阅读说明：本技术 一种超材料吸波器及其制造方法 (Metamaterial wave absorber and manufacturing method thereof ) 是由 姜鑫鹏 杨俊波 张振福 于 2020-12-04 设计创作，主要内容包括：本申请涉及一种超材料吸波器及其制造方法,所述方法包括：将吸波器底端的介质层设置为氮化钛,并确定所述介质层厚度为W,将吸波器的填充层设置为氮化硅,并确定所述填充层厚度为T；在所述介质层和所述填充层之间预设为氮化钛的光栅层,并将所述光栅层预设为纳米柱结构；利用遗传算法模型对吸波器的吸收效率进行计算,分别确定光栅层的直径和高度的范围；对所述光栅层的直径和高度的范围进行仿真优化,确定最终所述直径和高度的参数值,根据所述参数值的结果,在所述介质层和所述填充层之间设置光栅层。该方法中利用算法实现对周期性纳米结构的优化,进而产生性能优异的宽带完美吸收结构。所制造的吸波器能够对光波吸收效率的最大化。(The application relates to a metamaterial wave absorber and a manufacturing method thereof, wherein the method comprises the following steps: setting a dielectric layer at the bottom end of the wave absorber as titanium nitride, determining the thickness of the dielectric layer as W, setting a filling layer of the wave absorber as silicon nitride, and determining the thickness of the filling layer as T; presetting a grating layer of titanium nitride between the dielectric layer and the filling layer, and presetting the grating layer into a nano-pillar structure; calculating the absorption efficiency of the wave absorber by using a genetic algorithm model, and respectively determining the ranges of the diameter and the height of the grating layer; and carrying out simulation optimization on the range of the diameter and the height of the grating layer, determining the final parameter values of the diameter and the height, and arranging the grating layer between the dielectric layer and the filling layer according to the result of the parameter values. The method realizes the optimization of the periodic nano structure by utilizing an algorithm, and further generates a broadband perfect absorption structure with excellent performance. The manufactured wave absorber can maximize the absorption efficiency of light waves.)

1. A manufacturing method of a metamaterial wave absorber is characterized by comprising the following steps:

setting a dielectric layer at the bottom end of the wave absorber as titanium nitride, determining the thickness of the dielectric layer as W, setting a filling layer of the wave absorber as silicon nitride, and determining the thickness of the filling layer as T;

presetting a grating layer of titanium nitride between the dielectric layer and the filling layer, and presetting the grating layer into a nano-pillar structure;

calculating the absorption efficiency of the wave absorber by using a genetic algorithm model, and respectively determining the ranges of the diameter and the height of the grating layer;

and carrying out simulation optimization on the range of the diameter and the height of the grating layer, determining the final parameter values of the diameter and the height, and arranging the grating layer between the dielectric layer and the filling layer according to the result of the parameter values.

2. The method for manufacturing the metamaterial wave absorber as claimed in claim 1, wherein the presetting of the grating layer of titanium nitride between the dielectric layer and the filling layer and the presetting of the grating layer to be a nano-pillar structure comprises:

determining a unit structure of the wave absorber according to the thickness W of the medium layer and the thickness T of the filling layer, and setting the unit structure to be a cuboid with the length, the width and the thickness of P, P and L respectively;

setting the grating layer of the nano-pillar structure as a first grating layer and a second grating layer respectively, wherein the first grating layer is arranged above the second grating layer;

according to the length, the width and the thickness of the unit structure, an initial range of the thickness d1 and an initial range of the diameter d2 of the first grating layer are preset, and an initial range of the thickness c1 and an initial range of the diameter c2 of the second grating layer are preset.

3. The method for manufacturing the metamaterial wave absorber as claimed in claim 1, wherein the calculating the absorption efficiency of the wave absorber by using the genetic algorithm model to respectively determine the ranges of the diameter and the height of the grating layer comprises:

performing simulation on an initial structure consisting of the dielectric layer and the filling layer to obtain the reflectivity and the transmissivity in different wavelength ranges;

determining the absorptivity of the initial structure at the corresponding wavelength according to the reflectivity and the transmissivity;

and determining the initial range of the diameter and the height of the grating layer by using a genetic algorithm through the absorption rate and the coupling effect generated by the Mie resonance of the grating layer.

