porous barium titanate foam. 9. The method of claim 8,
The method of manufacturing an electromagnetic wave absorber including a porous barium titanate foam, further comprising the step of adjusting the thickness of the electromagnetic wave absorber according to the pore density of the porous barium titanate foam.

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