Thermal insulation composite structure and method of manufacture

Abstract

This invention belongs to the field of electromagnetic compatibility and thermal control, and provides a thermal insulation composite structure and its preparation method. The composite structure includes, from the outside to the inside, an outer protective layer, an outer infrared reflective and thermal insulation layer, and an inner infrared reflective and active heating layer. A metal metasurface structure layer is disposed on the surface of the outer infrared reflective and thermal insulation layer, and the inner infrared reflective and active heating layer includes a grid unit surrounded by conductive fine wires, with a metal metasurface structure disposed in the gaps inside the grid unit. Through an asymmetric multilayer architecture and subwavelength metal metasurface design, this invention achieves dual thermal management functions of passive infrared reflective thermal insulation and active electric heating temperature control while ensuring low electromagnetic wave transmission loss. It also has optional configurations such as zoned anti-icing and high-temperature resistant multilayer thermal insulation, and features a thin and light structure, high wave transmittance, and excellent thermal insulation performance.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic compatibility and thermal control, specifically a thermal insulation composite structure and its preparation method. Background Technology

[0002] Ground-based electromagnetic signal transceivers typically need to operate 24 / 7 in complex outdoor environments, facing extreme temperatures, severe cold, and drastic diurnal temperature variations. Existing protective covers are mostly made of simple fiberglass or acrylonitrile-butadiene-styrene (ABS) engineering plastics, which have the following drawbacks in practical applications:

[0003] 1. In high-temperature summer environments, heat buildup inside the equipment enclosure can create a "greenhouse effect," causing signal processing modules to overheat and shut down. In low-temperature winter environments, electronic components struggle to start, often requiring significant energy for auxiliary heating and insulation, increasing operating costs. 2. While traditional metal insulation layers (such as aluminum foil reflective layers) offer good infrared reflection and insulation, they can create a Faraday cage effect, strongly reflecting or shielding electromagnetic waves within the operating frequency band, severely degrading the antenna's transmit and receive sensitivity. 3. The traditional "outer protective layer + insulation cotton + inner metal shielding layer" structure is not only bulky and hinders equipment miniaturization, but also prone to peeling and moisture accumulation between layers under alternating hot and cold conditions, leading to performance degradation.

[0004] To address the problems raised in the background art, those skilled in the art have proposed a thermal insulation composite structure and its preparation method. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a thermal insulation composite structure and its preparation method, thereby resolving the issues in the prior art.

[0006] A thermal insulation composite structure includes an outer protective layer, an outer infrared reflective and heat-insulating layer, and an inner infrared reflective and active heating layer, which are stacked sequentially from the outside to the inside.

[0007] A metal metasurface structure layer is provided on the surface of the outer infrared reflective and heat-insulating layer facing the outer protective layer;

[0008] The inner infrared reflection and active heating layer includes multiple grid units formed by conductive fine wires, and a metal metasurface structure is disposed in the internal voids of the grid units;

[0009] The metal metasurface structure layer and the metal metasurface structure inside the grid unit are configured such that the reflectivity to infrared thermal radiation is greater than 90%, and the transmittance to electromagnetic waves in the working frequency band is such that the composite structure does not constitute electromagnetic shielding.

[0010] Preferably, the external infrared reflective and heat-insulating layer includes a core material, and the metal metasurface structure layer is attached to the surface of the core material.

[0011] Preferably, the core material is aramid paper honeycomb or polymethacrylamide foam.

[0012] Preferably, the metal metasurface structure layer and the metal metasurface structure inside the grid unit are both composed of periodically arranged metal patterns, with a period g of 50 μm - 500 μm, a metal linewidth w of 3 μm - 20 μm, and an aperture ratio of 85% - 95%.

[0013] Preferably, the linewidth of the conductive fine lines on the inner infrared reflection and active heating layer is 0.05 mm - 0.2 mm; the equivalent side length or diameter of the internal voids of the grid unit is 5 mm - 20 mm.

