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Proceedings Paper

Bulk magnetic terahertz metamaterial based on TiO2 microresonators (Conference Presentation)
Author(s): Christelle Kadlec; Michal Sindler; Filip Dominec; Hynek Němec; Catherine Elissalde; Patrick Mounaix; Petr Kuzel

Paper Abstract

Dielectric spheres with high permittivity represent a Mie resonance-based metamaterial. Owing to its high far-infrared permittivity and low dielectric losses, TiO2 is a suitable material for the realization of magnetic metamaterials based on micro-resonators for the terahertz (THz) range. In a previous work, we experimentally demonstrated the magnetic effective response of TiO 2 microspheres dispersed in air, forming nearly a single-layer sample enclosed between two sapphire wafers [1]. Here we embedded the polycrystalline TiO2 microparticles into a polyethylene matrix, which enabled us to prepare a rigid bulk metamaterial with a controllable concentration of micro- resonators. TiO2 microspheres with a diameter of a few tens of micrometers were prepared by a bottom up approach. A liquid suspension of TiO2 nanoparticles was first spray-dried producing fragile TiO2 microspheres. These were subsequently sintered in a furnace at 1200° C for two hours, in order to consolidate individually each sphere. The particles show polycrystalline rutile structure with a porosity of 15%. The microspheres were finally sieved and sorted along their diameters in order to obtain a narrow size distribution. They were mixed with polyethylene powder and a pressure of 14 MPa was used to prepare rigid pellets with random spatial distribution of the TiO2 microspheres. Using finite-difference time-domain simulations, we investigated how the filling fraction and the ratio between the permittivities of the microspheres and the host matrix affect the position and the strength of the magnetic response associated with the lowest Mie mode. We found that a range of negative effective magnetic permeability can be achieved for sufficiently high filling factors and contrasts between the permittivities of the resonators and the embedding medium. Using time-domain THz spectroscopy we experimentally characterized the response of the realized structures and confirmed the magnetic character of their response. The retrieved spectra of the effective dielectric permittivity and magnetic permeability were analyzed within Mie theory and Maxwell-Garnett effective medium model in a quasi-stationary regime. We found out that the TiO2 microparticles embedded in polyethylene to fabricate the rigid metamaterials were probably elliptical [2]. To provide a better understanding of the electromagnetic behavior we will also show a near- field THz response of both isotropic polycrystalline and anisotropic monocrystalline TiO2 microsphere [3,4]. In the anisotropic case, the microparticles were sintered at 1400° C. The annealing process melted polycrystalline particle clusters into single crystal TiO2 spheres. It resulted in a strong dielectric anisotropy of the spheres since the ordinary and extraordinary permittivities of bulk rutile in the THz range are 80 and 150, respectively. A splitting of the first Mie mode into two orthogonal magnetic dipole modes was then detected. The discussed examples show a high potential of TiO2 micro-resonators to realize magnetic THz metamaterials, from cheap mechanically stable structures up to anisotropic resonators. References [1] H. Němec et al., App. Phys. Lett. 100, 061117 (2012) [2] M. Šindler et al., Opt. Express 24, 18304 (2016) [3] O. Mitrofanov et al., Opt. Express 22, 23034 (2014), [4] I. Khromova et al., Laser Photon. Rev. 10, 681 (2016)

Paper Details

Date Published: 8 June 2017
PDF: 2 pages
Proc. SPIE 10227, Metamaterials XI, 102270X (8 June 2017); doi: 10.1117/12.2270538
Show Author Affiliations
Christelle Kadlec, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Michal Sindler, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Filip Dominec, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Hynek Němec, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Catherine Elissalde, Institut de Chimie de la Matière Condensée de Bordeaux (France)
Patrick Mounaix, Univ. Bordeaux 1 (France)
Petr Kuzel, Institute of Physics of the ASCR, v.v.i. (Czech Republic)

Published in SPIE Proceedings Vol. 10227:
Metamaterials XI
Vladimír Kuzmiak; Peter Markos; Tomasz Szoplik, Editor(s)

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