| People demand for electronic equipment increasing year by year,caused the human more exposure to electromagnetic radiation pollution,at the same time,the electromagnetic interference among various components has become more serious,how to eliminate or reduce the electromagnetic pollution problem is the research focus of each country.At present,"thin,light,wide and strong" is the development trend of absorbing materials.Cork charcoal as a kind of natural carbon material,has the advantages of low cost,low density,environmental friendly,good sustainability and so on.Its special hexagonal microscopic honeycomb structure can help reflect and absorb microwave,which provides the possibility for the design of high quality absorbing materials.The main research contents of this paper are as follows:(1)The cork of cork oak with natural honeycomb structure was prepared by "onestep carbonization method".The wave absorption performance of cork was studied by using four-probe resistivity tester and vector network analyzer(VNA),and the influence of carbonization temperature on the wave absorption performance of cork was discussed.Then SEM,XRD and Raman spectroscopy were used to characterize the microstructure,crystal structure and graphitization degree of the sample,and the reason for its good absorbing performance was explored.The results show that the carbonized cork has good wave absorption performance.When the carbonization temperature is 800℃,the prepared cork charcoal meets the best impedance matching and dielectric loss.The maximum absorption intensity is-27.26dB at 8.92GHz,and the frequency band width is 1.79GHz,which shows the best wave absorption ability.This is because with the rise of carbonization temperature,the functional groups of cork tend to be simplified,graphitization degree gradually increased,the resistivity gradually decreased,the dielectric constant gradually increased,resulting in the improvement of cork absorption capacity.(2)In order to increase the absorption intensity of cork charcoal or increase the absorption band width,and improve the absorbing performance of cork charcoal,this topic from two ways to carry out research:One approach is simply to mix the sample with metal iron in equal proportion.It is found that the dielectric constant increases with the increase of metal addition amount after mixing.When the mixing ratio of the sample and metal iron is 1:1,the maximum absorption intensity is-27.15dB at 11.67GHz,and the frequency band width is 2.55GHz.Absorbed bandwidth increased by about 42.5%.The increase of frequency band means that cork charcoal/metal composite can cover a larger frequency range,providing conditions for covering multiple radiation sources with different frequencies.Another way is to prepare cork/ferrite composites by "two-step carbonization".Four-probe resistivity tester,VNA,EDX,XPS and XRD were used to investigate the wave absorption performance.It was found that after treatment,Fe3O4 successfully adhered to the pores and carbon walls of cork cells,forming cork/ferrite composites.The dielectric constant of the material changes obviously with the change of solution concentration,and the main loss mechanism is electrical loss.When the impregnation concentration of Fe(NO3)3 is 0.12mol/L,the composite material has the best wave absorption performance,the maximum absorption intensity is-30.74dB at 6.18GHz,and the frequency band width is 1.54GHz.Compared with pure cork carbon,the cork/ferrite composite has a higher absorption strength,an increase of about 12%,which means that the cork/ferrite composite has a better absorption effect.(3)CST software was used to simulate the radiation of cork-based absorbing thin plate under electromagnetic excitation,and the single-layer medium model was used to calculate the electromagnetic shielding SE value in MATLAB,indicating that corkbased absorbing material has good radiation protection effect.On this basis,this paper proposes the application form of cork charcoal based absorbing materials in the field of indoor radiation protection,to meet the requirements of different radiation sources in indoor environment absorbing waves.For outdoor broadcast tower,communication base station or indoor with large radiation source,the absorption screen and absorption wall decoration to block the space,for mobile phones,microwave ovens,PC and other small and medium-sized radiation sources,the cabinet,box,screen and other forms of absorption of electromagnetic radiation.Four types of absorbing products,such as wireless charging mobile phone absorbing box with controllable absorbing function,folding absorbing screen,combined absorbing wall decoration material and rechargeable absorbing cabinet with adjustable space,were explored and designed.Through the design of the appropriate form of absorbing products,can meet most indoor environment under the radiation demand,promote the cork related industry development,promote the cork in the field of indoor radiation application. |
