Directional radiation device and use

Abstract

Disclosed in the present invention are a directional radiation device and a use. By regulating radiation on the basis of a specified angle or angle range, broad spectrum angle asymmetric directional thermal radiation in an infrared band is achieved, and the geometric structure of an asymmetric unit can be adjusted to enhance infrared radiation at a specific angle. By changing the material of a spectral selection layer, the wavelength of thermal radiation is regulated, thereby achieving spectral selective emission in the infrared band. By attaching a porous membrane on the directional radiation device, the reflectivity of the directional radiation device for a visible band is enhanced, thereby truly achieving passive radiation cooling on both vertical and inclined surfaces.

Description

Directional radiation device and its application

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 24, 2023, with application number 202311070954.5 and invention name “Wide spectrum asymmetric angle selective thermal radiation device and application”, the entire contents of which are incorporated by reference into this application.

[0002] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 24, 2023, with application number 202311070952.6 and invention name “Spectrally selective asymmetric thermal radiation device and its preparation method”, the entire contents of which are incorporated by reference into this application.

[0003] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 24, 2023, with application number 202311070953.0 and invention name “Application of Directional Radiative Devices in Radiative Refrigeration”, the entire contents of which are incorporated by reference into this application. Technical Field

[0004] The present invention relates to the field of thermal radiation technology, and in particular to a directional radiation device and its application. Background Art

[0005] Thermal radiation is inherently broadband, incoherent, and non-directional. Any object with a temperature above absolute zero radiates energy outward. Directed thermal radiation can improve energy transfer efficiency and reduce energy loss in undesired directions. It has significant application prospects in areas such as stray light suppression in optical systems, radiative heat transfer, radiative drive, radiative heating, radiative cooling, infrared encryption, and radiative temperature control.

[0006] Currently, periodic gratings, gradient ENZ materials, multilayer films and other structures can be used to control the temporal and spatial coherence of thermal radiation, but the emissivity of the above designs is symmetrically distributed in space, and the radiation lacks directionality. Some designs also break the structural symmetry to produce asymmetric thermal radiation, but the existing designs are limited to narrow band or narrow angle or polarization dependence. There are currently designs that achieve directional radiation through micro-nano structures, but because the structural size is small compared to the radiation wavelength, the way the thermal radiation is emitted is limited. The standing wave effect selectively enhances or weakens the radiation of a specific polarization state, causing such smaller devices to have serious polarization dependence problems. In order to maximize the energy transfer efficiency, directional thermal radiation devices need to have both broadband and non-polarization characteristics. Therefore, polarization-independent wide-spectrum angle-selective asymmetric thermal radiation devices are very important for achieving directional radiation in the infrared band.

[0007] Applications such as infrared sensing, infrared imaging, radiation temperature control, radiation heating, and radiation cooling require thermal radiation control within a specific infrared band and a larger angle range. Therefore, it is also necessary to be able to simultaneously control the radiation angle and the corresponding infrared spectrum to make the directional radiation device have spectral selectivity and angular selectivity. Summary of the Invention

[0008] One object of the present invention is to provide a directional radiation device with wide spectrum and angle selection characteristics, which solves the problems of narrow bandwidth, narrow adjustment angle, symmetrical thermal radiation, polarization dependence and other problems existing in existing radiators; and on this basis, optimizes the material of the radiation surface so that it only radiates incident waves in a specific spectral band, thereby realizing directional radiation with spectral selectivity, polarization independence, angle asymmetry and controllable; another object is to provide an application of a directional radiation device, and apply the directional radiation device to radiation cooling, thereby enhancing the infrared radiation in the atmospheric window while reducing the absorption of radiation from the ground and surrounding objects, and ultimately realizing the radiation cooling function of a surface at a specific angle, such as realizing radiation cooling in a vertical plane or an inclined plane at any angle.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A directional radiation device, comprising: a plurality of asymmetric units having an infrared absorbing material as a substrate, each asymmetric unit comprising a reflective surface, a radiating surface, and a bottom surface, the reflective surface being provided with a first infrared reflecting layer, and the bottom surface having a width greater than or equal to 50 microns;

[0011] The included angle α between the radiating surface and the bottom surface, and the included angle β between the reflecting surface and the bottom surface, are used to select the directional radiation angle by changing α and β. The adjustable range of the radiation angle is -90° to 90°.

[0012] The included angles α between the radiation surfaces and the bottom surfaces of the multiple asymmetric units are all 90°, and the included angles β between the reflection surfaces and the bottom surfaces increase or decrease in sequence.

[0013] Preferably, α+β≥90°, and the asymmetric unit has different effects on incident waves at different incident angles:

[0014] When the incident angle θ≤-β, the incident wave is in the reflection zone, and the asymmetric unit reflects the incident wave;

[0015] When the incident angle is -β≤θ≤90°-2β, the incident wave is in the transition zone, and the asymmetric unit partially reflects and partially absorbs the incident wave;

[0016] When the incident angle θ≥90°-2β, the incident wave is in the absorption zone, and the asymmetric unit absorbs the incident wave;

[0017] Among them, the normal direction of the bottom surface is 0°, the direction of the reflecting surface is the negative area, and the direction of the radiating surface is the positive area;

[0018] By adjusting the angle β between the reflecting surface and the bottom surface, the ranges of the reflecting area, the transition area and the absorption area can be changed.

