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Ferromagnetic Resonance Enhanced Electrically Small Antennas


An innovative idea that ferromagnetic resonance (FMR) can be utilized to improve the radiation efficiency and input impedance matching for electrically small antennas (ESAs) simultaneously is proposed. This idea is inspired by the recent discovery that using magnetic materials with extremely large imaginary permeability can still achieve high radiation efficiency in designs of ESAs. The equation of radiation efficiency for ESAs as a function of ferrites’ complex permeability is re-derived based on the field modeling and analysis of an ideal thin-film ferrite radiator to verify the discovery. Furthermore, taking FMR into consideration, a conclusion is made that the gilbert damping factor of the resonance determines radiation efficiency more essentially than of ferrites. The first practical design for the proposed FMR enhanced ESAs has been realized through a modified, small single loop antenna loaded with a thin-film yttrium-iron-garnet (YIG) core. A real physical prototype has been fabricated and evaluated through both full-wave simulations and experiments. The simulation results match to the experimental results, demonstrating the efficacy and significance of the idea. Novel frequency-independent, equivalent circuit models for small loops and FMR enhanced ESAs have been developed in this paper to guide the design of highly efficient ESAs in the future. The circuit models prove to be trustworthy in predicting input impedance and radiation efficiency by comparing with full-wave simulations and agreed.

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