Abstracts - Dipartimento di Elettronica Applicata

Meta 2010 & FEM 2010 – Rome, 13-15 December 2010
Metamaterials based on Non-Foster Elements
Silvio Hrabar (1) , Igor Krois (1) , Ivan Bonic (1) , and Aleksandar Kiricenko (1)
(1) University of Zagreb, Faculty of Electrical Engineering and Computing, Zagreb,
Croatia– E-mail:Silvio.Hrabar@fer.hr
It is well known that any passive metamaterial must satisfy basic dispersion
constraints:
� ����( �)
� ��
� � 0 , � �� � �(
�)
� ��
� �0.
(1)
This fundamental issue is a cause of inherent narrowband behavior of all
metamaterials (SNG, DNG, SNZ, DNZ). In [1], a possibility of going around the
basic dispersion constrains by the use of non-Foster active elements such as negative
capacitors and negative inductors, was predicted theoretically. Very recent
experimental studies [2,3] showed that is indeed possible to build active (almost)
dispersionless ENZ and MNZ metamaterials. Here, the basic physics of non-Foster
metamaterials will be reviewed and several illustrative examples of practical
prototypes developed at University of Zagreb will be presented. These include a 2D
ENZ unit cell for broadband 2D electromagnetic cloak (Fig. 1) and a broadband ENZ
RF transmission line with superluminal phase and group velocities (Fig. 2). Finally,
currently investigated novel concepts of matched ‘EM nihility’ and frequency
independent active transmission lines will be highlighted.
C 2+
C 1-
��� �
NIC circuit located on the
ground plane
microstrip line
via hole to negative C
a substrate
Effective
permittivity
Fig. 1: (After [2]), Upper: 2D active ENZ
unit cell, Lower: Microstrip realization
References
[1] S. Tretyakov, ‘Meta-materials with wideband negative permittivity and permeability’,
Microwave and Optical Technology Lett., Vol. 31, No. 3, pp. 163-165, November 2001
[2] S. Hrabar, I. Koris, A. Kiricenko, ‘Towards Active Dispersionless ENZ Metamaterial for
Cloaking Applications’ , Metamaterials, Vol. 4 No. 2-3, pp. 89-97. August-September 2010
[3] S. Hrabar, I. Krois, I.Bonic, A Kiricenko, ‘Experimental Investigation of Active Broadband ENZ
Transmission line’, Proc. on ‘Metamaterial Congress 2010, p.p 63-65, Karlsruhe, September 2010
53
Z 0
�x=����
CNE
Realistic
Realistic CNE
Realistic CNE
C
�x=����
C
�x=����
2.0
1.9
1.8
1.7
1.6
1.5 active ENZ off
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
m10
0.4
0.3
0.2
0.1
0.0
m11 active ENZ on
0 5 10 15 20 25 30 35 40 45 50
freq, MHz
Fig. 2: (After [3]) Upper : RF active ENZ
transmission line, Lower: Measurement results
C