Broadband infrared radiation omnidirectional controller and design method thereof

Abstract

The present application relates to the field of radiation heat transfer, and particularly relates to a broadband infrared radiation omnidirectional directional controller and a design method thereof. The present application sets the upper and lower layers of the control layer with high and low emissivity materials into a specific structure, so that the high emissivity is only shown in the view area around the surface normal, and the low emissivity is shown outside the view area, so as to realize the omnidirectional directional control of infrared radiation. The present application is applicable to the plane size and height of the hollow area, which are both greater than 10 times the incident wave length range, and can be applied to infrared camouflage. Compared with the existing one-dimensional infrared radiation directional control, the omnidirectional infrared directional controller of the present application can realize higher heat transfer efficiency in the field of radiation heat transfer, can realize omnidirectional thermal camouflage capability in the field of infrared camouflage, and can realize directional heat dissipation in the field of electronic component heat management, etc.

Description

Technical Field

[0001] This invention relates to the field of radiative heat transfer, specifically to a broadband infrared radiation omnidirectional controller and its design method, which can be applied to thermal camouflage, solar heating, radiative cooling and waste heat recovery, etc. Background Technology

[0002] The global landscape is no longer simply about an arms race between powerful nations; the energy war is intensifying, and countries urgently need higher energy conversion rates in the solar energy field. The miniaturization, integration, and intelligence of electronic devices inevitably lead to the need for thermal management. Thus, "infrared radiation directional control," designed to address these issues, has emerged.

[0003] Thermal radiation is a phenomenon in which an object with a temperature above absolute zero radiates electromagnetic waves. Electromagnetic radiation with wavelengths between 0.75 and 1000 μm is called infrared radiation. It typically possesses characteristics such as non-directionality, incoherence, non-polarization, and a broad spectrum, making directional control of infrared radiation a formidable challenge. With scientific advancements, the mainstream methods for achieving directional control of infrared radiation currently include two approaches: one is the formation of subwavelength metasurface structures, and the other is multilayer film structures based on ENZ (near-zero gradient materials). The corresponding disadvantages are that subwavelength metasurfaces can only achieve narrowband directional control, while multilayer films of ENZ suffer from complex fabrication processes and can only achieve p-polarization directional control. Summary of the Invention

[0004] To address the aforementioned problems and shortcomings, and to resolve the issues existing in current infrared radiation directional control methods, this invention provides a broadband infrared radiation omnidirectional controller and its design method. Based on the principle of geometric optics propagation, a cellular microstructure is designed, and through material selection and size design, omnidirectional directional control of infrared radiation is achieved.

[0005] A broadband infrared radiation omnidirectional controller consists of a control layer and a protection layer.

[0006] The control layer is a two-layer structure composed of high and low emissivity materials. The high / low emissivity material is selected as the lower base layer, while the upper low / high emissivity material completely covers the base layer. The emissivity difference between the high and low emissivity materials is ≥0.4, and the transmittance of the upper material to infrared light is less than 10% to meet infrared isolation requirements. The upper low / high emissivity material is patterned in a continuous manner, dividing it into continuous, hollowed-out regions. Using the plane of the base layer as the XY plane and the thickness direction as the Z-axis, the patterned upper low / high emissivity material, viewed from the Z-axis direction, includes:

[0007] The observation angle of the hollowed-out area is determined by a cutoff angle θ (e.g.) Figure 3As shown in the figure: when the observation angle is less than the cutoff angle θ, the high / low emissivity material of the substrate layer can be seen; while when the observation angle is greater than the cutoff angle θ, only the low / high emissivity material of the upper layer can be seen.

[0008] The planar dimensions and height of the hollowed-out area are both greater than 10 times the wavelength of the incident wave. During use, it completely covers the target area to ensure that the incident wave reflects and propagates upon reaching the controller; Δε>ε 小 Δε represents the theoretical emissivity change of the entire controller, ε 小 Minimum theoretical emissivity variation set for the application target; 0°<θ≤70°, θ<θ 大 θ 大 The maximum theoretical cutoff angle set for the application target.

