Research On Perfect Absorber Based On Surface Plasmons

The metamaterial is a composite material consisting of periodic or non-periodic structures,and has novel properties not found in natural materials.It has the unique ability to manipulate electromagnetic waves and can effectively modulate the amplitude,phase and polarisation properties of light,and has attracted a great deal of attention from researchers in the fields of materials and optics.Much progress has been made in solar absorbers,sensors and hyperlenses.Through rational design and parameter tuning of metamaterials,devices have been designed to cover a wide range of wavelength bands.As a branch of metamaterial devices,metamaterial perfect absorbers have attracted a lot of attention.The small size of metamaterial perfect absorbers allows for complete absorption of light,and both narrowband and broadband absorbers offer superior performance compared to conventional absorbers.In this thesis,FDTD software is used to design a metamaterial perfect absorber based on surface equipartition exciters and to investigate its optical properties.The main studies are as follows:(1)A metamaterial narrow-band perfect absorber with a simple pie structure was designed to achieve three narrow-band absorption peaks with 99.5%,88.9% and 99.4%,respectively,the narrowest of which has a half-peak width of 12 nm.the physical mechanism of each absorption peak was analysed in conjunction with electric field and parametric scanning.The performance of the absorber as a refractive index sensor was analysed by changing the top layer material to investigate the effect of the material on the absorber.The S-parameters were also extracted and parameters such as the equivalent impedance of the metamaterial were calculated.The positions of the absorption peaks calculated according to the equivalent medium theory are consistent with the simulation results.By changing the structural parameters,the absorber can be changed into a doubleband perfect absorption.(2)A multi-narrow-band perfect absorber based on a tetragonal block array with a silver square array on the top layer was designed to achieve three absorption peaks,two of which achieved 99.4% and 99.8% absorption with half-peak widths of 8 nm and 12 nm,respectively.The physical mechanism behind the absorption peaks was obtained.The effect of the material on the absorption results was analysed by varying the material of the top structure.The sensing performance of the absorber was also investigated by varying the ambient refractive index.(3)A versatile perfect absorber that can achieve both narrow-band and broad-band absorption by adjusting the direction of the incident light is designed.Light incident from the upper and lower surfaces can give narrow-band perfect absorption and broad-band perfect absorption respectively.The narrow-band absorption has three absorption peaks,two of which can reach 99.3% and 99.9% with half-peak widths of 3 nm and 11 nm respectively,while the broadband absorption has an average absorption of 97.3% in the range of 600 nm to 2100 nm and an average absorption of 93.7% for TE and 93.3% for TM polarisation at an oblique incidence of 60°.The average absorption of TE and TM polarisation at an oblique incidence of 60° is 93.7% and 93.3% respectively.The physical mechanism behind the perfect absorption of the absorber is also analysed.