Directional radiation device based on parabolic optical reflection characteristics and preparation method

Abstract

The invention discloses a directional radiation device based on parabolic optical reflection characteristics, and relates to the field of radiation refrigeration, the directional radiation device based on parabolic optical reflection characteristics comprises a reflection surface unit and an absorption surface unit; each reflecting surface unit is obtained by rotating a section of parabola around a tangent line at one end point of the parabola; the absorption surface unit is obtained by rotating a connecting line of a focus and a vertex of the parabola around the tangent line; the tangent line is in the vertical direction. Infrared radiation angle range regulation and control are realized by utilizing optical characteristics of a parabola, a two-dimensional parabola structure is changed into three dimensions and is practically applied in a three-dimensional space, a periodic array structure is utilized, space utilization maximization and high efficiency are realized through reasonable placement, a micron size is adopted, and the occupied space is small.

Description

Technical Field

[0001] The present invention relates to the technical field of radiative cooling, in particular to a directional radiation device based on the parabolic optical reflection characteristic and a preparation method thereof. Background Art

[0002] Thermal radiation is a phenomenon of electromagnetic wave radiation emitted by an object due to its temperature. Any object with a temperature higher than absolute zero can generate thermal radiation, and thermal radiation can freely propagate in a vacuum or a low gas density environment. Thermal radiation is non-directional, that is, the radiation energy spreads evenly in all directions. Radiative cooling technology is a passive cooling technology that can reflect solar heat by controlling the optical properties of the object surface and continuously radiate heat to the high altitude through the atmospheric window, thereby effectively reducing the surface temperature. Passive radiative cooling technology is a technology that does not require additional energy input and realizes cooling through natural environmental conditions. By reducing the absorption rate of the object in the near-infrared band (using high-reflective materials), the solar heat gain is minimized, and radiative cooling is effectively realized. It has great potential in achieving sustainable and efficient cooling. In recent years, radiative cooling technology has entered a golden age of development, experiencing a blowout growth in the academic community, and at the same time has also attracted extensive attention in the industrial community, giving birth to many start-up companies globally. Various high-performance radiative cooling materials based on thermal emitters have been developed one after another. For example: Polymer-based radiative cooling films are composed of various polymer materials, such as polyethylene (PE), polyethylene terephthalate (PET), etc. By multilayer composite or adding special nanoparticles, they can exhibit high emissivity in a specific infrared band (such as 8-13 μm). These films can be made very thin and have the characteristics of light weight and good flexibility. Radiative cooling coatings based on pigments and binders contain special infrared radiation pigments, such as certain rare earth metal oxides or carbon black, and are coated on the object surface after being mixed with the binder, having high emissivity in the infrared band. Metal radiative cooling plates take metal plates as the substrate, and the surface is specially treated, such as anodization or coating with high-emissivity materials, to form a plate-like structure with radiative cooling function. For example, taking aluminum as the substrate and coating materials such as silicon dioxide on the surface to form a radiative cooling plate with high emissivity. Nanostructured coatings utilize nanotechnology, such as coatings constructed by nanoparticles, nanowires or nanotubes, etc., and achieve efficient thermal radiation in the infrared band through the special optical properties of the nanostructure.

[0003] Despite fruitful academic achievements, practical applications still face the challenges of many environmental factors and diverse functional requirements. In radiative cooling technology, it is expected that objects will achieve high radiation efficiency within a certain range of angles in the infrared band, so as to achieve efficient heat dissipation. However, existing radiative cooling devices made according to the principles of geometric optics do not have good angle selectivity, resulting in high infrared radiation in non-target angle ranges and thus energy release, which cannot achieve a good radiative cooling effect. Moreover, most radiative cooling devices cannot achieve excellent angle selectivity in complex environments with high-rise buildings, and can only achieve a good cooling effect in open environments. Furthermore, some optical characteristic devices based on two-dimensional planes are not suitable for three-dimensional space. Therefore, it is crucial to achieve directional control of thermal radiation angles in complex environments.

