DAYTIME RADIATIVE DEVICE

Abstract

The invention relates to a daytime radiative cooling device comprising a reflective portion consisting of an alternating stack of layers A and layers B, said layers A consisting of at least one material A selected from among Nb.sub.2O.sub.5, TiO.sub.2 and Ta.sub.2O.sub.5 and said layers B consisting of at least one material B selected from among SiO.sub.2 and Al.sub.2O.sub.3. The invention also relates to a method for determining the reflective portion of a daytime radiative cooling device. Finally, the invention relates to a method for determining the emitting portion of a daytime radiative cooling device.

Claims

1. A daytime radiative cooling device comprising a reflective portion for the wavelengths from 260 nm to 2,500 nm consisting of an alternating superposition of layers A and of layers B, said layers A consisting of at least one material A selected from among Nb.sub.2O.sub.5, TiO.sub.2 and Ta.sub.2O.sub.5, said layers B consisting of at least one material B selected from among SiO.sub.2 and Al.sub.2O.sub.3.

2. The device according to claim 1, wherein each layer A and each layer B has a respective and independent thickness from 1 to 1,750 nm.

3. The device according to claim 1, wherein the reflective portion comprises at least 70 layers.

4. The device according to claim 1, further comprising a emitting portion of wavelengths from 7,500 to 13,300 nm comprising at least one layer C consisting of a material C selected from among Nb.sub.2O.sub.5, SiO.sub.2, SiC, TiO.sub.2, Ta.sub.2O.sub.5 and Al.sub.2O.sub.3, the material C being different from the material(s) A and the material(s) B of the reflective portion, the reflective portion being arranged on the emitting portion.

5. The device according to claim 4, wherein the emitting portion comprises at least one superposition of at least one layer C and of at least one layer B, the selected material B and material C being different.

6. The device according to claim 4, wherein all of the layers C have a total thickness of at least 1.5 ?m.

7. The device according to claim 1, wherein the structure of the reflective portion is determined by automated means implementing the following steps: a) providing a base reflection structure, said structure having a thickness and consisting of at least one layer A and/or of at least one layer B, said layer A consisting of a material A selected from among Nb.sub.2O.sub.5, TiO.sub.2 and Ta.sub.2O.sub.5 and said layer B consisting of a material B selected from among SiO.sub.2 and Al.sub.2O.sub.3, b) determining an improved reflection structure by means of the following sub-steps: i. selecting a wavelength whose reflection is to be improved, said wavelength being selected from a range of reflection wavelengths from 260 nm to 2,500 nm, ii. selecting a material to be inserted according to the following criteria: said material to be inserted is selected from among those of the material B if the base reflection structure consists of a layer A, said material to be inserted is selected from among those of the material A if the base reflection structure consists of a layer B, said material to be inserted is selected from among those of the material A or from those of the material B in all other cases, iii. determining the number of new layers to be inserted into the base reflection structure and their position within the base reflection structure, a new layer consisting of said material to be inserted and inserted according to the thickness of the base reflection structure, said number and said position being determined according to the selected wavelength and the selected material to be inserted, iv. determining the thickness of the or each new layer and obtaining an improved reflection structure in which the new layer(s) is/are incorporated, c) determining a reflection performance value ?.sub.R of the improved structure using the following formula ${?}_R=\frac{1}{\sqrt{N}}\sqrt{\underset{i=1}{\overset{N}{.Math.}}\frac{{\left(R_{\mathrm{SRA}}\left({?}_i\right)-R_{FM}\left({?}_i\right)\right)}^2}{{\mathrm{tol}}^2}}$ where ?.sub.i is a wavelength in the range of reflection wavelengths, N is the number of spectral wavelengths in the range of reflection wavelengths, R.sub.SRA(?.sub.i) is the coefficient of reflection obtained for the improved reflection structure at the wavelength ?.sub.i, R.sub.FM(?.sub.i) is the coefficient of reflection to be reached at the wavelength ?.sub.i, and tol has a value of 0.1, d) if ?.sub.R has a value lower than or equal to a reference value ?.sub.Rref, determining the improved reflection structure as corresponding to the reflective portion of the daytime radiative device; or if ?.sub.R has a value higher than the reference value ?.sub.Rref, repeating steps b) to d) while selecting the base reflection structure as being the improved reflection structure determined in step b).

8. The device according to claim 4, wherein the structure of the emitting portion is determined by automated means implementing the following steps: a) providing a base emissivity structure, said structure having a thickness and consisting of at least one layer C and/or of at least one layer B, said layer C consisting of a material C selected from among Nb.sub.2O.sub.5, SiO.sub.2, SiC, TiO.sub.2, Ta.sub.2O.sub.5 and Al.sub.2O.sub.3 and said layer B consisting of a material B selected from among SiO.sub.2 and Al.sub.2O.sub.3, the material C being different from the material B and different from the material(s) A of the reflective portion, b) determining an improved emissivity structure by means of the following sub-steps: i. selecting a wavelength whose reflection is to be improved, said wavelength being selected from a range of reflection wavelengths from 7,500 nm to 13,300 nm, ii. selecting a material to be inserted according to the following criteria: said material to be inserted is selected from among those of the material B if the base emissivity structure consists of a layer C, said material to be inserted is selected from among those of the material C if the base emissivity structure consists of a layer B, said material to be inserted is selected from among those of the material C or from those of the material B in all other cases, iii. determining the number of new layers to be inserted into the base emission structure and their position within the base emissivity structure, a new layer consisting of said material to be inserted and inserted according to the thickness of the base emissivity structure, said number and said position being determined according to the selected wavelength and the selected material to be inserted, iv. determining the thickness of the or each new layer, and obtaining an improved emissivity structure in which the new layer(s) is/are incorporated, c) determining an absorption performance value ?.sub.A of the improved structure using the following formula ${?}_A=\frac{1}{\sqrt{N}}\sqrt{\underset{i=1}{\overset{N}{.Math.}}\frac{{\left(A_{\mathrm{SEA}}\left({?}_i\right)-A_{FM}\left({?}_i\right)\right)}^2}{{\mathrm{tol}}^2}}$ where ?.sub.i is a wavelength in the emission wavelength range, N is the number of wavelengths in the emission wavelength range, A.sub.SRA(?.sub.i) is the coefficient of absorption obtained for the improved structure at the spectral wavelength ?.sub.i, A.sub.FM(?.sub.i) is the coefficient of absorption to be reached at the spectral wavelength ?.sub.i, and tol has a value of 0.1, d) if ?.sub.A has a value lower than or equal to a reference value ?.sub.Aref, determining the improved emissivity structure as corresponding to the emitting portion of the daytime radiative device; or if ?.sub.A has a value higher than the reference value (?.sub.ref, repeating steps b) to d) while selecting the base emissivity structure as being the improved emissivity structure determined in step b).