[0019] Preferably, a spectral selection layer is also provided on the radiation surface. The spectral selection layer is made of a material that has an absorption effect on a specific spectral band. The specific spectral band is the same as the incident wave spectral band that needs to be directional radiated. The application material of the spectral selection layer is adjusted according to application requirements and the intrinsic absorption of the material to achieve spectral selective regulation of directional radiation.

[0020] Preferably, a second infrared reflecting layer is further provided between the spectrum selective layer and the substrate.

[0021] Preferably, the infrared emission band of the infrared absorbing material is 4-20 microns, and its emissivity is greater than or equal to 0.5.

[0022] Preferably, the infrared reflectivity of the first infrared reflecting layer and the second infrared reflecting layer is greater than 60%.

[0023] Preferably, the substrate material is at least one of a polymer and a metal.

[0024] Preferably, the infrared absorbing material on the radiation surface is a polymer, a multilayer film, a carbon nanotube, a ceramic, or a resin, and the first infrared reflecting layer and the second infrared reflecting layer are at least one of silver, aluminum, gold, titanium, copper, chromium, ITO, AZO, GZO, FTO, MXenes, a metasurface, a nanophotonic crystal, or a multilayer film.

[0025] Preferably, the reflecting surface and / or the radiating surface is a free-form surface.

[0026] Preferably, the spectrum selection layer is made of a material that has an absorption effect on the 8-13 micron spectrum band, and the second infrared reflection layer is made of a material that has reflection properties for both sunlight and infrared, so as to achieve radiative cooling.

[0027] Preferably, the spectrum selective layer is made of silicon nitride.

[0028] Preferably, in response to different infrared spectrum requirements, the spectrum selective layer adopts a polymer or multilayer film with limited thickness and spectrum selectivity.

[0029] Preferably, in response to different visible and infrared spectrum requirements, the reflective surface can use visible high-absorption infrared high-reflection materials, visible high-transmittance infrared high-reflection materials; the radiating surface can use visible high-absorption infrared broadband or spectrally selective high-reflection materials, visible high-transmittance infrared broadband or spectrally selective high-reflection materials.

[0030] Preferably, the substrate of the asymmetric unit can be prepared by at least one of reverse molding, imprinting, photolithography, mechanical scribing, and injection molding. An application of a directional radiation device comprises attaching a porous membrane to the top of the asymmetric unit of the directional radiation device to enhance the reflectivity of sunlight. The pore size of the porous membrane is 0.2-2.5 microns. The porous membrane has high reflectivity in the 0.25-1.5 micron band and high direct transmission in the 8-13 micron band.

[0031] The directional radiation device attached with the porous film is tilted or vertically set, with the radiation surface facing the sky and the reflection surface facing the ground.

[0032] Preferably, the porous membrane is made of UHMWPE and / or HDPE.

[0033] Compared with the existing technology, the above technical solution has the following advantages:

[0034] The present invention can achieve asymmetric distribution of emissivity in different spatial angle ranges by adjusting the angle β between the reflecting surface and the bottom surface and the angle α between the radiating surface and the bottom surface of the asymmetric unit; it can increase infrared radiation at a specified angle according to actual needs to realize infrared radiation function at a specific angle; the design of the increasing or decreasing angle of the asymmetric unit enables the directional radiation device to meet the problem of differences in the radiation angle ranges required in different areas under different application scenarios; and the width of the asymmetric unit is set to be no less than 50 microns, which effectively avoids the problem of polarization dependence.

[0035] The present invention can radiate part of the spectrum band through the spectrum selection layer to achieve spectrum selection, and can adjust the radiation spectrum band by replacing the spectrum selection layer to meet different practical needs.

[0036] The present invention applies a directional radiation device to the field of radiation cooling, and attaches a porous film to the directional radiation device, thereby effectively improving the reflectivity in the visible band while ensuring high transmittance in the infrared band.

[0037] The present invention realizes radiative cooling of vertical or inclined surfaces for the first time, and can increase infrared radiation at specified angles according to actual needs, thereby realizing infrared radiation function at specific angles. On the one hand, it can achieve higher sunlight reflection and enhance infrared radiation within the atmospheric window; on the other hand, it can reduce the absorption of radiation from the ground and surrounding objects, ensuring that the radiation energy from the sun and the ground is less than the energy radiated out, thereby realizing passive radiative cooling function of vertical or inclined surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] FIG1 is a schematic diagram of a portion of the structure of a directional radiation device with wide spectrum asymmetric angular selectivity provided according to Embodiment 1 of the present invention;

[0040] FIG2 is a schematic diagram of a reflection region, a transition region, and an absorption region provided in Embodiment 1 of the present invention;

[0041] 3 is a diagram showing changes in emissivity of a directional radiation device with the same bottom surface width as a function of the incident angle and the included angle β according to a simulation experiment provided in the first embodiment of the present invention;

[0042] FIG4 is a graph showing changes in emissivity with bottom width and angle β in TE polarization mode according to the first embodiment of the present invention;

[0043] FIG5 is a graph showing changes in emissivity with bottom width and angle β under TM polarization mode according to the first embodiment of the present invention;

