Electromagnetic wave absorbing structure with high-temperature resistance and chemical resistance

Abstract

The present invention relates to an electromagnetic wave absorbing structure and, more specifically, to an electromagnetic wave absorbing structure comprising: a first composite layer including a first ceramic matrix and quartz fibers impregnated in the first ceramic matrix; and a second composite layer including a second ceramic matrix and cobalt-coated quartz fibers impregnated in the second ceramic matrix, wherein the second composite layer is disposed on the first composite layer, and thus can have excellent chemical resistance and thermal stability, such that the second composite layer can exhibit excellent electromagnetic wave absorption performance not only at room temperature but also in an ultra-high temperature environment of 1000°C or higher.

Description

Electromagnetic wave absorbing structure with high temperature resistance and chemical resistance

[0001] The present invention relates to an electromagnetic wave absorbing structure capable of exhibiting excellent electromagnetic wave absorption performance not only at room temperature but also in an ultra-high temperature environment of 1000°C or higher.

[0002] With the advancement of detection technologies, the application of stealth technology has become essential for the survivability of aircraft and weapon systems such as guided weapons. Stealth technology refers to the technology that conceals the detection of friendly aircraft from acoustic, optical, infrared, and electromagnetic signatures. Minimizing electromagnetic signatures is the most crucial core technology.

[0003] Technologies for reducing the radar cross section (RCS) of stealth aircraft primarily include airframe shaping, absorbent paints, and electromagnetic wave-absorbing structures. Radar-absorbing structures (RAS) are multifunctional composites that fundamentally function as load-bearing and transmission structures while also absorbing electromagnetic waves.

[0004] Conventional radar absorbing structures achieve electromagnetic properties by adding nano-loss materials to the matrix. However, achieving superior electromagnetic wave absorption performance requires dispersing a high weight fraction of nanoparticles. This method introduces uncertainty in the electromagnetic and mechanical properties, depending on the particle dispersion state, and imposes limitations on the design of various electromagnetic wave absorbing structures.

[0005] Currently, metal materials such as molybdenum, tantalum, and tungsten are primarily used in high-temperature heat-resistant components of aircraft. However, these materials suffer from limitations such as limited operating temperatures, poor oxidation resistance in oxidizing environments, and low fracture toughness. Furthermore, attempts are being made to implement stealth composite structures based on polymer composites for heat-resistant structures. However, these methods face limitations such as limited operating temperatures due to their low glass transition temperature, low fracture toughness, and low mechanical strength, making them difficult to apply in extreme environments such as ultra-high temperatures.

[0006] The technical problem to be achieved by the present invention is to provide an electromagnetic wave absorbing structure that can have excellent chemical resistance and thermal stability and exhibits excellent electromagnetic wave absorption performance not only at room temperature but also in an ultra-high temperature environment of 1000°C or higher.

[0007] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

[0008] One embodiment of the present invention provides an electromagnetic wave absorbing structure, comprising: a first composite layer including a first ceramic matrix and quartz fibers impregnated in the first ceramic matrix; and a second composite layer including a second ceramic matrix and cobalt-coated quartz fibers impregnated in the second ceramic matrix; wherein the second composite layer is positioned on the first composite layer.

[0009] An electromagnetic wave absorbing structure according to one embodiment of the present invention can have excellent chemical resistance and thermal stability, and can exhibit excellent electromagnetic wave absorption performance not only at room temperature but also in an ultra-high temperature environment of 1000°C or higher.

[0010] The effects of the present invention are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the attached drawings.

[0011] FIG. 1 is a cross-sectional view schematically illustrating an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0012] Figure 2 is a drawing schematically showing an example of use of an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0013] Figure 3 briefly illustrates a manufacturing process of an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0014] Figure 4 shows the manufacturing process of the above aluminosilicate matrix.

[0015] Part (a) of Fig. 5 shows an SEM image of cobalt coated quartz fiber manufactured in Manufacturing Example 4.

[0016] Part (b) of Fig. 5 shows the EDS analysis results of cobalt coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Example 4.

[0017] Part (a) of Fig. 6 shows the XPS analysis results for cobalt-coated quartz fibers and pristine quartz fibers manufactured in Manufacturing Examples 1, 3, and 5.

