Coupling mechanisms in metamaterials
Final Report Abstract
The project is devoted to studies of how metamaterials properties can be affected by interactions between individual elements. These interactions lead to slow waves of coupling, which have great potential for applications mainly on account of their versatility and simplicity of design, helped also by the ease with which they can be produced, the relatively simple mathematical description of their operation, and the vast frequency range (from the MHz to the THz region) in which they can operate. Due to the waves of inter-element coupling, metamaterials may provide the basis for a variety of near-field manipulating devices subwavelength components, such as waveguides, power dividers, polarisers, phase shifters and lenses with subwavelength resolution. Major findings of the present project can be structured into three themes: (1) understanding the coupling mechanisms; (2) novel types of waves of coupling and (3) their applications. We were able tackle a number of fundamental problems achieving original results not published previously which contributed to completing and further developing the emerging picture of physics in metamaterials with inter-element coupling, to arrive at analytical expressions, to verify them numerically and/or experimentally, and to propose potential applications. While studying coupling mechanisms, we developed a method of calculation of electric and magnetic coupling for arbitrarily positioned elements of arbitrary shape. Our method, verified numerically and experimentally in the GHz frequency range, and numerically in the THz frequency range, will aid the design of near-field manipulating devices. One of the most striking fundamental results is the dramatic reduction of the magnetic coupling due to inertia of the electrons in metamaterials operating in the THz frequency range. We have investigated various types of waves of coupling: (i) For the first time to our knowledge, properties of surface and, more generally, evanescent magnetoinductive waves in metamaterials were studied and the operation of a magnetoinductive subwavelength lens explained. (ii) A new type of a diatomic metamaterial with an alternating (electric/magnetic) type of coupling between elements has been proposed and verified experimentally, and applications proposed for parametric amplification to compensate losses or to enhance signals in the magnetic resonance imaging as well as for a steerable forward/backward antenna. (iii) An effective medium theory incorporating inter-element coupling in an anisotropic metamaterial has been developed, which allowed us to identify configurations capable of propagating both bulk and surface modes resulting from coupling of electromagnetic radiation to magnetoinductive waves. Understanding of coupling mechanisms and properties of magneto- and electroinductive waves has allowed us to propose a way to realise electrically-small superdirective antennas. We suggested that the required rapid current distribution can be imposed by propagating slow magnetoinductive waves. Conditions for two-element and three-element superdirective antennas were formulated, and preliminary experimental data confirm our predictions. It is envisaged that this direction of research may lead to realisation of genuine superdirective metamaterials, which can find applications in medicine both for therapeutical and diagnostic purposes.
Publications
- Generalized Brillouin diagrams for evanescent waves in metamaterials with interelement coupling, Phys. Rev. B 81, 115110 (2010)
E. Tatartschuk, A. Radkovskaya, E. Shamonina, L. Solymar
- Surface waves at an interface of two metamaterial structures with interelement coupling, Phys. Rev. B 82, 045430 (2010)
A. Radkovskaya, E. Tatartschuk, C.J. Stevens, D.J. Edwards, E. Shamonina, L. Solymar
- Dimer and polymer metamaterials with alternating electric and magnetic coupling, Phys. Rev. B 84, 125121 (2011)
A. Radkovskaya, O. Sydoruk, E. Tatartschuk, N. Gneiding, C.J. Stevens, D.J. Edwards, E. Shamonina
- Magnetoinductive polaritons: Hybrid modes of metamaterials with interelement coupling, Phys. Rev. B 85, 155146 (2012)
E. Shamonina
- Mapping inter-element coupling in metamaterials: Scaling down to infrared, J. Appl. Phys. 111, 094904 (2012)
E. Tatartschuk, N. Gneiding, F. Hesmer, A. Radkovskaya, E. Shamonina
(See online at https://doi.org/10.1063/1.4711092) - Circuit model optimization of a nano split ring resonator dimer antenna operating in infrared spectral range, J. Appl. Phys. 116, 164311 (2014)
N. Gneiding, O. Zhuromskyy, E. Shamonina, and U. Peschel
(See online at https://doi.org/10.1063/1.4900479) - Maximum directivity of arbitrary dipole arrays, IET Microw. Antennas Propag. 9, 101–107 (2014)
E. Shamonina, L. Solymar
(See online at https://doi.org/10.1049/iet-map.2014.0268) - Superdirectivity by virtue of coupling between meta-atoms, in Proc. 7th Int. Congress on Advanced Electromagnetic Materials in Microwaves and Optics (Metamaterials’2014), pp. 97-99 (2013)
E. Shamonina and L. Solymar
(See online at https://doi.org/10.1109/MetaMaterials.2013.6808965)
