Enhanced thermal stability of dielectric, energy storage, and discharge efficiency in a structurally frustrated piezoelectric system: Erbium modified Na 0.5 Bi 0.5 TiO 3 -BaTiO 3

No abstract

Superdirective antennas developed over the last century have received renewed interest in recent years from the development of metamaterials. these arrays of electromagnetic resonators (or meta-atoms) carrying short wavelength electro-and/or magneto-inductive waves support current distributions with very high spatial frequency as required by the classical conditions for superdirectivity. As meta-atoms can have both electric and magnetic dipole characteristics (and hence radiation properties), developing antennas exploiting these distributions can challenge conventional intuitions regarding the optimal configurations required. In this work we are reporting the development of a genuinely superdirective array using split ring resonators (SRRs). We provide a comprehensive analytical model characterizing the radiation from SRR dimers in which excitation of only one split ring leads to superdirective radiation via mutually coupled modes. our model exploits simple circuit descriptions of coupled resonant circuits, combined with standard radiation formulae for curvilinear current distributions. Using this simple model we are able to map directivity against possible SRR locations and orientations in two dimensions and identify the unique optimal configuration which meets the requirements for superdirective emission. We validate the theoretical findings by comparison to both full wave simulations and experiments showing that our SRR dimer achieves endfire directivity very close to the maximum theoretical value. Directional and smart antennas are one of the approaches that could be used to increase the capacity and flexibility of wireless systems in future integrated gigabit communications (5G and beyond). The advantages of a steerable antenna system include the possibility of tracking a terminal signal and mitigating interference between network nodes, thus improving network capacity. Directional antennas can also improve power efficiency 1. The most common technique to realize a directive antenna consists in assembling a multiple-antenna array in which the radiation pattern can be reinforced in a particular direction and suppressed in undesired directions. By individually controlling each array element in phase and amplitude, the direction of radiation can be electronically steered (phased arrays) 2. Multi-element arrays are by now widely used in based stations of cellular networks, but simple implementation for mobile devices is severely constrained by the need for small antennas, the conventional phased array techniques for enhancing the directivity leading to a significant increase of the antenna size and requiring a separate RF chain for each antenna element. On the other hand, antenna miniaturization is usually achieved at the expense of efficiency, bandwidth, directivity and gain, but especially miniaturized antennas tends to present a practically omnidirectional radiation pattern. However, future regulations might require the use of adaptive directional antennas also for mobile terminals, due to the invaluable role...