| The surface plasmon is a resonance form of free electrons in metal particles.It has many novel optical and electromagnetic properties,such as the enhancement of local electromagnetic fields,the selective absorption and scattering of light,the subwaveleng constraint of electromagnetic waves.Surface plasmon include two types,one of them is propagating surface plasmonic and the other is localized surface plasmon.The former appears on interface of metal film and dielectric medium,it can transmit along the film for a long distance.This form is called propagating surface plasmon.The latter is on metal particles,due to the shock of free electrons are localized by the size,so called the localized surface plasmon.In recent years,due to the development of processing technology and simulation analysis methods,the mechanism of the surface plasmon has also gradually deepened.The plasmonics has also developed into a new hot subject,and have broad application prospects in the information,energy,chemistry,biology and other fields.In this paper,the CST of commercial software based on finite difference time domain method is used to simulate and vector network analyzer is used to verified by.The resonance characteristics of spiral unit,the coupling characteristics of spiral particles,the coupling characteristics of spiral pentamer,and the design,simulation,experimental study and principle analysis of the three-band broadband bandpass filter are studied.The main content of this paper is divided into three parts:(1)The surface plasmon resonance forms and coupling laws of helical structural units and helical dimer are studied.Through analysis of the simulation results,these phenomenons are explained with hybridization theory.The main conclusions are as follows: There are two modes in the helical dimer,which contain forward coupling and reverse coupling.The reverse coupling reduces the radiation loss,resulting in the decrease of the resonance linewidth.The reverse coupling mode can effectively improve the sensor quality factor.These conclusions can help us better understand the hybridization of plasmons and provide analytical method for the coupling in complex structures.In addition,the hybridization effect of spoof surface plasmon can significantly improve the sensor quality factor,which provides a new thought for structural design of high sensitive sensors based on metamaterials.(2)The resonance modes of spiral pentamer can be divided into two groups,which are the electric Fano resonance magnetic Fano resonance.The two groups ofresonances originate from the destructive coupling of the central particle and the peripheral tetramer.The existence of electromagnetic Fano resonances on the spiral pentamer structure are verified by simulation and experiment.As the particle spacing increases,the coupling between particles decreases.The intensity of the magnetic Fano resonance is sensitive to the variation of the incident angle of electromagnetic wave,while the electric Fano resonance is not affected.(3)A triple-band metamaterial broadband bandpass filter(BPF)which is independent to polarization and stable at wide-angle incidence is designed,fabricated and tested.Simulation results show that the designed BPF has three broadband passbands.The center frequencies are 7.22,10.10,14.46 GHz.3 dB relative bandwidthsare17.5%,20.2% and 17.4% The transmission efficiencies at center frequency are-0.85 dB,-0.69 dB and-1.73 dB,respectively.This BPF is insensitive to the electromagnetic wave polarization,because the structure is rotational symmetry.Additionally,three bands of the designed BPF can still keep stable performance,when incident angle reaches 40 °.By monitoring the surface current distributions at resonant frequencies,we analyze the physical mechanism of the triple-band filtering.The proposed triple-band metamaterial broadband BPF is hopeful to take part in multi-frequency imaging technology,information communications and other fields owing to its multi-band filtering,independent to polarization and stable at wide-angle incidence. |
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