[0009] The protective layer is disposed below the substrate layer to protect the control layer and prevent it from being torn apart during transfer or preparation.

[0010] Furthermore, the hollowed-out area is cylindrical (e.g., ...). Figure 4 As shown in the figure, it is easy to process and the cutoff angle does not change with the azimuth angle.

[0011] Furthermore, the planar shape of the hollowed-out area is a regular hexagon (e.g., ...). Figure 2 As shown in the figure, the upper low / high emissivity material is covered on the base layer in a honeycomb structure, and the cutoff angle does not change abruptly with the azimuth angle (the change is relatively small), and the density of the honeycomb cells is 2-15000 cells / cm². 2 When applied to infrared camouflage, it ensures excellent camouflage performance in all directions while also being lightweight and having good mechanical properties. In this case, both a and c are greater than 10 times the incident wavelength.

[0012] In the honeycomb structure, a is the side length of the honeycomb cell, b is the thickness of the honeycomb wall, c is the honeycomb height, h is the thickness of the base layer, t is the thickness of the protective layer, and ε is the thickness of the honeycomb. 底 ε is the emissivity of the substrate material. 侧 Emissivity of the upper material; Δε>ε 小 Δε represents the theoretical emissivity change of the entire controller, ε 小 The minimum theoretical emissivity variation is set for the application target. b < a, 0.05mm ≤ a ≤ 5mm, 0 < b ≤ 0.5mm, 0.1mm ≤ c ≤ 5mm, 0.05mm ≤ h ≤ 3mm, 0.1mm ≤ t ≤ 3mm; the entire controller is applicable to the incident wave wavelength range of <1 / 10 of the structural parameters. This is because, according to the principle of optical propagation, theoretically, the controller can achieve directional control only if the incident wave reflects and propagates when the controller's structural parameters are >10 times the incident wave wavelength. Therefore, there exists a theoretical cutoff angle θ and a theoretical emissivity variation Δε.

[0013]

[0014] Viewed from the Z-axis onto the XY plane, with the X-axis as the polar axis, the horizontal angle between the line and the target direction line in the counterclockwise direction is called the azimuth angle β. The angle between the straight line connecting a point on the edge of the honeycomb cell and the center inversion point and the surface normal (perpendicular line) is called the cutoff angle θ (e.g., ...). Figure 3 As shown in the diagram, when the observation angle is less than the cutoff angle θ, the high / low emissivity material at the bottom of the tank can be seen, while when the observation angle is greater than the cutoff angle θ, only the low / high emissivity material on the tank wall can be seen; θ < θ 大 θ 大 The maximum theoretical cutoff angle set for the application target. Cutoff angles exist in all directions, and the magnitude of the cutoff angle fluctuates slightly with changes in azimuth.

[0015]

[0016] Furthermore, the high emissivity material is an emissivity material ≥ 0.7 (such as a polymer material), the low emissivity material is an emissivity material ≤ 0.3, and the protective layer material is polyimide or polyethylene terephthalate.

[0017] Furthermore, the infrared light transmittance of the upper low / high emissivity material is preferably less than 5% or less than 1% to achieve better infrared isolation effect.

[0018] Furthermore, the upper low / high emissivity material is covered by an integral extension of the lower base layer material, with the surface of the extension area covered by the upper material. That is, the base layer material on the same plane extends upward and protrudes in the area covered by the upper material as an internal mechanical support component for the upper protruding part, so as to improve the mechanical performance of the entire controller.

[0019] Furthermore, the cutoff angle θ is reduced by 10% to compensate for the problem of the actual value being too large due to the processing technology.

[0020] Furthermore, a layer of infrared-transparent medium with characteristic wavelength band is also prepared on the exposed area of ​​the control layer of the controller to protect the controller and improve its durability.

