Micro-capsule having Electromagnetic Wave Absorbing Property and Electromagnetic Wave Absorbing Structure

Abstract

The present invention relates to a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure. A microcapsule according to an embodiment of the present invention comprises a phase change core composed of a material whose phase changes according to temperature, a polymer shell surrounding the phase change core, and core particles of an electromagnetic wave absorption material dispersed within the phase change core; wherein, when at least one region of the phase change core undergoes a phase change to a liquid state according to a temperature change, the core particles disperse and move within the liquid state of the phase change core. Through this, heat generated during the operation of drones and the like can be utilized to improve electromagnetic wave absorption performance.

Description

Technology Field

[0001] The present invention relates to a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure, and more specifically, to a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure that can be applied to stealth functions such as drones. Background Technology

[0002] In the modern battlefield, drone (UAV) detection systems are rapidly evolving from the X-band (8–12 GHz) and Ku-band (12–18 GHz) to the millimeter wave (mmWave: Ka-band 35 GHz, W-band 77 GHz and 94 GHz) bands.

[0003] Conventional electromagnetic wave absorbing coatings (RAM) are predominantly single-layer passive structures in which carbon-based and magnetic-based fillers are dispersed in a polymer binder, and they have structural limitations that limit absorption to narrow bands and cannot actively respond to changes in the operating environment.

[0004] In particular, as modern drone detection systems simultaneously operate multiple detection means such as radar (X / Ku-band), millimeter wave (mmWave), and infrared (IR, 8–14 μm), it is difficult to respond to multiple detection threats with conventional passive RAMs that are limited to single-band absorption.

[0005] In addition, when applying RAM onto a metal substrate, the substrate surface is under short-circuit boundary conditions (impedance Z 0) This entails an impedance mismatch problem that causes total internal reflection of incident electromagnetic waves. Prior art literature

[0006] Korean Patent Publication No. 10-2024-0102889 The problem to be solved

[0007] Accordingly, the present invention has been devised to resolve the above-mentioned problems, and aims to provide a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure capable of resolving the impedance mismatch problem caused by the substrate surface forming a short-circuit boundary condition.

[0008] In addition, another objective of the present invention is to provide a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure that can utilize the heat generated during the operation of a drone, etc., to improve electromagnetic wave absorption performance.

[0009] In addition, another objective is to provide a microcapsule and an electromagnetic wave absorption structure having an electromagnetic wave absorption function that allows for enhanced mmWave active absorption when utilizing operational heat, while maintaining passive X / Ku-band absorption functions in low-temperature operating environments such as winter or high altitudes.

[0010] In addition, there is another objective to provide a microcapsule and an electromagnetic wave absorbing structure that implements infrared shielding functions along with electromagnetic wave absorption. means of solving the problem

[0011] The above objective is achieved according to the present invention by a microcapsule having an electromagnetic wave absorption function, comprising: a phase change core composed of a material whose phase changes according to temperature; a polymer shell surrounding the phase change core; and core particles of an electromagnetic wave absorption material dispersed within the phase change core; wherein, when at least one region of the phase change core undergoes a phase change to a liquid state according to a temperature change, the core particles disperse and move within the liquid state of the phase change core.

[0012] Here, the phase change core may be provided as an inorganic hydrated salt-based phase change material composed of one or more complexes of Na2SO4·10H2O, Na2HPO4·12H2O, CaCl2·6H2O, CH3COONa·3H2O, and Na2S2O3·5H2O, or an organic phase change material composed of one or more complexes of paraffin, palmitic acid, stearic acid, lauric acid, and caprylic acid, or a thermal radiation switching type phase change material including vanadium dioxide and doped vanadium dioxide.

[0013] In addition, the thermal radiation switching type phase change material comprises vanadium dioxide doped with at least one of tungsten and molybdenum, and the phase transition temperature can be controlled to a range of 30 to 55 degrees.

[0014] And, the core particle may comprise a methyl-based nanomaterial composed of one or more of Ti3C2Tx, Ti2CTx, and V2CTx; a carbon-based nanomaterial composed of one or more of graphene and carbon nanotubes; a magnetic nanomaterial composed of one or more of Fe3O4, NiFe2O4, CoFe2O4, MnFe2O4, and ZnFe2O4; a ceramic-based nanomaterial composed of one or more of silicon carbide (SiC), zinc oxide (ZnO), copper oxide (CuO), molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN); or a composite of two or more of the methyl-based nanomaterial, the carbon-based nanomaterial, the magnetic nanomaterial, and the ceramic-based nanomaterial.

