PROJEKTI
   

Project
Acronym: NOFSLON 
Name: Non-Foster Source-load Networks and Metasurfaces 
Project status: From: 2015-06-01 To: 2017-05-31 (Completed)
Contract number:  
Action line: EOARD - European Office of Aerospace Research and Development 
Type (Programme): Ostali 
Instrument: Ostalo 
Project cost: 100.000,00 USD
Project funding: 100.000,00 USD
Project coordinator
Organisation Name: Sveučilište u Zagrebu Fakultet elektrotehnike i računarstva 
Organisation adress: Unska 3, 10000 Zagreb 
Organisation country: Hrvatska 
Contact person name: prof.dr.sc. Silvio Hrabar 
Contact person email: Email 
Croatian partner
Organisation name: Fakultet elektrotehnike i računarstva 
Organisation address: Unska 3, 10000 Zagreb, Hrvatska 
Contact person name: prof.dr.sc. Silvio Hrabar
Contact person tel:
6129-828  Contact person fax:  
Contact person e-mail: Email 
Partners
Organisation nameCountry
Short description of project
Although almost fifteen years have passed from the introduction of the field of electromagnetic metamaterials, the successful engineering applications are still very rare due to inherent significant losses and a narrow operating bandwidth. These inherent drawbacks of all known (passive) metamaterials are not caused by applied technology (as it is usually believed) but rather by the basic background physics. Actually, every artificial passive structure (or every continuous material), equivalent permittivity or permeability of which is smaller than 1 must be dispersive due to the energy-dispersion constraints (and their circuit-theory equivalent known as Foster theorem). Thus, regardless of the internal structure of any passive metamaterial, its bandwidth and loss will be always inevitably mutually dependent, or constrained. Recently a very interesting approach that might work around this inherent limitation, based on so-called non-Foster elements (active electronic circuits, which behave as negative capacitors or negative inductors), has been proposed by our group. The most successful published designs of active non-Foster metamaterials showed operating bandwidth 1:700 or more than 9 octaves, that surpasses all passive metamaterials developed so far. Unfortunately, non-Foster elements are very often unstable, which makes design and manufacturing process very difficult, sensitive, and challenging. Here, we propose a 24-month effort that should significantly suppress (or even completely avoid) stability problems not only in the field of non-Foster metamaterials, but also in the older (but still notmatured) field of broadband non-Foster matching. This research will be based on two ideas recently put forward by our group: the inherent stability of a network that comprises solely negative elements and the source with negative internal reactance (so-called ‘non-Foster source’). Concerning the first idea, we believe that is possible to construct inherently stable 1D or 2D network (or more generally, the 1D or 2D active metamaterial), all the lumped elements of which are negative (i.e. negative capacitors, negative inductors and negative resistors). This network can be considered as the electromagnetic analog of antimatter (which is stable per se but becomes unstable when it is in contact with ordinary matter). Thus, it is important to assure that any system that contains both non-Foster and Foster parts have negative ‘equivalent net reactance’ and negative ‘equivalent netresistance’. If this requirement is met, in principle it should be possible to construct stable broadband SNG/DNG 1D/2D transmission lines and metasurfaces. These may include broadband polarizationmanipulation metasurface, collimating metasurfaces, bianisotropic or even non-reciprocal metasurfaces. The second idea is expected to turn inherent instability of the non-Foster reactance (which is always considered as a serious drawback) into a very useful feature. Briefly, if a negative resistance is added to a non-Foster reactance (a negative capacitor or a negative inductor) the whole circuit behaves as Thevenen source (an oscillator) with negative internal impedance (‘non-Foster source’). Such a source (if designed properly) can deliver maximal power to ordinary passive load (for instance to an antenna) within very broad (theoretically infinite) bandwidth. Such a method drops out classical matching, in which a transmitter, a matching network, and an antenna are different blocks. Here, a transmitter, a single radiator or an antenna array become nearly dispersionless and inherently broadband non-Foster-based source-antenna system. This approach could enable manufacturing of nearly perfectly matched transmitter-antenna systems with a bandwidth ten times larger than the existing designs. During the time scale of the proposed project, the analytical model and the design procedure of entirely negative non-Foster source-load network, non-Foster source and associated non-Foster metasurfaces will developed. In order to verify these theoretical results, appropriate RF demonstrators in the form of broadband SNG/DNG transmission line and/or metasurface will be designed, manufactured and tested.  
Short description of the task performed by Croatian partner
 


   

Design by: M. Mačinković

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