CN112433277B

CN112433277B - Glass photonic crystal selective wave absorber based on DBS algorithm

Info

Publication number: CN112433277B
Application number: CN202011412879.2A
Authority: CN
Inventors: 姜鑫鹏; 杨俊波; 马汉斯
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2020-12-05
Filing date: 2020-12-05
Publication date: 2022-03-22
Anticipated expiration: 2040-12-05
Also published as: CN112433277A

Abstract

The invention belongs to a selective wave absorber applied to radiation cooling, in particular to a glass photonic crystal selective wave absorber based on DBS algorithm, so as to further realize the purpose of radiation cooling, wherein the wave absorber is composed of a periodic structure, and one periodic structure unit comprises an optimized selective absorption area, an absorption layer and a reflection layer; the selective absorber designed based on the DBS algorithm solves the problems of multilayer loss in the process of manufacturing the multilayer radiation cooling selective absorber and the unsatisfactory effect of the algorithm optimization radiation cooling absorber, and realizes the selective absorber which has excellent performance and single material and can be produced in batches.

Description

Glass photonic crystal selective wave absorber based on DBS algorithm

Technical Field

The invention belongs to a selective wave absorber applied to radiation cooling, in particular to a glass photonic crystal selective wave absorber based on a DBS algorithm, and further achieves the purpose of radiation cooling.

Background

The practice of radiative cooling dates back to centuries, where systematic studies were truly performed by humans in the 20 th century. Research has shown that in the atmosphere, for light waves of 8-13 μm, the radiation energy can be transmitted directly to space (kelvin temperature system) outside 3K. Studies have shown that high emission can be derived to be equivalent to high absorption using the blackbody radiation formula. Therefore, the selective wave absorber is expected to provide a feasible solution for solving the global warming problem to realize high absorption (high emission) of the wave band. In addition, high reflectivity (up to 100%) of the device in the wavelength band of 8 μm or less is also necessary, which aims to obtain an equilibrium temperature lower than the ambient temperature in sunlight, thereby achieving the functions of cooling, condensing water, and the like. In order to maximize the energy heat flux of the selective wave absorber, it is important to achieve high emissivity for the atmosphere transparent window and high reflectivity for the wavelength band below 8 μm.

In order to meet the requirements of radiation cooling, namely, the requirements of high emissivity of the device for 8-13 μm light waves and high reflectivity below 8 μm, the overall design needs to be started from multiple angles of selecting device materials, designing device structures and the like. Currently, typical radiation cooling structures generally use multi-layer micro-nano materials to achieve high reflectivity for light waves below 8 μm and high emissivity for light waves below 8-13 μm [ a.p.raman, m.a.anoma, l.zhu, e.rehaeli, and s.fan, "Passive radiation cooling below ambient temperature arrangement direct light," Nature, 515(7528),540-4(2014) ]. However, due to the mutual influence among the layers of the multilayer material, the simulation result is often very different from the actual product, so that the radiation cooling effect is not obvious, and particularly the effect of generating high emissivity for 8-13 μm is not obvious. Peiyan Yang et al propose a solution to achieve radiative cooling for a single layer of a new material polymer [ p.yang, c.chen, and z. m.zhang, "advanced-layer structure with a received-high magnetic recovery for a digital radial cooling," sol.energy 169, 316-324 (2018) ]. The use of new materials such as monolayer polymers limits the possibility of further optimization of the materials, and the new materials are often not conducive to mass production. Therefore, the selective wave absorber with excellent performance, simple material and mass production is a problem to be solved in the field of radiation cooling.

With the extensive research of algorithms in recent years, many devices designed based on algorithms break through the periodic and orderly thinking of traditional devices, and further achieve more excellent performance compared with the traditional devices. Yu Shi et al first utilized genetic algorithms for layer Optimization Design for thermal radiative cooling [ Y.Shi, W.Li, A.Raman, and S.Fan, "Optimization of multi-layer optical films with a metallic algorithm and mixed integrator programming," ACS photon.5,684(2018) ], Jiang Guo et al studied the selective absorption of the corresponding atmospheric transparent windows using Bayesian algorithms [ J.Guo, S.Ju, and J.Shiomi, "Design of a high-level selective chemical structural by physical matrices information," Optit.Lett.45 (2),343 (2020) ]. However, the layer optimization based on the algorithm is rigorous for the algorithm to find the objective function, so that the optimization result is not comparable to that of the traditional multilayer micro-nano material. In addition, algorithm-based layer optimization still fails to address the interplay between multi-layer materials. The DBS algorithm solves the drawbacks of the original structure by optimizing the structural details without changing the existing materials. Hansi Ma et al's DBS algorithm-based Ultra-small-size large-bandwidth mode filter, because DBS algorithm itself is stronger in purpose and better in optimization effect, breaks through the technical bottleneck and a series of technical difficulties of the conventional mode filter (H.Ma, J. Huang, K.Zhang, and J.Yang), "Ultra-compact and effective 1 x 2 mode converters based on rotatable direct-bind-search algorithm," Opt.express,28(11),17010-9 (2020). Therefore, the application of the DBS algorithm to the design of a radiation-cooled selective absorber can bring some breakthroughs.