[0014] Preferably, the inner infrared reflection and active heating layer are divided into at least one first region and at least one second region in the plane, and the metal coverage of the first region is higher than that of the second region.

[0015] Preferably, the first region is located at the edge of the composite structure, and the conductive wires or the metal metasurface structure in this region are configured to connect to an external power source to achieve anti-icing heating through the Joule heating effect.

[0016] Preferably, the external infrared reflective and heat-insulating layer adopts a multi-layer heat-insulating structure, which includes, from the outside to the inside, a ceramic matrix composite layer, an aerogel layer, and a base layer on which the metal metasurface structure layer is disposed.

[0017] A method for preparing the above-mentioned thermal insulation composite structure includes the following steps:

[0018] S1. A metal layer is formed on the first flexible thin film substrate;

[0019] S2. The metal layer on the first flexible thin film substrate is patterned to form a metal metasurface structure layer with a periodic structure.

[0020] S3. The first flexible thin film substrate with a metal metasurface structure layer obtained in step S2 is attached to the first surface of the core material to form an external infrared reflection and heat insulation layer.

[0021] S4. A metal layer is formed on the second flexible thin film substrate and patterned to form a grid unit surrounded by conductive fine lines, and a metal metasurface structure is formed in the internal voids of the grid unit.

[0022] S5. The second flexible film substrate obtained in step S4 is attached to the second surface of the core material opposite to the first surface to form an inner infrared reflection and active heating layer.

[0023] S6. The composite obtained in step S5 is laminated with the outer protective layer.

[0024] Preferably, the metal layer is formed by vacuum evaporation or magnetron sputtering in steps S1 and S4, and the patterning process in steps S2 and S4 is photolithography, etching or laser engraving; the core material is aramid paper honeycomb or polymethacrylamide foam.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The outer infrared reflective and heat insulation layer of this invention utilizes the high infrared reflectivity (>90%) of the metal metasurface structure to lock the heat of the equipment inside, achieving passive heat preservation; the inner infrared reflective and active heating layer generates heat when energized under extremely cold conditions, actively compensating for heat and solving the cold start problem.

[0027] 2. By designing the metal structure as a subwavelength periodic metasurface and millimeter-level grid, according to the equivalent medium theory, this structure exhibits low-loss transmission characteristics for electromagnetic waves in the L-band, S-band and other operating frequency bands, thus avoiding the signal shielding problem of traditional metal insulation layers.

[0028] 3. This invention uses honeycomb core material or foam core material as the heat insulation skeleton, combined with the metasurface structure on the flexible film substrate, resulting in a compact and lightweight overall structure. Furthermore, the lamination composite process avoids delamination and moisture problems.

[0029] 4. The inner heating layer of the present invention can be designed in sections, increasing the metal coverage in high-risk areas of edge icing, achieving precise local heating and de-icing, and ensuring the normal operation of the antenna rotation mechanism. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the cross-sectional structure of the thermal insulation composite structure of the present invention.

[0031] In the picture:

[0032] 1. Outer protective layer; 2. Outer infrared reflection and heat insulation layer; 21. Core material; 22. Metal metasurface structure layer; 3. Inner infrared reflection and active heating layer. Detailed Implementation

[0033] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0034] like Figure 1 As shown:

[0035] Example 1: The thermal insulation composite structure provided in this example includes, from the outside to the inside, an outer protective layer 1, an outer infrared reflective and heat insulation layer 2, and an inner infrared reflective and active heating layer 3.

[0036] 1. Outer protective layer 1

[0037] Polyimide (PI) film or polytetrafluoroethylene (PTFE) coated glass cloth is selected, with a preferred thickness of 0.1mm-0.5mm. This type of material has an extremely low dielectric constant (ε<3.2) and loss tangent, which can effectively resist outdoor rain and ultraviolet radiation, and has minimal impact on electromagnetic wave transmission.

[0038] 2. External infrared reflection and heat insulation layer 2

[0039] The layer includes a core material 21 and a metal metasurface structure layer 22 attached to its surface.

