Radlab Seminar

Active non-Foster Metamaterials - A New Paradigm in Electromagnetics

Professor Silvio Hrabar

University of Zagreb
Friday, June 08, 2012
3:00pm - 4:00pm
1005 EECS

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About the Event

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, 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, some new research directions that include ultra-broadband volumetric EM nihility metamaterials, frequency-independent transmission lines and active reconfigurable metamaterials, will be highlighted.


Silvio Hrabar was born in Trogir, Croatia in 1962. He received Dipl. Ing. and M.S. degrees from University of Zagreb, Croatia and a Ph.D degree from Brunel University of West London, United Kingdom, all in electrical engineering. In the past, he was employed at various consulting, development, research and teaching positions both in industry and academia, in the fields of radio engineering, microwave electronics, antenna engineering, electromagnetic compatibility, electromagnetic metrology, computational electromagnetics and electrostatics. Currently, he is affiliated with University of Zagreb, Croatia, where he is a Professor of applied electromagnetics. His research interest includes applied electromagnetics, electromagnetic compatibility, antennas, microwave measurements and microwave engineering. He is author of one textbook, several book chapters, and many conference reports and journal papers. He also serves as a reviewer for IEEE Transaction on Antennas and Propagation, IEEE Antennas and Propagation Letters, IEEE Transaction on Microwave Theory and Techniques, Journal of Radio Science, Physical Review Letters, Applied Physics Letters, and Journal of Applied Physics. He is a member of IEEE Societies on Antennas and propagation, Microwave theory and techniques, Instrumentation and measurements, and Geoscience and Remote Sensing . Professor Hrabar is a chair of Metamaterial group at Faculty of Electrical Engineering and Computing (FER), University of Zagreb.

Additional Information

Contact: Karla Johnson

Phone: 764-0500


Sponsor(s): IEEE Southeastern Michigan Section - Chapter IV (Trident)

Open to: Public