[0004] Currently, most widely used radiative cooling devices utilize the principle of reflection. Specifically, they use materials such as Ag that are transparent to visible light and highly reflective in the mid-infrared band as the reflective layer, and materials such as Ag that are transparent to visible light, highly absorbent, and highly emissive to infrared light as the emissive layer. Through specific structural designs, these devices absorb infrared radiation from small atmospheric angles and re-emit it back along the original optical path. Infrared radiation from other angles is reflected in various directions, thereby achieving directional control of the infrared radiation angle. However, these radiative cooling devices often contribute to light pollution and pose a threat to the environment.

[0005] In order to make such devices have good angular selectivity, and through two-dimensional geometric optical properties, reasonable rotation and placement along the axis to achieve good angular selectivity in three-dimensional space, the existing technology has achieved good angular selectivity in two-dimensional space, but for light waves radiated in any direction in three-dimensional space, there is no good angular selectivity.

[0006] In order to solve this shortcoming, the present invention utilizes the optical properties of the parabola to rotate the designed reference plane along the axis to achieve three-dimensionalization. Summary of the invention

[0007] In view of the above problems in the prior art, the present invention is proposed.

[0008] Therefore, the problem to be solved by the present invention is how to achieve three-dimensional angle selection of the radiant cooling device.

[0009] To solve the above technical problems, the present invention provides the following technical solutions: a directional radiation device based on parabolic optical reflection characteristics, comprising a reflecting surface unit and an absorbing surface unit; the reflecting surface unit is obtained by rotating a segment of a parabola around a tangent at one end point; the absorbing surface unit is obtained by rotating a line connecting the focus and vertex of the parabola around the tangent; the tangent is in a vertical direction.

[0010] As a preferred embodiment of the directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the reflection surface unit sequentially includes a protective layer, a transparent conductive layer, and an infrared absorption layer from outside to inside; the absorption surface unit sequentially includes the protective layer and the infrared absorption layer from outside to inside.

[0011] As a preferred embodiment of the directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the reflection surface unit and the absorption surface unit correspond one by one and are arranged on the substrate in the form of a face-centered cubic or hexagonal close-packed array.

[0012] As a preferred embodiment of the directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the protective layer is an Al2O3 thin film, the material of the transparent conductive layer is fluorine-doped tin oxide, the material of the infrared absorption layer is Si3N4, and the substrate is a flexible glass substrate.

[0013] As a preferred embodiment of the directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the thickness of the protective layer is 1 to 100 nm, the thickness of the transparent conductive layer is 10 to 1000 nm, and the thickness of the infrared absorption layer is 1 to 1000 μm.

[0014] In a second aspect, a method for preparing a directional radiation device based on the parabolic optical reflection characteristics is applicable to preparing the above-mentioned directional radiation device. The method includes providing a substrate; forming an infrared absorption layer on the substrate; the above-mentioned reflection surface unit and the absorption surface unit are the same; forming a transparent conductive layer region-selectively on the absorption surface unit; and forming a conformal protective layer on the outer surface of the micro-nano structure.

[0015] As a preferred embodiment of the method for preparing a directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the micro-nano structure is prepared by a single-point diamond turning lathe or a nanoimprinting method.

[0016] As a preferred embodiment of the method for preparing a directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the infrared absorption layer is formed by chemical vapor deposition using a silicon source and a nitrogen source as precursors, and the deposition temperature is 300 - 800 °C.

[0017] As a preferred embodiment of the method for preparing a directional radiation device based on the parabolic optical reflection characteristics of the present invention, the following applies: the transparent conductive layer is formed by magnetron sputtering, the deposition temperature is 20 - 500 °C, an organic material layer is coated on the absorption surface unit before the deposition process starts, and the organic material layer is removed by chemical solution immersion after the deposition process ends to achieve region-selective addition of the transparent conductive layer.

[0018] As a preferred embodiment of the preparation method of the directional radiation device based on the parabolic optical reflection characteristics of the present invention, wherein: the formation of the protective layer adopts electron beam deposition or magnetron sputtering.

[0019] The beneficial effects of the present invention are as follows: The present invention utilizes the optical characteristics of the parabola to realize the regulation of the infrared radiation angle range, three-dimensionalizes the two-dimensional parabolic structure, and applies it in the three-dimensional space. By using the periodic array structure and arranging it reasonably, the space utilization is maximized and made efficient. With a micron-level size, it occupies a small space. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a single structure diagram of the directional radiation device based on the parabolic optical reflection characteristics.