[0044] FIG6 is a hemispherical distribution diagram of emissivity obtained from a simulation experiment for radiation direction provided in the first embodiment of the present invention;

[0045] FIG7 is a physical diagram of a directional radiation device with wide spectrum asymmetric angular selectivity provided according to the first embodiment of the present invention;

[0046] FIG8 is a simulation calculation diagram of the emissivity of a directional radiation device with wide spectral asymmetric angular selectivity varying with angle and wavelength under the conditions of a height-to-width ratio of 2:3, a width W of 1 mm, and an incident wave wavelength λ of 4-20 μm, provided in accordance with the first embodiment of the present invention;

[0047] FIG9 is a structural diagram of a directional radiation device with gradually increasing β angles provided by embodiment 1 of the present invention;

[0048] 10 is a schematic diagram of a partial structure of a directional radiation device with spectrum selection characteristics provided according to Embodiment 2 of the present invention;

[0049] 11 is a structural diagram of a directional radiation device with spectral selection characteristics and an increasing β angle according to the second embodiment of the present invention;

[0050] FIG12 is a schematic diagram of radiation from the reflection zone, transition zone, and absorption zone provided in the second embodiment of the present invention;

[0051] FIG13 is a graph showing the emissivity of a directional radiation device according to a second embodiment of the present invention as a function of the incident angle;

[0052] 14 is a graph showing the emissivity variation with the incident angle by replacing the spectrum selection layer material with PDMS according to the second embodiment of the present invention;

[0053] FIG15 is a graph showing changes in emissivity with bottom surface width under TE polarization mode according to the second embodiment of the present invention;

[0054] FIG16 is a graph showing the variation of emissivity with bottom surface width in the TM polarization mode according to the second embodiment of the present invention;

[0055] 17 is a flowchart of preparing a directional radiation device with spectral selection characteristics according to the second embodiment of the present invention;

[0056] FIG18 is a structural diagram of a directional radiation device applied to radiative cooling according to a third embodiment of the present invention;

[0057] FIG19 is a schematic diagram of avoiding mutual interference between adjacent buildings by using an angle-selective radiation device when two buildings are close to each other according to a third embodiment of the present invention;

[0058] FIG20 is a diagram showing an outdoor radiant cooling test according to a third embodiment of the present invention;

[0059] FIG21 is an outdoor energy distribution diagram provided according to the third embodiment of the present invention and a comparison diagram of the temperature difference between a directional radiation device, a conventional refrigerator, commercial white paint and the environment over time.

[0060] The reference numerals are as follows:

[0061] 1 is the reflecting surface, 2 is the radiating surface, 3 is the bottom surface, 4 is the first infrared reflecting layer, 5 is the spectrum selection layer, 6 is the substrate, 7 is the second infrared reflecting layer, and 8 is the porous membrane. DETAILED DESCRIPTION

[0062] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0063] The following description sets forth specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art will be able to make similar generalizations without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Example 1

[0064] As shown in Figure 1, a specific embodiment of the present invention provides a directional radiation device with wide spectral asymmetric angle selectivity, including multiple asymmetric units with infrared absorbing material as the substrate 6, the infrared emission band of the infrared absorbing material is 4-20 microns, and its emissivity is greater than or equal to 0.5.

[0065] Each asymmetric unit includes a reflective surface 1, a radiating surface 2 and a bottom surface 3, and is in a triangle shape as a whole. The reflective surface 1 is coated with a first infrared reflective layer 4 with an infrared reflectivity greater than 60%.

[0066] Definition: The angle between the radiation surface 2 and the bottom surface 3 is α, and the angle between the reflection surface 1 and the bottom surface 3 is β. This definition is also applicable to the second and third embodiments.

[0067] In order to achieve directional radiation and overcome polarization dependence, the α of the asymmetric unit is required to be ≠ β. Preferably, α>β, and the width of the bottom surface 3 is greater than or equal to 50 microns. Based on the above structure, the angle of directional radiation can be selected by changing α and β, and the radiation angle is -90° to 90°. The angle β between the reflecting surface 1 and the bottom surface 3 of multiple asymmetric units shows a sequentially increasing or decreasing change to meet the requirements of different regions for different radiation angles. When the radiation angle required by all regions is the same, multiple asymmetric units can also adopt the same angle β.

[0068] As a preferred embodiment, the angle α between the radiation surface 2 and the bottom surface 3 of multiple asymmetric units is 90°, the angle β between the reflection surface 1 and the bottom surface 2 is the same, and satisfies 0.1≤tanβ≤10. At this time, the asymmetric unit appears as a right triangle, H represents the height of the asymmetric unit, that is, the length of the radiation surface 2; W represents the width of the asymmetric unit 3, that is, the length of the bottom surface 3; r represents the ratio of the height H to the width W of the asymmetric unit.

