Study On Dielectric Properties Of Graphene Solution In Microwave Band

Graphene is a kind of two-dimensional carbon material mainly composed of carbon atoms after SP2 hybridization.It has a honeycomb structure,and its thickness is only the thickness of single atomic layer.Due to its unique structure,graphene exhibits many excellent characteristics,such as high light transmittance,high electron mobility,high thermal conductivity,large specific surface area and so on.Due to these unique properties,graphene shows great research value and bright application prospects in many fields,such as microelectronics,organic optoelectronics,energy storage,biomedicine and composites.As one of the important parameters of graphene photoelectric characteristics,dielectric constant has been studied by many scholars.However,at present,the dielectric constant of graphene is only studied for graphene film,graphene derivatives or graphene composites,not for graphene solution.Graphene solution can be used in the preparation of lithium-ion batteries and graphene composites Therefore,the theoretical calculation of graphene and the experimental study of the dielectric constant of graphene solution are carried out in this paper.Firstly,the theoretical analysis of single-layer graphene,water and graphene solution is carried out,and the effects of Kubo and Drude conductivity formulas on the calculation of graphene conductivity,dielectric constant and refractive index are applied.It is found that the conductivity and refractive index of graphene calculated by the two formulas are similar in the 1GHz-10~5GHz band,but the dielectric constants in the microwave band are different.The reason for this difference is that Drude formula ignores the inter band transition of graphene compared with Kubo formula.The dielectric constant of water is calculated according to Debye equation.The real part of the complex permittivity of water increases with the increase of frequency,and the imaginary part first increases and then decreases with the increase of frequency.The dielectric constant of graphene solution was calculated according to Maxwell-Garnett formula.With the increase of graphene volume fraction,the absolute values of the real part and imaginary part of the dielectric constant of graphene solution are increasing.Secondly,the graphene solution was experimentally studied,and the dielectric constants of graphene solutions with three concentrations（2mg/ml,1mg/ml and0.5mg/ml）were measured when they were placed in 0.5mm diameter capillary and0.9mm diameter capillary respectively.The dielectric constant of graphene solution with the same concentration increases with the increase of insertion depth.At the same depth of the resonator,the dielectric constant of graphene solution increases with the increase of concentration.The dielectric constants of the graphene solution measured are slightly different under the same temperature,the same humidity and the same frequency.The reasons for these differences are the error when adjusting the depth into the resonator,the different dispersion of the graphene solution itself,and the difference when converting the wavelength by using the wavelength frequency scale comparison table,each frequency corresponds to a certain range of wavelengths and is converted into frequency.The influence of capillary on the results is analyzed.The 0.5mm diameter capillary has a greater influence on the dielectric constant of graphene solution.The dielectric constant of water is measured.The real part of the measured dielectric constant increases with the increase of the depth into the resonator.