[0040] The core material 21 is made of aramid paper honeycomb with a thickness of 5mm-20mm. The aramid paper honeycomb significantly reduces heat conduction by utilizing the air gaps within its honeycomb cells, thus playing a primary role in heat insulation.

[0041] In the fabrication process, a metal layer (such as aluminum or copper) is first deposited on a polyethylene terephthalate (PET) film, which serves as the first flexible film substrate, using vacuum evaporation or magnetron sputtering. Then, a periodically arranged metal pattern, known as the metal metasurface structure layer 22, is formed using photolithography or laser engraving. The period g of this metal metasurface structure layer 22 is 50-500 μm, the linewidth w is 3-20 μm, the metal thickness is 0.1-2 μm, and the aperture ratio is 85%-95%.

[0042] Subsequently, the PET film with the metal metasurface structure layer 22 is attached to the upper surface (i.e., the first surface, facing the outside of the radome) of the aramid paper honeycomb core material 21. Since the period of the metal metasurface structure layer 22 is much smaller than the operating wavelength of the device (e.g., L-band wavelength of about 150mm or more), it acts as an equivalent homogeneous medium for incident electromagnetic waves, allowing electromagnetic waves to pass through efficiently. At the same time, the high metal coverage ratio exhibits extremely high reflectivity (measured >90%) in the infrared band (thermal radiation), which can reflect the heat dissipated inside the device back, achieving heat preservation.

[0043] 3. Inner infrared reflection and active heating layer 3

[0044] This layer is formed on the lower surface of the core material 21 (i.e., the second surface, facing the inside of the device).

[0045] On a second flexible thin film substrate (PET), periodic grid cells formed by conductive fine lines are formed using a similar process. The grid cells are bounded by conductive fine lines, and metallic metasurface structures with the same parameters as the aforementioned outer surface are also fabricated in the internal voids.

[0046] The conductive wires have a line width of 0.05mm-0.2mm, and the gaps they form are rhomboid or regular hexagonal, with an equivalent side length of 5mm-20mm.

[0047] Thickened edge busbars are installed at the edge of the grid for connecting external temperature control circuits. When the equipment is started in extremely cold weather, the external circuit is powered on, and the current flows through the conductive wires and the metal metasurface structure in the gaps, generating heat by utilizing the Joule heating effect of the metal film to achieve active thermal compensation for the inside of the equipment.

[0048] Example 2: This example is basically the same as the previous example, except that the inner infrared reflection and active heating layer 3 are optimized based on the structure of Example 1.

[0049] The inner infrared reflective and active heating layer 3 is not uniformly designed across the entire plane, but is divided into a first region (edge ​​anti-icing zone) and a second region (center wave-transparent zone).

[0050] The first region corresponds to the edge position after the composite structure is formed. The line width of the metal metasurface structure or the line width of the mesh conductive fine lines in this region are thickened, so that the metal coverage of the first region is higher than that of the second region (for example, the coverage of the first region is increased to more than 70%).

[0051] In this region, the width of the thickened edge busbar is correspondingly increased. In practical use, the external power supply prioritizes or supplies power to the conductive wires and metasurface structure in the first region. Due to the relatively concentrated resistance in this region, significant Joule heating is generated after power is applied, which can quickly melt the frozen rain or ice layer attached to the edge of the equipment enclosure, preventing the antenna rotation mechanism from jamming or the antenna radome's wave transmission performance from being distorted due to icing. Meanwhile, the central wave transmission area maintains a high aperture ratio to ensure that the signal transmission quality is not affected.

[0052] Example 3:

[0053] In response to situations where high-power transmitting antennas (such as high-power phased array radars) experience strong near-field thermal radiation or extremely high external ambient temperatures, this embodiment upgrades the structure of the external infrared reflector and heat insulation layer 2.

[0054] The outer infrared reflective and heat-insulating layer 2 adopts a multi-layer heat-insulating structure instead of a single honeycomb core material 21. This multi-layer heat-insulating structure, from the outside to the inside, includes:

[0055] Ceramic matrix composite layer: Located on the outermost layer, it is resistant to high temperature and oxidation, and can withstand the impact of external high-temperature airflow or strong sunlight exposure.