[0069] The substrate material of substrate 6 is a polymer or metal, or a combination of polymer and metal. In this embodiment, a resin, specifically a PDMS solution, is used. The substrate 6 can be prepared by at least one of reverse molding, embossing, photolithography, scribing, and injection molding. In this embodiment, the substrate 6 is prepared by injection molding. Specifically, the PDMS solution is poured into a mold with a closed periphery and a periodic right-angled inverse triangle structure. The mold is heated at 75°C to set the shape. After cooling and solidification, the mold is removed to obtain an infrared absorbing material substrate 6 having a periodic right-angled triangle structure. A 50nm-500nm silver film is formed on the inclined surface (i.e., the reflective surface) of substrate 6 using magnetron sputtering, thermal evaporation, or electron beam deposition as the first infrared reflective layer 4. To ensure the quality of the silver film and its adhesion to the PDMS substrate 6, a 2-10nm chromium film can be pre-formed as an adhesion layer. Based on comprehensive testing, the silver film thickness is preferably 100nm-200nm.

[0070] As shown in Figure 2, taking the asymmetric unit of a right triangle as an example, it illustrates the different effects of the asymmetric unit on incident waves at different incident angles:

[0071] First, define the normal direction of the bottom surface 3 as 0°, the direction close to the reflecting surface 1 as the negative area, the direction close to the radiating surface 2 as the positive area, and the incident angle of the incident wave as θ.

[0072] When the incident angle of the incident wave is θ≤-β, the incident wave is in the reflection zone, and the asymmetric unit reflects the incident wave. Based on the law of reflection, all incident waves will be reflected.

[0073] When the incident angle of the incident wave is -β≤θ≤90°-2β, the incident wave is in the transition zone, and the asymmetric unit partially reflects and partially absorbs the incident wave. Part of the incident wave will be incident on the position near the top of the reflecting surface 1, and this part of the incident wave will be reflected; the other part of the incident wave will be incident on the position near the bottom of the reflecting surface 1, and this part of the incident wave will be reflected by the reflecting surface 1 and hit the radiating surface 2, and this part of the incident wave will be absorbed by the radiating surface 2;

[0074] When the incident angle θ of the incident wave is ≥90°-2β, the incident wave is in the absorption zone, and the asymmetric unit completely absorbs the incident wave. Part of the incident wave is directly incident on the radiation surface 2, and the other part is incident on the reflection surface 1 and then incident on the radiation surface 2 after reflection.

[0075] Based on the above principle analysis, it can be seen that the range of the reflection area, transition area, and absorption area can be changed by adjusting the angle β between the reflection surface 1 and the bottom surface 3 (i.e., the aspect ratio of the asymmetric unit). To verify the above effect, multiple sets of simulation experiments were conducted, and the following 8 sets of simulation experimental data are provided for demonstration:

[0076] Experiment 1: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 0.2;

[0077] Experiment 2: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 0.4;

[0078] Experiment 3: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 0.6;

[0079] Experiment 4: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 0.8;

[0080] Experiment 5: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 1.0;

[0081] Experiment 6: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 1.2;

[0082] Experiment 7: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio is 1.4;

[0083] Experiment 8: The width of the bottom surface 3 is 1 mm, and the height-to-width ratio coefficient is 1.6.

[0084] As shown in Figure 3, when the height-width ratio coefficient of the asymmetric unit changes, the emissivity will change with the incident angle θ. The wavelength of the incident wave in the above 8 groups of experiments is 8μm. It can be seen that when the height-width ratio coefficient of the asymmetric unit changes in experiments 1 to 8, the emissivity also changes with angle. When the height-width ratio coefficient of the asymmetric unit is 1.6 (Experiment 8), the device emissivity begins to show a significant increase in emissivity from an angle of -60°. When the angle is -30°, the emissivity is close to 1, and then it shows high emissivity; but when the height-width ratio coefficient of the asymmetric unit is 0.2 (Experiment 1), it can be seen that the device emissivity is greatly suppressed. From the angle position close to 0°, the device emissivity gradually increases until it is close to 1 at 60°, and the emissivity remains at 1 from 60° to 90°. It can be seen that the relevant characteristics of the device's emissivity changing with angle can be adjusted by adjusting the height-width ratio of the asymmetric unit. The aspect ratio of the asymmetric unit can be adjusted by fixing the width W to adjust the height H, or by fixing the height H to adjust the width W, or by adjusting both the height H and the width W simultaneously.

[0085] In addition, in order to solve the polarization dependence problem existing in the prior art, the embodiment of the present invention also studies the width problem of the bottom surface 3. By fixing the height-to-width ratio coefficient of the asymmetric unit and adjusting the height H and width W at the same time, multiple groups of simulation experiments are carried out, and the influence of structural size on asymmetric radiation under different polarization modes is given.

[0086] As shown in Figures 4 and 5, with an incident wave wavelength of 8 μm and a fixed aspect ratio of 2:3, the angular distribution and magnitude of the emissivity change as the width increases from 2 μm to 1000 μm. When the width is less than 5 μm, the emissivity in the TE polarization mode is close to zero, while the TM polarization mode is at a higher emissivity, and the angular distribution of the emissivity remains symmetrical. As the width increases from 5 μm to 50 μm, asymmetric emissivity distributions are observed in both polarization modes. The TE polarization mode exhibits more emissivity peaks, and their peak values ​​gradually increase, indicating that increasing the width results in a higher emissivity of the asymmetric element for infrared radiation within a specific wavelength range. This demonstrates a relationship between the infrared radiation characteristics and the size of the asymmetric element. When the width W exceeds 50 μm, the infrared radiation performance stabilizes, and the emissivity distributions for both polarization modes are essentially identical, overcoming polarization dependence.