[0018] Part (b) of Fig. 6 shows the VSM analysis results for cobalt-coated quartz fibers and pristine quartz fibers manufactured in Manufacturing Examples 1 to 5.

[0019] Parts (a) and (b) of Fig. 7 show the real and imaginary parts of the complex permittivity in the X-band band of the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Examples 1 to 5, respectively.

[0020] Parts (a) and (b) of Fig. 8 show the real and imaginary parts of the complex permeability in the X-band band of the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Examples 1 to 5, respectively.

[0021] Parts (a) and (b) of Fig. 9 respectively show the real and imaginary parts of the complex permittivity according to temperature in the X-band band of the cobalt-coated quartz fiber manufactured in Manufacturing Example 5.

[0022] Parts (a) and (b) of Fig. 10 respectively show the real and imaginary parts of the complex permittivity according to temperature in the X-band band of the pristine quartz fiber.

[0023] Figure 11 shows the return loss according to temperature in the X-band band of the electromagnetic wave absorbing structure manufactured in the example.

[0024] Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0025] Throughout this specification, when it is said that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0026] Throughout this specification, the unit “parts by weight” may mean the weight ratio between each component.

[0027] Throughout this specification, “A and / or B” means “A and B, or A or B.”

[0028] Throughout this specification, terms including ordinal numbers, such as "first" and "second," are used to distinguish one component from another and are not limited by the ordinal numbers. For example, within the scope of the invention, the first component may also be referred to as the second component, and similarly, the second component may be referred to as the first component.

[0029] Hereinafter, the present invention will be described in more detail.

[0030] One embodiment of the present invention provides an electromagnetic wave absorbing structure, comprising: a first composite layer including a first ceramic matrix and quartz fibers impregnated in the first ceramic matrix; and a second composite layer including a second ceramic matrix and cobalt-coated quartz fibers impregnated in the second ceramic matrix; wherein the second composite layer is positioned on the first composite layer.

[0031] An electromagnetic wave absorbing structure according to one embodiment of the present invention can have excellent chemical resistance and thermal stability, and can be applied to an ultra-high temperature environment of 1000°C or higher, and can exhibit excellent electromagnetic wave absorption performance not only at room temperature but also in an ultra-high temperature environment of 1000°C or higher.

[0032] FIG. 1 is a cross-sectional view schematically illustrating an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0033] Referring to FIG. 1, an electromagnetic wave absorbing structure (100) includes a first composite layer (110) and a second composite layer (120) provided on the first composite layer (110). The first composite layer (110) is formed by impregnating a first ceramic matrix (112) with quartz fibers (111), and the second composite layer (120) is formed by impregnating a second ceramic matrix (122) with cobalt-coated quartz fibers (121).

[0034] In this specification, "quartz fiber" may refer to glass fiber with a SiO2 purity of at least 99%. In this specification, "pristine quartz fiber" refers to uncoated quartz fiber. Quartz fiber exhibits excellent heat resistance, maintaining its properties even in ultra-high-temperature environments exceeding 1,000°C, and may also exhibit excellent chemical resistance and mechanical properties.

[0035] According to one embodiment of the present invention, the thickness of the quartz fiber can be used without limitation.

[0036] An electromagnetic wave absorbing structure according to one embodiment of the present invention has excellent chemical resistance and mechanical properties by including quartz fibers in the first composite layer and the second composite layer, and thus can be applied as a support structure for aircraft, etc. In addition, the electromagnetic wave absorbing structure has excellent heat resistance by including quartz fibers in the first composite layer and the second composite layer, and thus its properties can be maintained even in an ultra-high temperature environment of 1000°C or higher, and therefore can be applied as a structure for a part requiring high temperature heat resistance, such as an aircraft nozzle part.

[0037] An electromagnetic wave absorbing structure according to one embodiment of the present invention may include cobalt-coated quartz fibers in the second composite layer. The cobalt-coated quartz fibers may be quartz fibers coated with cobalt. By coating the cobalt on the quartz fibers, the electromagnetic properties of the quartz fibers may be changed. Specifically, the cobalt-coated quartz fibers may have increased permittivity and magnetic permeability compared to pristine quartz fibers.