9. A method for determining the structure of the reflective portion of a daytime radiative cooling device according to claim 1, wherein automated means implement the following steps: a) providing a base reflection structure, said structure having a thickness and consisting of at least one layer A and/or of at least one layer B, said layer A consisting of a material A selected from among Nb.sub.2O.sub.5, TiO.sub.2 and Ta.sub.2O.sub.5 and said layer B consisting of a material B selected from among SiO.sub.2 and Al.sub.2O.sub.3, b) determining an improved reflection structure by means of the following sub-steps: i. selecting a wavelength whose reflection is to be improved, said wavelength being selected from a range of reflection wavelengths from 260 nm to 2,500 nm, ii. selecting a material to be inserted according to the following criteria: said material to be inserted is selected from among those of the material B if the base reflection structure consists of a layer A, said material to be inserted is selected from among those of the material A if the base reflection structure consists of a layer B, said material to be inserted is selected from among those of the material A or from those of the material B in all other cases, iii. determining the number of new layers to be inserted into the base reflection structure and their position within the base reflection structure, a new layer consisting of said material to be inserted and inserted according to the thickness of the base reflection structure, said number and said position being determined according to the selected wavelength and the selected material to be inserted, iv. determining the thickness of the or each new layer, and obtaining an improved reflection structure in which the new layer(s) is/are incorporated, c) determining a reflection performance value ?.sub.E of the improved structure using the following formula ${?}_R=\frac{1}{\sqrt{N}}\sqrt{\underset{i=1}{\overset{N}{.Math.}}\frac{{\left(R_{\mathrm{SRA}}\left({?}_i\right)-R_{FM}\left({?}_i\right)\right)}^2}{{\mathrm{tol}}^2}}$ where ?.sub.i is a wavelength in the range of reflection wavelengths, N is the number of spectral wavelengths in the range of reflection wavelengths, R.sub.SRA(?.sub.i) is the coefficient of reflection obtained for the improved reflection structure at the spectral wavelength ?.sub.i, R.sub.FM(?.sub.i) is the coefficient of reflection to be reached at the wavelength ?.sub.i, and tol has a value of 0.1, d) if ?.sub.R has a value lower than or equal to a reference value ?.sub.Rref, determining the improved reflection structure as corresponding to the reflective portion of the daytime radiative device; or if ?.sub.R has a value higher than the reference value ?.sub.Rref, repeating steps b) to d) while selecting the base reflection structure as being the improved reflection structure determined in step b).

10. A method for determining the emitting portion of a daytime radiative device according to claim 4, wherein automated means implementing the following steps: a) providing a base emissivity structure, said structure having a thickness and consisting of at least one layer C and/or of at least one layer B, said layer C consisting of a material C selected from among Nb.sub.2O.sub.5, SiO.sub.2, SiC, TiO.sub.2, Ta.sub.2O.sub.5 and Al.sub.2O.sub.3 and said layer B consisting of a material B selected from among SiO.sub.2 and Al.sub.2O.sub.3, the material C being different from the material B, b) determining an improved emissivity structure by means of the following sub-steps: i. selecting a wavelength whose reflection is to be improved, said wavelength being selected from a range of reflection wavelengths from 7,500 nm to 13,300 nm, ii. selecting a material to be inserted according to the following criteria: said material to be inserted is selected from among those of the material B if the base emissivity structure consists of a layer C, said material to be inserted is selected from among those of the material C if the base emissivity structure consists of a layer B, said material to be inserted is selected from among those of the material C or from those of the material B in all other cases, iii. determining the number of new layers to be inserted into the base emission structure and their position within the base emissivity structure, a new layer consisting of said material to be inserted and inserted according to the thickness of the base emissivity structure, said number and said position being determined according to the selected wavelength and the selected material to be inserted, iv. determining the thickness of the or each new layer and obtaining an improved emissivity structure in which the new layer(s) is/are incorporated, c) determining an absorption performance value ?.sub.A of the improved structure using the following formula: ${?}_A=\frac{1}{\sqrt{N}}\sqrt{\underset{i=1}{\overset{N}{.Math.}}\frac{{\left(A_{\mathrm{SEA}}\left({?}_i\right)-A_{FM}\left({?}_i\right)\right)}^2}{{\mathrm{tol}}^2}}$ where ?.sub.i is a wavelength in the emission wavelength range, N is the number of wavelengths in the emission wavelength range, A.sub.SRA(?.sub.i) is the coefficient of absorption obtained for the improved structure at the spectral wavelength ?.sub.i, A.sub.FM(?.sub.i) is the coefficient of absorption to be reached at the spectral wavelength ?.sub.i, and tol has a value of 0.1, d) if ?.sub.A has a value lower than or equal to a reference value ?.sub.Aref, determining the improved emissivity structure as corresponding to the emitting portion of the daytime radiative device; or if ?.sub.A has a value higher than the reference value ?.sub.Aref, repeating steps b) to d) while selecting the base emissivity structure as being the improved emissivity structure determined in step b).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0281] FIG. 1 is a flowchart showing the steps of the method for determining the structure of a reflective portion or of an emitting portion of a daytime radiative device according to the invention.

[0282] FIG. 2 is a flowchart showing the steps for determining the performance values ?.sub.R and ?.sub.A in the context of the method for determining the structure of a reflective portion or of an emitting portion of one daytime radiative device according to the invention.

[0283] FIG. 3 is a flowchart showing the steps of determining the selection of a wavelength in the context of the method for determining the structure of a reflective portion or of an emitting portion of a daytime radiative device according to the invention.

[0284] FIG. 4 is a flowchart showing the steps of determining the optimum positions for inserting the new layer(s) in the context of the method for determining the structure of a reflective portion or of an emitting portion of a device daytime radiative according to the invention.

[0285] FIG. 5 is a flowchart showing the steps of executing a genetic algorithm in the context of the method for determining the structure of a reflective portion or of an emitting portion of a daytime radiative device according to the invention.

[0286] FIG. 6 is a flowchart showing the steps of executing a simplex algorithm in the context of the method for determining the structure of a reflective portion or of an emitting portion of a daytime radiative device according to the invention.

[0287] FIG. 7 is a graph showing the reflection spectrum of the wavelengths 260 nm to 2,500 nm by a daytime radiative cooling device according to the invention. The radiance of the solar spectrum AM1.5 is also shown. The x-axis corresponds to the wavelengths. The Y-axis to the left corresponds to the coefficient of reflection (1 corresponds to 100% reflection). The Y-axis to the right corresponds to the radiance of the solar spectrum AM1.5 in W.Math.m.sup.?2.Math.Nm.sup.?1.

