Naslov
Negative Capacitor and Negative Inductor Pave the Way to Ultra-broadband Metamaterials and Metasurfaces

Autori
Hrabar, Silvio

Izvornik
Aalto University, Helsinki

Vrsta, podvrsta
Ostale vrste radova, ostalo

Godina
2012

Ključne riječi
metamaterials ; negative capacitor ; negative inductor

Sažetak
The majority of proposed applications of metamaterials are based on ‘negative’ (MNG, ENG, DNG) or ‘plasma-like’ (ENZ, MNZ) metamaterials. It would be very convenient if these metamaterials were dispersionless and, therefore, of broadband nature. However, it is well known that all ‘negative’ and ‘plasma-like’ metamaterials exhibit pronounced dispersion accompanied with a narrow operating bandwidth. This is the inherent drawback of all known passive (meta)materials and it seriously limits possible applications. A typical example is the anisotropic cloak, in which the dispersion limits fractional operating bandwidth to a value smaller than 1%. It is important to stress that the dispersion problem is caused by basic physics and not by applied technology, as it is usually believed. A very interesting idea that might work around this inherent limitation has been proposed recently. It is based on so-called non-Foster elements. These are active electronic circuits, which behave as negative capacitors or negative inductors, violating energy-dispersion constraints and Foster reactance theorem. Negative capacitors and negative inductors have dispersion curves that are the exact inverse of the dispersion curves of ordinary ‘positive’ elements. Therefore, one could expect that the dispersion of ordinary passive metamaterials can be compensated for with the ‘inverse’ dispersion of non-Foster elements, resulting in extremely broadband behavior. Possible applications of this novel concept could be broadband cloaking devices, broadband artificial magnetic conductors and exotic metasurfaces, dispersionless feeding networks in antenna arrays, and broadband phase shifters in communication technology In this talk, intriguing background physics of non-Foster metamaterials that includes several counter-intuitive phenomena such as an absence of dispersion, broadband superluminal phase and group velocities, inherent gain etc., will be explained. In addition, several state-of-the-art examples of extremely broadband 1D and 2D active ENZ and MNZ metamaterials developed at University of Zagreb, will be presented. Obtained bandwidth of these prototypes spans more than four octaves, which is considerably wider than the bandwidth of all passive metamaterials available at present. In the final part of the talk, a new research direction that deals with reconfigurable active ENZ-MNZ-DPS metamaterials and active broadband DB surfaces will be discussed.

Izvorni jezik
Engleski

POVEZANOST RADA