[0015] In addition, the polymer shell may be composed of one or more composites of melamine-formaldehyde (MF), urea-formaldehyde (UF), polyurea (PUa), polyurethane (PU), polymethyl methacrylate (PMMA), epoxy resin (EP), silica (SiO2), polyimide (PI), acrylic resin (AC), phenolic resin (PF), and cyclodextrin-based materials.

[0016] In addition, the polymer shell may have a porous structure, an elastic structure, or a double-wall structure to correspond to the volume change according to the phase change of the phase change core.

[0017] In addition, the above core particles may be 0.1 wt% or more and 30 wt% or less relative to the above phase change core.

[0018] The above objective is achieved, according to another embodiment of the present invention, in an electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, the structure comprises a plurality of coating layers sequentially applied to the substrate; wherein the outermost coating layer from the substrate may have the plurality of microcapsules dispersed therein.

[0019] And, here, the plurality of coating layers include a first layer adhered to the substrate, a second layer applied to the first layer, a third layer applied to the second layer, and a fourth layer forming the outermost coating layer; the fourth layer absorbs electromagnetic waves in the high frequency band (mmWave) when in contact with air, the third layer absorbs electromagnetic waves in the X / Ku-band that pass through the fourth layer, the second layer gradients the electromagnetic resistance, and the first layer adheres to the substrate and can transfer the electromagnetic resistance.

[0020] And, the third layer may include a plurality of composite fillers comprising a dielectric loss material composed of one or more of carbon nanotubes (CNT), magnetic nanometals and carbon black, and a magnetic loss material composed of one or more of MnZn ferrite, NiZn ferrite, BaFe12O19, carbonyl iron (Cl), and FeSiAl flakes.

[0021] In addition, a thermal diffusion member composed of either pitch-based carbon fiber (Pitch-CF, 520, thermal conductivity 400 W / m·K or higher) or highly oriented graphite fiber may be oriented and dispersed in the in-plane direction of the third layer to form a thermal diffusion path that diffuses heat from the substrate side in the plane direction to heat the microcapsule inside the fourth layer.

[0022] In addition, the second layer comprises high-dielectric ceramic nanoparticles composed of one or more of BaTiO3, SrTiO3, BaSrTiO3 (BST), PbZrTiO3 (PZT), and lead lanthanum titanate (PLT), thereby creating a continuous gradient of the electromagnetic wave resistance between the substrate and the air outside the fourth layer from the substrate side to the air side, which can suppress the reflection of electromagnetic waves.

[0023] In addition, the fourth layer may shield infrared rays by having infrared shielding particles dispersed therein, which are composed of any one of silicon carbide (SiC), boron nitride (BN), aluminum (Al), nano flakes, aluminum oxide (Al2O3), vanadium dioxide (VO2) powder, or a composite thereof.

[0024] In addition, the fourth layer may be composed of any one or more of polyurethane (PU), epoxy (EP), silicone (SI), acrylic (AC), polyimide (PI), fluoropolymer (FP), polyester (PES), polyamide (PA), phenolic resin (PF), bismaleimide resin (BMI), and a composite of two or more of these, and a mixture thereof. Effects of the invention

[0025] According to the above configuration, the present invention provides a microcapsule and an electromagnetic wave absorption structure having an electromagnetic wave absorption function that can resolve the impedance mismatch problem caused by the substrate surface forming a short-circuit boundary condition.

[0026] In addition, according to the present invention, a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure are provided, which can utilize heat generated during the operation of a drone, etc., to improve electromagnetic wave absorption performance.

[0027] In addition, a microcapsule and an electromagnetic wave absorption structure are provided that have an electromagnetic wave absorption function capable of enhancing mmWave active absorption when utilizing operational heat, while maintaining a passive X / Ku-band absorption function in low-temperature operating environments such as winter or high altitude.

[0028] In addition, a microcapsule and an electromagnetic wave absorption structure are provided, which implement infrared shielding functions along with electromagnetic wave absorption. Brief explanation of the drawing

[0029] FIGS. 1 and 2 are drawings showing a microcapsule having an electromagnetic wave absorption function according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating the operating principle of a microcapsule having an electromagnetic wave absorption function according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of an electromagnetic wave absorbing structure that absorbs electromagnetic waves according to an embodiment of the present invention, and FIG. 5 is a drawing showing an example of a composite filler according to an embodiment of the present invention, and FIGS. 6 to 9 are drawings showing experimental results of a microcapsule having an electromagnetic wave absorption function and an electromagnetic wave absorption structure according to an embodiment of the present invention. Specific details for implementing the invention

[0030] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the present invention, and the present invention is defined only by the scope of the claims.

