engleski

Broadband Epsilon-Near-Zero (ENZ) and Mu-Near-Zero (MNZ) Active Metamaterial

In this study reports 12-month research effort undertaken to understand, and eventually overcome, one of the most serious drawbacks of all passive metamaterials: the inherent narrowband operation. We found that this narrowband operation is limited by basic physics (by the energy-dispersion constraints) and not by imperfections of available technology. However, we also found possible to go around this drawback by the incorporation of active non-Foster elements in the metamaterial structure. It is known that, under some circumstances, all active elements (including the non-Foster elements) may cause stability problems. We thoroughly analyzed this issue and found that commonly used frequency-domain methods of stability prediction are not applicable in the case of non-Foster elements. Therefore, we developed a simple circuit-theory approach of accessing stability of non-Foster elements in time domain. Using developed method, we have proved that is indeed possible to build stable ENZ and MNZ metamaterials with multi-octave bandwidth and almost flat dispersion curve. This theoretical and numerical investigation has been complemented with the development of experimental proof-of-concept prototypes, in RF (up to 100 MHz) and lower microwave range (up to 2 GHz). Developed prototypes comprise: the negative capacitors, the unit cells of active 2D ENZ metamaterials, and the active ENZ transmission line. All the prototypes were hand-crafted using standard FET and OPAMP SMD components. The measurements revealed multi-octave bandwidth, which is significantly better than the bandwidth of all passive metamaterials reported so far. All achieved results clearly show that the novel proposed concept of non- Fosterelement-based active metamaterial is correct. Finally, we have shown that this can enable ultra-broadband operation of the previously reported narrowband plasmonic and transformation-electromagnetic cloaks.

metamaterials; negative capacitors

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