engleski

Active non-Foster Metamaterials From Invisibility to Superluminal Dispersion-free Transmission Lines

One of the drawbacks of all passive metamaterials available at the present state of the art is their inherent narrow-band operation caused by basic dispersion constraints. The narrow-band operation is a serious obstacle in many applications such as antennas or electromagnetic invisibility (cloaking technology). In this talk, the concept of active Epsilon-Near-Zero and Mu-Near-Zero non-Foster metamaterial, recently introduced at University of Zagreb is reviewed. This approach goes around the basic dispersion constraints of a passive material and, therefore, enables ultra-broadband operation. A basic idea deals with the decrease of a free-space capacitance or a free-space inductance with the help of negative capacitors and negative inductors, respectively. Using this recipe it is possible to construct (almost) dispersionless ENZ and MNZ metamaterials. The basic properties of these active materials (dispersion and stability) were investigated with the help of commercial circuit simulator. Simulation results showed that is possible to achieve either electric or magnetic ‘plasmonic’ behavior in a wide frequency band (limited by the characteristics of active negative converters). Several experimental prototypes of basic RF active ‘plasmonic’ transmission lines and 2D metamaterials, developed at University of Zagreb, will be presented. Measurements revealed dispersionless equivalent permittivity and permeability within a frequency band of four octaves, which may be used for ultra-broadband cloaking. In addition, it was found that developed structures also support superluminal phase velocity and superluminal group velocity. Although this behavior is counter-intuitive, it is perfectly compatible with the causality and general relativity. Finally, some new research directions that deal with electromagnetic nihility and frequency-independent transmission lines and antennas will be highlighted.

metamaterials; negative capacitor; superluminal

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