4. The method for manufacturing the metamaterial wave absorber as claimed in claim 2, wherein the range of the diameter and the height of the grating layer is optimized through simulation, final parameter values of the diameter and the height are determined, and the grating layer is arranged between the dielectric layer and the filling layer according to the result of the parameter values, and the method comprises the following steps:

respectively taking the thickness and the diameter of the first grating layer and the thickness and the diameter of the first grating layer as design variables, and carrying out simulation optimization on the average absorption rate;

iteration is carried out by taking the average absorption rate as an optimization objective function, and simulation analysis is carried out on the electromagnetic equivalent models of the dielectric layer, the grating layer and the filling layer to obtain the reflectivity and the transmissivity of the corresponding structure;

deducing the absorptivity according to the reflectivity and the transmissivity, and outputting structural parameters corresponding to the optimal average absorptivity when the iteration times reach a design algebra;

and obtaining final parameter values of the diameter and the height from the structural parameters, and setting the grating layer according to the parameter values.

5. The method for manufacturing the metamaterial wave absorber as claimed in claim 3, wherein the genetic algorithm model is as follows:

wherein d1 and d2 respectively represent the thickness and radius of the first grating layer; c1, c2 denote the thickness and radius, λ, respectively, of the second grating layer₁Represents the initial wavelength of the incident electromagnetic wave, and is set to 0.25 μm; lambda [ alpha ]_nThe cutoff wavelength of the incident electromagnetic wave was set to 2.5 μm; r (λ) is the reflectance and T (λ) is the transmittance.

6. A metamaterial wave absorber, comprising: the grating wave absorber comprises a medium layer, a grating layer and a filling layer, wherein the medium layer is of a bottom layer structure of the wave absorber, the grating layer is arranged above the medium layer, the filling layer is arranged on the periphery and the top end of the grating layer, and the grating layer is wrapped in the filling layer.

7. The metamaterial wave absorber of claim 6, wherein the dielectric layer is made of titanium nitride, the grating layer is made of titanium nitride, and the filling layer is made of silicon nitride.

8. The metamaterial wave absorber according to claim 6 or 7, wherein the grating layer is a double-layer nano-pillar structure and comprises a first grating layer and a second grating layer, and the first grating layer is disposed above the second grating layer.

9. The metamaterial wave absorber of claim 8, wherein the dielectric layer is 0.25 μm thick, and the filler layer is 0.08 μm thick; the thickness of the first grating layer is 95nm, the radius of the first grating layer is 97nm, the thickness of the second grating layer is 95nm, and the radius of the second grating layer is 178 nm.

Technical Field

The application relates to the technical field of solar energy, in particular to a metamaterial wave absorber and a manufacturing method thereof.

Background

The solar energy has a very wide application prospect as a green clean energy, and the combination of the solar energy acquisition and the broadband wave absorber based on the metamaterial is expected to realize the solar energy acquisition with higher efficiency, so that the utilization rate of the solar energy is improved. At present, some solar wave absorbers based on metamaterials realize effective absorption of solar spectrum. Blackbodies are an ideal physical concept that can absorb all electromagnetic waves without reflection and transmission, and their extraordinary properties are widely used in the optical field, which in turn creates a range of functional devices such as optical stealth, photo-thermal energy harvesting, photodetectors, etc. Based on metamaterials and having excellent properties, physical phenomena similar to black bodies can be generated. The nano-processing based metamaterials such as nanoparticles, nano-strips, nano-column structures and the like have realized large-scale preparation. And the processing technology is mature day by day, and a plurality of metamaterials based on nano processing can realize the absorption performance of incident light waves with arbitrary polarization and large angles.

However, most wave absorbers based on metamaterials can only realize the absorption of light waves in a narrow band range. In addition, some structures are quite complex, and although the processing technology can meet the requirement, the yield is low. In addition, due to the limitations of the conventional design method, the optimization of the oriented structural parameters is often limited in the structural design process. This will lead to a result that the structure optimization falls into local optimality, and thus its optimized structure is not a true optimal structure.