[0021] The design method of the above-mentioned cellular broadband infrared radiation omnidirectional controller includes the following steps:

[0022] Step 1: Based on the application scenario and target object, first determine ε 底 ε 侧 The types of protective layer materials and their corresponding thicknesses h and t, where 0.05mm≤h≤3mm and 0.1mm≤t≤3mm.

[0023] Step 2: Determine b based on the type and properties of the material selected in Step 1, where 0 < b ≤ 0.5 mm, and the corresponding processing method; when b > 0.1 mm, the preferred processing method is a CNC engraving machine; when 0.001 mm < b ≤ 0.1 mm, photolithography is preferred; when 0 < b ≤ 0.001 mm, electron beam exposure is preferred.

[0024] Step 3: Determine a and c based on the application scenario and the target object's need for thinness and lightness, where 0.05mm ≤ a ≤ 5mm and 0.1mm ≤ c ≤ 5mm; simultaneously satisfying Δε > ε 小 and θ<θ 大 .

[0025] First, fix c to determine the final value of a; or draw a curve showing the relationship between a and c, and choose the optimal value based on the application scenario.

[0026] In summary, the controller provided by this invention uses high- and low-emissivity materials for the upper and lower layers of the control layer, respectively, to create a specific structure. This results in high emissivity only within the viewing area around the center located on the surface normal (perpendicular line), and low emissivity outside the viewing area, thereby achieving omnidirectional directional control of infrared radiation. Ultimately, this invention achieves omnidirectional directional control of broadband infrared radiation within a range where the planar dimensions and height of the hollowed-out area are both greater than 10 times the incident wavelength, and can be applied to infrared camouflage. Attached Figure Description

[0027] Figure 1 This is a design flowchart of an embodiment of the present invention;

[0028] Figure 2 This is a partial enlarged view of the control layer in the embodiment;

[0029] Figure 3 This is a schematic diagram of the structural parameters of the controller's honeycomb aperture in an embodiment;

[0030] Figure 4 A magnified view of a portion of the controller in the hollowed-out area of ​​the cylindrical structure;

[0031] Figure 5 This is a schematic diagram illustrating the application of the controller in the field of radiative heat transfer.

[0032] Figure 6 This is a schematic diagram illustrating the application of controllers in the field of heat dissipation for electronic devices. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings.

[0034] A design method for a broadband infrared radiation omnidirectional controller (e.g.) Figure 1As shown in the figure, this embodiment takes a controller with a honeycomb structure as the upper layer material loaded on the base layer as an example, and includes the following steps:

[0035] Step 1: Based on the application scenario and target object, first determine ε 底 ε 侧 The types of protective layer materials and their corresponding thicknesses h and t, where 0.05mm≤h≤3mm and 0.1≤t≤3mm.

[0036] In this embodiment, in order to obtain a high theoretical emissivity change Δε, it is preferred that the difference in emissivity between the high emissivity material and the low emissivity material is ≥0.7, the emissivity of the high emissivity material is ≥0.9, and the low emissivity material is selected with an emissivity ≤0.1.

[0037] Because polymer materials are flexible and typically have an emissivity >0.9, high-emissivity materials are usually chosen when flexible devices are required, such as polydimethylsiloxane, polymethyl methacrylate, and polyimide. Low-emissivity materials are usually common metals, such as aluminum and silver.

[0038] High emissivity material selection: polydimethylsiloxane, polymethyl methacrylate, polyimide; polycarbonate, polyethylene terephthalate, polyethylene naphthalate, high-density polyethylene, low-density polyethylene, linear low-density polyethylene; polyethylene, polypropylene, polystyrene, polyvinyl chloride, nylon, polycarbonate, polyurethane, polytetrafluoroethylene, polyethylene terephthalate, paint, cement, basalt, butyl rubber, cis-butadiene rubber, chloroprene rubber, ethylene propylene diene monomer (EPDM) rubber, acrylate rubber, polyurethane rubber, silicone rubber, fluororubber, polyisoprene, nylon, polyester, acrylic polyester fibers, aramid, polypropylene fibers; acrylic resins derived from epoxy resins, polyesters, polyethers, and polyurethanes; polyurethanes (polyurea) derived from isocyanates and polyols (or polyamines); isocyanate derivatives having at least one acrylic side group; epoxy resins other than acrylic-modified epoxy resins; and mixtures and combinations thereof. Polydimethylsiloxane, polymethyl methacrylate, and polyimide are particularly preferred.