[0038] According to one embodiment of the present invention, the content of cobalt included in the cobalt-coated quartz fiber may be 5 parts by weight to 150 parts by weight based on 100 parts by weight of Si included in the cobalt-coated quartz fiber. Specifically, the content of cobalt may be 20 parts by weight to 100 parts by weight, 25 parts by weight to 95 parts by weight, or 40 parts by weight to 95 parts by weight based on 100 parts by weight of Si.

[0039] According to one embodiment of the present invention, the cobalt-coated quartz fiber can form cobalt oxide (Co3O4) by oxidizing cobalt at a high temperature, and can have semiconductor properties due to the presence of cobalt oxide, and thus the electrical conductivity of the cobalt-coated quartz fiber can increase as the temperature increases.

[0040] According to one embodiment of the present invention, the cobalt-coated quartz fiber may be coated by a physical vapor deposition method. The physical vapor deposition method may be, for example, thermal evaporation, electron beam evaporation, or sputtering. The physical vapor deposition method may preferably be a sputtering method. By coating cobalt on the quartz fiber by a sputtering method, cobalt can be continuously and homogeneously coated on the entire surface of the fiber.

[0041] According to one embodiment of the present invention, the first ceramic matrix and the second ceramic matrix may include the same or different ceramic compounds.

[0042] Since the ceramic compound has a high content of inorganic components, the electromagnetic wave absorbing structure according to one embodiment of the present invention may have excellent chemical resistance and heat stability, and may be cured at room temperature. Since the ceramic compound is used as a matrix for the first composite layer and the second composite layer, the electromagnetic wave absorbing structure has excellent heat resistance, and thus its physical properties can be maintained even in an ultra-high temperature environment of 1000°C or higher, and thus can be applied as a structure for parts requiring high temperature heat resistance, such as aircraft nozzle parts.

[0043] According to one embodiment of the present invention, the first ceramic matrix and the second ceramic matrix may include the same or different ceramic compounds, and may be selected from the group consisting of oxides, nitrides, carbides, and combinations thereof of, for example, silicon, aluminum, titanium, zirconium, etc.

[0044] According to one embodiment of the present invention, at least one of the first ceramic matrix and the second ceramic matrix may include an aluminosilicate. The aluminosilicate matrix is ​​a geopolymer-based ceramic matrix that forms a polymer-like network during the curing process, and thus can be synthesized at room temperature or at a low temperature of 100°C or lower.

[0045] According to one embodiment of the present invention, the thickness of the electromagnetic wave absorbing structure and each composite layer can be appropriately adjusted according to the target frequency band.

[0046] According to one embodiment of the present invention, the thickness of the electromagnetic wave absorbing structure and each composite layer can be designed to have an electromagnetic wave absorption performance of 90% or more in the X-band.

[0047] In this specification, the X-band band means a band of frequencies from 8.2 GHz to 12.4 GHz.

[0048] According to one embodiment of the present invention, the optimal thickness of the electromagnetic wave absorbing structure and each composite layer can be obtained through a commercial program, MATLAB R2011b (MathWorks Inc., USA), and an analysis program, CST Microwave Studio (Computer System Technology GmbH, Germany), based on the measured permittivity and permeability values ​​for each composite layer.

[0049] Specifically, when the complex permittivity and complex permeability values ​​at 10 GHz of the cobalt-coated quartz fiber included in the second composite layer are 11.17-j21.30 and 1.02-j0.04, respectively, the optimal total thickness of the electromagnetic wave absorbing structure may be 3 mm or more and 4 mm or less, the optimal thickness of the first composite layer may be 2.85 mm or more and 3.7 mm or less, and the optimal thickness of the second composite layer may be 0.15 mm or more and 0.3 mm or less.

[0050] According to one embodiment of the present invention, the ratio of the thickness of the first composite layer to the thickness of the second composite layer may be 10:1 to 20:1. Specifically, the ratio of the thickness of the first composite layer to the thickness of the second composite layer may be 10:1 to 18:1, 10:1 to 16:1, 12:1 to 20:1, 14:1 to 20:1, 14:1 to 16:1.

[0051] An electromagnetic wave absorbing structure according to one embodiment of the present invention may have a reflection loss of -10 dB or less in the X-band frequency band even in an ultra-high temperature environment of 1000 ℃ or higher. Specifically, by having the above reflection loss, an electromagnetic wave absorption capacity of 90% or more in the X-band frequency band can be exhibited even in an ultra-high temperature environment of 1000 ℃ or higher.