[0056] Aerogel layer: Located in the middle layer, it uses the extremely low thermal conductivity of aerogel (<0.02W / m·K) to form a super heat insulation barrier, blocking the conduction of external heat into the interior.

[0057] Base layer: Located at the innermost layer, its surface is provided with the metal metasurface structure layer 22, which is used to reflect the heat generated inside the device itself.

[0058] Experimental example:

[0059] 1. Infrared reflectivity and thermal insulation performance test (corresponding to Example 1)

[0060] Sample preparation:

[0061] Comparative Example 1: Pure aramid paper honeycomb core material of the same thickness is used to composite with the outer protective layer, without any metal metasurface structure (i.e., the metal parts of layer 22 and layer 3 are removed).

[0062] Example 1 Sample: The structure described in Example 1 of this invention is adopted, wherein the metal metasurface structure has a period g = 200 μm, a linewidth w = 10 μm, and an aperture ratio of 90%.

[0063] Test method:

[0064] Infrared reflectance: The normal reflectance of the sample in the 8-14µm far-infrared band (the main band of thermal radiation) was measured using a Fourier transform infrared spectrometer (FTIR) with an integrating sphere accessory.

[0065] Passive thermal insulation performance: Two samples were fabricated into sealed chambers of the same size, each equipped with a heating element of the same power to simulate the heating effect of the device. The time required for the internal temperature of the chamber to drop from 10℃ to 0℃ (thermal insulation duration) was monitored at an ambient temperature of -10℃.

[0066] Active heating performance: The inner infrared reflector of the sample from Example 1 was connected to the active heating layer 3 via a DC power supply, and a voltage of 5V (power density 0.3W / cm²) was applied. The time required for the temperature of the inner surface of the sample to rise from -10℃ to 10℃ was measured at an ambient temperature of -10℃.

[0067] The test results are shown in Table 1:

[0068] sample 8-14 μm infrared reflectance (%) Cooling time inside the enclosure (min) Active heating time (s) Comparative Example 1 12.5 8 - Example 92.3 35 28

[0069] As shown in the table above, Embodiment 1 of the present invention, by introducing a specific metallic metasurface structure on the surface of the core material, significantly increases its reflectivity in the thermal radiation band from 12.5% ​​to 92.3%. In the simulated heat preservation test, the cooling time of Embodiment 1 was more than three times longer than that of Comparative Embodiment 1, fully demonstrating the excellent passive infrared reflection heat preservation effect of the present invention. Simultaneously, in the active heating test, Embodiment 1 achieved a rapid temperature rise of 20°C in only 28 seconds at low power density, verifying its excellent active thermal compensation capability. The above results collectively demonstrate that the present invention possesses efficient dual thermal management functions.

[0070] 2. Electromagnetic wave transmission performance test (corresponding to Example 1)

[0071] Sample preparation:

[0072] Comparative Example 2: The same structure was used, but the metal metasurface structure was replaced with a solid aluminum foil (0.05 mm thick) covering the entire surface.

[0073] Example 1 Sample: Same as above.

[0074] Test method:

[0075] Insertion loss of samples was tested in the frequency range of 1-4 GHz (covering L-band and S-band) using a vector network analyzer and a focusing lens antenna.

[0076] Test results:

[0077] sample 2 GHz Insertion Loss (dB) 3 GHz Insertion Loss (dB) Does it cause signal blocking? Comparative Example 2 -45.2 -50.8 Yes (completely blocked) Example 1 -0.8 -1.2 No (normal communication)

[0078] Test data shows that traditional solid aluminum foil structures exhibit extremely high insertion loss in the microwave frequency band, resulting in severe electromagnetic shielding. However, Embodiment 1 of this invention, due to its subwavelength periodic metasurface design, exhibits extremely low insertion loss (<1.5dB) in commonly used communication frequency bands, with negligible impact on electromagnetic wave propagation. This achieves excellent electromagnetic wave transmission compatibility while maintaining efficient thermal management.

