Electromagnetic Response Mechanism And Epsilon-Negative Mechanism Of Ceramic-Based/Carbon-Based Percolate Composite

Epsilon-negative Material,as a branch of metacomposite,named the materials with negative permittivity and has potential applications in electromagnetic attenuation,capacitor,microwave antenna,and wireless power transmission.Meanwhile,when negative permittivity be used as a physical parameters,the tunability of its value,frequency band,and dispersion become a prerequisite for application.Guided by the percolation theory,using the preparation methods of percolation material systems with different functional bodies,the effective regulation of frequency band,size,and dispersion characteristics can be achieved.This subject prepared iron-barium titanate ceramic composite material,MWCNTs-barium titanate ceramic composite material,silver-barium titanate ceramic composite material by mechanical mixing-high temperature sintering and in-situ impregnation method;C/C self-permeable composite material from the cellulose precursor.Barium titanate ceramics have high dielectric constant at room temperature,low loss,ferroelectricity,piezoelectricity,and are easy to prepare.C/C composite materials from organic precursors are lightweight,environmentally friendly and easy to prepare.X-ray diffractometer(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),Raman spectrometer(Raman),and thermogravimetric analyzer(TG-DSC)were used to characterize the microstructure and microstructure of the composite.Agilent was used.The impedance analyzer characterizes the electrical and dielectric properties of the material,and uses ZsimpWin impedance analysis software for equivalent circuit analysis.The mechanism of negative dielectric generation is explored with the help of permeation models,free electron models,electric dipole models,and equivalent circuit models..The specific research contents are as follows:(1)MWCNTs-BaTiO3 ceramic matrix epsilon-negative material.Multi-walled carbon nanotubes with a length-to-diameter ratio of about 8000 were selected as the functional phase,acid-washing and ultrasonic dispersion were used to enhance their dispersion in the ceramic matrix,and traditional ceramic preparation methods were used to obtain permeable composite materials to achieve negative dielectric properties.The samples with carbon nanotube loading of 7wt%and 10wt%showed negative dielectric behavior from positive value to negative at 300MHz-1 GHz and 900Mhz-1GHz,and the negative dielectric behavior under the entire test frequency band under 12wt%and 14wt%load.The electrical percolation threshold is 9.96,and there is a transition between jump conductance and metalloid conductance near the permeation threshold.(2)Metal-barium titanate epsilon-negative material.Fe-BaTiO3 composite material and Ag-BaTiO3 composite material,using high-energy ball mill mechanical mixing and wet impregnation reduction to introduce conductive functional body into the barium titanate ceramic matrix,using the insulating matrix to "dilute" the free electron concentration The barium titanate composite material exhibits negative dielectric behavior in the 100-200MHz frequency band in samples with a content of more than 50wt%,and shows a positive dielectric at high frequencies;the silver-barium titanate composite material exhibits negative dielectric behavior under a 50wt%load.Through the controllable negative dielectric properties in different frequency bands,the lower limit of negative dielectric frequency was explored,and the effects of permeable composite materials with different functional bodies of the same insulating matrix on negative dielectric properties were compared.(3)Preparation of C/C self-permeation composite materials:the use of cellulose in the carbonization process of organic matter to amorphous carbon and graphitization process to build a self-permeation network to characterize the dielectric properties under radio frequency,carbonization temperature exceeds 500 At℃,stable and weak negative dielectric properties are achieved in the radio frequency band.At the same time,as the graphitization degree of the carbon material increases,the negative dielectric behavior also changes.The electron model and the electric dipole model were used to fit the negative dielectric spectrum to explore the effect of carbon materials with different electron concentrations on the negative dielectric performance,and the electrical performance was analyzed using an equivalent circuit model.