[0288] FIG. 8 is a graph showing the absorption spectrum of the wavelengths 7,500 to 13,500 nm by a daytime radiative cooling device according to the invention. The atmospheric transmittance is also shown. The x-axis corresponds to the wavelengths. The Y-axis to the left corresponds to the absorption (1 corresponds to 100% absorption). The Y-axis to the right corresponds to the atmospheric transmittance (transmission coefficient in intensity).

[0289] FIG. 9 is a graph showing the reflection and absorption spectra of the wavelengths 1 to 14,000 nm by a daytime radiative cooling device according to the invention. The x-axis corresponds to the wavelengths. The Y-axis to the left corresponds to the coefficient of reflection. The Y-axis to the right corresponds to the absorption.

[0290] FIG. 10 is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 7,500 to 13,300 nm (x-axis) for SiO.sub.2.

[0291] FIG. 11 is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 7,500 to 13,300 nm (x-axis) for SiC.

[0292] FIG. 12a is a graph showing the refractive index (y-axis to the left) and the extinction coefficient (y-axis to the right) as a function of the wavelengths of the range 250 nm to 2,500 nm (x-axis) for Nb.sub.2O.sub.5.

[0293] FIG. 12b is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 7,500 to 13,300 nm (x-axis) for Nb.sub.2O.sub.5.

[0294] FIG. 13a is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 250 nm to 2,500 nm (x-axis) for Al.sub.2O.sub.3.

[0295] FIG. 13b is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 7,500 to 13,300 nm (x-axis) for Al.sub.2O.sub.3.

[0296] FIG. 14a is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 250 nm to 2,500 nm (x-axis) for TiO.sub.2.

[0297] FIG. 14b is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 7,500 to 13,300 nm (x-axis) for TiO.sub.2.

[0298] FIG. 15a is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 250 nm to 2,500 nm (x-axis) for Ta.sub.205.

[0299] FIG. 15b is a graph showing the refractive index n (y-axis to the left) and the extinction coefficient k (y-axis to the right) as a function of the wavelengths of the range 7,500 to 13,300 nm (x-axis) for Ta.sub.205.

[0300] FIG. 16 is a graph showing the total performance R.sub.AM1.5 in percentage for the reflection of the wavelengths from 260 nm to 2,500 nm as a function of the number of layers of a cooling radiative device according to the invention consisting of a reflective portion (alternation of Nb.sub.2O.sub.5 and SiO.sub.2 layers) and an emitting portion. In the used device, the number of layers of the reflective portion was variable and the emitting portion consisted of one single layer of SiC with a thickness of 4.995 ?m. One could see that starting from 70 layers of the reflective portion, a total performance of at least 90% is obtained. Each cooling radiative device for which the total performance is lower than 90% is represented by a point, and each device for which the total performance is higher than 90% is represented by a star.

[0301] FIG. 17 is a graph showing the balance temperature in Celsius (? C.) as a function of the number of layers of the number of layers of a cooling radiative device according to the invention consisting of a reflective portion (alternation of Nb.sub.2O.sub.5 and SiO.sub.2 layers) and an emitting portion. In the used device, the number of layers of the reflective portion was variable and the emitting portion consisted of one single layer of SiC with a thickness of 4.995 ?m. The balance temperature represents the difference between the equilibrium temperature of the device and the external temperature. In this case, the considered external temperature was 300K. One could see that starting from 70 layers of the reflective portion, a balance temperature of 0 or less is obtained, and therefore a refrigeration effect.

[0302] FIG. 18 is a graph showing two reflection spectra of the wavelengths from 260 nm to 2,500 nm: a target reflection spectrum (black line curve), called figure of merit, and a reflection spectrum (clear grey line curve) obtained by experimental measurements using a Universal Reflectance Accessy (URA) module of a Lambda 1050 spectrophotometer (Perkin Elmer?) on a reflective portion of a daytime device according to the invention of 72 layers. The X-axis corresponds to the wavelengths from 0 to 3,000 nm. The Y-axis corresponds to the reflection percentage.

[0303] FIG. 19 shows three histograms (a, b and c) representing the theoretical thickness (black bar) and the obtained thickness (white bar) for each layer of a reflective portion of a daytime radiative device according to the invention consisting of 72 layers (histogram (a): layers 1 to 23; histogram (b): layers 24 to 47; histogram (c): layers 48 to 72). On each histogram, the Y-axis represents the thickness of the layers (in nm) and the X-axis represents the number of the layer. The layer bearing the number 1 is the lowest layer of the reflective portion, namely the first deposited layer, and the layer bearing the number 72 is the uppermost layer, namely the last deposited layer.

EXAMPLES

Example 1: Determination of the Reflective Portion and of the Emitting Portion of a Cooling Radiative Device

[0304] The Inventors have developed a method allowing determining the reflective and emitting portions of a cooling radiative device. This common method is illustrated in FIGS. 1 to 7. The input parameters of the method are modified according to the portion, reflective or emitting, whose structure is determined.

[0305] The first step 101 illustrated in FIG. 1 corresponds to the initialisation of the parameters specific to each portion whose structure is determined (materials A/B/C of the base structure and thickness(s)). For the reflective portion, the base structure corresponds to a SiO.sub.2 layer with a thickness of 500 nm. For the emitting portion, the base structure corresponds to a SiO.sub.2 layer with a thickness of 500 nm.

[0306] The second step 102 is a main loop with a pass condition test in step 118. In the context of the reflective portion, this consists in having reflection performances ?.sub.R lower than ?.sub.Rref=1. For the emitting portion, this consists in having a reflection performance ?.sub.A lower than ?.sub.Aref=5.

[0307] The values ?.sub.R and ?.sub.A are established using a method described in FIG. 2. Step 201 corresponds to the input of the parameters of the tested structure: thickness and refractive index of the material of each layer forming the tested structure. The refractive index of air and of a Si substrate being also considered. Step 202 corresponds to a test loop of all of the wavelengths of the considered range: from 260 nm to 2,500 nm for the reflective portion and 7,500 to 13,300 for the emitting portion. Step 203 corresponds to the allocation of the number of transfer matrices necessary to describe the considered structure (a 2?2 matrix for each thin layer). Step 204 corresponds to the multiplication of the transfer matrices to obtain the resulting matrix of the substrate assembly, tested structure and air. Step 205 corresponds to the calculation of the observable reflection R, transmission T and absorption A quantities based on the resulting matrix. Step 206 corresponds to the calculation of the values ?.sub.R and ?.sub.A according to the equations mentioned hereinabove in the description. For these calculations, the figure of merit shows a spectral reflection quantity R of 1 for each wavelength from 260 nm to 2,500 nm, and an absorption spectral quantity A of 1 for each wavelength from 7,500 nm to 13,000 nm. Step 207 corresponds to the recording of the values R, T and A for each structure and of the values ?.sub.R and ?.sub.A.