[0031] The terms used in this specification are for describing embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. The terms "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other components in addition to the components mentioned. Throughout the specification, the same reference numerals refer to the same components, and "and / or" includes each of the mentioned components and all combinations of one or more. Although terms such as "first," "second," etc., are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical scope of the invention.

[0032] Unless otherwise defined, all terms used herein (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0033] Hereinafter, embodiments according to the present invention will be described in detail with reference to the attached drawings.

[0034] FIGS. 1 and FIGS. 2 are drawings showing a microcapsule (100) having an electromagnetic wave absorption function according to an embodiment of the present invention.

[0035] The microcapsule (100) according to an embodiment of the present invention may be manufactured with a diameter of 1 μm or more and 500 μm or less, but the size is not limited thereto.

[0036] Referring to FIGS. 1 and 2, a microcapsule (100) according to an embodiment of the present invention may be configured to include a phase change core (110), a polymer shell (120), and a plurality of core particles (130).

[0037] The phase change core (110) according to an embodiment of the present invention may be composed of a material whose phase changes according to temperature.

[0038] In one embodiment, the phase change core (110) may be provided with an inorganic hydrated salt-based phase change material composed of one or more of Na2SO4·10H2O, Na2HPO4·12H2O, CaCl2·6H2O, CH3COONa·3H2O, and Na2S2O3·5H2O.

[0039] As another example, the phase change core (110) may be provided with an organic phase change material composed of one or more of paraffin, palmitic acid, stearic acid, lauric acid, and caprylic acid.

[0040] As another example, the phase change core (110) may be provided with a thermal radiation switching type phase change material including vanadium dioxide and doped vanadium dioxide. Here, the thermal radiation switching type phase change material may include vanadium dioxide doped with at least one of tungsten and molybdenum, and the phase transition temperature may be controlled to a range of 30 to 55 degrees.

[0041] The phase change material constituting the phase change core (110) according to the embodiment of the present invention is not limited to the above-described embodiment, and other materials having a phase transition temperature consistent with the technical concept of the present invention may be applied. In addition, it may be composed of at least two composites of inorganic hydrated salt-based phase change materials, organic-based phase change materials, and thermal radiation switching-type phase change materials.

[0042] A polymer shell (120) according to an embodiment of the present invention is configured to surround a phase change core (110) and forms the outer shell of a microcapsule (100) according to an embodiment of the present invention. Here, the thickness of the polymer shell (120) is provided in a range of 0.1 μm or more and 50 μm or less, as an example.

[0043] In one embodiment, the polymer shell (120) may be composed of one or more composites of melamine-formaldehyde (MF), urea-formaldehyde (UF), polyurea (PUa), polyurethane (PU), polymethyl methacrylate (PMMA), epoxy resin (EP), silica (SiO2), polyimide (PI), acrylic resin (AC), phenolic resin (PF), and cyclodextrin-based materials.

[0044] Additionally, the polymer shell (120) may have a porous structure, an elastic structure, or a double-wall structure to correspond to the volume change due to the phase change of the phase change core (110).

[0045] The core particles (130) according to an embodiment of the present invention are dispersed inside the phase change core (110) and may be provided with a material that absorbs electromagnetic waves. The core particles (130) may be manufactured in nano size and dispersed inside the phase change core (110).

[0046] In one embodiment, the core particle (130) may be composed of a Mxene-based nanomaterial consisting of any one of Ti3C2Tx, Ti2CTx, and V2CTx or a composite of two or more of them. Alternatively, the core particle (130) may be composed of a carbon-based nanomaterial consisting of any one of graphene, carbon nanotubes, or a composite of them.

[0047] As another example, the core particle (130) may include a magnetic nanomaterial composed of one or more of Fe3O4, NiFe2O4, CoFe2O4, MnFe2O4, and ZnFe2O4. Alternatively, it may include a ceramic nanomaterial composed of one or more of silicon carbide (SiC), zinc oxide (ZnO), copper oxide (CuO), molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN).

[0048] Here, the core particle (130) may include two or more composites of Mxene-based nanomaterials, carbon-based nanomaterials, magnetic nanomaterials, and ceramic-based nanomaterials.

[0049] In one embodiment, the content of the core particles (130) may be in the range of 0.1 wt% or more and 30 wt% or less relative to the phase change core (110).

[0050] According to the above configuration, the phase change core (110) of the microcapsule (100) undergoes a phase change to a liquid state in at least one region depending on the temperature change, and the core particles (130) inside the phase change core (110) are dispersed and moved within the phase change core (110) that has changed to a liquid state, thereby increasing the electromagnetic wave absorption efficiency.

