Speaker: Wei Gu
Affiliation: UCLA Ph.D. Candidate

Abstract:  There are two major challenges remaining in designing electrically small antennas (ESAs) with further size reduction. First, the input impedance of ESAs is difficult to be matched without increasing the volume and complexity of antenna geometry or adding an external matching circuit. Second, ESAs normally have extremely low efficiency.

In this talk, an innovating idea that ferromagnetic resonance (FMR) can be utilized to improve the radiation efficiency and input impedance matching for ESAs simultaneously is proposed. This idea is inspired by the recent discovery that using magnetic materials with extremely large µ” can achieve high efficiency in the design of ESAs. Considering the state of the art, most of the studies and realizations of permeable ESAs are still based only on bulky ferrites. Thin-film ferrites have been widely utilized in RF circulators and isolators, but not radiators. In this talk, it is proposed also for the first time to combine the merits of thin-film ferrites and FMR in the design of ESAs.

In Section II, the expression of the radiation efficiency is re-derived from modeling an ideal thin-film ferrite loaded radiator, based on assumed field distributions inside the material. The ideal radiator with thin-film yttrium-iron-garnet (YIG) is simulated in HFSS. The equivalent circuit model for this ideal radiator is structured by importing the RLC tank for spin motion. Radiating power calculated through the physics model, the full-wave simulation and the circuit model are compared to validate the accuracy of the physics model and the spin-motion circuit model in characterizing ferrite antenna parameters.

In Section III, an FMR enhanced ESA is designed in the form of a modified, stripe-pattern small single loop accommodating a YIG thin-film. The input impedance and radiation efficiency of this ESA with and without thin-film YIG loaded are simulated in HFSS and compared. The theory arisen from Section II will be verified by this practical design of an FMR enhanced ESA. Improvements in ESA’s performance due to FMR can be clearly observed from the full-wave simulation results. A novel, frequency-independent equivalent circuit model for small magnetic dipoles is developed by means of re-examining the E-field component of an ideal small loop. The new circuit model is able to predict the input impedance and radiation efficiency of magnetic ESAs to the first self-resonance frequency. A comprehensive, lump-element equivalent circuit model for FMR enhanced ESAs is formed by introducing the RLC tank for spin motion to the new circuit model for small loops. The two circuit models are both validated by comparing full-wave simulations with circuit calculations for input impedance and radiation efficiency respectively.

In Section IV, a prototype fabricated based on the design in Section III is displayed. The setup for conducting near-field measurements of the prototype is demonstrated. Full-wave simulations for near-field measurements are performed. The close match between HFSS simulations and near-field measurements shows the feasibility of the idea discussed in this talk and the correctness of the relationship between µ” and radiation enhancement. The reasons for the lack of far-field measurements are explained.

At last, a complete summary of all achievements presented in this talk is given. Future improvements and potential applications of FMR enhanced ESAs are described.

Biography: Wei Gu received his B.S. degree in Electrical and Electronic Engineering from Beijing Institute of Technology, Beijing, China, in 2013 and the M.S. degree in Electrical Engineering from the University of California at Los Angeles (UCLA), Los Angeles, USA, in 2016. He joined the Digital Microwave Laboratory at UCLA in 2014 to pursue the PhD degree in Electrical and Computer Engineering and conduct research on dynamic characterizations for magnetic materials and novel electrically small antenna design with magnetic materials, as a Graduate Student Researcher, under the supervision of Prof. Y. E. Wang. He has also served as a Teaching Assistance in ECE230A at UCLA for two years and counting. His current research interests include antenna theory and design, micro-magnetism for RF applications and circuit modeling of RF devices.

For more information, contact Prof. Yuanxun “Ethan” Wang (ywang@ee.ucla.edu)

Date(s) - Sep 05, 2019
3:00 pm - 5:00 pm

E-IV Faraday Room #67-124
420 Westwood Plaza - 6th Flr., Los Angeles CA 90095