[0039] Low emissivity material selection: vacuum-deposited aluminum, vacuum-deposited silver, vacuum-deposited platinum, vacuum-deposited gold, vacuum-deposited tin, steel, and 18-8 polished stainless steel. Vacuum-deposited aluminum is a particularly preferred option.

[0040] Protective layer material selection: plastic rolls, rubber, asphalt coatings; high-density polyethylene, low-density polyethylene, polyvinyl chloride, chlorinated polyethylene, chlorosulfonated polyethylene, polyolefins, ethylene-propylene rubber, chloroprene rubber, butene rubber, thermoplastic synthetic rubber, alcohol rubber. Polyimide and polyethylene terephthalate are preferred.

[0041] Step 2: Determine b based on the type and properties of the material selected in Step 1, where 0 < b ≤ 0.5 mm, and the corresponding processing method; considering the precision of the processing technology, when b > 0.1 mm, the processing method is CNC engraving machine; when 0.001 mm < b ≤ 0.1 mm, photolithography is used; when 0 < b ≤ 0.001 mm, electron beam exposure technology is used.

[0042] Step 3: Determine a and c based on the application scenario and the target object's need for thinness and lightness, where 0.05mm ≤ a ≤ 5mm and 0.1mm ≤ c ≤ 5mm; simultaneously satisfying Δε > ε 小 and θ<θ 大 θ 大 The maximum theoretical cutoff angle set for the application target, ε 小 The minimum theoretical emissivity variation set for the application target.

[0043] First, fix c to determine the final value of a; or draw a curve showing the relationship between a and c, and choose the optimal value based on the application scenario.

[0044] The theoretical range of the cutoff angle θ is 0°-180° (0° represents a single-layer planar membrane structure with high emissivity; 180° represents a double-layer planar membrane structure with a lower top and higher bottom). The theoretical range of the emissivity variation Δε is between 0 and 1 (when ε...). 底 =ε 侧 When Δε can take the value 0, and when the bottom material of the groove is a blackbody, ε 底 =1, ε side selects metal ε 侧 →0, when a is much greater than b, Δε approaches 1 infinitely; the cutoff angle θ in this embodiment is as follows: Figure 3 As shown.

[0045]

[0046] The ratio of the area of ​​high-emissivity material to the area of ​​low-emissivity material can be used to measure the changes in the controller's maximum and theoretical emissivity. The changes in maximum and theoretical emissivity vary with... It increases as it grows. The tangent value represents the theoretical cutoff angle, and the cutoff angle varies with... It increases as it increases.

[0047] In the field of radiative heat transfer, a larger theoretical emissivity change is desirable to improve thermal efficiency. This minimum emissivity change ε, which just barely satisfies the requirement for high thermal efficiency, is defined as the minimum emissivity change. 小 (like Figure 5(As shown). At this time, the cutoff angle is 0° < θ ≤ 70°. This is because the material naturally has directional control when the cutoff angle is > 70°, while the cutoff angle is ≤ 70°, so that the controller can play a role in improving thermal efficiency by concentrating heat (for example, when the angle is greater than 70°, the emissivity of a flat metal increases with the angle, while the emissivity of an insulating medium decreases with the angle).

[0048] In the field of electronic device heat dissipation, the noise and distortion caused by temperature changes in electronic components are extremely harmful. Dissipating heat only at a small angle (θ≤45°) will greatly improve heat management (e.g., Figure 6 (As shown).