[0051] FIG. 1 is a drawing illustrating the case where the phase change core (110) of the microcapsule (100) is in a solid state, and FIG. 2 is a drawing illustrating the case where the phase change core (110) of the microcapsule (100) is in a liquid state. In FIG. 2, the reference number of the phase change core (110) in the liquid state is expressed as 111.

[0052] Reference number 131 in FIGS. 1 and 2 is a boundary surface of a core particle (130) dispersed inside a phase change core (110) in a solid state, and both the inside and outside of the boundary surface (131) correspond to the phase change core (110).

[0053] FIG. 3 is a diagram illustrating the operating principle of a microcapsule (100) having an electromagnetic wave absorption function according to an embodiment of the present invention.

[0054] As shown in FIG. 1, when a temperature above the phase transition temperature is applied to the microcapsule (100) of the solid phase change core (110), the phase change core (110) is converted to a liquid state as shown in FIG. 2 and FIG. 3, and in the liquid state phase change core (110), the molten phase change material and the H2O aqueous solution coexist.

[0055] As the core particles (130) flow within this liquid state, dipole relaxation loss (150), interface polarization loss (151), and conduction loss (152) occur together, thereby improving the absorption performance of electromagnetic waves, especially mmWave.

[0056] The dipole relaxation loss (150) causes H2O molecules (140) to be rotated polarized by the electromagnetic field of the mmWave, thereby converting the energy of the mmWave into heat and providing the effect of absorbing electromagnetic waves.

[0057] The interfacial polarization loss (151) provides the effect of absorbing electromagnetic waves by consuming the energy of the mmWave due to the Maxwell-Wagner effect, where charges (+ / -) accumulate at the interface between the core particle (130) and H2O.

[0058] And, the conduction loss (152) is the electrons (e) between the flakes of the core particle (130). - As the device moves, the energy of the mmWave is consumed, that is, converted into heat in Joules, thereby providing the effect of absorbing electromagnetic waves.

[0059] Meanwhile, FIG. 4 is a cross-sectional view of an electromagnetic wave absorbing structure (10) that absorbs electromagnetic waves according to an embodiment of the present invention.

[0060] Referring to FIG. 4, the electromagnetic wave absorbing structure (10) according to an embodiment of the present invention may be configured to include a plurality of coating layers sequentially applied to a substrate (20). In one embodiment, the substrate (20) may be a surface structure of a drone for imparting a stealth function.

[0061] Here, among the plurality of coating layers, the outermost coating layer has the aforementioned microcapsules (100) dispersed therein.

[0062] In the embodiment illustrated in FIG. 4, the electromagnetic wave absorbing structure (10) is exemplified as being composed of four coating layers, and below, the first layer (200), second layer (300), third layer (400), and fourth layer (500) are defined and described sequentially from the substrate (20). Here, as previously described, a plurality of microcapsules (100) are dispersed within the fourth layer (500), which is the outermost coating layer.

[0063] The fourth layer (500) according to an embodiment of the present invention forms the outermost layer of the electromagnetic wave absorption structure (10) and comes into contact with air. Here, a plurality of microcapsules (100) are dispersed within the fourth layer (500), so that electromagnetic waves in a high-frequency band, for example mmWave, introduced from the outside are absorbed by the microcapsules (100).

[0064] In one embodiment, the fourth layer (500) may be composed of any one or more of polyurethane (PU), epoxy (EP), silicone (SI), acrylic (AC), polyimide (PI), fluoropolymer (FP), polyester (PES), polyamide (PA), phenolic resin (PF), bismaleimide resin (BMI), and a mixture thereof.

[0065] Additionally, the fourth layer (500) can shield infrared rays by having infrared shielding particles (510) dispersed therein, which are composed of any one of silicon carbide (SiC), boron nitride (BN), aluminum (Al), nano flakes, aluminum oxide (Al2O3), vanadium dioxide (VO2) powder, or a composite thereof.

[0066] According to an embodiment of the present invention, the third layer (400) is configured to absorb X / Ku-band electromagnetic waves that have passed through the fourth layer (500).

[0067] In one embodiment, a plurality of composite fillers (410) may be dispersed and arranged in the third layer (400). As shown in FIG. 5, the composite filler (410) according to an embodiment of the present invention has a core-shell structure. More specifically, the composite filler (410) may be composed of an inner core (411), an intermediate core (412), and an outer shell (413).

[0068] The inner core (411) according to the embodiment of the present invention may be made of a magnetic loss material composed of one or more of the ferrite series, for example, MnZn ferrite, NiZn ferrite, BaFe12O19, carbonyl iron (Cl), and FeSiAl flakes.