[0052] An electromagnetic wave absorbing structure according to one embodiment of the present invention may have a maximum reflection loss value of -20 dB or less at a temperature of 1000 ℃ or higher.

[0053] Figure 2 is a drawing schematically showing an example of use of an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0054] Referring to FIG. 2, when an electromagnetic wave absorbing structure is used, the first composite layer may be placed on a reflector. The reflector may be a material that reflects electromagnetic waves and preferably may include a perfect electrical conductor (PEC).

[0055] Hereinafter, a method for manufacturing an electromagnetic wave absorbing structure according to one embodiment of the present invention will be described.

[0056] Figure 3 briefly illustrates a manufacturing process of an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0057] First, cobalt-coated quartz fibers and quartz fibers are prepared. Any quartz fiber with the properties described above can be used without limitation. Cobalt-coated quartz fibers can be prepared by coating quartz fibers with cobalt using physical vapor deposition.

[0058] Part (a) of Fig. 3 is a schematic diagram schematically showing the sputtering method, which is one of the physical vapor deposition methods.

[0059] In addition, the first ceramic matrix and the second ceramic matrix are prepared to include the same or different ceramic compounds as described above. Preferably, at least one of the first ceramic matrix and the second ceramic matrix may include an aluminosilicate.

[0060] Figure 4 shows the manufacturing process of the above aluminosilicate matrix.

[0061] Then, the first composite layer is manufactured by impregnating the first ceramic matrix with quartz fibers. The impregnation may be performed by hand lay-up.

[0062] Typically, the hand layup process involves placing reinforcing fibers on a mold, pouring the matrix over them, and then using a brush or roller to evenly impregnate the fibers into the matrix. This hand layup process can be repeated until the optimal thickness of the first composite layer described above is achieved.

[0063] A second composite layer is prepared by impregnating cobalt-coated quartz fibers into a second ceramic matrix. The hand layup process can be repeated until the optimal thickness of the second composite layer described above is achieved.

[0064] Part (c) of Fig. 3 illustrates the process of impregnating quartz fibers or cobalt-coated quartz fibers into aluminosilicate using the hand layup method.

[0065] Then, the first composite layer and the second composite layer are laminated and combined using a hand layup method, and then cured to manufacture an electromagnetic wave absorbing structure.

[0066] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0067] Manufacturing Example 1

[0068] Part (a) of Fig. 9 is a schematic diagram schematically showing the sputtering method.

[0069] Quartz fiber fabric (Saint-Gobain, Quartzfabric 200GW100) measuring 200 mm in width and 220 mm in length was prepared. Cobalt was deposited on the quartz fiber by sputtering, a physical vapor deposition method. First, argon gas was injected into the vacuum chamber of the DC sputtering device. The cobalt to be coated was placed at the cathode, and the quartz fiber was placed at the anode. Then, voltage was applied to deposit and coat the cobalt on the quartz fiber for 5 minutes. The deposition time was 5 minutes, and the cobalt content in the cobalt-coated quartz fiber was approximately 6.6 parts by weight based on 100 parts by weight of the Si component of the cobalt-coated quartz fiber.

[0070] Manufacturing Example 2

[0071] Cobalt-coated quartz fiber was manufactured in the same manner as in Manufacturing Example 1, except that cobalt was deposited on the quartz fiber for 10 minutes to coat it. At this time, the content of cobalt contained in the cobalt-coated quartz fiber was approximately 21.7 parts by weight based on 100 parts by weight of the Si component of the cobalt-coated quartz fiber.

[0072] Manufacturing Example 3

[0073] Cobalt-coated quartz fiber was manufactured in the same manner as in Manufacturing Example 1, except that cobalt was deposited on the quartz fiber for 15 minutes to coat it. At this time, the content of cobalt contained in the cobalt-coated quartz fiber was approximately 26.6 parts by weight based on 100 parts by weight of the Si component of the cobalt-coated quartz fiber.

