Patent ID: 8712736

Claim:
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−R IR where R IR 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.