[0308] Step 103 corresponds to the calculation of the reflection R, transmission T and absorption A optical quantities of the tested structure. These quantities are obtained by executing steps 201 to 205 described before.

[0309] Step 104 corresponds to the selection of the length used in step 106 during the Needle insertion method. This step is detailed in FIG. 3. In FIG. 3, step 301 corresponds to the recovery of all of the spectral data of the tested structure (R, T and A) and those of a figure of merit. The figure of merit has a reflection spectral quantity R of 1 for each wavelength from 260 nm to 2,500 nm, and an absorption spectral quantity A of 1 for each wavelength from 7,500 nm to 13000 nm. Step 302 corresponds to a test loop of all of the wavelengths of the considered range: from 260 nm to 2,500 nm for the reflective portion and 7,500 to 13,300 for the emitting portion. For each wavelength, steps 303 and 304, and optionally 305, are carried out. Step 303 corresponds to the calculation of the difference between the spectral data and the figure of merit at the given wavelength. Step 304 corresponds to the comparison of this value with the maximum difference value found before. By default, the maximum difference value is 0. Step 305 is executed if the comparison gives a difference greater than the maximum difference. This value then becomes the new maximum difference for the next iterations. When all of the wavelengths have been tested, step 306 is executed and corresponds to the selection of the wavelength for which the maximum difference has been preserved.

[0310] Step 105 corresponds to the selection of the material that will form the new layers inserted into the base structure. For the reflective portion, this material corresponds to that having a refractive index value furthest from that of the host material of the base structure. Since the host material is SiO.sub.2, the selected material is Nb.sub.2O.sub.5. For the emitting portion, SiC has been selected.

[0311] Step 106 corresponds to the search for the optimum positions in the thickness of the base structure where the new layers are inserted. This step is detailed in FIG. 4.

Step 401 corresponds to the calculation of the spatial derivative of the spectral quantity R as a function of the thickness of the base structure while considering the refractive index of the material of the new layers and the selected wavelength. Step 402 corresponds to the determination of the number of new layers to be inserted into the base reflection structure as corresponding to the number of times the derivative is cancelled by passing from a negative extremum to a positive extremum. Step 403 corresponds to the determination of the position of the new layer(s) to be inserted into the base reflection structure as corresponding to each of the values of z for which the derivative is cancelled by passing from a negative extremum to a positive extremum. Step 404 corresponds to the recording of the values of the determined thicknesses and to the redistribution of the thicknesses as a function of the position where the new layers will be inserted.

[0312] Step 107 is a conditional loop for passage to step 110. In the context of the reflective portion, this consists in having reflection performances ?.sub.R lower than ?.sub.Rref (?.sub.Rref is 1). For the emitting portion, this consists in having the reflection performances ?.sub.A lower than ?.sub.Aref (?.sub.Aref is 5).

[0313] Step 108 corresponds to the application of a genetic algorithm to minimise the value ?.sub.R Or ?.sub.A of the considered structure, while considering only the new layers. The detail of this step is given in FIG. 5. Step 501 corresponds to the initialisation of the initial population of parent individuals each corresponding to a generation of random thicknesses for the or each new layer. Each thickness is comprised between 1 and 1,750 nm. In step 502, the value ?.sub.R Or ?.sub.A of the parent individuals is calculated using the method described in FIG. 2. Step 503 is a sorting of the parent individuals according to their value ?.sub.R Or ?.sub.A. Step 504 is a conditional step for passage to step 109. The first condition for passage to step 109 is whether the value of the parent individual having the lowest value ?.sub.R Or ?.sub.A is lower than the value ?.sub.Rref Or ?.sub.Aref respectively. The second condition for passage to step 109 is whether 150,000 iterations of steps 505 to 507 have been carried out. Step 505 corresponds to the stochastic roulette selection of the parent individuals. During this step, a scaling algorithm is used, which is a scaling technique imposed by the roulette selection mode. This consists of a truncated sigma scaling with the type of the coefficients scal=1, scalvarp=0.5, scalvarp1=1, scalvarp2=2. Step 506 corresponds to the crossing of these individuals according to the preceding selection in order to obtain child individuals. These crossings are sbx crossings according to the probability of applying a crossing to a parent pc=0.6. Step 507 corresponds to the mutation of the child individuals by mutation and the obtainment of an offspring of child individuals. The mutation applied to each child is a non-uniform mutation controlled by the parameter b=1 (b=1 exploratory otherwise Local search b=25) and the probability of applying a mutation to an individual pm=0.005. At step 508, the value ?.sub.R Or ?.sub.A of the child individuals of the offspring is calculated using the method described in FIG. 2. Step 509 is a sorting of the child individuals of the offspring according to their value ?.sub.R Or ?.sub.A. Step 510 allows keeping the best child individuals of the previous generation if the best individual of the offspring has a value ?.sub.R Or ?.sub.A lower than the best individual of the previous generation.

[0314] Step 109 corresponds to the application of a simplex algorithm to minimise the value ?.sub.R Or ?.sub.A of the child individuals of the best offspring obtained in step 108. This step is described in detail in FIG. 6. Step 601 corresponds to the collection of the data of the child individuals of the best offspring. Step 602 corresponds to the sorting of the child individuals according to their value ?.sub.R Or ?.sub.A by the PIKSRT subroutine, based on the Document Numerical recipes in fortran 77.

[0315] Step 603 corresponds to the definition of the simplex vertices based on the data of the individuals. Step 604 is a conditional loop with a test of the value ?.sub.R Or ?.sub.A, according to the considered structure, or of 55,000 iterations of steps 605 to 610 to pass to step 611. Step 606 corresponds to the sorting of the heights of the vertices of the simplex. Step 607 corresponds to the calculation of the value ?.sub.R or ?.sub.A, according to the considered structure, for each simplex. Step 608 corresponds to the reflection from the highest point for each simplex, leading, depending on the obtained result, to step 609 of extrapolation of the simplex by a 2 factor or to step 610 of contraction of the simplex by a 0 factor, Step 611 corresponds to obtaining, following steps 609 or 610, an improvement in the simplex vertices. Step 612 corresponds to the recording of the individual thickness data retained for the rest of the process.

[0316] Step 110 is optional and corresponds to merging of contiguous layers of the same material.

[0317] Step 111 is optional and corresponds to the removal of the layers with an excessively fine thickness.