Disclosure of Invention

In view of the above, it is necessary to provide a metamaterial wave absorber and a method for manufacturing the metamaterial wave absorber.

In a first aspect, an embodiment of the present invention provides a method for manufacturing a metamaterial wave absorber, including the following steps:

setting a dielectric layer at the bottom end of the wave absorber as titanium nitride, determining the thickness of the dielectric layer as W, setting a filling layer of the wave absorber as silicon nitride, and determining the thickness of the filling layer as T;

presetting a grating layer of titanium nitride between the dielectric layer and the filling layer, and presetting the grating layer into a nano-pillar structure;

calculating the absorption efficiency of the wave absorber by using a genetic algorithm model, and respectively determining the ranges of the diameter and the height of the grating layer;

and carrying out simulation optimization on the range of the diameter and the height of the grating layer, determining the final parameter values of the diameter and the height, and arranging the grating layer between the dielectric layer and the filling layer according to the result of the parameter values.

Further, presetting a grating layer of titanium nitride between the dielectric layer and the filling layer, and presetting the grating layer to be a nano-pillar structure, includes:

determining a unit structure of the wave absorber according to the thickness W of the medium layer and the thickness T of the filling layer, and setting the unit structure to be a cuboid with the length, the width and the thickness of P, P and L respectively;

setting the grating layer of the nano-pillar structure as a first grating layer and a second grating layer respectively, wherein the first grating layer is arranged above the second grating layer;

according to the length, the width and the thickness of the unit structure, an initial range of the thickness d1 and an initial range of the diameter d2 of the first grating layer are preset, and an initial range of the thickness c1 and an initial range of the diameter c2 of the second grating layer are preset.

Further, the calculating the absorption efficiency of the wave absorber by using the genetic algorithm model to respectively determine the ranges of the diameter and the height of the grating layer includes:

performing simulation on an initial structure consisting of the dielectric layer and the filling layer to obtain the reflectivity and the transmissivity in different wavelength ranges;

determining the absorptivity of the initial structure at the corresponding wavelength according to the reflectivity and the transmissivity;

and determining the initial range of the diameter and the height of the grating layer by using a genetic algorithm through the absorption rate and the coupling effect generated by the Mie resonance of the grating layer.

Further, performing simulation optimization on the range of the diameter and the height of the grating layer, determining final parameter values of the diameter and the height, and setting the grating layer between the dielectric layer and the filling layer according to the result of the parameter values, including:

respectively taking the thickness and the diameter of the first grating layer and the thickness and the diameter of the first grating layer as design variables, and carrying out simulation optimization on the average absorption rate;

iteration is carried out by taking the average absorption rate as an optimization objective function, and simulation analysis is carried out on the electromagnetic equivalent models of the dielectric layer, the grating layer and the filling layer to obtain the reflectivity and the transmissivity of the corresponding structure;

deducing the absorptivity according to the reflectivity and the transmissivity, and outputting structural parameters corresponding to the optimal average absorptivity when the iteration times reach a design algebra;

and obtaining final parameter values of the diameter and the height from the structural parameters, and setting the grating layer according to the parameter values.

Further, the genetic algorithm model is as follows:

wherein d1 and d2 respectively represent the thickness and radius of the first grating layer; c1, c2 denote the thickness and radius, λ, respectively, of the second grating layer₁Represents the initial wavelength of the incident electromagnetic wave, and is set to 0.25 μm; lambda [ alpha ]_nThe cutoff wavelength of the incident electromagnetic wave was set to 2.5 μm; r (λ) is the reflectance and T (λ) is the transmittance.

On the other hand, the embodiment of the invention also provides a metamaterial wave absorber, which comprises: the grating wave absorber comprises a medium layer, a grating layer and a filling layer, wherein the medium layer is of a bottom layer structure of the wave absorber, the grating layer is arranged above the medium layer, the filling layer is arranged on the periphery and the top end of the grating layer, and the grating layer is wrapped in the filling layer.

Furthermore, the dielectric layer is made of titanium nitride, the grating layer is made of titanium nitride, and the filling layer is made of silicon nitride.

Furthermore, the grating layer is a double-layer nano-pillar structure, and comprises a first grating layer and a second grating layer, wherein the first grating layer is arranged above the second grating layer.

