Design And Absorption Characteristics Of Composite Nanoantenna Based On Multiple Resonances

Nanoantenna extends the antenna theory to the nanometer scale.By studying the surface plasmon,the electromagnetic wave is coupled into the sub wavelength space to realize the near-field enhancement of electromagnetic field.Nano-antennas based on surface plasmon polaritons have excellent performance and wide application prospects in energy harvesting,optical imaging and sensors.Nano-antennas with single structure have problems such as narrow absorption band,so it is often difficult to meet the requirements of perfect absorption.To solve the problem,this paper mainly uses the multi-resonance characteristics of composite structure to design nanoantenna with perfect absorption.We analyze the surface plasmon resonances by changing the structure,size and material of the nanoantenna to realize broadband absorption.In this paper,the multi-slot cross bowtie nanoantenna and the MIM four-headed arrow nanoantenna based on composite structure are designed,and the absorption characteristics are analyzed by the finite-difference time-domain method.The specific work is as follows.Firstly,the excitation and resonance conditions of surface plasmon polaritons are studied.In order to solve the problem of narrow absorption band and low absorption efficiency in the current single structure,the multi-slot cross bowtie nanoantenna based on multiple resonances is designed.The structure is to etch rectangular slots on the top cross bowtie layer.Starting from the structure of multi-slot cross bowtie nanoantenna,the effects of physical parameters,incident angle and polarization angle on the absorption characteristics of the nanoantenna are studied by using the finite-difference time-domain method.By changing the distribution of free electrons on the surface of the nanoantenna,the distribution of the surface plasmon resonances can be adjusted to realize the perfect absorption in the wide band.The results show that the multi-slot cross bowtie nanoantenna has good absorption characteristics in the waveband of 400-1800 nm,and the average absorptivity is up to 90.27%,the relative absorption bandwidth is 127%.The nanoantenna is insensitive to the polarization angle,and can maintain an average absorptivity of 83% under large incident angle.Secondly,aiming at the limitation of materials,the metal-insulator-metal three-layer nanostructure was established on the basis of multi-resonance composite structure.While noble metal is used in the multi-slot cross bowtie nanoantenna,the four-headed arrow nanoantenna use titanium because it is abundant in earth's geology and has good heat resistance.The finite difference time domain method is used to analyze the absorption characteristics and the influence of physical parameters.In addition,the absorption mechanism of the four-headed arrow nanoantenna is analyzed by the distribution of electric and magnetic fields.The experimental results show that the four-headed arrow nanoantenna has good absorption characteristics in visible and near-infrared waveband,with an average absorptivity of 95.21%,a maximum absorptivity of 99.9% and a relative absorption bandwidth of 148% in the 300-2000 nm waveband.The nanoantenna is polarization independent and can maintain an average absorptivity of more than 90% at large incident angle.The two kinds of nanoantenna designed in this paper have perfect absorption characteristics in visible and near-infrared region,and can achieve high absorptivity in the wide band.This is of certain reference value for the design of nanoantenna with composite structure in the future,and has important research value for the application in the field of energy harvesting.