[0022] Figure 2 It is a single structure cross-sectional view of the directional radiation device based on the parabolic optical reflection characteristics.

[0023] Figure 3 It is a schematic diagram of the rotation formation of the reflection unit and the emission unit.

[0024] Figure 4 It is a schematic diagram of the parabolic optical principle.

[0025] Figure 5 It is a schematic diagram of the design principle of the directional radiation device.

[0026] Figure 6 It is a schematic diagram of the simulation of the directional radiation device.

[0027] Figure 7 It is a polar coordinate diagram of the absorption rate of the directional radiation device for incident light at different angles.

[0028] Figure 8 It is a schematic diagram for determining the unit parameters of the directional radiation device.

[0029] Figure 9 It is a schematic diagram of the process for preparing the infrared absorption layer.

[0030] Figure 10 It is a schematic diagram of the process for preparing the micro-nano structure mold.

[0031] Figure 11 It is a schematic diagram of the process for preparing the micro-nano structure.

[0032] Figure 12 Schematic diagram of the process for preparing a transparent conductive layer and a protective layer. Specific embodiments

[0033] To make the above objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings of the specification.

[0034] In the following description, many specific details are set forth to facilitate a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0035] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they embodiments that are mutually exclusive of other embodiments individually or selectively.

[0036] Referring to Figure 1 and Figure 2 , for the first embodiment of the present invention, this embodiment provides a directional radiation device based on the parabolic optical reflection characteristic. The device includes a reflecting surface unit 1 and an absorbing surface unit 2.

[0037] The shape of the reflecting surface unit 1 is obtained by rotating a section of a parabola around the axis HL. Specifically, referring to Figure 3 , it is a section of a parabola with O as the vertex and F as the focus. At the other endpoint H of the parabola, a tangent line is made at this point, and the tangent line is in the vertical direction. The parabola is rotated 360° around the tangent line, thus obtaining the reflecting surface unit 1, which is similar to the shape of a cone, except that the two side edges of the axial section of the cone are parabolas.

[0038] On the other hand, the vertex O and the focus F are connected to obtain the line segment OF, and the line segment OF is also rotated 360° around the tangent line, thus obtaining the absorbing surface unit 2, which is an annular surface.

[0039] Both the reflecting surface unit 1 and the absorbing surface unit 2 are stacked on the substrate 6. The reflecting surface unit 1, from the inside out, is successively: an infrared absorption layer 5, a transparent conductive layer 4, and a protective layer 3. And the absorbing surface unit 2 has only one protective layer 3 on the basis of the infrared absorption layer 5.

[0040] Preferably, the substrate 6 is a flexible substrate, preferably glass or transparent plastic (PMMA, PC, PET, etc.), which can provide good support. Its tensile strength and impact resistance are much higher than those of ordinary substrates, and it has good transparency and luster, greatly enhancing the mechanical strength and light transmittance of the overall structure. The material of the infrared absorption layer 5 is Si3N4, which is a high-temperature refractory substance, resistant to high pressure and high temperature, and can achieve visible light transparency and high emission of mid-infrared light. The material of the transparent conductive layer 4 is fluorine-doped tin oxide, and its transmittance in the visible light band (400-700nm) reaches 80% - 90%, ensuring low absorption of visible light, and its reflectivity in the infrared band usually exceeds 70%, achieving high reflection of mid-infrared light. The material of the protective layer 3 is Al2O3, which is a thin film transparent in both the solar band (0.3-2.5μm) and the mid-infrared band (8-14μm), and has the performance of forming a film at low temperature, playing the role of a protective functional film.

[0041] Preferably, the thickness of the protective layer 3 is 1 - 10nm, the thickness of the transparent conductive layer 4 is 1 - 10nm, and the thickness of the infrared absorption layer 5 is 1 - 1000μm.

[0042] The reflection surface units 1 and the absorption surface units 2 are arranged in a one-to-one correspondence on the substrate 6 in the form of a face-centered cubic or hexagonal close-packed array. The array formed by the reflection surface units 1 and the absorption surface units 2 can achieve the directional regulation of the mid-infrared radiation angle range in the atmosphere and expand it to three-dimensional space.