[0318] Step 112 is a conditional loop for passage to step 115. In the context of the reflective portion, this consists in having reflection performances ?.sub.R lower than ?.sub.Rref=1. For the emitting portion, this consists in having reflection performances ?.sub.A lower than ?.sub.Aref=5.

[0319] Steps 113 and 114 are based on steps 108 and 109. In these steps, the considered individuals correspond to the entire structures, including the new layers and the host layers.

[0320] Steps 115 and 116 correspond to steps 110 and 111 respectively.

[0321] Step 117 corresponds to step 103.

[0322] Step 118 corresponds to recording the data (layers, materials, thicknesses) relating to the structure of the reflective portion or of the structure of the emitting portion. As regards the emitting portion, the automated means have implemented in step 119 the compilation of the layers of material B and C, and the removal of the compiled layer B.

[0323] Step 120 is a step of stopping the automated means.

[0324] A daytime radiative cooling device determined by the aforementioned method had the following values ?.sub.R and ?.sub.A: ?.sub.R=0.275 and ?.sub.A=1.095. The different layers of this device are described in the following table:

TABLE-US-00004 TABLE 4 Number of Thickness the layer (in nm) Material 1 247.0 Nb.sub.2O.sub.5 2 267.0 SiO.sub.2 3 271.5 Nb.sub.2O.sub.5 4 30.8 SiO.sub.2 5 27.5 Nb.sub.2O.sub.5 6 57.1 SiO.sub.2 7 70.2 Nb.sub.2O.sub.5 8 22.0 SiO.sub.2 9 25.5 Nb.sub.2O.sub.5 10 251.2 SiO.sub.2 11 78.7 Nb.sub.2O.sub.5 12 118.3 SiO.sub.2 13 61.0 Nb.sub.2O.sub.5 14 325.6 SiO.sub.2 15 591.3 Nb.sub.2O.sub.5 16 117.1 SiO.sub.2 17 201.7 Nb.sub.2O.sub.5 18 301.3 SiO.sub.2 19 53.3 Nb.sub.2O.sub.5 20 4.6 SiO.sub.2 21 274.3 Nb.sub.2O.sub.5 22 70.1 SiO.sub.2 23 3.2 Nb.sub.2O.sub.5 24 131.1 SiO.sub.2 25 94.9 Nb.sub.2O.sub.5 26 139.7 SiO.sub.2 27 125.6 Nb.sub.2O.sub.5 28 166.4 SiO.sub.2 29 55.2 Nb.sub.2O.sub.5 30 64.6 SiO.sub.2 31 3.8 Nb.sub.2O.sub.5 32 84.5 SiO.sub.2 33 76.3 Nb.sub.2O.sub.5 34 20.9 SiO.sub.2 35 8.6 Nb.sub.2O.sub.5 36 96.1 SiO.sub.2 37 91.6 Nb.sub.2O.sub.5 38 35.7 SiO.sub.2 39 31.7 Nb.sub.2O.sub.5 40 24.6 SiO.sub.2 41 22.3 Nb.sub.2O.sub.5 42 2.7 SiO.sub.2 43 32.2 Nb.sub.2O.sub.5 44 13.5 SiO.sub.2 45 25.8 Nb.sub.2O.sub.5 46 215.4 SiO.sub.2 47 99.3 Nb.sub.2O.sub.5 48 36.4 SiO.sub.2 49 65.8 Nb.sub.2O.sub.5 50 65.2 SiO.sub.2 51 42.4 Nb.sub.2O.sub.5 52 135.3 SiO.sub.2 53 1.3 Nb.sub.2O.sub.5 54 204.5 SiO.sub.2 55 6.6 Nb.sub.2O.sub.5 56 5.1 SiO.sub.2 57 22.6 Nb.sub.2O.sub.5 58 2.8 SiO.sub.2 59 1.8 Nb.sub.2O.sub.5 60 72.6 SiO.sub.2 61 195.5 Nb.sub.2O.sub.5 62 290.1 SiO.sub.2 63 166.3 Nb.sub.2O.sub.5 64 7.0 SiO.sub.2 65 60.6 Nb.sub.2O.sub.5 66 140.8 SiO.sub.2 67 17.6 Nb.sub.2O.sub.5 68 36.8 SiO.sub.2 69 2.2 Nb.sub.2O.sub.5 70 6.1 SiO.sub.2 71 25.2 Nb.sub.2O.sub.5 72 135.3 SiO.sub.2 73 149.4 Nb.sub.2O.sub.5 74 133.4 SiO.sub.2 75 115.6 Nb.sub.2O.sub.5 76 239.8 SiO.sub.2 77 74.0 Nb.sub.2O.sub.5 78 1.2 SiO.sub.2 79 115.6 Nb.sub.2O.sub.5 80 213.3 SiO.sub.2 81 81.9 Nb.sub.2O.sub.5 82 28.2 SiO.sub.2 83 112.8 Nb.sub.2O.sub.5 84 341.4 SiO.sub.2 85 19.3 Nb.sub.2O.sub.5 86 1.6 SiO.sub.2 87 259.9 Nb.sub.2O.sub.5 88 270.3 SiO.sub.2 89 29.3 Nb.sub.2O.sub.5 90 4.2 SiO.sub.2 91 39.8 Nb.sub.2O.sub.5 92 14.1 SiO.sub.2 93 139.1 Nb.sub.2O.sub.5 94 57.3 SiO.sub.2 95 4.2 Nb.sub.2O.sub.5 96 9.4 SiO.sub.2 97 13.7 Nb.sub.2O.sub.5 98 143.3 SiO.sub.2 99 23.8 Nb.sub.2O.sub.5 100 8.7 SiO.sub.2 101 113.8 Nb.sub.2O.sub.5 102 107.3 SiO.sub.2 103 150.5 Nb.sub.2O.sub.5 104 19.5 SiO.sub.2 105 11.2 Nb.sub.2O.sub.5 106 76.3 SiO.sub.2 107 106.8 Nb.sub.2O.sub.5 108 258.5 SiO.sub.2 109 133.2 Nb.sub.2O.sub.5 110 119.3 SiO.sub.2 111 1.3 Nb.sub.2O.sub.5 112 6.3 SiO.sub.2 113 8.8 Nb.sub.2O.sub.5 114 12.9 SiO.sub.2 115 7.7 Nb.sub.2O.sub.5 116 50.3 SiO.sub.2 117 89.4 Nb.sub.2O.sub.5 118 222.3 SiO.sub.2 119 106.0 Nb.sub.2O.sub.5 120 52.7 SiO.sub.2 121 47.3 Nb.sub.2O.sub.5 122 172.2 SiO.sub.2 123 38.3 Nb.sub.2O.sub.5 124 26.9 SiO.sub.2 125 2.8 Nb.sub.2O.sub.5 126 3.1 SiO.sub.2 127 139.8 Nb.sub.2O.sub.5 128 232.8 SiO.sub.2 129 48.5 Nb.sub.2O.sub.5 130 19.5 SiO.sub.2 131 94.8 Nb.sub.2O.sub.5 132 98.2 SiO.sub.2 133 24.1 Nb.sub.2O.sub.5 134 131.8 SiO.sub.2 135 101.5 Nb.sub.2O.sub.5 136 168.8 SiO.sub.2 137 88.5 Nb.sub.2O.sub.5 138 43.7 SiO.sub.2 139 42.6 Nb.sub.2O.sub.5 140 76.4 SiO.sub.2 141 33.0 Nb.sub.2O.sub.5 142 76.5 SiO.sub.2 143 64.0 Nb.sub.2O.sub.5 144 5.7 SiO.sub.2 145 25.0 Nb.sub.2O.sub.5 146 115.2 SiO.sub.2 147 74.6 Nb.sub.2O.sub.5 148 34.3 SiO.sub.2 149 129.5 Nb.sub.2O.sub.5 150 33.1 SiO.sub.2 151 41.0 Nb.sub.2O.sub.5 152 24.1 SiO.sub.2 153 80.8 Nb.sub.2O.sub.5 154 59.1 SiO.sub.2 155 80.6 Nb.sub.2O.sub.5 156 332.1 SiO.sub.2 157 22.2 Nb.sub.2O.sub.5 158 54.9 SiO.sub.2 159 166.0 Nb.sub.2O.sub.5 160 245.9 SiO.sub.2 161 168.5 Nb.sub.2O.sub.5 162 182.7 SiO.sub.2 163 44.9 Nb.sub.2O.sub.5 164 13.6 SiO.sub.2 165 5.5 Nb.sub.2O.sub.5 166 114.5 SiO.sub.2 167 48.0 Nb.sub.2O.sub.5 168 1.8 SiO.sub.2 169 178.0 Nb.sub.2O.sub.5 170 12.3 SiO.sub.2 171 40.0 Nb.sub.2O.sub.5 172 151.2 SiO.sub.2 173 149.9 Nb.sub.2O.sub.5 174 23.5 SiO.sub.2 175 6.7 Nb.sub.2O.sub.5 176 258.3 SiO.sub.2 177 51.8 Nb.sub.2O.sub.5 178 102.8 SiO.sub.2 179 14.1 Nb.sub.2O.sub.5 180 3.8 SiO.sub.2 181 70.3 Nb.sub.2O.sub.5 182 109.1 SiO.sub.2 183 16.2 Nb.sub.2O.sub.5 184 5.3 SiO.sub.2 185 5,220.3 SiC