Further, the thickness of the dielectric layer is 0.25 μm, and the thickness of the filling layer is 0.08 μm; the thickness of the first grating layer is 95nm, the radius of the first grating layer is 97nm, the thickness of the second grating layer is 95nm, and the radius of the second grating layer is 178 nm.

The beneficial effect of this application is: the embodiment of the invention discloses a metamaterial wave absorber and a manufacturing method thereof, wherein the method comprises the following steps: setting a dielectric layer at the bottom end of the wave absorber as titanium nitride, determining the thickness of the dielectric layer as W, setting a filling layer of the wave absorber as silicon nitride, and determining the thickness of the filling layer as T; presetting a grating layer of titanium nitride between the dielectric layer and the filling layer, and presetting the grating layer into a nano-pillar structure; calculating the absorption efficiency of the wave absorber by using a genetic algorithm model, and respectively determining the ranges of the diameter and the height of the grating layer; and carrying out simulation optimization on the range of the diameter and the height of the grating layer, determining the final parameter values of the diameter and the height, and arranging the grating layer between the dielectric layer and the filling layer according to the result of the parameter values. The method realizes the optimization of the periodic nano structure by utilizing an algorithm, and further generates a broadband perfect absorption structure with excellent performance. Through the regulation and control of heredity and variation in the genetic algorithm, the problem of local optimization can be effectively solved, and an optimized structure which is better than the traditional structure design is found. The wave absorber manufactured by the method can maximize the light wave absorption efficiency, and the utilization efficiency of solar energy is obviously improved.

Drawings

FIG. 1 is a schematic structural diagram of a metamaterial wave absorber in one embodiment;

FIG. 2 is a schematic flow chart of a manufacturing method of the metamaterial wave absorber in one embodiment;

FIG. 3 is a schematic flow chart illustrating presetting of initial thickness and diameter of a grating layer in one embodiment;

FIG. 4 is a schematic flow chart illustrating the process of determining the initial thickness and diameter of the grating layer in one embodiment;

FIG. 5 is a schematic diagram of a process for optimizing grating layer structure parameters according to an embodiment;

FIG. 6 is a schematic structural parameter diagram of a metamaterial wave absorber in one embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The method for manufacturing the metamaterial wave absorber can be manufactured in the metamaterial wave absorber shown in figure 1.

In one embodiment, as shown in fig. 2, a method for manufacturing a metamaterial wave absorber is provided, which is described by taking the metamaterial wave absorber manufactured in fig. 1 as an example, and includes the following steps:

step 201, setting a dielectric layer at the bottom end of a wave absorber as titanium nitride, determining the thickness of the dielectric layer as W, setting a filling layer of the wave absorber as silicon nitride, and determining the thickness of the filling layer as T;

step 202, presetting a grating layer of titanium nitride between the dielectric layer and the filling layer, and presetting the grating layer into a nano-pillar structure;

step 203, calculating the absorption efficiency of the wave absorber by using a genetic algorithm model, and respectively determining the ranges of the diameter and the height of the grating layer;

and 204, performing simulation optimization on the range of the diameter and the height of the grating layer, determining the final parameter values of the diameter and the height, and arranging the grating layer between the dielectric layer and the filling layer according to the result of the parameter values.

Specifically, the initial structural materials and dimensions are determined according to design requirements; a two-layer structure was determined in which the thickness T of the upper layer silicon nitride was 0.25 μm and the thickness W of the lower layer titanium nitride was 0.08 μm. Let λ be incident wavelength, R (λ) be reflectance, T (λ) be transmission, and a (λ) be absorption of the wave-absorbing structure for the corresponding wavelength, which is expressed as a (λ) ═ 1-R (λ) -T (λ), the reflectance R (λ) and the transmittance T (λ) corresponding to the initial structure are obtained by FDTD simulation software, and the absorption is derived. The wave-absorbing structure principle of the embodiment of the invention is that the intrinsic absorption of the titanium nitride material and the double-layer grating structure are combined to generate the perfect absorption of Mie resonance on specific resonance wavelength, thereby realizing the broadband continuous absorption. In addition, the periodic nanostructure is optimized by utilizing a genetic algorithm, so that a broadband perfect absorption structure with excellent performance is generated. Through the regulation and control of heredity and variation in the genetic algorithm, the problem of local optimization can be effectively solved, and an optimized structure which is better than the traditional structure design is found.