[0043] Based on the above, in order to better verify the technical effects of the present invention, the working principle of the present invention is analyzed as follows:

[0044] Referring to Figure 4 , for a parabola with O as the vertex and F as the focus, the angle between OF and the vertical plane is θ, and B is an arbitrary point on half of the parabola. The incident light FB emitted from the focus F is reflected by the parabola plane, and the reflected light is BE. Then BE is parallel to the straight line OF. This is the optical property of the parabola, that is, the light beam emitted from the focus F in any direction is parallel to the line connecting the vertex O and the focus F of the parabola after being reflected by the parabola. That is, the angle between BE and the vertical plane is also θ. Therefore, we can draw the angle bisector l of ∠FBE. This angle bisector l is the normal at the reflection point B, and ∠α1 = ∠α2. Now there is a point A located between the line segment OF. The light AB emitted from point A is also reflected at point B (the reflected light is BC). As can be seen from the figure, the incident angle ∠β1 > ∠α1. Similarly, the reflected angle ∠β2 > ∠α2. That is, the angle between BC and the vertical plane is less than θ.

[0045] It can thus be concluded that for any incident light wave passing through the line OF connecting the vertex and the focus of the parabola, after being reflected by the parabola plane, its reflection angle is always greater than the reflection angle parallel to the focal line. According to the reversibility of the light path, any light ray with an angle less than θ with the vertical plane y will pass through the line segment OF after being reflected by the parabola, while the incident light with an angle greater than θ with the vertical plane will not pass through the line segment OF. Through this characteristic of the parabola, directional control of the angle can be achieved.

[0046] Based on the above, referring to Figure 5 , take a point H on the parabola. The tangent line passing through point H is parallel to the vertical plane and serves as the rotation axis to rotate and obtain the reflection surface unit 1 as shown in Figure 1 . According to the optical characteristics of the parabola, any incident light with an angle less than α m with the vertical plane will pass through the line segment OF after being reflected by the parabola. The line segment OF rotates to form the absorption surface unit 2. The absorption surface unit 2 is made of an infrared high-absorbing material, and the reflection surface unit 1 is made of an infrared high-reflecting material. Thus, it can be achieved that the infrared radiation light waves with an angle less than α m with the vertical plane can be absorbed by the absorption surface unit 2 after being reflected by the reflection surface unit 1 and all be emitted back to the atmosphere, while the infrared radiation with an angle greater than α m with the vertical plane will be directly reflected back to the atmosphere after passing through the reflection surface unit 1.

[0047] To verify this theory, a simulation experiment was conducted. In the experiment, the horizontal plane was set as 0°, and the vertical plane was set as 90°. The incident light was set in the mid-infrared band, and the corresponding functional film layers were coated on the surface of the device unit. The parallel light incident at different angles completely covered the absorption surface. And since the device of this patent is applicable to the horizontal ground, the situation of incident light from below the ground is not considered. The simulation schematic diagram is as shown in Figure 6 . And 19 groups of data were measured with the incident angle as the variable and a polar coordinate diagram was generated. The data is shown in the following table:

[0048] Angle of incidence / degree 0 5 10 15 20 25 Absorptance / % 0.052 3.864 6.851 8.396 17.231 25.674

[0049] Continued Table 1:

[0050] Angle of incidence / degree 30 35 40 45 50 55 Absorptance / % 25.674 40.725 50.060 58.904 63.492 68.904

[0051] Continued Table 2:

[0052] Angle of incidence / degree 60 65 70 75 80 85 90 Absorptance / % 72.784 76.092 79.012 81.292 82.952 93.992 94.248

[0053] Referring to Figure 7 , for the incident light with a larger incident angle and closer to the vertical plane, the absorption rate of the device is higher. Among them, for the incident light with an angle between 60° and 90° with the horizontal plane and an angle between 0° and 30° with the vertical plane passing through this device, the absorption rate reaches more than 70%, which meets the theoretical expectation.