Disclosure of Invention

The invention aims to solve the technical problems that the existing radiation cooling selective wave absorber has multiple layers due to the use of multiple layers of materials, and the algorithm is utilized to optimize the selective wave absorber, so that the radiation cooling effect of a device is poor.

The technical scheme adopted by the invention is as follows: a glass photonic crystal selective wave absorber based on DBS algorithm is composed of a periodic structure, wherein one periodic structure unit comprises an optimized selective absorption region 1, an absorption layer 2 and a reflection layer 3;

the material of the optimized selective absorption region 1 is glass photonic crystals, the period of the optimized selective absorption region is P, the optimized selective absorption region is divided into NxN square unit cells, each unit cell is not perforated or perforated, and N is a positive integer;

the preferred cell size meets the following requirements:

(1) side length a of the divided square cell

In the formula, t is the drilling depth, the requirement on the depth-to-depth ratio aims to meet the requirement of the current processing technology, and the depth selection is obtained by using a depth heuristic curve, namely, the drilling depth with the best effect of the selective wave absorber generated by the DBS algorithm is used under the condition that the square cells have the same size and the formula (1) is met. The depth t of the punched holes is 3 μm, and the DBS final optimized structure with the depth of about 3 μm has the average absorption rate lower than that of 3 μm.

(2) The size of the unit cell is 1/N of one period P of the optimized selective absorption area;

(3) under the condition of meeting the processing technology standard, the structure optimized by the DBS algorithm can realize the minimum reflectivity (maximum absorptivity, given by FOM) in the optimized interval.

The absorption layer 2 is made of silicon dioxide, has the thickness of w, and is used for effective absorption of 8-13um light waves and low-loss transmission of 1-6um light waves;

the reflective layer 3 is made of silver and has a thickness h, so that incident light waves can be effectively reflected at the position of the silver film.

The cell size a ranges between 1 μm and P.

The invention has the following beneficial effects: the selective wave absorber designed based on the DBS algorithm is used for realizing radiation cooling. When light waves below 8 μm are incident on the selective wave absorber from above, the incident light is reflected with very little loss due to the high transmittance of the silica material itself and the high reflectance of the underlying silver reflective film. When light waves in the range of 8-13 mu m are incident to the glass photonic crystal from above, on one hand, due to the high absorption of the silicon dioxide material to the wave band, the incident light waves have a layer loss (layer absorption) phenomenon, and on the other hand, due to the existence of the glass photonic crystal, the light waves corresponding to two intrinsic high reflection peaks of the original silicon dioxide generate a local mode in the glass crystal, so that the absorption spectrum is effectively improved. It is worth noting that this structure has a high absorptivity, i.e. high emissivity, in the range of 8-13 μm, due to the theory relating to black body radiation thermal emissivity, where thermal emissivity is proportional to absorptivity.

The selective absorber designed based on the DBS algorithm solves the problems of multilayer loss in the process of manufacturing the multilayer radiation cooling selective absorber and the unsatisfactory effect of the algorithm optimization radiation cooling absorber, and realizes the selective absorber which has excellent performance and single material and can be produced in batches.

Drawings

FIG. 1 is a schematic diagram of a periodic structure of a Glass Photonic Crystal (GPC) selective wave absorber based on DBS algorithm;

FIG. 2 is a unit structure diagram of a glass photonic crystal selective wave absorber based on DBS algorithm;

FIG. 3 is a schematic diagram of a two-dimensional planar structure of a cell of the device of the present invention; (wherein the perforated part is black)

FIG. 4 is a schematic diagram of the initial structure of a device of the present invention (corresponding to FIG. 2) when one cell is not optimized;

FIG. 5 is a schematic diagram of a plane wave (space light) incident glass photonic crystal selective wave absorber structure unit;

FIG. 6 is a graph comparing an emission spectrum of 8-13 μm with a reflection spectrum of 1-8 μm with and without a glass photonic crystal;

Detailed Description

The invention provides a glass photonic crystal selective wave absorber based on DBS algorithm, a schematic diagram of a periodic three-dimensional structure of the glass photonic crystal selective wave absorber is shown in figure 1, a schematic diagram of a three-dimensional structure of a unit in the periodic structure is shown in figure 2, and the glass photonic crystal selective wave absorber comprises an optimized selective absorption region 1, an absorption layer 2 and a reflection layer 3.

The optimized selective absorption region 1 is made of glass photonic crystals, and the thickness t of the optimized selective absorption region 1 is 3 microns; the material of the absorption layer 2 is silicon dioxide, the thickness of the absorption layer 2 is 11 μm, the material of the reflection layer 3 is silver, and the thickness h is 0.5 μm.

Silver is widely used as an ideal conductor material in an infrared band, so that a silver film is plated at the bottom end of a silicon dioxide absorption layer, so that incident light waves are effectively reflected at the position of the silver film, and the principle of the silver-coated silicon dioxide absorption layer is similar to that of a mirror.

