Metamaterials are artificial structures, engineered to provide unusual electromagnetic properties, not found in naturally occurring materials. Although the tremendous research efforts have been put into investigation of these structures in the last decade, there are still very few real-world engineering applications reported so far. This lack of applications is a consequence of two main problems: the significant losses and narrow bandwidth. These problems are caused by basic background physics, namely by the energy-dispersion constraints. The most successful designs nowadays offer losses of 0.2 dB – 0.5 dB per unit cell, while the operational bandwidth does not exceed 20%. In addition, there is a closely related issue of reliable characterization of metamaterials which is a very demanding task, especially in the case of highly complex anisotropic volumetric metamaterials and planar metamaterials. The general ‘extraction’ method that can be applied to arbitrarily complex 3D anisotropic metamaterials or complex metasurfaces has not been published so far. In this project, all three problems (enlarging the bandwidth, decreasing the losses and developing characterization methods for general metamaterial structures) are tackled, together with a proposal of practical engineering applications.

In the first part, passive techniques for broadening the bandwidth of metamaterials are investigated. The design strategy is based on the combination of electromagnetic band-gap structures with ordinary transmission lines. The appropriate design tool, based on combined numerical-analytical approach, is developed. The correctness of proposed approach is verified by fabrication and measurements on the prototypes of low-loss broadband gapwaveguide components, operating in microwave regime.

In the second part, active techniques for broadening operational bandwidth of metamaterials are investigated. The basic idea involves incorporation of non-Foster elements (negative capacitors and negative inductors) into ordinary transmission-line structures. In such a way, it is possible to overcome energy-dispersion constraints and achieve ultrabroadband operation (relative bandwidth of more than four octaves). Further increase of the versatility is achieved by development, fabrication, and measurement of RF non-Foster metamaterial with in-situ reconfigurable unit cell, able to achieve either DPS-ENZ or DPSMNZ behavior. This approach enables different applications such as: cloaking, antennas, and artificial surfaces.

In the third part, reliable extraction methods, able to fully characterize general 2D and 3D metamaterial structures, are developed. The methods are tested by design, fabrication and measurements of anisotropic 2 1/2D cloak and DB metasurface in microwave regime. Finally, the extension to characterization of graphene metasurfaces, operating in optical regime, is proposed.

Project title: Passive and Active Metamaterial Structures for Guiding, Scattering and Radiation of Electromagnetic Energy

Project ID: UKF 9/13

Leading institution: Faculty of Electrical Engineering and Computing, University of Zagreb

Duration: 24 months (starting 15.10.2013.)

Project budget: 1.380.000,00 HRK