[0054] In addition, for the determination of device parameters: as Figure 8 shown, let the length of OF be p / 2, and it deviates from the y-axis of the plane rectangular coordinate system by an angle α m angle, then the polar coordinate equation of this parabola is:

[0055]

[0056] Let a point on the parabola be H(ρ0,θ0), x0 = ρ0cosθ0, y0 = ρ0sinθ0, and the tangent at point H is perpendicular to the y-axis, that is:

[0057]

[0058] From equations (1), (2), and (3), we can obtain:

[0059] 2ρ0sin(θ0 - α m )cosθ0 + 2pcosθ0 - ρ0sinθ0cos(θ0 - α m ) = 0 (4)

[0060] Substitute equation (1) into equation (3) and simplify to get:

[0061] sinθ0sin(2θ0 - 2α m ) = cosθ0[3 - cos(2θ0 - 2α m )] (5)

[0062] From equation (5), the relationship between θ0 and α m is obtained. Substitute equations (1) and (2) to find the height HL = l = ρ0sinθ0 of the paraboloid and the inner diameter OL = ρ0sinθ0, and then the relationship between HL and α m is obtained. Among them, both α m and p are known quantities set.

[0063] As an optional embodiment, the present invention also provides a preparation method for a directional radiation device based on the optical reflection characteristics of a parabola, which is applicable to preparing the above-mentioned directional radiation device.

[0064] First, according to the size derivation formula of the previous embodiment, set α m to 30°, and some parabola parameters can be listed as shown in the following table:

[0065]

[0066] The specific method includes:

[0067] Step 1: Prepare the substrate 6:

[0068] (1) A glass substrate layer with a large enough length and width and a height of 5 μm is polished, cleaned, and dried by chemical mechanical polishing.

[0069] Step 2: Add the infrared absorption layer 5.

[0070] Using chemical vapor deposition (CVD), an emission layer with a thickness of 1 - 1000 μm is added to the substrate 6. Preferably, the material is Si3N4. Silicon source (SiH4) and nitrogen source (NH3) are used as precursors. These precursors react after being heated or excited in the reaction chamber, and a Si3N4 material layer, that is, the infrared absorption layer 5, is covered on the surface of the substrate 6, as Figure 9 shown.

[0071] Step 3: Fabricate the micro-nano structure. Refer to Figure 10 and Figure 11 , specifically:

[0072] (1) Fabricate a mold by photolithography. Photoresist (SU-8 series photoresist) can be selected.

[0073] Use a spin coater to uniformly coat the photoresist on a substrate such as a silicon wafer or a quartz wafer. The spin coating thickness is controlled within 1000 - 1500 μm to ensure that the parabolic structure can be completely etched.

[0074] a: Grayscale exposure: Use a photolithography device (such as an ultraviolet photolithography device). Place the mask of the designed parabolic array structure pattern (micro-nano structure) above the photoresist and perform the exposure operation.

[0075] b: Post-baking and development: After exposure, perform post-baking to enhance the chemical properties of the photoresist. Then use the corresponding developer (SU-8 developer) for development. The development time depends on the photoresist thickness and the exposure situation. The unexposed or exposed parts are dissolved by development, thereby forming a pattern of a micron-scale parabolic array structure on the photoresist, that is, the micro-nano structure.

[0076] c: Transfer the parabolic array structure pattern formed on the photoresist to the silicon wafer or quartz wafer substrate by soft etching method, thus completing the mold made of silicon wafer or quartz wafer for convenient mass production of subsequent devices.

[0077] (2) Use nanoimprint lithography to etch a parabolic array structure on the Si3N4 material layer.

[0078] (a): Use a spin coater to evenly apply a soft stamp adhesive above the emission layer. The spin coating thickness is controlled within 1000 - 1500 μm to ensure that a complete parabolic array structure can be etched on the soft stamp adhesive.

[0079] (b): Use a mold to engrave a pattern of a parabolic array structure on the soft printing adhesive. Place the prepared silicon mold above the soft printing adhesive, heat and apply pressure to press the silicon mold into the soft printing adhesive layer, and demold after ultraviolet curing.

[0080] (c): Transfer the parabolic array structure pattern formed on the soft printing adhesive to the target emission layer by soft etching method, thus obtaining a parabolic structure array.

[0081] Step Four: Add an infrared absorption layer 5, a transparent conductive layer 4 and a protective layer 3. Refer to Figure 12 , specifically:

[0082] (1) Selectively add a 10 - 1000 nm transparent conductive layer, i.e., a reflective layer, in a region - selective manner by chemical vapor deposition. The material is fluorine - doped tin oxide.

[0083] (a): Coat a thin film of organic material on the absorption surface unit defined by the expected structure by magnetron sputtering to ensure the subsequent removal of the reflective layer film on the absorption surface unit.