[0069] The outer shell (413) is composed of a dielectric material, for example, carbon nanotubes (CNT), magnetic nanometals and carbon black, or a composite of two or more of them.

[0070] And, the intermediate core (412) is an interfacial polarization layer, and Maxwell-Wagner interfacial polarization loss occurs. That is, it forms an interface between a magnetic loss material and a dielectric loss material with different dielectric properties, and allows charge to accumulate. Through this, the propagation energy from X / Ku-band electromagnetic waves passing through the fourth layer (500) is converted into heat, thereby providing the effect of absorbing X / Ku-band electromagnetic waves.

[0071] Meanwhile, a heat diffusion member may be disposed in the third layer (400) of the present invention. Here, the heat diffusion member may be oriented and dispersed in the in-plane direction of the third layer (400) to diffuse heat from the substrate (20) side in the plane direction, thereby forming a heat diffusion path that heats the microcapsule (100) inside the fourth layer (500).

[0072] Through this, when heat generated from the substrate (20), for example, a drone, is sequentially transferred through the first layer (200) and the second layer (300), the heat diffusion member diffuses the heat in the planar direction, thereby heating the microcapsules (100) dispersed in the fourth layer as a whole and inducing a phase change.

[0073] Here, the thermal diffusion member may be composed of either pitch-based carbon fiber (Pitch-CF, 520, thermal conductivity 400 W / m·K or higher) or highly oriented graphite fiber.

[0074] The second layer (300) according to an embodiment of the present invention can gradient the electromagnetic resistance (impedance). In one embodiment, the second layer (300) may include high-dielectric ceramic nanoparticles composed of one or more of BaTiO3, SrTiO3, BaSrTiO3 (BST), PbZrTiO3 (PZT), and lead lanthanum titanate (PLT).

[0075] Through this, the electromagnetic wave resistance between the substrate (20) and the air outside the fourth layer (500) is continuously gradiented from the substrate (20) side toward the air side to suppress the reflection of electromagnetic waves.

[0076] Here, the first layer (200) is bonded to the substrate (20) to transfer the electromagnetic resistance. The first layer (200) may be composed of ceramic and epoxy adhesive.

[0077] In this way, the fourth layer (500) absorbs high-frequency (mmWave) electromagnetic waves, the third layer (400) absorbs X / Ku-band electromagnetic waves that have passed through the fourth layer (500), the second layer (300) acts as a gradient layer for electromagnetic wave resistance, and the first layer (200) acts as a transition layer for electromagnetic wave resistance, thereby minimizing the reflection of electromagnetic waves and enabling effective absorption of electromagnetic waves.

[0078] Hereinafter, experimental results of a microcapsule (100) having an electromagnetic wave absorption function and an electromagnetic wave absorption structure (10) according to an embodiment of the present invention will be described with reference to FIGS. 6 to 9.

[0079] FIG. 6 is a diagram showing the reflection loss (RL) characteristics before and after phase change of a microcapsule (100) according to an embodiment of the present invention.

[0080] Microcapsules (100) (diameter 50±10 μm) composed of core particles (130) of 5 wt% Ti3C2Tx MXene, phase change core (110) of paraffin (Tm = 45°C), and polymer shell of melamine-formaldehyde (thickness 5±1 μm) were dispersed at 15 vol% in the fourth layer (500) (PU binder, thickness 1.5 mm).

[0081] Reflection loss (RL) in the 26–40 GHz band was measured using the free-space method with a vector network analyzer (VNA, Keysight N5227B), and the measurement results are shown in [Table 1] and Figure 6.

[0082] [Table 1]

[0083]

[0084] As shown in [Table 1] and Figure 6, above the phase transition temperature (55°C), the maximum RL was improved to -30.1 dB (35 GHz), and the effective absorption bandwidth increased to 14.2 GHz (RL improvement of 18.9 dB and bandwidth increase rate of 407%) compared to before the phase transition. This is attributed to the combined increase in conduction loss and Maxwell-Wagner interfacial polarization loss due to the free movement of MXene flakes within the liquid state PCM.

[0085] FIG. 7 is a graph comparing the X / Ku-band reflection loss of a single-layer structure with an electromagnetic wave absorption structure (10) according to an embodiment of the present invention, i.e., a four-layer structure.

