Photonic-Radiative-Cooler

Data files and Matlab codes for analyzing a multilayer thin-film photonic radiative cooler. The repository contains codes for calculating the reflectance of a planar multilayer dielectric structure as a function of wavelength (for any arbitrary incident angles), plotting solar spectrm and atmospheric transmission, and evaluating the cooling power of a multilayer photonic structures. The refractive index data of several optical thin-film dielectric materials, solar spectrum data, atomospheric absorption data is also included in the repository. The source of the data files are cited in Ref. [1].

Reflectivity Calculation (reflectance_TE.m and reflectance_TM.m file)

These are Matlab functions to calculate the reflectance of a planar multilayer structure. The functions have the form:

R_TE = reflectance_TE(n0,nsubs,n_layers,d_layers,theta_in,lambda)

The arguments are listed below. The geometry of the layers is also show.

  n0 = refractive index of the input medium                 |--------------------------------|
  nsubs = refractive index of the substrate                 |                                |
  n_layers = refractive indices of the thin-film layers     |              Air               |  
  theta_in = incident angle (in radians)                    |                                |  
  lambda = wavelength                                       |--------------------------------| 
                                                            |            Layer 1             |
  R_TE = output = reflectivity                              |--------------------------------|
                                                            |            Layer 2             |
                                                            |--------------------------------|
                                                            |               .                |
                                                            |               .                |
                                                            |               .                |
                                                            |--------------------------------|
                                                            |            Layer N             |  
                                                            |--------------------------------|
                                                            |                                |
                                                            |           Substrate            |   
                                                            |                                |   
                                                            |--------------------------------|

Emissivity (or Reflectivity) Spectrum Calculations (spectrum_out.m file)

Theis are Matlab function calculates the emissivity (emissivity = 1 - reflectivity) or a multilayer structure as a function of wavelength for a given incidence angle. reflectance_TE.m and reflectance_TM.m functions are called within this function. It has the form:

yout = spectrum_out(M_mat,A_payload,theta_in,min_d,max_d)

The arguments are listed below.

M_mat = Matrix containing material reflectivity data
A_payload = Matrix containing layer materials and thickness data
theta_in = Incidence angle
min_d = minimum allowed thickness of a layer
max_d = maximum allowed thickness of a layer
yout = emissivity = 1 - reflectivity

The min_d and max_d values are required as the layer thickness values in the input matrix A_payload is normalized with respect to those values.

Linking to an Optimization Algoirthm (fitness.m file)

For a given multilayer structure, the fitness.m file calculates the squared error between the desired emissivity and the emissivity of the structure. The function arguments are:

M_mat = Matrix containing material reflectivity data
A_payload = Matrix containing layer materials and thickness data
flag_fig = boolean variable indicating whether the output should be plotted or not
yout = -(sum of squared error)

The desired emissivity is defined withing the fitness.m file. The structure emissivity is calculated by calling the reflectance_TE and reflectance_TM files. The errors for TE and TM excitations are summed in yout.

This function can be used as the cost function of an optimization algorithm.

Sample output

For an example structure, some of the output plots are shown below:

Reference

Please cite the following paper if you use this repository for your research.

1. Mohammad Asif Zaman, "Photonic radiative cooler optimization using Taguchi's method." International Journal of Thermal Sciences 144 (2019): 21-26. https://doi.org/10.1016/j.ijthermalsci.2019.05.019