Design And Optimization Of Multi-slot Nanoantenna

Nanoantenna is a kind of antenna of nanometer magnitude.Nanoantenna is different from traditional microwave and RF antennas.The working waveband of the nanoantenna is optical waveband,and the theory of the nanoantenna is Surface Plasmon Polaritons(SPPs).We can adjust the SPPs by changing the size,structure,material and so on of the nanoantenna.The nanoantenna can work in a variety of fields.In recent years,since the amount of fossil fuels has increased and the environment has been seriously polluted,clean and renewable energy is particularly important.Traditional solar cells have some problems,such as low conversion efficiency and large influence of working environment.Researchers designed various SPPs-based nanoantennas for energy harvesting.Compared with traditional solar cells,nanoantennas have advantages of wide absorption waveband,high absorptivity and low environmental impact.In this paper,a multi-resonant U-shaped slot nanoantenna is designed by the traditional nanoantenna design method,and the genetic algorithm(GA)is used to design a double bowtie double ring shaped slot nanoantenna.Firstly,the multi-resonant U-shaped slot nanoantenna is designed based on the SPPs.We use the Finite-Difference Time-Domain(FDTD)method to compute the absorption characteristics of the nanoantenna array and the influence of the physical parameters.The nanoantenna consists of two elements nanoantenna with rectangular shape and with four u-shaped slots.The slots change the free electron distribution and surface current trend of silver nanoparticles.Therefore,the high absorptivity nanoantenna can be obtained by changing the size of four U-shaped slots to adjust the SPPs.The results show that the nanoantenna array has good absorption characteristics in the 400-1400 nm waveband,and the average absorptivity of the nanoantenna array is over 50%.In addition,due to the large number of adjustable parameters of the nanoantenna,the nanoantenna with different structures and sizes exhibit different characteristics,which can meet various environmental requirements.Secondly,the double bowtie double ring shaped slot nanoantenna is designed based on GA.The traditional design method of nanoantenna is based on empirical formula.When the nanoantenna has many adjustable parameters,the design process is very complicated,and it is difficult to realize multi-parameter synchronous control.The GA has advantages of self-adaptability,versatility,parallel computing,population searching,simple operation,and so on.It can easily realize multi-parameter synchronous control.It can also be used to calculate high-performance nanoantenna with high accuracy.Therefore,we use GA to optimize the structure of nanoantenna.GA is an adaptive random search algorithm that imitates the principle of ‘Survival of the fittest,the survival of the fittest' of natural world.It uses fitness function to control population evolution.The selection operation is used to screen the population.New populations are generated through crossover and mutation operations.The fitness of the population is higher and higher after the evolution of the population.Finally,the nanoantenna that meets the requirements is obtained.It is found that the double bowtie double ring shaped slot nanoantenna optimized by GA has better absorption characteristics.The average absorptivity of the array is over 77% in the 400-1800 nm waveband.In 400-1200 nm and 1460-1650 nm wavebands,the absorptivity is over 60%.The light absorbing capability of the nanoantenna is independent of the incident light polarization state in the 400-1800 nm waveband,and it can keep up an average absorptivity of 70% with the large incident angle varying between-60° and 60°.The two kinds of nanoantennas in this paper have the characteristics of wide absorption waveband and high absorptivity,and they can harvest the energy of visible light and IR.The solar absorbers with these nanoantennas can solve problems that are low conversion efficiency and low efficiency at night and rainy days of traditional solar cells.Moreover,the optimization algorithm can reduce the randomness and blindness of the nanoantennas design,and the precision of the high-performance nanoantennas design is improved.