[0087] To verify the directional radiation performance of a directional radiation device with wide-spectrum asymmetric angular selectivity, simulation experiments were conducted with a height-to-width ratio of 2:3, a width of 1 mm, and an incident wave wavelength of 8 microns. As shown in Figure 6, half of the device's hemispherical radiation area has high emissivity (i.e., high radiation), while the other half has low emissivity (i.e., high reflection), achieving wide-spectrum asymmetric directional thermal radiation.

[0088] As shown in Figure 7, based on the above, a directional radiation device with broad spectral asymmetric angular selectivity was fabricated. The device exhibits different reflection characteristics for incident waves at different angles of incidence. Simulation calculations show that the device's emissivity varies with angle and wavelength, as shown in Figure 8.

[0089] In addition, the reflecting surface 1 and / or the radiating surface 2 can also be a free-form surface. For example, when the reflecting surface 1 is a convex or concave arc surface, the angle β should be the slope of the tangent of the arc surface at the intersection of the incident wave and the reflecting surface 1. In this case, directional radiation can also be achieved, but the radiation range and angle will change, and the basic principle remains unchanged. When the radiating surface 2 is a concave arc surface, the situation is basically the same as when it is a plane. When the radiating surface 2 is a convex arc surface, a part of the light in the transition zone in the plane state will originally be emitted, but in the arc state, a part of it will be blocked and absorbed by the radiating surface 2, and the basic principle remains unchanged.

[0090] As shown in Figure 9, the asymmetric elements of a directional radiator feature a gradually varying angle β to meet the varying radiation angle requirements of different regions. Each asymmetric element or group of elements has a different β, enabling a spatial angular distribution of high and low radiation performance for each element or group of elements.

[0091] In actual production needs, directional radiation devices are often used in fields such as radiation cooling, radiation heating, or radiation propulsion, and have good application prospects. Specifically, by adjusting the radiation angle range of the directional radiation device, a cooling effect can be achieved on the inclined or vertical surface of a specific object or area. This technology can be applied to scenes with cooling needs such as building exterior walls and automobiles; alternatively, by controlling the radiation angle range of the directional radiation device, heat can be accurately transferred to the target object that needs to be heated, causing the object to heat up and achieve a fast and efficient heating process. This technology can be applied in fields such as industry, medicine, laboratories, and aerospace. Using the directional radiation device as a radiation source to generate high-efficiency radiation to achieve a propulsion effect, this technology can be applied to spacecraft propulsion systems such as solar sails and photon thrusters. Example 2

[0092] As shown in Figure 10, a specific embodiment of the present invention provides a directional radiating device with spectrally selective properties. The device comprises multiple asymmetric units, each consisting of a substrate 6 and a coating on its surface. The substrate 6 can be made of resin or any other material, preferably a polymer suitable for molding, to facilitate its fabrication. The substrate 6 is triangular in shape and comprises a reflective surface 1, a radiating surface 2, and a bottom surface 3. A fully covering second infrared reflective layer 7 is coated on the surface of the substrate 6. A fully covering spectrally selective layer 5 is coated on the fully covering second infrared reflective layer 7. Finally, a first infrared reflective layer 4 is applied only to the reflective surface of the fully covering spectrally selective layer 5. The infrared reflectivity of the first infrared reflective layer 4 and the fully covering second infrared reflective layer 7 is greater than 90%. Highly reflective metals such as silver and aluminum can be used. Testing has determined that a 100-400 nm silver film on the surface of the substrate 6 provides the best results. To ensure the quality of the silver film and its adhesion to the PDMS substrate, a 2-10 nm chromium film can be pre-formed as an adhesion layer. The spectral selection layer 5 only has an absorption effect on a specific spectral band, and the specific spectral band is the spectral band that requires directional radiation. Therefore, the application material of the spectral selection layer 5 can be adjusted according to application requirements and the intrinsic absorption of the material to achieve spectral selective regulation of directional radiation. The emissivity of the spectral selection layer 5 should not be lower than 0.2. Replacing the application material of the spectral selection layer 5 according to actual needs is an important innovative content of the present invention.

[0093] To meet different infrared spectrum requirements, the spectrum selective layer 5 can be made of a polymer or multilayer film with limited thickness and spectral selectivity. To meet different visible and infrared spectrum requirements, the reflective surface 1 can be made of a visible high-absorption infrared high-reflection material or a visible high-transmittance infrared high-reflection material. The radiating surface 2 can be made of a visible high-absorption infrared broadband or spectrally selective material or a visible high-transmittance infrared broadband or spectrally selective material. In Example 2, a 4-micron thick silicon nitride film is selected to mainly target spectrally selective emission from the atmospheric window. When the spectrum selective layer 5 is made of a silicon nitride film, a second infrared reflective layer 7 is also provided on the bottom surface of the spectrum selective layer 5. Silicon nitride produces a relatively obvious emission peak or emission band within the infrared spectrum range, but silicon nitride has relatively low absorption of visible light and has high transparency in the visible spectrum band. Therefore, silicon nitride cannot effectively reflect the visible spectrum band. Therefore, a silver film is provided below the silicon nitride film to reflect incident waves in the visible spectrum band.

