Toroidal topology appears in many types of metamaterials, which makes it impossible to describe the electrodynamic properties of such objects correctly without toroidal dipole. Dynamic toroidal dipole is excited by a closed loop of magnetic dipoles, which are caused by electric currents flowing along the meridians of the torus (poloidal currents). One of the most promising cases of toroidal excitation is toroidal excitation in planar metamaterials, which we discuss in this work. We show the peculiar properties of such metamaterials, like extremely high Q-factor and strong electric and magnetic field localization and tunable toroidal metamaterials. Especially we discuss the role of losses in toroidal metamaterials: radiating and non-radiating nature and show that the playing with them can be crucial for effects of high Q-factor applications. We demonstrate experimental characteristics that are in good agreement with modeling results. To prove the toroidal nature of our metamaterial we show the results of multipole expansion that considers toroidal dipole response.
Nikita Volsky, Vitaly Chuguevsky, Kristina Schegoleva, and Alexey A. Basharin, "Planar toroidal metamaterials: the role of losses, tunability and applications (Conference Presentation)," Proc. SPIE 10227, Metamaterials XI, 102270K (Presented at SPIE Optics + Optoelectronics: April 27, 2017; Published: 15 August 2017); https://doi.org/10.1117/12.2265856.5463341866001.
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