[0074] Manufacturing Example 4

[0075] Cobalt-coated quartz fiber was manufactured in the same manner as in Manufacturing Example 1, except that cobalt was deposited on the quartz fiber for 20 minutes to coat it. At this time, the content of cobalt contained in the cobalt-coated quartz fiber was approximately 46.4 parts by weight based on 100 parts by weight of the Si component of the cobalt-coated quartz fiber.

[0076] Manufacturing Example 5

[0077] Cobalt-coated quartz fiber was manufactured in the same manner as in Manufacturing Example 1, except that cobalt was deposited on the quartz fiber for 25 minutes to coat it. At this time, the content of cobalt contained in the cobalt-coated quartz fiber was approximately 90.6 parts by weight based on 100 parts by weight of the Si component of the cobalt-coated quartz fiber.

[0078] To confirm whether the metal coating was uniformly performed on the cobalt-coated quartz fibers manufactured in Manufacturing Examples 1 to 5, SEM (Scanning electron microscope) images were checked, and EDS (Energy-dispersive X-ray spectrum) analysis was performed to confirm the content of cobalt particles according to the sputtering deposition time.

[0079] Table 1 shows the EDS results for the cobalt-coated quartz fibers manufactured in Manufacturing Examples 1 to 5. The carbon element detected in the EDS analysis results is not an element actually included in the cobalt-coated quartz fibers, and may have been detected due to contamination of the chamber and sample during EDS analysis.

[0080] Detected element manufacturing example 1 Manufacturing example 2 Manufacturing example 3 Manufacturing example 4 Manufacturing example 5Si23.77 wt%22.46 wt%24.08 wt%26.32 wt%22.29 wt%Co1.58 wt%4.87 wt%6.40 wt%12.21 wt%20.19 wt%O60.33 wt%57.41 wt%53.23 wt%40.81 wt%43.14 wt%C14.32 wt%15.26 wt%16.29 wt%20.67 wt%14.39 wt%

[0081] Part (a) of Fig. 5 shows a SEM image of the cobalt-coated quartz fiber manufactured in Manufacturing Example 4. Part (b) of Fig. 5 shows the EDS analysis results of the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Example 4. Referring to part (a) of Fig. 5, it was confirmed that cobalt metal particles were coated on the surface of the quartz fiber, and it was confirmed that the cobalt metal coating layer was uniformly formed in the cross-sectional image of the cobalt-coated quartz fiber. XPS (X-ray photoelectron spectroscopy) analysis was performed on the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Examples 1, 3, and 5 to confirm the plating property of the cobalt particles according to the sputtering deposition time.

[0082] Part (a) of Fig. 6 shows the XPS analysis results for cobalt-coated quartz fibers and pristine quartz fibers manufactured in Manufacturing Examples 1, 3, and 5.

[0083] Referring to part (a) of Fig. 6, it was confirmed that the peak value indicating the binding energy size of cobalt increases as the sputtering deposition time increases.

[0084]

[0085] *VSM (Vibrating sample magnetometer) analysis was performed on the cobalt-coated quartz fibers and pristine quartz fibers manufactured in Manufacturing Examples 1 to 5 to measure the magnetization values.

[0086] Part (b) of Fig. 6 shows the VSM analysis results for cobalt-coated quartz fibers and pristine quartz fibers manufactured in Manufacturing Examples 1 to 5.

[0087] Referring to part (b) of Fig. 6, the horizontal axis of the magnetic hysteresis curve represents the magnetic field and the vertical axis represents the magnetization value. As the sputtering deposition time increases, the slope of the magnetic hysteresis curve increases, and through this, it was confirmed that as the sputtering deposition time increases, the permeability of the cobalt-coated quartz fiber increases. In addition, it was confirmed that as the sputtering deposition time increases, the saturation magnetization of the cobalt-coated quartz fiber increases.

[0088] In order to obtain electromagnetic properties necessary for manufacturing an electromagnetic wave absorbing structure, complex permittivity and complex permeability were measured using a free space measurement system in the X-band (8.2-12.4 GHz) frequency band for cobalt-coated quartz fibers and pristine quartz fibers manufactured in Manufacturing Examples 1 to 5.

[0089] Parts (a) and (b) of Fig. 7 show the real and imaginary parts of the complex permittivity in the X-band band of the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Examples 1 to 5, respectively.

[0090] Referring to parts (a) and (b) of Fig. 7, it was confirmed that the dielectric constant increases as the sputtering deposition time increases.