[0094] To achieve directional radiation and overcome polarization dependence, the asymmetric unit also requires α>β, and the width of the bottom surface 3 is greater than or equal to 50 microns. Based on the above structure, the directional radiation angle can be selected by changing α and β, and the radiation angle is -90° to 90°.

[0095] As shown in FIG11 , as a preferred embodiment, the included angle α between the radiation surface 2 and the bottom surface 3 of the multiple asymmetric units is 90°, and the included angle β between the reflection surface 1 and the bottom surface 2 increases or decreases in sequence.

[0096] As a preferred embodiment, the angle α between the radiating surface 2 and the bottom surface 3 of the multiple asymmetric units is 90°. A specified number of asymmetric units are divided into a group, and the asymmetric unit angle β in each group of asymmetric units is the same. The asymmetric unit angle β in different groups of asymmetric units increases or decreases in sequence.

[0097] As a preferred embodiment, the infrared absorption material on the radiation surface 2 is a polymer, a multilayer film, a carbon nanotube or a ceramic.

[0098] As a preferred embodiment, the first infrared reflecting layer 4 and the second infrared reflecting layer 7 are both at least one of silver, aluminum, gold, titanium, copper, chromium, ITO, AZO, GZO, FTO, MXenes, metasurface, nanophotonic crystal, and multilayer film.

[0099] As a preferred embodiment, the angle α between the radiation surface 2 and the bottom surface 3 of multiple asymmetric units is 90°, the angle β between the reflection surface 1 and the bottom surface 2 is the same, and satisfies 0.1≤tanβ≤10. At this time, the asymmetric unit appears as a right triangle, H represents the height of the asymmetric unit, that is, the length of the radiation surface 2; W represents the width of the asymmetric unit 3, that is, the length of the bottom surface 3; r represents the ratio of the height H to the width W of the asymmetric unit.

[0100] As shown in Figure 12, taking the asymmetric unit of a right triangle as an example, the different effects of the asymmetric unit on incident waves at different incident angles are explained:

[0101] First, define the normal direction of the bottom surface 3 as 0°, the direction close to the reflecting surface 1 as the negative area, the direction close to the radiating surface 2 as the positive area, and the incident angle of the incident wave as θ.

[0102] When the incident angle of the incident wave is θ≤-β, the incident wave is in the reflection zone, and the asymmetric unit reflects the incident wave. Based on the law of reflection, all incident waves will be reflected.

[0103] When the incident angle of the incident wave is -β≤θ≤90°-2β, the incident wave is in the transition zone, and the asymmetric unit partially reflects and partially absorbs the incident wave. Part of the incident wave will be incident on the position near the top of the reflecting surface 1, and this part of the incident wave will be reflected; the other part of the incident wave will be incident on the position near the bottom of the reflecting surface 1, and this part of the incident wave will be reflected by the reflecting surface 1 and hit the radiating surface 2, and this part of the incident wave will be absorbed by the radiating surface 2;

[0104] When the incident angle θ of the incident wave is ≥90°-2β, the incident wave is in the absorption zone, and the asymmetric unit completely absorbs the incident wave. Part of the incident wave is directly incident on the radiation surface 2, and the other part is incident on the reflection surface 1 and then incident on the radiation surface 2 after reflection.

[0105] Based on the above principle analysis, it can be seen that the ranges of the reflection area, transition area and absorption area can be changed by adjusting the angle β between the reflection surface 1 and the bottom surface 3 (ie, the aspect ratio of the asymmetric unit).

[0106] As shown in Figure 13, the simulated emissivity of a spectrally selective asymmetric thermal radiation device for incident waves at different angles of incidence reveals that, due to the inherent properties of silicon nitride, it exhibits a strong absorption peak only within the atmospheric window, resulting in high emissivity only in the 8-16 micron range. The spectrum exhibits three regions as it changes with angle: the reflection region, the transition region, and the absorption region. These regions correspond to the low-emissivity region at the bottom, the medium-emissivity region in the middle, and the high-emissivity region at the top of the graph.

[0107] As shown in FIG14 , if the silicon nitride material is replaced with a 4-μm-thick PDMS material, a spectrally selective asymmetric thermal radiation characteristic of 8-14 μm can be achieved.

[0108] As shown in Figures 15 and 16, when the aspect ratio of the asymmetric unit is fixed at 2:3, the angular distribution and numerical value of the emissivity change as the width gradually increases from 2μm to 100μm. When the width gradually increases to 50μm, there are more emissivity peaks in the TE and TM polarization modes, and the peak value of the emissivity peaks also gradually increases. This means that the increase in width causes the asymmetric unit to have a higher emission capacity for infrared radiation in a specific wavelength range. It is proven that the infrared radiation characteristics are related to the size of the asymmetric unit. When the width W exceeds 50 microns, the infrared radiation performance is stable, and the emissivity distribution of the two polarization modes is basically the same. At this time, the polarization dependence has been overcome. Therefore, the width of the bottom surface 3 should be greater than 50 microns. The existing technology all studies nanoscale structures and is limited by the polarization state of the incident wave. This is the fundamental difference between the present invention and existing research. In addition, the reflective surface 1 and / or the radiating surface 2 can also be a free-form surface.