[0086] The reflection loss of a single-layer RAM (comparative example: carbon black / NiZn ferrite / epoxy, thickness 3 mm) and a four-layer structure (total thickness 4 mm: first layer 0.3 mm / second layer 0.8 mm / third layer 1.4 mm / fourth layer 1.5 mm) of an electromagnetic wave absorbing structure (10) according to an embodiment of the present invention was measured for comparison in the 8~18 GHz (X-band: 8~12 GHz, Ku-band: 12~18 GHz) band.

[0087] [Table 2]

[0088]

[0089] Referring to [Table 2] and Fig. 7, it was confirmed that the electromagnetic wave absorption structure (10) according to an embodiment of the present invention has a maximum RL of -28.5 dB, which is about 2.0 times better than a single-layer RAM, and an effective absorption bandwidth (RL < -10 dB) of 9.6 GHz (8.4~18.0 GHz), which is about 4.6 times better, enabling full coverage of the X-band and Ku-band.

[0090] This is the result of the synergistic effect of the reflection suppression effect caused by the impedance gradient structure of the second layer (300) of the electromagnetic wave absorption structure (10) according to an embodiment of the present invention and the magnetodeonomic composite loss mechanism of the composite filler (410) of the third layer (400).

[0091] FIG. 8 is a graph comparing the temperature response characteristics of a microcapsule (100) depending on whether a thermal diffusion member (420) (Pitch-CF) according to an embodiment of the present invention is applied.

[0092] After placing a drone substrate (thickness 2 mm, Al 6061 alloy) in a 50°C constant temperature bath, a K-type thermocouple was embedded near the microcapsule (100) inside the fourth layer (500) to measure the temperature change over time.

[0093] The comparative example is one in which a thermal diffusion member (420) is not applied to the third layer (400), and a specimen was used in which pitch-based carbon fibers (Pitch-CF, thermal conductivity 420 W / m·K) were oriented and dispersed at 10 wt% in the in-plane direction of the third layer (40) as the thermal diffusion member (420) according to the embodiment of the present invention.

[0094] [Table 3]

[0095]

[0096] As shown in [Table 3] and FIG. 8, when the Pitch-CF thermal diffusion member (420) is applied, the time for the microcapsule (100) to reach the PCM phase transition temperature (45°C) is reduced from 187 seconds to 52 seconds, improving the response speed by approximately 3.6 times. This is a result of the high thermal conductivity (420 W / m·K) of the in-plane oriented Pitch-CF rapidly diffusing the heat generated by the substrate in the plane direction to achieve uniform heating over the entire fourth layer (500), confirming that the transition to the mmWave active absorption mode during drone operation is significantly accelerated.

[0097] Figure 9 is a graph comparing the electromagnetic shielding effect (SE) of Pitch-CF alone and a Cu-plated Pitch-CF grid.

[0098] A specimen was prepared in which 10 wt% of Cu-Pitch-CF, which is electroplated with 10 μm of Cu on the same fiber as a pitch-based carbon fiber (Pitch-CF, thermal conductivity 420 W / m·K), was dispersed in-plane orientation in a grid (line width 0.5 mm, grid spacing 5 mm) in the third layer (400).

[0099] The shielding effectiveness (SE) in the 2–18 GHz band was measured using the Coaxial Transmission Line Method, and the in-plane thermal conductivity was measured using the Hot Disk Method.

[0100] [Table 4]

[0101]

[0102] As shown in [Table 4] and Figure 9, when a Cu-plated pitch-based carbon fiber grid (Cu plating thickness 10 μm, line width 0.5 mm, grid spacing 5 mm) was applied, the in-plane thermal conductivity was improved by 16% to 487 W / m·K compared to Pitch-CF alone, and the electromagnetic shielding effect (SE) increased by more than 24 dB on average across the entire X / Ku-band (8 GHz: +24.3 dB, 12 GHz: +25.3 dB, 18 GHz: +22.1 dB).

[0103] In addition, a frequency selective shielding (FSS) effect around 10.4 GHz was confirmed at a grid spacing of 5 mm, and the time to reach the phase transition temperature (45°C) of the microcapsule (100) was further shortened from 52 seconds to 44 seconds.

[0104] Hereinafter, an example of a method for manufacturing a microcapsule (100) according to an embodiment of the present invention will be described. The manufacturing method described below is intended to provide sufficient process information for a person skilled in the art to carry out the present invention, and it should be understood that the technical concept of the present invention is not limited thereto.

[0105] In-situ interfacial polymerization method (based on melamine-formaldehyde shell)

[0106] First, regarding the dispersion of core particles (130), core particles (130), such as Ti₃C₂T■ MXene and Fe₃O₄ nanoparticles, are ultrasonically treated (20 kHz, 30 minutes) with a dispersant (SDS or CTAB, 0.1~1 wt%) to eliminate aggregation, and then uniformly dispersed into a phase change core (130), which is a phase change material (PCM) in a molten state (Tm or higher).

