Design And Sensing Performance Of Narrow-band Metamaterial Absorber Based On Surface Plasmon Resonance

Surface Plasmons(SPs)are the collective oscillations of free electrons on metal surfaces under the excitation of external electromagnetic fields.It can manipulate light on the micro-nano scale.Metamaterials are new materials discovered when people are exploring nano-optical devices.Their material properties depend on their structure rather than the materials that compose them.Surface plasmon-based metamaterials have attracted extensive attention due to their unique optical properties and good steerability,which can be used to fabricate various optical devices,such as perfect absorbers,structural colors devices and filter etc.The combination of surface plasmons and metamaterials is a new focus for exploring the interaction between light and matter at the subwavelength scale.However,it still has some shortcomings that make it difficult to meet the manufacture of high-quality optical devices,such as narrow incident angle,low absorption rate,single frequency band,and low sensing sensitivity.This paper firstly introduces the excitation principle and types of SPs in detail,its application fields are also introduced.Next,we introduce the principles and applications of metamaterials.Then,the numerical simulation methods and software used in this study are introduced.Based on the above physical principles and simulation methods,we propose three narrow-band metamaterial perfect absorbers and explore their sensing properties.1.A dual-band metamaterial absorber(MMA)with wide-angle and high absorptivity is designed using a traditional metal-dielectric-metal structure.The top resonant element of the absorber is a periodic array structure consisting of double-ring resonators with different radii connected with four strips.After numerical simulation by the finite element method,it has two absorption peaks with absorption rates of 99.9%and 99.8%,and the corresponding line width of the two absorption peaks are 9.7 nm and 9.8 nm,respectively.The metamaterial absorber can maintain high absorptivity in a wide range of incident angles.The electric field distribution and the current distribution show that the perfect absorption of the two-band is a common result of the coupling between the elements and the coupling between the inner and outer rings.In addition,the hexapole plasmon mode can be observed at the outer ring at the second absorption peak.The dual-band narrow plasmon resonance has a potential application in optical sensing.It can be used to measure the concentration of aqueous glucose.The sensitivities of the two absorption peaks are 178 nm/RIU and 232 nm/RIU,respectively,and the corresponding quality factors in vacuum are 18.5 and 23.7,respectively.2.Two dual-band ultra-narrowband MMAs are designed with an all-metal structure.The double-groove structure is obtained by etching two grooves on a cuboid metal block.The spectrum obtained by finite element calculation shows that the structure has two absorption peaks,and the absorption rates are 99.9% and 68.3%,respectively.The full width at half maximum of the two peaks is only 0.72 nm and 2.93 nm,respectively.The electric field distribution shows that the double absorption originates from the coupling between the gap plasmon resonance and the SPP mode.The double disc structure is composed of a cuboid metal block and two-disc depressions with the same radius on its surface.The spectrum obtained by the finite element calculation shows that the structure has two narrow-band absorption peaks.After parameter optimization,their absorption rates are as high as 99.9% and 99.7%.nm.Through the analysis of the electric field distribution and the magnetic field distribution,the double absorption originates from the coupling of the LSP mode and the SPP mode.Narrow-band perfect absorption is very suitable for refractive index sensing.We calculated and simulated the spectra of these two structures in different concentrations of glucose solution,and found that they both have good sensing performance.The two peak sensitivities of the double-groove structure are 524 nm/RIU and 598 nm/RIU with quality factors of 728 and 204,respectively.The sensitivities of the two peaks in the double-disk structure are 529 nm/RIU and 607 nm/RIU,respectively,with quality factors of 787 and 403.