The Design Of Temperature Responsive Metamaterials And Its Properties

Metamaterials represent a class of artificially designed periodic composite materials.Through the careful design of the microstructure,the unique physical properties can be obtained.The electromagnetic wave propagation characteristics can be greatly modulated,and it can be widely used in the plasmon induced transparency,photonic crystals,radiative cooling,multi-band perfect absorber and some functional-related devices.The unit cell of the metamaterials are composed of metal,dielectric,or the combination of metal and dielectric.However,once structures are manufactured,their properties are difficult to manipulate.Materials with response characteristics of temperature,magnetic field and electric field can endow metamaterials with dynamic response characteristics,which has been a hot research spot in recent years.To endow the device thermal tunable performance,temperature responsive materials such as graphene,vanadium dioxide,Dirac semimetals,indium antimonide can be selected to achieve dynamic control of device performance and meet the needs of different functional applications.In this paper,we have designed four responsive metamaterials based on the finite element method theory.The concrete research are as follows:1.In order to obtain a dynamically adjustable plasmon induced transparency phenomenon in a non-contact way,we theoretically and numerically investigate the thermal tunable PIT by taking into account of electrons and phonons interaction in graphene metamaterials.The novel structure consists of two hollow square graphene and a rectangular strip in right middle,each of them acting as a bright mode.To fully explore the physical origin of the transparency window,the Lorentz coupled oscillator theory is employed.Good agreement can be achieved with the numerical results,which further verifies our calculations.To alter the PIT effect,the influence on the transparency window with different temperature and polarization angle are elaborately examined.The bandwidth of the transparent window gets wider with the lower temperature and switchable transparent window appears with varied polarization angle.As a potential application in the slow light device,the group index and group delay are also calculated with the temperature from 60 K to 500 K.Our proposed thermal tunable PIT structure may open up a new avenue in the application of controllable optical filters,switchers and optical memories.2.The graphene based metal-insulator-metal(MIM)metamaterials is investigated to realize an active and adjustable multi-band perfect absorber,which is composed of an asymmetric double T-shaped cavity on the top layer.As the symmetry of T-shaped cavities is broken,the previous dual-band absorption will be converted to tri-band absorber.The corresponding electric field is provided at each resonant position to investigate the physical mechanism.More interestingly,these resonant peaks will split into multiband with further destruction of the central symmetry.In addition,non-contact dynamic control of perfect absorption is explored by tuning the Fermi energy and the polarization angle of the incoming wave.Finally,the sensitivity of our proposed design is examined with different concentrations of CS₂ dropped into the cavities.The results demonstrate that the refraction index per unit can reach up to 1673.33 nm/RIU.Therefore,this work delivers a new strategy to design tunable multi-band absorbers and has potential applications in highly tunable optical switchers,sensors and filters.3.In order to obtain the adjustable photonic crystals,we numerically investigate1D photonic crystals with alternating VO₂ and Si O₂ layers through transfer matrix method.The dispersion relation agrees well with the transmittance obtained by the finite element calculation.Tunable band gaps are achieved with the thermal stimuli of VO₂.Concretely,the bandwidth is getting narrower and red shift occurs with the higher temperature in VO₂(M)/Si O₂ photonic crystals structure.Based on the phase change characteristics of VO₂,we can flexibly adjust the original structure as VO₂(M)/VO₂(R)/Si O₂.Increasing the phase ratio of VO₂(M)to VO₂(R),the band gap width gradually becomes wider and blue shift occurs.The discrete layers of gradient composites on the dispersion of 1D photonic crystal is also investigated,which enhances the feasibility in practical operation.Thus,our proposed thermal modulation PCs structure pave a new way to realize thermal tunable optical filters and sensors.4.An efficient thermal emitter for selectively radiative cooling is realized with vanadium dioxide metamaterials.The novel structure consists of a patterned VO₂metamaterials on the multilayer substrate and a composite layer on it.To obtain the enhanced emissivity,the influence of top composite layer and external stimuli are comprehensively optimized.The emissivity can reach up to 95.2%in the metal phase of VO₂ with composite layer in the atmospheric window,which is due to strong localization of the electric filed in the cavity.The influence on the emissivity with different incident angles and geometric parameters are investigated elaborately.Finally,the cooling power is calculated with a high value of 710 W/m² at 383 K,which is significantly higher than that of previous works.Thus,our proposed tunable emitter with high performance will be beneficial to the dynamic radiative cooling system and may open up a potential application in the building cooling and intelligent windows.