[0109] As shown in Figure 17, a preparation method for the spectrally selective directional radiation device described in Example 2 is proposed. The method involves injecting a PDMS solution into a mold that is sealed on all sides and features periodic inverted right-angled triangles. The mold is then heated at 75°C to 80°C for final shaping. After cooling and solidification, the mold is then reversed to obtain a structure with multiple asymmetric units. A 100nm-500nm silver film is then formed on the structure using magnetron sputtering or thermal evaporation to fully cover the structure. After the silver film stabilizes, a 4-micron silicon nitride film is grown on the silver film surface. After the silicon nitride film stabilizes, the angle between the sample and the electron beam coating direction is adjusted to form a 100nm-400nm silver film only on the silicon nitride film on reflective surface 1, completing the preparation of the spectrally selective asymmetric thermal radiation device. Compared to the traditional method of directly coating two surfaces, this layer-by-layer coating process is simpler, achieves better process results at the intersection of the two surfaces, and reduces the rate of defective products. Example 3

[0110] As shown in Figure 18, an embodiment of the present invention provides an application of a directional radiant device in radiative cooling. Its structure is based on the spectrally selective directional radiant device described in Example 2. The specific application scenario is a vertical or inclined surface. In the prior art, radiative cooling is primarily achieved through nanophotonic crystal structures, porous materials, and polymer coatings. Although these materials can achieve good radiative cooling on horizontal surfaces, on vertical or inclined surfaces, the ground also generates a large amount of thermal radiation, which greatly weakens the cooling performance of the device, or even eliminates the cooling effect. Taking a vertical surface as an example, in the hot summer, the ground absorbs solar radiation and heats up to around 50-60 degrees Celsius. For the exterior walls of buildings, this results in a significant heat gain. Existing radiative cooling materials, when applied to building surfaces for radiative cooling, can only reduce the impact of incoming solar radiation energy. They cannot address ground radiation. The sum of the radiant energy from the sun and the ground is still greater than the energy radiated outward. Therefore, conventional radiative cooling materials lack passive cooling properties and cannot achieve true cooling.

[0111] In this embodiment, the spectrally selective layer 5 on the radiating surface 2 of the directional radiation device is composed of a 4-micron-thick silicon nitride film. Although silicon nitride produces a distinct emission peak or band in the infrared spectrum, it has relatively low absorption of visible light and high transparency in the visible range, making it ineffective for directional radiation of visible light. Therefore, a silver film (second infrared reflective layer 7) is placed between the spectrally selective layer 5 and the substrate 6 to reflect visible light. The first infrared reflective layer 4 on the reflective surface 1 reflects radiation from the ground and the environment, preventing energy absorption. Because metals inherently absorb some ultraviolet light, the first infrared reflective layer 4 absorbs a significant portion of sunlight energy, resulting in a poor cooling effect and even the inability to achieve passive cooling. Therefore, a layer of polyethylene porous membrane 8, specifically made of ultra-high molecular weight polyethylene (UHMWPE) and / or high-density polyethylene (HDPE), is placed on top of the asymmetric unit. The pore size of the pores in the porous membrane 8 matches the wavelength of sunlight, with a pore size of 0.2-2.5 microns. The porosity and film thickness can be designed based on requirements. The porous membrane 8 has high reflectivity in the visible light band of 0.25-1.5 microns and high direct transmittance in the atmospheric transparent window band of 8-13 microns. When the porous membrane 8 is combined with the directional radiator, the reflectivity in the visible light band can be increased while ensuring the directional radiator's directional radiation in the infrared band, greatly enhancing the radiative cooling effect.

[0112] Since the embodiment of the present invention is mainly used to achieve cooling, the radiation energy it needs to overcome is solar radiation, ground radiation, and environmental radiation. The directional radiation device reflects the visible light portion of solar radiation, radiates the infrared light portion, and reflects the ground and environmental radiation to prevent energy absorption. As shown in Figure 19, the directional radiation device is tilted or set vertically, with the radiation surface 2 facing the sky and the reflection surface 1 facing the ground. When applied to radiative cooling of building exterior walls, it is necessary to design asymmetric units with a gradual β variation based on the obstruction of surrounding buildings to meet the different radiation angle range requirements in different areas of the building.

[0113] Compared to the prior art, the present invention not only overcomes solar radiation, but also solves the ground and environmental radiation, and further improves the reflection effect of the visible light band through the porous membrane. The sum of the energy of the directional radiation device from solar radiation, ground and environmental radiation, minus the energy directionally radiated by the radiation surface 2 and the energy reflected by the reflection surface 1, is a negative value, which truly realizes passive cooling. However, the prior art does not solve the ground and environmental radiation, and the value obtained is still a positive value. Therefore, the prior art cannot achieve true cooling, but only reduces the temperature impact of solar radiation as much as possible. In addition, the existing radiation refrigerator does not have an angle selection function and cannot achieve directional radiation. Therefore, it can only be set horizontally and is not suitable for directional radiation on inclined or vertical surfaces. The directional radiation device of the embodiment of the present invention can achieve angle selection by adjusting the angle between the reflection surface 1 and the bottom surface 3.

