Research Topics

During 2018-2020, we modified the traditional three-section rectangular waveguide system for characterizing the anisotropic ferrimagnetism of magnetite at microwave regime. A rigorous retrieval procedure was proposed, which utilizes both the advantages of transmission/reflection method (broadband) and resonant method (sensitive) to accurately determine the permittivity, saturation magnetization, and magnetic linewidth of ferrite materials. The theoretical model and experimental results were respectively published in “Progress in Electromagnetics Research C” (Prog. Electromagn. Res. C 90, 195-208 (2019)) and “The Journal of Magnetism and Magnetic Materials” (J. Magn. Magn. Mater. 505, 166712 (2020)).  

Since the aforementioned dielectric characterization schemes all suffer from the difficulties in sample preparation and loading for measurement. Those troublesome processes lead to low-efficiency and high-uncertainty characterization and might even raise the risk of sample damage. In 2020-2021, we developed a fast and non-destructive dielectric characterization system at 31-35 GHz. By the aid of the highly-confined nature of the fringing field of the TE01 mode at a cylindrical waveguide open end, we can directly probe the sheeted samples and retrieve their local complex permittivity. The retrieved data of near ten kinds of polymers (such as Teflon, PP, PE, FR4, etc.) have been reported in “Polymers” (Polymers 12, 1891 (2020).). Unimicron Technology Corporation is highly interested in this technique for the quality control in their PCB production.

In addition to the waveguide systems whose allowed bandwidth is usually limited by the operating mode’s cutoff, since 2020, we tried to develop several coaxial-type systems for broadband characterization from 0.1-20 GHz and 0.1-40 GHz. Very different from the commercial coaxial probe, a full-coaxial scheme and a coaxial-to-circular cutoff junction were designed, which can greatly reduce the required amount of sample. Broadband dielectric data of liquids can facilitate the investigation their underlying molecular relaxation processes and the interaction/correlation between molecules. In 2021, we used this system to characterize the broadband dielectric spectrums of common alcohols, acids, and their binary mixtures. By fitting with proper relaxation models, we clearly observed different types of the heterogeneous dipole-dipole interaction between ethanol and four acid molecules. In 2022, these findings have been published in a high-impact journal: “Journal of Molecular Liquids” (J. Mol. Liq. 353, 118755 (2022)).