[0084] (b): Coat the entire structure surface with a transparent conductive layer by magnetron sputtering.

[0085] (c): Dissolve the organic material film layer on the surface of the absorption surface unit with a specified solvent, thereby retaining the transparent conductive layer in the regions other than this.

[0086] (2) Coat an organic protective layer of 1 - 100 nm on the overall surface of the parabolic array structure by magnetron sputtering again. After completion, annealing treatment can be carried out as needed, heating at a certain temperature for a period of time to improve the performance of the thin film, such as improving the density and stability of the thin film.

[0087] In summary, the beneficial effects of the present invention are as follows:

[0088] 1. Utilize the optical properties of the parabola to realize the regulation of the infrared radiation angle range near the vertical direction.

[0089] 2. Three - dimensionalize the two - dimensional parabola structure for practical application in three - dimensional space.

[0090] 3. Utilize the periodic array structure to maximize and optimize space utilization through reasonable placement.

[0091] 4. Adopt a micron - level size, occupying a small space.

[0092] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A directional radiation device based on the optical reflection characteristics of a parabola, characterized in that: It includes a reflecting surface unit (1) and an absorbing surface unit (2); The reflecting surface unit (1) is obtained by rotating a section of parabola around the tangent at one of its endpoints; The absorbing surface unit (2) is obtained by rotating the line connecting the focus and the vertex of the parabola around the tangent; The tangent is in the vertical direction.

2. The directional radiation device based on the parabolic optical reflection characteristic according to claim 1, wherein: The reflecting surface unit (1) sequentially includes a protective layer (3), a transparent conductive layer (4), and an infrared absorption layer (5) from outside to inside; the absorbing surface unit (2) sequentially includes the protective layer (3) and the infrared absorption layer (5) from outside to inside.

3. The directional radiation device based on the parabolic optical reflection characteristic according to claim 2, wherein: The reflecting surface unit (1) and the absorbing surface unit (2) correspond one by one and are arranged on the substrate (6) in the form of a face-centered cubic or hexagonal close-packed array.

4. The directional radiation device based on the parabolic optical reflection characteristic according to claim 3, wherein: The protective layer (3) is an Al2O3 thin film, the transparent conductive layer (4) is fluorine-doped tin oxide, the material of the infrared absorption layer (5) is Si3N4, and the substrate (6) is a flexible glass substrate.

5. The directional radiation device based on the parabolic optical reflection characteristic according to claim 4, characterized in that: The thickness of the protective layer (3) is 1 - 100 nm, the thickness of the transparent conductive layer (4) is 10 - 1000 nm, and the thickness of the infrared absorption layer (5) is 1 - 1000 μm.

6. A preparation method of a directional radiation device based on the optical reflection characteristics of a parabola, characterized in that: An infrared absorption layer (5) is formed on the substrate (6); Micro-nano structures are formed in the infrared absorption layer (5); the shapes of the micro-nano structures are the same as those of the reflecting surface unit (1) and the absorbing surface unit (2) as claimed in claim 1; A transparent conductive layer (4) is formed region-selectively on the absorbing surface unit (2); A conformal protective layer (3) is formed on the outer surface of the micro-nano structures.

7. The preparation method of the directional radiation device based on the parabolic optical reflection characteristic according to claim 6, characterized in that: The micro-nano structures are prepared by a single-point diamond turning machine or a nanoimprinting method.

8. The preparation method of the directional radiation device based on the parabolic optical reflection characteristic according to claim 7, characterized in that: The infrared absorption layer (5) is formed by chemical vapor deposition, using a silicon source and a nitrogen source as precursors, and the deposition temperature is 300 - 800 °C.

9. The preparation method of the directional radiation device based on the parabolic optical reflection characteristic as described in claim 8, characterized in that: The transparent conductive layer (4) is formed by magnetron sputtering, the deposition temperature is 20 - 500 °C, an organic material layer is coated on the absorbing surface unit (2) before the deposition process starts, and the organic material layer is removed by chemical solution immersion after the deposition process ends to achieve region-selective addition of the transparent conductive layer (4).

10. The preparation method of the directional radiation device based on the parabolic optical reflection characteristic according to claim 9, characterized in that: The protective layer (3) is formed by electron beam deposition or magnetron sputtering.

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