[0325] Another daytime radiative cooling device determined by the aforementioned method with the following value ?.sub.Rref=1 and ?.sub.Aref=5 had the following values ?.sub.R and ?.sub.A: ?.sub.R=0.265 and ?.sub.A=2.814. The different layers of this device are described in the following table:

TABLE-US-00005 TABLE 5 Number of Thickness the layer (in nm) Material 1 201.3 Nb.sub.2O.sub.5 2 317.8 SiO.sub.2 3 219.3 Nb.sub.2O.sub.5 4 32.7 SiO.sub.2 5 25.2 Nb.sub.2O.sub.5 6 65.0 SiO.sub.2 7 77.5 Nb.sub.2O.sub.5 8 20.2 SiO.sub.2 9 24.0 Nb.sub.2O.sub.5 10 246.7 SiO.sub.2 11 92.4 Nb.sub.2O.sub.5 12 100.6 SiO.sub.2 13 72.5 Nb.sub.2O.sub.5 14 263.1 SiO.sub.2 15 565.8 Nb.sub.2O.sub.5 16 130.0 SiO.sub.2 17 227.3 Nb.sub.2O.sub.5 18 242.4 SiO.sub.2 19 51.6 Nb.sub.2O.sub.5 20 5.3 SiO.sub.2 21 238.5 Nb.sub.2O.sub.5 22 60.1 SiO.sub.2 23 3.0 Nb.sub.2O.sub.5 24 130.1 SiO.sub.2 25 78.0 Nb.sub.2O.sub.5 26 142.3 SiO.sub.2 27 127.9 Nb.sub.2O.sub.5 28 164.8 SiO.sub.2 29 44.7 Nb.sub.2O.sub.5 30 64.6 SiO.sub.2 31 4.0 Nb.sub.2O.sub.5 32 81.3 SiO.sub.2 33 82.2 Nb.sub.2O.sub.5 34 20.5 SiO.sub.2 35 7.0 Nb.sub.2O.sub.5 36 98.8 SiO.sub.2 37 74.6 Nb.sub.2O.sub.5 38 38.1 SiO.sub.2 39 25.8 Nb.sub.2O.sub.5 40 28.7 SiO.sub.2 41 18.9 Nb.sub.2O.sub.5 42 2.4 SiO.sub.2 43 33.6 Nb.sub.2O.sub.5 44 13.5 SiO.sub.2 45 21.2 Nb.sub.2O.sub.5 46 248.7 SiO.sub.2 47 100.8 Nb.sub.2O.sub.5 48 40.7 SiO.sub.2 49 60.4 Nb.sub.2O.sub.5 50 55.1 SiO.sub.2 51 50.9 Nb.sub.2O.sub.5 52 113.3 SiO.sub.2 53 1.5 Nb.sub.2O.sub.5 54 196.5 SiO.sub.2 55 7.5 Nb.sub.2O.sub.5 56 4.2 SiO.sub.2 57 19.2 Nb.sub.2O.sub.5 58 3.2 SiO.sub.2 59 1.7 Nb.sub.2O.sub.5 60 59.4 SiO.sub.2 61 224.4 Nb.sub.2O.sub.5 62 306.3 SiO.sub.2 63 195.9 Nb.sub.2O.sub.5 64 6.0 SiO.sub.2 65 65.0 Nb.sub.2O.sub.5 66 160.5 SiO.sub.2 67 14.9 Nb.sub.2O.sub.5 68 32.4 SiO.sub.2 69 1.8 Nb.sub.2O.sub.5 70 5.8 SiO.sub.2 71 20.7 Nb.sub.2O.sub.5 72 120.9 SiO.sub.2 73 159.4 Nb.sub.2O.sub.5 74 132.8 SiO.sub.2 75 119.2 Nb.sub.2O.sub.5 76 212.3 SiO.sub.2 77 60.5 Nb.sub.2O.sub.5 78 1.3 SiO.sub.2 79 103.9 Nb.sub.2O.sub.5 80 186.9 SiO.sub.2 81 68.1 Nb.sub.2O.sub.5 82 25.5 SiO.sub.2 83 134.8 Nb.sub.2O.sub.5 84 295.7 SiO.sub.2 85 15.6 Nb.sub.2O.sub.5 86 1.9 SiO.sub.2 87 253.5 Nb.sub.2O.sub.5 88 296.9 SiO.sub.2 89 34.4 Nb.sub.2O.sub.5 90 4.6 SiO.sub.2 91 34.8 Nb.sub.2O.sub.5 92 12.8 SiO.sub.2 93 150.6 Nb.sub.2O.sub.5 94 46.5 SiO.sub.2 95 4.5 Nb.sub.2O.sub.5 96 7.7 SiO.sub.2 97 13.3 Nb.sub.2O.sub.5 98 166.3 SiO.sub.2 99 19.9 Nb.sub.2O.sub.5 100 10.3 SiO.sub.2 101 91.1 Nb.sub.2O.sub.5 102 118.3 SiO.sub.2 103 125.6 Nb.sub.2O.sub.5 104 22.2 SiO.sub.2 105 10.9 Nb.sub.2O.sub.5 106 66.9 SiO.sub.2 107 121.9 Nb.sub.2O.sub.5 108 276.1 SiO.sub.2 109 127.3 Nb.sub.2O.sub.5 110 122.6 SiO.sub.2 111 1.6 Nb.sub.2O.sub.5 112 5.6 SiO.sub.2 113 10.5 Nb.sub.2O.sub.5 114 12.0 SiO.sub.2 115 9.1 Nb.sub.2O.sub.5 116 40.6 SiO.sub.2 117 76.0 Nb.sub.2O.sub.5 118 250.5 SiO.sub.2 119 102.7 Nb.sub.2O.sub.5 120 55.3 SiO.sub.2 121 38.9 Nb.sub.2O.sub.5 122 146.6 SiO.sub.2 123 36.6 Nb.sub.2O.sub.5 124 22.5 SiO.sub.2 125 2.3 Nb.sub.2O.sub.5 126 2.8 SiO.sub.2 127 119.7 Nb.sub.2O.sub.5 