Method for designing sunlight-reflection and heat-radiation multilayer film

A design method, comprising:

• a step of dividing a solar wavelength range into a predetermined m of first to mth wavelength regions, wherein m is an integer of one or larger,
• a first step of applying a multilayer film designing method to the first wavelength region to design a first stack portion formed of a multilayer film, said multilayer film designing method comprising;
• (a) a step of setting at least two candidate materials for forming the multilayer film and a number of layers of the multilayer film;
• (b) a step of designing a combination of the candidate materials and a layer thickness by using a genetic algorithm including:
• (b-1) a step of setting at least
• a number of individuals (n),
• a selection method,
• a crossover method and a probability of crossover, and
• a probability of mutation;
• (b-2) an initialization step of producing a set number of individuals of a first generation each having a set number of layers;
• and
• (b-3) a loop step of repeating sub steps (i) to (iii) until a number of generations reaches a predetermined number of generations or until an individual satisfying a predetermined evaluation criterion is obtained:
• (i) an evaluation step of evaluating the thus produced n individuals with evaluation functions;
• (ii) a selection step of selecting individuals to be subjects to a next step from the n individuals based on the evaluation;
• and
• (iii) a next-generation producing step of producing n individuals of a next generation from the selected individuals in accordance with the set crossover method and probability of crossover and the set probability of mutation,
• the evaluation function including:
• evaluation function 1:
• αs=1−Rs
• wherein Rs represents a reflectance of solar energy in a wavelength range used for design, within a solar radiation wavelength range;
• evaluation function 2:
• ∈H
• wherein ∈H=1−RIR where RIR represents a reflectance of heat radiation energy in a wavelength range used for design, within a heat radiation wavelength range;
• and
• if m is 2 or larger, further performing a second step to an mth step by repeating kth step from k=2 to k=m, wherein k is an integer from two to m,
• the kth step being a step of designing a multilayer structure, in which a kth stack portion formed of a multilayer film is placed on a structure including the first stack portion to a (k−1)th stack portion stacked sequentially, by applying the design method to a wavelength region including the first to kth wavelength regions to design the kth stack portion to be placed on the (k−1)th stack portion, on the condition that a layer structure of the first to (k−1)th stack portions is not changed.