[0079] Three-zone heating and anti-icing performance test (corresponding to Example 2)

[0080] Sample preparation:

[0081] Example 2 Sample: Using the structure described in Example 2 of the present invention, the metal coverage of the edge area (first area) is 75%, and the metal coverage of the center area (second area) is 10%.

[0082] Comparative test: The central area of ​​the sample in Example 2 was heated only by electricity.

[0083] Test method:

[0084] Inside a -5°C environmental chamber, supercooled water mist was continuously sprayed onto the sample surface, causing a 2mm thick ice layer to form. Subsequently, an electric current (power density 0.5W / cm²) was applied to the first edge region of Example 2, and the time required for the ice layer to completely melt and the temperature distribution of the melted area were recorded.

[0085] Test results:

[0086] electrified area Time taken for the ice to melt (s) Temperature rise in the central wave-transmitting area (°C) Center heating only 180 (edge ​​residue) 15 Edge heating only 45 (Completely melted) 2

[0087] Experiments show that by concentrating power on the first edge region with high metal coverage, dense Joule heat can be generated in a short time (45 seconds), rapidly melting the edge ice layer and ensuring the normal operation of the rotating mechanism at the edge of the structure. At the same time, since the heat is concentrated near the edge busbars, the temperature rise in the central low-coverage region is minimal and will not affect the electromagnetic transmission medium characteristics in the direction of the antenna's main beam, achieving a balance between precise anti-icing and wave transmission performance.

[0088] 4. Thermal insulation performance test of multi-layer high-temperature resistant structure (corresponding to Example 3)

[0089] Sample preparation:

[0090] Comparative Example 3: The single-layer honeycomb core structure of Example 1 was used.

[0091] Sample of Example 3: The sample used was a combination of the ceramic matrix composite layer, aerogel layer and metal metasurface structure layer of Example 3.

[0092] Test method:

[0093] The sample was placed on a hot stage, with the stage temperature set to 200℃ (simulating external high-temperature exposure or high-temperature exhaust). A thermocouple was placed on the other side (inner side) of the sample to monitor the temperature change of the inner surface over 30 minutes.

[0094] Test results:

[0095] sample Hot plate temperature (°C) Inner surface temperature (°C) after 30 minutes Comparative Example 3 200 98 Example 3 200 52

[0096] As shown above, under extreme high-temperature impact of 200℃, the internal temperature of Comparative Example 3, which uses ordinary honeycomb core material, rapidly rises to 98℃. However, Example 3 of this invention, by introducing a ceramic matrix composite material and an aerogel insulation layer, successfully suppressed the internal temperature to 52℃, significantly reducing the conduction of external heat into the equipment. This demonstrates that this multi-layer structure possesses excellent "external high-temperature intrusion prevention" capabilities, making it particularly suitable for protecting high-power transmitting antennas or equipment in high-temperature and harsh environments.

[0097] 5. Tests on structural thinness and interlayer bonding strength (corresponding to beneficial effect 3)

[0098] Sample preparation:

[0099] Comparative Example 4: Traditional structure of “outer fiberglass protective layer (2mm) + thermal insulation cotton (10mm) + inner aluminum foil shielding layer (0.1mm)”.

[0100] Example 1 Sample: Same as above.

[0101] Test method:

[0102] Measure the weight per unit area and total thickness of both samples. Perform a 90° peel strength test according to GB / T 2792 standard to evaluate the interlayer bond strength.

[0103] Test results:

[0104] sample Weight per unit area (kg / m²) Total thickness (mm) Interlayer peel strength (N / 25mm) Comparative Example 4 4.8 15.2 12.5 Example 1 1.9 6.5 28.7

[0105] Data shows that the unit area weight of Embodiment 1 of the present invention is only about 40% of that of the traditional structure, and the total thickness is reduced by more than half. At the same time, due to the use of a lamination composite process of flexible film substrate and core material, the interlayer peel strength is more than doubled, effectively avoiding the defects of traditional structure that are prone to delamination and moisture during use, verifying the beneficial effects of the present invention in terms of lightweight, thinness, high integration and high reliability.