[0049] In different fields and among different users, the requirements for the two parameters mentioned above vary. By rationally designing the dimensions of a, b, and c, the cutoff angle θ and the theoretical emissivity change Δε can be controlled.

[0050] Figure 2 A partially enlarged view of the control layer of the flexible cellular broadband infrared radiation omnidirectional controller of this embodiment is shown, where 100 is the high emissivity layer, 121 is the cellular aperture, and 122 is the cellular wall. Figure 3 This is a perspective view of the cell. For any angle greater than the cutoff angle θ, the emissivity exhibited by the controller is the same as the emissivity of the cell wall. The magnitude of the cutoff angle θ varies slightly with the azimuth angle, and the period of the cutoff angle with the azimuth angle is...

[0051] Typically, the actual cutoff angle θ measured will be slightly larger than the theoretical cutoff angle θ due to the influence of the manufacturing process. Considering that the measured viewing angle may increase due to the direct emission after two reflections from the bottom of the honeycomb aperture, the theoretical value of the cutoff angle θ is further reduced by 10% to compensate for the negative impact of external factors.

[0052] Figure 4 This is a magnified view of a portion of the controller control layer in the hollowed-out area of ​​the cylindrical structure. 100 represents the high emissivity layer (base layer), 131 represents the hollowed-out cylinder, and 132 represents the upper layer material. Using a hollowed-out cylinder facilitates processing and ensures that the cutoff angle remains unchanged regardless of azimuth.

[0053] Figure 5 This diagram illustrates the application of a controller in radiative heat transfer. The honeycomb wall concentrates the energy radiated from the bottom of the honeycomb structure directly above, improving the heat conversion efficiency of the receiver. The theoretical emissivity change that just meets this heat conversion efficiency requirement is defined as the minimum emissivity change ε. 小 .

[0054] Figure 6This diagram illustrates the application of a controller in the field of heat dissipation for electronic devices. As the integration of components increases, reducing thermal interaction between them becomes a challenge. The controller of this invention can reflect the heat radiated by electronic components through the honeycomb walls, directing it at a small angle to the perpendicular (surface normal). This reduces temperature changes caused by thermal interaction between electronic components, thereby reducing noise and distortion, and significantly improving heat management.

[0055] As can be seen from the above embodiments, compared with the existing one-dimensional infrared radiation directional control, the omnidirectional infrared directional control provided by the present invention can achieve higher heat transfer efficiency in the field of radiation heat transfer, achieve omnidirectional thermal camouflage capability in the field of infrared camouflage, and achieve directional heat dissipation in the field of electronic component thermal management.

Claims

1. A broadband infrared radiation omnidirectional directional controller, characterized in that: It consists of a control layer and a protection layer; The control layer is a two-layer structure composed of high and low emissivity materials, covering the target area. The high / low emissivity material is selected as the base layer of the lower layer, and the low / high emissivity material of the upper layer completely covers the base layer. The emissivity difference between the high and low emissivity materials is ≥0.4, and the transmittance of the upper material to infrared light is less than 10% to meet the requirements of infrared isolation. The low / high emissivity material of the upper layer is patterned in a through-hole manner, dividing the low / high emissivity material of the upper layer into continuous hollow areas. Taking the plane containing the substrate as the XY plane and the thickness direction as the Z-axis, the upper low / high emissivity materials, as patterned from the Z-axis direction, are: The observation angle of the hollowed-out area is determined by a cutoff angle θ: when the observation angle is less than the cutoff angle θ, the high / low emissivity material of the base layer can be seen; while when the observation angle is greater than the cutoff angle θ, only the low / high emissivity material of the upper layer can be seen. The planar dimensions and height of the hollowed-out area are both greater than 10 times the wavelength of the incident wave. During use, it completely covers the target area to ensure that the incident wave reflects and propagates upon reaching the controller; Δε>ε 小 Δε represents the theoretical emissivity change of the entire controller, ε 小 Minimum theoretical emissivity variation set for the application target; 0°<θ≤70°, θ<θ 大 θ 大 The maximum theoretical cutoff angle set for the application target; The protective layer is disposed below the substrate layer to protect the control layer and prevent it from being torn apart during transfer or preparation.

