Size-dependent permittivity of alumina powder at microwave frequency

Tien-Fu Yang^1*, Hsien-Wen Chao¹, Tsun-Hsu Chang¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Tien-Fu Yang, email:yang168@gapp.nthu.edu.tw

Alumina has been one of the widely used ceramic materials due to its high permittivity, low dielectric loss, good thermal conductivity, and low cost. In developing emerging electronic devices, the size effect of materials plays an essential role, especially in the application of composite materials. This work uses a simulation-based effective medium model (the hybrid model) to study the size effect on the complex permittivity of alumina powder at a frequency of 2.45 GHz. Sampled alumina are packed in a Teflon container and placed on the top of the central rod within a resonant cavity to obtain the frequency responses by the enhanced-field method (EFM). The experimental frequency response, received by a network analyzer, is compared with the simulation by a full-wave simulator (high-frequency structure simulator (HFSS)). Contours are established by the simulation to map the measured resonant frequencies and quality factors to the complex permittivity of each sample. Four classical effective medium theories (EMTs) are applied to examine the proposed method. The Landau-Lifshitz-Looyenga (LLL) model best fits the measurement and agrees with the hybrid method. The complex permittivity of alumina powder is observed to decrease with the increase in size. A power relation is introduced to fit the obtained permittivity with sizes ranging from nanometers to micrometers, and the result is explained by the induced surface-charge effect.

Keywords: Dielectric Measurement, Size Effect, Hybrid Model