In one embodiment, as shown in fig. 3, the process of presetting the grating layer includes:

step 301, determining a unit structure of the wave absorber according to the thickness W of the dielectric layer and the thickness T of the filling layer, and setting the unit structure to be a cuboid with the length, the width and the thickness of P, P and L respectively;

step 302, setting the grating layer of the nano-pillar structure as a first grating layer and a second grating layer respectively, wherein the first grating layer is arranged above the second grating layer;

step 303, presetting an initial range of the thickness d1 and an initial range of the diameter d2 of the first grating layer, and presetting an initial range of the thickness c1 and an initial range of the diameter c2 of the second grating layer according to the length, the width and the thickness of the unit structure.

Specifically, as shown in the structural parameter schematic diagram of the metamaterial wave absorber shown in fig. 6, in this embodiment, the design area P × L of the unit structure is provided, where the unit period side length P is 0.4 μm, and the unit structure size thickness L is T + W is 0.25+0.08 is 0.33 μm, and the design variables optimized by the genetic algorithm in the design are the structural parameters of the double-layer grating structure, specifically including the cylinder thicknesses c1 and d1 of each layer of cylindrical grating and the radii c2 and d2 of each layer of cylindrical grating. The value range of the design variable is as follows:

0≤c₁+d₁＝D≤0.25μm,

0≤d₂≤c₂≤0.4μm,

for the first grating layer and the second grating layer, due to the perfect symmetry of the cylinder, a symmetric boundary condition is also set in the simulation process, so that the calculation amount of simulation is reduced.

In one embodiment, as shown in fig. 4, for determining the initial thickness and diameter of the grating layer, the method comprises:

step 401, performing simulation on an initial structure formed by the set dielectric layer and the set filling layer to obtain reflectivity and transmissivity in different wavelength ranges;

step 402, determining the absorptivity of the corresponding wavelength in the initial structure according to the reflectivity and the transmissivity;

and 403, determining the initial range of the diameter and the height of the grating layer by using a genetic algorithm through the coupling effect generated by the absorption rate and the Mie resonance of the grating layer.

In one embodiment, as shown in fig. 5, the process of optimizing the parameters of the grating layer structure includes:

step 501, respectively taking the thickness and the diameter of the first grating layer and the thickness and the diameter of the first grating layer as design variables, and performing simulation optimization on the average absorption rate;

step 502, iteration is carried out by taking the average absorption rate as an optimization objective function, and simulation analysis is carried out on the electromagnetic equivalent models of the dielectric layer, the grating layer and the filling layer to obtain the reflectivity and the transmissivity of the corresponding structure;

step 503, deducing the absorptivity according to the reflectivity and the transmissivity, and outputting structural parameters corresponding to the optimal average absorptivity when the iteration times reach a design algebra;

and step 504, obtaining final parameter values of the diameter and the height from the structural parameters, and setting a grating layer according to the parameter values.

In addition, the genetic algorithm model is:

wherein d1 and d2 respectively represent the thickness and radius of the first grating layer; c1, c2 denote the thickness and radius, λ, respectively, of the second grating layer₁Represents the initial wavelength of the incident electromagnetic wave, and is set to 0.25 μm; lambda [ alpha ]_nThe cutoff wavelength of the incident electromagnetic wave was set to 2.5 μm, R (λ) was the reflectance, and T (λ) was the transmittance.