128 255.3 SiO.sub.2 129 56.6 Nb.sub.2O.sub.5 130 22.0 SiO.sub.2 131 103.3 Nb.sub.2O.sub.5 132 112.9 SiO.sub.2 133 27.2 Nb.sub.2O.sub.5 134 107.4 SiO.sub.2 135 86.3 Nb.sub.2O.sub.5 136 174.6 SiO.sub.2 137 85.5 Nb.sub.2O.sub.5 138 44.4 SiO.sub.2 139 39.0 Nb.sub.2O.sub.5 140 62.0 SiO.sub.2 141 33.6 Nb.sub.2O.sub.5 142 74.9 SiO.sub.2 143 68.5 Nb.sub.2O.sub.5 144 6.6 SiO.sub.2 145 29.3 Nb.sub.2O.sub.5 146 113.9 SiO.sub.2 147 80.9 Nb.sub.2O.sub.5 148 40.8 SiO.sub.2 149 106.8 Nb.sub.2O.sub.5 150 39.2 SiO.sub.2 151 35.8 Nb.sub.2O.sub.5 152 26.0 SiO.sub.2 153 69.8 Nb.sub.2O.sub.5 154 63.1 SiO.sub.2 155 92.9 Nb.sub.2O.sub.5 156 268.2 SiO.sub.2 157 18.8 Nb.sub.2O.sub.5 158 48.8 SiO.sub.2 159 173.5 Nb.sub.2O.sub.5 160 233.4 SiO.sub.2 161 139.1 Nb.sub.2O.sub.5 162 192.4 SiO.sub.2 163 38.4 Nb.sub.2O.sub.5 164 15.0 SiO.sub.2 165 4.5 Nb.sub.2O.sub.5 166 116.3 SiO.sub.2 167 40.0 Nb.sub.2O.sub.5 168 2.1 SiO.sub.2 169 142.4 Nb.sub.2O.sub.5 170 13.1 SiO.sub.2 171 36.2 Nb.sub.2O.sub.5 172 180.4 SiO.sub.2 173 132.2 Nb.sub.2O.sub.5 174 19.8 SiO.sub.2 175 7.4 Nb.sub.2O.sub.5 176 207.1 SiO.sub.2 177 61.4 Nb.sub.2O.sub.5 178 82.7 SiO.sub.2 179 11.5 Nb.sub.2O.sub.5 180 3.6 SiO.sub.2 181 81.8 Nb.sub.2O.sub.5 182 90.6 SiO.sub.2 183 16.9 Nb.sub.2O.sub.5 184 6.0 SiO.sub.2 185 4,638.6 SiC

Example 2: Refrigeration Performances

[0326] This example discloses the total theoretical reflection and emissivity performances and the associated spectra of the first daytime radiative cooling device determined in Example 1. The reflection spectrum of the wavelengths from 260 nm to 2,500 nm by the daytime radiative device is shown in FIG. 7. The total performance for the reflection of these wavelengths is 97.25% and is obtained using the following formula

[00027]$\begin{array}{cc}{R}_{\mathrm{AM}1,5}=100.Math.\frac{{?}_{{?}_{\min }}^{{?}_{\max }}R\left(?\right)L_{\mathrm{AM}1,5}\left(?\right)d?}{{?}_{{?}_{\min }}^{{?}_{\max }}{L}_{\mathrm{AM}1,5}\left(?\right)d?}& \left[\mathrm{Math}38\right]\end{array}$

[0327] where [0328] ?.sub.max is 2,500 nm [0329] ?.sub.min is 260 nm [0330] R(?) is the coefficient of reflection of the daytime radiative device obtained for the wavelength ? [0331] L.sub.AM1.5(?)d? is the radiance of the Sun as a function of the wavelength ?.

[0332] The emission spectrum of the wavelengths from 7,500 nm to 13,300 nm by the daytime radiative device is shown in FIG. 8. The total performance for the emissivity of these wavelengths is 89.05% and is obtained using the following formula

[00028]$\begin{array}{cc}{?}_{\mathrm{AM}1,5}=100.Math.\frac{{?}_{{?}_{\min }}^{{?}_{\max }}A\left(?\right)T_{\mathrm{atm}}\left(?\right)d?}{{?}_{{?}_{\min }}^{{?}_{\max }}{T}_{\mathrm{atm}}\left(?\right)d?}& \left[\mathrm{Math}39\right]\end{array}$ [0333] where [0334] ?.sub.max is 13,300 nm [0335] ?.sub.min is 7,500 nm [0336] A(?) is the absorptivity value for the wavelength ? considering that with the Kirchhoff approximation at thermal equilibrium: ? (absorptivity)=? (emissivity) [0337] T.sub.atm(?)d? is the atmospheric transmittance as a function of the wavelength A.