[0091] Parts (a) and (b) of Fig. 8 show the real and imaginary parts of the complex permeability in the X-band band of the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Examples 1 to 5, respectively.

[0092] Referring to parts (a) and (b) of Fig. 8, it was confirmed that the investment rate increases as the sputtering deposition time increases.

[0093] The complex permittivity of the cobalt-coated quartz fiber and pristine quartz fiber manufactured in Manufacturing Example 5 was measured at the target frequency band, the X-band, using an ultra-high-temperature thermal chamber and a free-space measurement system. For accurate measurements, a 2-tier gated reflect line (GRL) calibration and time gating method were applied. First, the RF cable connecting the horn antenna and the network analyzer was calibrated using a calibration kit, and unnecessary reflections were corrected for the two horn antennas and the ultra-high-temperature thermal chamber located between them. The specimen was placed inside the ultra-high-temperature thermal chamber and heated at a rate of 3.3 ℃ / min, and the complex permittivity was measured at 300 ℃ intervals from 25 ℃ to 1200 ℃. For accurate measurements, the complex permittivity was measured after reaching the set temperature and maintaining it for 10 minutes.

[0094] Parts (a) and (b) of Fig. 9 respectively show the real and imaginary parts of the complex permittivity according to temperature in the X-band band of the cobalt-coated quartz fiber manufactured in Manufacturing Example 5.

[0095] Parts (a) and (b) of Fig. 10 respectively show the real and imaginary parts of the complex permittivity according to temperature in the X-band band of the pristine quartz fiber.

[0096] Referring to FIGS. 9 and 10, it was confirmed that the complex permittivity of both the pristine quartz fiber and the cobalt-coated quartz fiber increased as the temperature increased.

[0097] Example 1

[0098] Figure 9 illustrates a manufacturing process of an electromagnetic wave absorbing structure according to one embodiment of the present invention.

[0099] An aluminosilicate matrix was prepared and used as the first and second ceramic matrices.

[0100] Figure 10 illustrates a process for producing an aluminosilicate matrix according to one embodiment of the present invention.

[0101] Metakaolin was used as a precursor of the aluminosilicate compound, and KOH and K2SiO3 aqueous solutions were used as activators for rapid curing.

[0102] First, metakaolin was obtained by calcining kaolin (DUKSAN Co., Ltd / 312 g) at 800 ℃ for 4 hours. In addition, KOH (DAEJUNG CHEMICALS & METALS Co., Ltd / 208 g) and K2SiO3 (DAEJUNG CHEMICALS & METALS Co., Ltd / 104 g) were added to activate the mixed powder. Then, the powder and solution were mixed using a speed mixer at 2,000 rpm for 1 minute to obtain an aluminosilicate compound.

[0103] The first composite layer was formed by hand laying up 14 sheets of pristine quartz fibers and the aluminosilicate compound, thereby impregnating the pristine quartz fibers into the aluminosilicate matrix.

[0104] The second composite layer was formed by hand-laying one sheet of cobalt-coated quartz fiber manufactured in Manufacturing Example 5 and the aluminosilicate compound to impregnate the cobalt-coated quartz fiber into the aluminosilicate matrix.

[0105] Afterwards, the first and second composite layers were laminated by hand layup and molded using an autoclave at 80°C for 24 hours. The thickness of the manufactured electromagnetic wave absorbing structure was 3.419 mm.

[0106] Experimental example

[0107] Experiment to evaluate electromagnetic wave absorption performance according to temperature

[0108] To measure the temperature-dependent electromagnetic wave absorption performance of the electromagnetic wave absorbing structure manufactured in the examples, measurements were made using a free-space measurement system linked to an ultra-high-temperature thermal chamber. 2-Tier gated reflect line (GRL) calibration and time gating methods were applied.

[0109] The electromagnetic wave absorbing structure manufactured in Example 1 was placed inside an ultra-high temperature heat chamber, heated at a rate of 3.3 ℃ / min, and the electromagnetic wave absorption performance was measured at 300 ℃ intervals from 25 ℃ to 1200 ℃. The measurement results for the maximum reflection loss value, peak frequency, absorption frequency band (RL < -10 dB), and absorption bandwidth (RL < -10 dB) according to temperature of the electromagnetic wave absorbing structure manufactured in Example 1 are shown in Table 2.