[0107] Dispersion uniformity is confirmed by a particle size analyzer (DLS) and it is confirmed that the secondary particle size of the nanoparticles is 200 nm or less.

[0108] Then, emulsification is performed by adding the PCM melt containing the core particles (130) to an aqueous solution of polyvinyl alcohol (PVA, 1-3 wt%) and emulsifying it with a high-speed stirrer (300-600 rpm) or an ultrasonic emulsifier to form microdroplets of a target diameter (1-500 μm).

[0109] Capsule size is controlled using an inverse relationship in which droplet diameter decreases as stirring speed increases.

[0110] Then, the process of preparing the MF prepolymer is carried out by mixing melamine and a 37% formaldehyde aqueous solution in a molar ratio of 1:3 to 1:6 and reacting them at pH 8 to 9 and 70°C for 30 minutes to prepare a melamine-formaldehyde prepolymer.

[0111] Then, the in-situ polymerization and shell formation process is carried out by slowly adding the MF precondensate to the emulsion while adjusting the pH to 3.5–5.0 with acetic acid or hydrochloric acid, maintaining the temperature at 60–80°C, and stirring for 2–4 hours.

[0112] Under acidic conditions, the MF precondensate is condensed and cured on the surface of the PCM droplet to form a polymer shell (120). The shell thickness is controlled by the concentration of the MF precondensate (1 to 10 wt%) and the reaction time, and the target shell thickness range (0.1 to 50 μm) is confirmed by scanning electron microscope (SEM) cross-sectional analysis.

[0113] Then, a double-wall structure can be optionally formed by increasing the temperature from 80 to 90°C after the first shell is formed and adding an additional MF pre-condensate to form a second shell, thereby realizing a double-wall structure.

[0114] The double-wall structure significantly improves durability against volume expansion (about 10–15%) that occurs during PCM phase change.

[0115] Then, the generated microcapsules (100) are filtered, washed three times with deionized water, and dried in an oven at 40 to 60°C to obtain the final microcapsule (100) powder.

[0116] In forming the polymer shell (120), interfacial polymerization can be applied in the case of a polyurea (PUa) shell.

[0117] Specifically, regarding the dispersion of core particles (130), an oil phase is prepared by dissolving a diisocyanate (TDI or MDI, 2-5 wt%) in the PCM, which is the phase change core (110). Then, the oil phase is emulsified in an aqueous solution of a surfactant (SMA, 0.5-2 wt%) to form microdroplets. Then, when an aqueous solution of a diamine (DETA or EDA, 2-5 wt%) is slowly added, an interfacial reaction between the isocyanate and the amine proceeds at the surface of the droplets, and a polyurea shell is formed within minutes. Since this interfacial polymerization method proceeds at room temperature (15-30°C), it may be suitable for heat-sensitive PCMs (low-melting point paraffin, inorganic hydrated salt, etc.).

[0118] Although some embodiments of the present invention have been illustrated and described, those skilled in the art will understand that modifications can be made to these embodiments without departing from the principles or spirit of the invention. The scope of the invention will be defined by the appended claims and their equivalents. Explanation of the symbols

[0119] 10: Electromagnetic wave absorbing structure 100: Microcapsule 110: Phase change core 120: Polymer shell 130: Core particle 140: H2O molecule 200: 1st floor 300: 2nd floor 400: 3rd layer 410: Composite filler 411: Internal core 412: Intermediate core 413: Outer shell 500: 4th layer 510 : Shielding particles