[0338] The reflection and emission spectrum of the wavelengths from 260 nm to 15,000 nm is given in FIG. 9.

[0339] It should be interestingly noticed that the daytime radiative device of the invention is very effective in terms of reflection and emissivity of the wavelengths in the considered ranges of the spectrum and barely effective, and possibly very barely effective (close to 0), for the rest of the spectrum. This configuration ensures a good heat exchange with the space.

[0340] Based on the emissivity and reflection values of the daytime radiative device, the Inventors have determined the equilibrium temperature of said device under the ideal conditions of absence of conduction and convection and under a solar flux of 1,000.3 W.Math.m.sup.?2. For an ambient temperature of 300K (26.85? C.), the equilibrium temperature of the theoretical daytime radiative device is established at 270.99K (?2.16? C.), i.e. a deviation close to 30? C. At the same ambient temperature, the absolute value of the theoretical overall net power of said device is 109.7 W.Math.m.sup.?2. This value is exceptional and corresponds at most to twice the theoretical overall net power (40 W.Math.m.sup.2) reached with the device described in the document A. P. Raman et al, Nature, 2014, 515, 540-544 mentioned in the introduction.

Example 3: Protocol for Manufacturing a Cooling Radiative Device

[0341] The deposition of the different layers of the cooling radiative devices disclosed in Example 1 is carried out by magnetron cathode sputtering with optical tracking on an ELETTRORAVA? sputtering machine (ER-SM800) with an Intellemetrics? (IL570) reflectometry system installed inside the deposition chamber. First of all, a numerical simulation of the manufacturing process of the structure to be deposited is carried out using the Film maker software from Intellemetrics?. This allows determining the spectrophotometric tracking configuration of the samples during growth. This configuration allows establishing the wavelength at which each layer of a material will be controlled in reflection, to predict the turning points turning point during growth of the film and to predict the conditions for stopping each material.

[0342] Afterwards, the preparation of the substrate is carried out chemically, in order to suppress any defects, at the start of the growth of the thin film. A chemical treatment based on hydrofluoric acid with a concentration of 5% is performed for 30 seconds. The substrate is rinsed in 3 baths of ultrapure water for 1 minute each. The substrate is then dried under a stream of pure nitrogen to remove any trace of water.

[0343] A Si substrate is introduced into the deposition chamber where the indicated vacuum is 2 mTorr (1 mTorr=0.133322 pascal). The sample (substrate on its substrate holder) will be placed at a temperature whose measurement range will be set between 25? C. and 200? C. This step lasts for one hour at the pressure of 20 mtorr under an argon stream of 10 sccm (standard cubic centimetre per minute), the sample rotating at 20 revolutions per minute. The level of light intensity reflected by the substrate over the previously determined range of wavelengths is controlled.

[0344] It has been proceeded with the initiation of the ignition of the plasma. First of all, a working power is injected in several steps on the cathode with an argon pressure of 20 mTorr. This pressure is decreased to 15 m Torr and then to 10 m Torr to finish by a pressure of 5 mtorr always under a stream of 10 sccm of argon. Finally, the stabilisation of the plasma is reached for a deposition of 3 to 5 mTorr with an argon-based gas mixture for the first film. The gas mixture is modified according to the deposited material: [0345] SiC: Argon 100%, [0346] SiO.sub.2: Argon/O.sub.2 with a 75%/25% ratio, and [0347] Nb.sub.2O.sub.5: Argon/O.sub.2 with a 75%/25% ratio.

[0348] The first deposited portion is the emitting portion following the established alternation of the materials B and C in the example 1. The optical tracking of the film is carried out in real-time by a measurement of reflection at the wavelengths established before. The deposition time is adjusted during deposition by the thickness growth control system by in situ reflectometry. When the optical stop condition is reached for a material B of the emitter, the deposition thereof is stopped. The following material C is started up to the stop condition thereof. This leads to obtaining the final emitting structure.

[0349] Afterwards, the reflective portion is deposited over the emitting portion by following the established alternation of the materials A and B in Example 1. During this step, it is proceeded with a measurement of reflection at the wavelengths previously established by the Intellemetrics system. When the optical stop condition is reached for a material of the reflector, the deposition of the latter is stopped. The next material is started up to the stop condition thereof, and so on until depositing all of the layers and obtaining the reflective structure.

Example 4: Making and Performance of a Cooling Radiative Device

[0350] In this example, a daytime radiative device has been made consisting of a reflective portion featuring excellent reflection performances in the spectral range 250-1,500 nm and consisting of an alternation of 72 layers of SiO.sub.2 and Nb.sub.2O.sub.5. The figure of merit of the target reflection performances is shown in FIG. 18. The theoretical thicknesses (shown in FIG. 19) have been obtained by the method for determining the structure of a reflective portion of the invention based on the figure of merit.

[0351] The deposition of the different layers has been carried out with the same tooling as that described in Example 3. The steps for obtaining the substrate and stabilising the plasma are the same as those described in Example 3. The Si substrate had a thickness of 275 ?m.

[0352] A confocal configuration of 3 inch diameter targets made of Nb.sub.2O.sub.5 and SiO.sub.2 has been used. The constituent materials of the targets (Nb.sub.2O.sub.5 and SiO.sub.2) have been sprayed by means of an Oxygen/Argon plasma of 7/37 sccm respectively for the SiO.sub.2 layers and of 12/40 sccm respectively for the Nb.sub.205 layers. The distance between the targets and the deposition substrate was 20 cm. A power of 100 W and 325 W has been applied respectively for the SiO.sub.2 and Nb.sub.2O.sub.5 targets, which corresponds to a power density on the SiO.sub.2 target of 2.2 W/cm.sup.2 and on the Nb.sub.2O.sub.5 target of 7.7 W/cm.sup.2. The deposition rates of the two materials are comprised between 0.01 and 0.1 nm/s. Finally, the deposition pressure was 2 mtorr and the temperature of the substrate was 200? C.

[0353] The spectral reflectance of the obtained device has been measured by a Lambda 1050 spectrophotometer (Perkin Elmer?) equipped with a Universal Reflectance (URA) module with an angle of incidence of 8? and with transverse electric polarisation (TE). The obtained result is shown in FIG. 18 which shows the reflectance measured by the URA module. This figure shows that the obtained device has a spectral response that is very close to the targeted theoretical reflectance.

[0354] FIG. 19 shows for each layer on the one hand the target thickness and on the other hand the experimental thickness determined by the kinetics of deposition of the layers taking into account the deposition rate and the deposition time for each layer. The obtained differences between the target thicknesses and the experimental thicknesses were low with an average difference of 1.78?0.85%.