Specifically, before the optimization program is executed, relevant parameters of a genetic algorithm need to be set, 200 individuals are generated in each generation during calculation of the genetic algorithm, each individual is represented in a thirty-two bit binary coding form (wherein each eight bit represents one of the parameters c1, c2, d1 and d2), the number of generated parents is 20, the number of iterations of the whole algorithm is 20, and the termination condition is that individuals with the average absorption rate of more than 99% exist in filial generations or the number of iterations is set. Except that 20 parents will remain in the next population, the remaining children are generated by crossover and mutation processes. The crossing process is to randomly select the crossing point of the thirty-two bit binary codes of the two parents and replace and recombine the crossing point to form a new individual. The mutation probability is set to 0.1, and the mutation process is that the thirty-two binary random variation points of the new individual generated by the crossover process are mutated (i.e. the original code is 0 to 1, and the original code is 1 to 0), wherein the new individual generated by the mutation is the thirty-two binary code meeting the specification, i.e. c1, c2, d1 and d2 meet the above requirements. When the genetic algorithm is optimized, a group of design variable values are obtained according to codes and a script file is generated, each generated individual can be converted into a complete structure parameter (including c1, c2, d1 and d2) in simulation by the script file, a grating layer 2 is further introduced in the simulation, the script file is subjected to modeling simulation analysis in simulation software, namely, an electromagnetic equivalent model with a three-layer structure of a filling layer, a grating layer optimized by the algorithm and a dielectric layer corresponding to each individual is generated in the simulation, and 20 of the three-layer structure with the optimal absorption rate are reserved as a next generation parent. The above process is an iterative process, and when the program meets the termination condition or reaches the upper limit of the iteration times, the structural parameter with the maximum average absorption rate is output.

It should be understood that, although the steps in the above-described flowcharts are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least a portion of the steps in the above-described flowcharts may include multiple sub-steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the sub-steps or the stages is not necessarily sequential, but may be performed alternately or alternatingly with other steps or at least a portion of the sub-steps or stages of other steps.

In one embodiment, as shown in fig. 1, there is provided a metamaterial wave absorber, including: the grating absorber comprises a dielectric layer 103, a grating layer 102 and a filling layer 101, wherein the dielectric layer 103 is a bottom layer structure of the absorber, the grating layer 102 is arranged above the dielectric layer 103, the filling layer 101 is arranged on the periphery and the top end of the grating layer 102, and the grating layer 102 is wrapped in the filling layer.

The metamaterial wave absorber manufactured in this embodiment is a solar metamaterial wave absorber based on a genetic algorithm, and as shown in fig. 1, includes a filling layer 101, a grating layer 102, and a dielectric layer 103. The central axes of the double-layer nano-pillar structures are coincident. The whole algorithm optimizes the grating layer 102 to be wrapped between the medium layer 103 and the filling layer 101. Specifically, the grating layer 102 optimized by the algorithm is titanium nitride formed by etching with a lithography machine, and is formed by stacking two cylindrical structures, and the structural parameters of the double-layer grating layer 102 are optimized based on the genetic algorithm; the dielectric layer 103 is made of titanium nitride, the thickness T of the dielectric layer 103 is 0.08 μm, the filling layer 101 is made of silicon nitride, the thickness W of the filling layer is 0.25 μm, and the structural unit P is 0.4 μm.

Preferably, the grating layer 102 has a double-layer nano-pillar structure, the thickness of the whole grating layer is D, and the grating layer includes a first grating layer and a second grating layer, the first grating layer is disposed above the second grating layer, the grating layer 102 is made of titanium nitride, in an embodiment, as shown in fig. 6, the thickness of the first grating layer is 95nm, the radius of the first grating layer is 97nm, the thickness of the second grating layer is 95nm, and the radius of the second grating layer is 178 nm.

In addition, in the embodiment, the grating layer 102 combines the good absorption performance of the titanium nitride material for the visible light range, and the double-layer Mie resonance of titanium nitride and silicon nitride designed based on the genetic algorithm realizes the high-efficiency absorption in the near-infrared wavelength range. Mie resonance peaks at 1220nm and 2047nm were generated by the double layer Mie resonance. Thereby realizing the perfect absorption of the positions of the two Mie resonance peaks, and the absorption rates are respectively 94.9 percent and 99.9 percent. The metamaterial wave absorber provided by the embodiment has high average absorption rate absorption (92.6%) for electromagnetic waves in an effective solar spectrum range (0.25-2.5 microns). Compared with the structure provided by the traditional solar energy acquisition (absorption) structure, the structure provided by the method adopting the reverse design nano metamaterial structure is thinner and lighter, has smaller size and has higher absorption efficiency on the solar spectrum.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.