Studies On Dielectric Properties Evolvement Rule Of Porous Material At High Temperature For A Long Time

Nowadays, the rapid advancements of science and technological required faster speed and higher recession guidance, the performance of wave-transparent material using for making an antenna housing also need to increase significantly. Increasing the porosity of the materials can promote dielectric properties and performances transmission.However, as a result of the limitation of experimental conditions, It is hard to test microwave dielectric properties under the condition of high temperature. If we collect data only from experiment, the cost will be very high because of the expensive aircrafts, what’s more, we can’t get completed testing data due to the limit of the test condition. In view of the above problems, this paper concerned dielectric properties of porous silicon nitride ceramics after in-depth theoretical research. It also got the evolution trend of the dielectric properties under the condition of high temperature and high frequency, established the mathematical model which can fit with the limited experimental data well. The research contents are as follows:(1)Combined with the basic theory such as dielectric physics, the paper sufficiently analyzed and discussed polarization factor of silicon nitride to build a mathematical model for dielectric constant, dielectric loss, temperature coefficient of dielectric constant in high frequency and high temperature, then quantitatively analyzed the various variables impact on dielectric properties.(2)By analyzing two-phase composite models, this paper built a model for porous silicon nitride material, studied all kinds of factors that may impact dielectric performance, such as porosity,pore distribution,frequency and impurity ions. Furthermore, this paper quantitatively analyzed the extent of the impact, then focused on great influence effect to dielectric properties by Alkali metal and alkaline earth metal ions.(3)Considering working conditions, First of all, this paper combined with the reaction thermodynamics, analyzed possible oxidation reaction in the high temperature, fined temperature change point and influence factors. For the first time basing on the reaction dynamics, associated with a variety of parameters, proved the modeling’s correctness, reflected the relationship between the dielectric performance and the time(4)Studied on the impure ions of SiC, ZrO2, Al2O3 in porous silicon dioxide, doped different impurities with different mass percentages in porous ceramics respectively, then through comprehensive consideration chose best proportions with best dielectric properties under the condition of density meeting the requirement.