[0114] As shown in Figures 20 and 21, to verify the effectiveness of a directional radiator (with a porous membrane attached) for vertical radiative cooling, actual outdoor tests were conducted. The radiative cooling effects of the directional radiator (with a porous membrane attached) were compared with those of existing commercial white paint and conventional refrigerators. The temperature difference between the directional radiator, commercial white paint, and conventional refrigerator and the ambient temperature was plotted over time. During the experiment, the asymmetric unit of the directional radiator had a height of 0.66 mm and a width of 1 mm. Its spectrum exhibited high emissivity within the 8-13 micron atmospheric window. Within the device's hemispherical radiation area, half had high emissivity and the other half had low emissivity, achieving broadband, spectrally selective, asymmetric directional thermal radiation. As can be seen in the figures, compared to commercial white paint and conventional refrigerators, the embodiment of the present invention can achieve a cooling effect when the directional radiator is placed vertically, with the temperature approximately 2.5°C lower than the ambient temperature, achieving passive cooling. In contrast, the commercial white paint and conventional radiative cooling devices were approximately 6.4°C and 1.8°C higher than the ambient temperature, respectively, and did not achieve a true cooling effect.

[0115] It should also be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0116] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0117] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A directional radiation device, characterized in that: include: A plurality of asymmetric units using infrared absorbing materials as substrates, each asymmetric unit comprising a reflective surface, a radiating surface and a bottom surface, the reflective surface is provided with a first infrared reflective layer, and the bottom surface has a width greater than or equal to 50 microns; The included angle α between the radiating surface and the bottom surface, and the included angle β between the reflecting surface and the bottom surface, the directional radiation angle is selected by changing α and β, and the adjustable range of the radiation angle is -90° to 90°; The included angles α between the radiation surfaces and the bottom surfaces of the plurality of asymmetric units are all 90°, and the included angles β between the reflection surfaces and the bottom surfaces increase or decrease in sequence.

2. The directional radiation device according to claim 1, characterized in that: α+β≥90°, the asymmetric unit has different effects on incident waves at different incident angles: When the incident angle θ≤-β, the incident wave is in the reflection zone, and the asymmetric unit reflects the incident wave; When the incident angle is -β≤θ≤90°-2β, the incident wave is in the transition zone, and the asymmetric unit partially reflects and partially absorbs the incident wave; When the incident angle θ≥90°-2β, the incident wave is in the absorption zone, and the asymmetric unit absorbs the incident wave; Among them, the normal direction of the bottom surface is 0°, the direction of the reflection surface is the negative value area, and the direction of the radiation surface is the positive value area; By adjusting the angle β between the reflection surface and the bottom surface, the ranges of the reflection area, the transition area and the absorption area are changed.

3. The directional radiation device according to claim 1, characterized in that: A spectral selection layer is also provided on the radiation surface. The spectral selection layer adopts a material that has an absorption effect on a specific spectral band. The specific spectral band is the same as the incident wave spectral band that needs to be directional radiated. The application material of the spectral selection layer is adjusted according to the application requirements and the intrinsic absorption of the material to realize the spectral selective adjustment of the directional radiation.

4. The directional radiation device according to claim 3, characterized in that: A second infrared reflection layer is also arranged between the spectrum selection layer and the substrate.

5. The directional radiation device according to claim 1, characterized in that: The infrared emission band of the infrared absorption material is 4-20 microns, and its emissivity is greater than or equal to 0.

5.

6. The directional radiation device according to claim 4, characterized in that: The infrared reflectivity of the first infrared reflection layer and the second infrared reflection layer is greater than 60%.

7. The directional radiation device according to claim 1, characterized in that: The substrate material is at least one of a polymer and a metal, and the first infrared reflection layer and the second infrared reflection layer are at least one of silver, aluminum, gold, titanium, copper, chromium, ITO, AZO, GZO, FTO, MXenes, super surface, nanophotonic crystal, and multilayer film.

8. The directional radiation device according to claim 1, characterized in that: The reflecting surface and / or the radiating surface is a free-form surface.

9. The directional radiation device according to claim 4, characterized in that: The spectral selection layer is made of a material that has an absorption effect on the 8-13 micron spectrum, and the second infrared reflection layer is made of a material that has reflection properties for both sunlight and infrared, so as to realize radiation cooling.

10. The directional radiation device according to claim 9, characterized in that: The spectrum selection layer is made of silicon nitride.

11. The directional radiation device according to claim 9, characterized in that: The preparation process of the substrate of the asymmetric unit can adopt at least one of reverse molding, embossing, photolithography, scribing and injection molding.

12. An application of a directional radiation device, characterized in that: A porous film is attached to the top of the asymmetric unit of the directional radiation device as claimed in claim 10 to enhance the reflectivity of sunlight, the aperture size of the pores on the porous film is 0.2-2.5 microns, the porous film has a high reflection effect on the 0.25-1.5 micron band and a high direct transmission effect on the 8-13 micron band; The directional radiation device attached with the porous film is tilted or vertically arranged, with the radiation surface facing the sky and the reflection surface facing the ground.

13. The use of the directional radiation device according to claim 12, characterized in that: The porous membrane is made of UHMWPE and / or HDPE.

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