Abstract-Terahertz response of fractal meta-atoms based on concentric rectangular square resonators

Zhiqiang Song^1,a), Zhenyu Zhao^1,a),b), Wei Peng² and Wangzhou Shi¹
 HIDE AFFILIATIONS
1 Department of Physics, Shanghai Normal University, Shanghai 200234, China
2 State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
a) Z. Song and Z. Zhao contributed equally to this work.
b) Electronic mail: zyzhao@shnu.edu.cn
J. Appl. Phys. 118, 193103 (2015); http://dx.doi.org/10.1063/1.4936217

http://scitation.aip.org/content/aip/journal/jap/118/19/10.1063/1.4936217?TRACK=RSS

We investigate the terahertz electromagnetic responses of fractal meta-atoms (MAs) induced by different mode coupling mechanisms. Two types of MAs based on concentric rectangular square (CRS) resonators are presented: independent CRS (I-CRS) and junctional-CRS (J-CRS). In I-CRS, each resonator works as an independent dipole so as to result in the multiple resonance modes when the fractal level is above 1. In J-CRS, however, the generated layer is rotated by π/2 radius to the adjacent CRS in one MA. The multiple resonance modes are coupled into a single mode resonance. The fractal level increasing induces resonance modesredshift in I-CRS while blueshift in J-CRS. When the fractal level is below 4, the mode Q factor of J-CRS is in between the two modes of I-CRS; when the fractal level is 4 or above, the mode Q factor of J-CRS exceeds the two modes of I-CRS. Furthermore, the modulation depth (MD) decreases in I-CRS while it increases in J-CRS with the increase in fractal levels. The surfacecurrents analysis reveals that the capacitive coupling of modes in I-CRS results in the modesredshift, while the conductive coupling of modes in J-CRS induces the mode blueshift. A high Q mode with large MD can be achieved via conductive coupling between the resonators of different scales in a fractal MA.