FIG. 3 is a schematic diagram of a two-dimensional planar structure of a cell of the device of the present invention; it can be seen that the optimally selected absorption region is divided into 10 × 10 square unit cells, each unit cell is in a state of not punching or punching, wherein the punched portion is black, the non-punched portion is white, one square unit cell structure side length P is 10 μm, and the preferable unit cell size is a is 1 μm.

FIG. 4 shows a schematic diagram of an initial structure of a cell, which is a 14 μm thick silicon dioxide with a 0.5 μm thick silver film plated underneath, and shows the purpose of this diagram for convenience of comparison between the structure without and after punching.

Fig. 5 shows a simulation of the incidence of a plane wave (space light) into the periodic cell glass photonic crystal selective absorber to understand the general direction of light incidence and the position of the light source. Wherein A is a light source, and B is a unit of the glass photonic crystal selective wave absorber.

In addition, we used the simulation software FDTD Solutions from Lumerical corporation to simulate the absorption and reflection spectra of an incident light normal incidence Glass Photonic Crystal (GPC) selective absorber and initial structure with wavelengths of 1-13 μm, as shown in FIG. 6.

Before the glass photonic crystal structure is not added, the structure of the glass photonic crystal structure is schematically shown in fig. 4, and the glass photonic crystal structure is a simple structure in which silicon dioxide is covered on a silver film. When the incident light wave is normal incidence from above the structure, it has a reflectivity of 91% for incident waves of 1-6 μm and an absorbance of 71.8% for incident waves of 8-13 μm, as measured by FDTD. And the absorption rate of the structure for incident waves of 8-13 mu m is improved to 94% and the reflectivity is slightly reduced to 90.1% for incident waves of 1-6 mu m by introducing the glass photonic crystal (defect) through algorithm optimization. A comparison of the absorption spectrum with the reflection spectrum with a photonic crystal is shown in fig. 6. An increase in the selective absorption effect for 8-13 μm can be achieved mainly because the local modes of light waves in the band around the intrinsic reflection peak of silica (two absorption minima of the grey dotted line shown in the left diagram in fig. 6) occur in the glass photonic crystal structure. The influence on the reflectivity of the incident wave of 1-6 μm is not obvious, mainly because the wavelength of the glass photonic crystal structure is not matched, or the glass photonic crystal structure cannot make the local mode of the part of the wavelength occur, so the incident light of the wavelength band still reflects according to the original (initial structure) reflection spectrum. Of course a high reflectivity for incident waves of 1-6 μm is instead beneficial for the function of the selective absorber applied for radiation cooling. Meanwhile, the designed selective wave absorber device is also an important index for realizing the radiation cooling function for the high reflectivity of 1-6 mu m incident waves.

We obtained the structure of one cell in the periodic glass photonic crystal through DBS algorithm, which is the optimal result for the corresponding objective function and the preferred cell size. The periodic selective wave absorber formed by taking the structural unit as a template can realize selective absorption of light waves of 8-13 mu m and high reflection of light waves of 1-6 mu m. The specific implementation is as follows: the spatial light source of 1-13 μm was used to illuminate from above the GPC selective absorber, and the absorption spectrum was obtained by measuring the reflected light spectrum and the transmitted light spectrum (almost 0) from the underlying silver film. We also simulated this process using the simulation software FDTD Solutions from Lumerical corporation and obtained the beneficial properties described above.

In the process, the lower silver-plated film of the selected silicon dioxide material with the thickness of 14 μm can be utilized, the upper silver-plated film is etched by a photoetching machine to fix the point location, and the specific point location is etched in a fixed point manner as shown in the schematic diagram of the unit structure in FIG. 2. When the periodic structure is produced in a large scale, the unit structure can be used as a template to be imprinted in a large scale by utilizing a micron-scale imprinting technology.

Claims

1. A glass photonic crystal selective wave absorber based on DBS algorithm is characterized in that: the wave absorber is composed of a periodic structure, wherein one periodic structure unit comprises an optimized selective absorption region (1), an absorption layer (2) and a reflection layer (3);

the material of the optimized selective absorption region (1) is glass photonic crystals, the period is P, the optimized selective absorption region is divided into NxN square unit cells, N is a positive integer, and each unit cell is not punched or is punched;

the cell size meets the following requirements:

(1) side length a of the divided square cell

In the formula, t is the drilling depth, and the depth selection is obtained by using a tentative depth curve, namely, the drilling depth with the best effect of the selective wave absorber generated by the DBS algorithm is used under the condition that the sizes of square cells are the same and the formula (1) is satisfied;

(3) under the condition of meeting the processing technology standard, the minimum reflectivity in the optimization interval can be realized by utilizing the structure optimized by the DBS algorithm;

the reflecting layer 3 is made of silver and has a thickness h, and is used for effectively reflecting incident light waves at the position of the silver film.

2. A glass photonic crystal selective wave absorber based on DBS algorithm according to claim 1, wherein: the cell size a ranges between 1 μm and P.

3. A glass photonic crystal selective wave absorber based on DBS algorithm according to claim 1, wherein: the size of one period unit of the wave absorber is as follows: p is 10 μm, a is 1 μm, t is 3 μm, w is 11 μm, and h is 0.5 μm.