[0110] Figure 11 shows the reflection loss according to temperature in the X-band of the electromagnetic wave absorbing structure manufactured in the example.

[0111] Temperature [℃] Maximum return loss value [dB] Peak frequency [GHz] Absorption frequency band (RL < -10 dB) [GHz] Absorption bandwidth (RL < -10 dB ) [Hz] 25-19.70 11.15 8.76-12.43.64 300-19.52 11.00 8.65-12.43.75 600-19.28 10.91 8.48-12.43.92 900-21.15 10.75 8.2-12.44.2 1200-25.45 10.52 8.2-12.44.2

[0112] Referring to the above Fig. 11 and Table 2, the measurement results at room temperature of 25 ℃ showed a maximum reflection loss of -19.70 dB at 11.15 GHz, and an absorption bandwidth of less than -10 dB was achieved in the range of 8.76 GHz to 12.4 GHz. The maximum reflection loss value at 300 ℃ was -19.52 dB at 11.00 GHz, and an absorption bandwidth of less than -10 dB was achieved in the range of 8.65 GHz to 12.4 GHz. The maximum reflection loss at 600 ℃ was -19.28 dB at 10.91 GHz, and an absorption bandwidth of less than -10 dB was achieved in the range of 8.48 GHz to 12.4 GHz. The maximum reflection loss at 900 ℃ was -21.15 dB at 10.75 GHz, and an absorption bandwidth of less than -10 dB was achieved in the range of 8.2 GHz to 12.4 GHz. At 1200 ℃, the maximum reflection loss value was -25.45 dB at 10.52 GHz, and an absorption bandwidth of less than -10 dB was achieved in the range of 8.2 GHz to 12.4 GHz. In addition, it was confirmed that as the temperature increased, the peak frequency indicating the maximum reflection loss value moved to a low frequency band, and the absorption bandwidth having a reflection loss of less than -10 dB increased. In addition, referring to Table 2 above, it was confirmed that the electromagnetic wave absorbing structure according to one embodiment of the present invention exhibits excellent electromagnetic wave absorption performance not only at room temperature but also in an ultra-high temperature environment. Referring to Table 2 above, it was confirmed that the electromagnetic wave absorbing structure according to one embodiment of the present invention utilizes quartz fibers and a ceramic matrix having excellent heat resistance, and that the peak frequency change range from room temperature to 1200°C is only 0.6 GHz. In other words, it was confirmed that the electromagnetic wave absorbing structure according to one embodiment of the present invention does not experience a decrease in electromagnetic wave absorption performance depending on temperature.Although the present invention has been described above through limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

[0113] [Explanation of symbols]

[0114] 100: Electromagnetic wave absorbing structure

[0115] 110: First composite layer

[0116] 120: Second composite layer

[0117] 111: Quartz fiber

[0118] 112: First ceramic matrix

[0119] 121: Cobalt-coated quartz fiber

[0120] 122: Second ceramic matrix

Claims

1. As an electromagnetic wave absorbing structure, A first composite layer comprising a first ceramic matrix and quartz fibers impregnated in the first ceramic matrix; and A second composite layer comprising a second ceramic matrix, and cobalt-coated quartz fibers impregnated in the second ceramic matrix; The second composite layer is positioned on the first composite layer. Electromagnetic wave absorbing structure.

2. An electromagnetic wave absorbing structure according to claim 1, wherein the cobalt coating is formed by a physical vapor deposition method.

3. An electromagnetic wave absorbing structure according to claim 1, wherein the reflection loss in the X-band frequency band is -10 dB or less at a temperature of 1000 ℃ or higher.

4. An electromagnetic wave absorbing structure according to claim 1, wherein a ratio of the thickness of the first composite layer to the thickness of the second composite layer is 10:1 to 20:

1.

5. An electromagnetic wave absorbing structure according to claim 1, wherein at least one of the first ceramic matrix and the second ceramic matrix comprises aluminosilicate.

6. An electromagnetic wave absorbing structure according to claim 1, wherein the cobalt content of the cobalt-coated quartz fiber is 5 to 150 parts by weight based on 100 parts by weight of Si included in the cobalt-coated quartz fiber.

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