Claims

Claim 1 A microcapsule having an electromagnetic wave absorption function, comprising a phase change core composed of a material whose phase changes according to temperature, a polymer shell surrounding the phase change core, and core particles of an electromagnetic wave absorption material dispersed within the phase change core; wherein, when at least one region of the phase change core undergoes a phase change to a liquid state according to a temperature change, the core particles disperse and move within the liquid state of the phase change core. Claim 2 A microcapsule having an electromagnetic wave absorption function according to claim 1, wherein the phase change core is provided as an inorganic hydrated salt-based phase change material composed of one or more complexes of Na2SO4·10H2O, Na2HPO4·12H2O, CaCl2·6H2O, CH3COONa·3H2O, and Na2S2O3·5H2O, or an organic phase change material composed of one or more complexes of paraffin, palmitic acid, stearic acid, lauric acid, and caprylic acid, or a thermal radiation switching-type phase change material including vanadium dioxide and doped vanadium dioxide. Claim 3 A microcapsule having an electromagnetic wave absorption function according to claim 2, wherein the thermal radiation switching type phase change material comprises vanadium dioxide doped with at least one of tungsten and molybdenum, and the phase transition temperature is controlled to a range of 30 to 55 degrees. Claim 4 A microcapsule having an electromagnetic wave absorption function according to claim 1, wherein the core particle comprises: a methyl-based nanomaterial composed of one or more of Ti3C2Tx, Ti2CTx, and V2CTx; a carbon-based nanomaterial composed of one or more of graphene and carbon nanotubes; a magnetic nanomaterial composed of one or more of Fe3O4, NiFe2O4, CoFe2O4, MnFe2O4, and ZnFe2O4; a ceramic-based nanomaterial composed of one or more of silicon carbide (SiC), zinc oxide (ZnO), copper oxide (CuO), molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN); or a composite of two or more of the methyl-based nanomaterial, the carbon-based nanomaterial, the magnetic nanomaterial, and the ceramic-based nanomaterial. Claim 5 A microcapsule having an electromagnetic wave absorption function according to claim 1, wherein the polymer shell is composed of one or more composites of melamine-formaldehyde (MF), urea-formaldehyde (UF), polyurea (PUa), polyurethane (PU), polymethyl methacrylate (PMMA), epoxy resin (EP), silica (SiO2), polyimide (PI), acrylic resin (AC), phenolic resin (PF), and cyclodextrin-based materials. Claim 6 A microcapsule having an electromagnetic wave absorption function according to claim 5, wherein the polymer shell has a porous structure, an elastic structure, or a double-wall structure to correspond to the volume change according to the phase change of the phase change core. Claim 7 A microcapsule having an electromagnetic wave absorption function according to claim 5, characterized in that the core particles are 0.1 wt% or more and 30 wt% or less relative to the phase change core. Claim 8 An electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, comprising a plurality of coating layers sequentially applied to the substrate; wherein the outermost coating layer from the substrate is characterized in that a plurality of microcapsules according to any one of claims 1 to 7 are dispersed therein. Claim 9 An electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, characterized in that, in claim 8, the plurality of coating layers comprises a first layer adhered to the substrate, a second layer applied to the first layer, a third layer applied to the second layer, and a fourth layer forming the outermost coating layer; wherein the fourth layer absorbs electromagnetic waves in the high frequency band (mmWave) upon contact with air, the third layer absorbs electromagnetic waves in the X / Ku-band that pass through the fourth layer, the second layer creates a gradient of electromagnetic wave resistance, and the first layer adheres to the substrate to transfer electromagnetic wave resistance. Claim 10 An electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, wherein the third layer comprises a plurality of composite fillers including a dielectric loss material composed of one or more of carbon nanotubes (CNT), magnetic nanometals, and carbon black, and a magnetic loss material composed of one or more of MnZn ferrite, NiZn ferrite, BaFe12O19, carbonyl iron (Cl), and FeSiAl flakes. Claim 11 An electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, characterized in that, in the third layer, a thermal diffusion member composed of either pitch-based carbon fiber (Pitch-CF, 520, thermal conductivity 400 W / m·K or higher) or highly oriented graphite fiber is oriented and dispersed in the in-plane direction of the third layer to diffuse heat from the substrate side in the plane direction and form a thermal diffusion path that heats the microcapsule inside the fourth layer. Claim 12 An electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, characterized in that, in claim 9, the second layer comprises high-dielectric ceramic nanoparticles composed of any one or more of BaTiO3, SrTiO3, BaSrTiO3 (BST), PbZrTiO3 (PZT), and lead lanthanum titanate (PLT), thereby suppressing the reflection of electromagnetic waves by creating a continuous gradient of the electromagnetic resistance between the substrate and the air outside the fourth layer from the substrate side to the air side. Claim 13 An electromagnetic wave absorbing structure coated on a substrate, wherein the fourth layer is characterized by infrared shielding particles dispersed therein, which shield infrared rays, and wherein the fourth layer is composed of silicon carbide (SiC), boron nitride (BN), aluminum (Al), nano flakes, aluminum oxide (Al2O3), vanadium dioxide (VO2) powder or a composite thereof. Claim 14 An electromagnetic wave absorbing structure coated on a substrate to absorb electromagnetic waves, characterized in that, in claim 9, the fourth layer is composed of any one or more of polyurethane (PU), epoxy (EP), silicone (SI), acrylic (AC), polyimide (PI), fluoropolymer (FP), polyester (PES), polyamide (PA), phenolic resin (PF), bismaleimide resin (BMI), and a composite of two or more of these, and a mixture thereof.

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