2. The broadband infrared radiation omnidirectional controller as described in claim 1, characterized in that: The hollowed-out area is cylindrical so that the cutoff angle does not change with the azimuth angle.

3. The broadband infrared radiation omnidirectional controller as described in claim 1, characterized in that: The hollowed-out area has a regular hexagonal shape, and the upper low / high emissivity material covers the base layer in a honeycomb structure, ensuring that the cutoff angle does not change abruptly with the azimuth angle; the density of the honeycomb cells is 2-15000 cells / cm². 2 At this point, both a and c are greater than 10 times the wavelength of the incident wave. In the honeycomb structure, a is the side length of the honeycomb cell, b is the thickness of the honeycomb wall, c is the honeycomb height, h is the thickness of the base layer, t is the thickness of the protective layer, and ε is the thickness of the honeycomb. 底 ε is the emissivity of the substrate material. 侧 The emissivity of the upper layer material is: b < a, 0.05mm ≤ a ≤ 5mm, 0 < b ≤ 0.5mm, 0.1mm ≤ c ≤ 5mm, 0.05mm ≤ h ≤ 3mm, 0.1mm ≤ t ≤ 3mm. Looking at the XY plane from the Z-axis, with the X-axis as the polar axis, the horizontal angle between the counterclockwise direction and the target direction line is called the azimuth angle β. The angle between the straight line connecting a point on the edge of the honeycomb cell and the center inversion point and the surface normal is called the cutoff angle θ. When the observation angle is less than the cutoff angle θ, the high / low emissivity material at the bottom of the tank can be seen, while when the observation angle is greater than the cutoff angle θ, only the low / high emissivity material on the tank wall can be seen.

4. The broadband infrared radiation omnidirectional controller as described in claim 1, characterized in that: The high emissivity material is an emissivity ≥ 0.7, the low emissivity material is an emissivity ≤ 0.3, and the protective layer material is polyimide or polyethylene terephthalate.

5. The broadband infrared radiation omnidirectional controller as described in claim 1, characterized in that: The upper low / high emissivity material is covered by an integral epitaxial layer of the lower base layer material, with the epitaxial region surface covered by the upper material, to improve the mechanical performance of the entire controller.

6. The broadband infrared radiation omnidirectional controller as described in claim 1, characterized in that: The cutoff angle θ is set to be 10% smaller to compensate for the problem of the actual value being too large due to the processing technology.

7. The broadband infrared radiation omnidirectional controller as described in claim 1, characterized in that: The exposed area on the upper surface of the controller's control layer is also coated with a layer of infrared-transparent medium in the characteristic band to protect the controller and improve its durability.

8. The design method of the broadband infrared radiation omnidirectional controller as described in claim 3, comprising the following steps: Step 1: Based on the application scenario and target object, first determine the types of materials for the ε-bottom, ε-side and protective layer, as well as the corresponding thicknesses h and t, where 0.05mm≤h≤3mm and 0.1mm≤t≤3mm; Step 2: Determine b based on the type and properties of the material selected in Step 1, where 0 < b ≤ 0.5 mm, and the corresponding processing method; when b > 0.1 mm, the preferred processing method is a CNC engraving machine; when 0.001 mm < b ≤ 0.1 mm, photolithography is preferred; when 0 < b ≤ 0.001 mm, electron beam lithography is preferred. Step 3: Determine a and c based on the application scenario and the target object's need for thinness and lightness, where 0.05mm ≤ a ≤ 5mm and 0.1mm ≤ c ≤ 5mm; simultaneously satisfying Δε > ε and θ < θ. 大 ; First, fix c to determine the final value of a; or draw a curve showing the relationship between a and c, and choose the optimal value based on the application scenario.

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