[0106] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A thermal insulation composite structure, characterized in that: It includes an outer protective layer (1), an outer infrared reflective and heat-insulating layer (2), and an inner infrared reflective and active heating layer (3), which are stacked sequentially from the outside to the inside. The outer infrared reflective and heat-insulating layer (2) has a metal metasurface structure layer (22) on the side of its surface facing the outer protective layer (1); The inner infrared reflection and active heating layer (3) includes multiple grid units formed by conductive fine wires, and a metal metasurface structure is provided in the internal gaps of the grid units; The metal metasurface structure layer (22) and the metal metasurface structure inside the grid unit are configured such that the reflectivity to infrared thermal radiation is greater than 90%, and the transmittance to electromagnetic waves in the working frequency band is such that the composite structure does not constitute electromagnetic shielding.

2. The thermal insulation composite structure as described in claim 1, characterized in that: The external infrared reflective and heat-insulating layer (2) includes a core material (21), and the metal metasurface structure layer (22) is attached to the surface of the core material (21).

3. The thermal insulation composite structure as described in claim 2, characterized in that: The core material (21) is aramid paper honeycomb or polymethacrylamide foam.

4. The thermal insulation composite structure as described in claim 1, characterized in that: The metal metasurface structure layer (22) and the metal metasurface structure inside the grid unit are both composed of periodically arranged metal patterns with a period g of 50 μm-500 μm, a metal linewidth w of 3 μm-20 μm, and an aperture ratio of 85%-95%.

5. The thermal insulation composite structure as described in claim 1, characterized in that: The line width of the conductive fine line on the inner infrared reflection and active heating layer (3) is 0.05 mm - 0.2 mm; the equivalent side length or diameter of the internal void of the grid unit is 5 mm - 20 mm.

6. The thermal insulation composite structure as described in claim 1, characterized in that: The inner infrared reflection and active heating layer (3) is divided into at least one first region and at least one second region in the plane, wherein the metal coverage of the first region is higher than that of the second region.

7. The thermal insulation composite structure as described in claim 6, characterized in that: The first region is located at the edge of the composite structure, and the conductive wires or the metal metasurface structure in this region are configured to connect to an external power source to achieve anti-icing heating through the Joule heating effect.

8. The thermal insulation composite structure as described in claim 1, characterized in that: The external infrared reflective and heat insulation layer (2) adopts a multi-layer heat insulation structure, which includes, from the outside to the inside, a ceramic matrix composite layer, an aerogel layer, and a base layer on which the metal metasurface structure layer (22) is provided.

9. A method for preparing a thermal insulation composite structure as described in any one of claims 1-8, characterized in that: Includes the following steps: S1. A metal layer is formed on the first flexible thin film substrate; S2. The metal layer on the first flexible thin film substrate is patterned to form a metal metasurface structure layer with a periodic structure (22). S3. The first flexible thin film substrate with metal metasurface structure layer (22) obtained in step S2 is attached to the first surface of the core material (21) to form an external infrared reflection and heat insulation layer (2). S4. A metal layer is formed on the second flexible thin film substrate and patterned to form a grid unit surrounded by conductive fine lines, and a metal metasurface structure is formed in the internal voids of the grid unit. S5. The second flexible film substrate obtained in step S4 is attached to the second surface of the core material (21) opposite to the first surface to form an inner infrared reflection and active heating layer (3). S6. The composite obtained in step S5 is laminated with the outer protective layer (1).

10. The method for preparing a thermal insulation composite structure as described in claim 9, characterized in that: The metal layer is formed by vacuum evaporation or magnetron sputtering in steps S1 and S4, and the patterning process in steps S2 and S4 is photolithography, etching or laser engraving; the core material (21) is aramid paper honeycomb or polymethacrylamide foam.

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