A tunable multi-band metamaterial design using micro-split SRR structures

This paper presents the results of a feasibility study for the design of multi-band tunable metamaterials based on the use of micro-split SRR (MSSRR) structures. In this study, we have designed and constructed a conventional split-ring resonator (SRR) unit cell (type A) and two modified SRR unit cells having the same design parameters except that they contain two (type B) or four (type C) additional micro-splits on the outer square ring, along the arm having the main split. Transmission characteristics of the resulting MSSRR cells are obtained both numerically and experimentally and compared to those of the ordinary SRR unit cell. It is observed that the presence of the additional micro-splits leads to the increase of resonance frequency by substantial amounts due to the series capacitance effect. Next, we have designed and constructed 2 x 2 homogeneous arrays of magnetic resonators which consist of the same type of cells (either A, or B, or C). Such MSSRR blocks are found to provide only a single frequency band of operation around the magnetic resonance frequency of the related unit cell structure. Finally, we have designed and constructed 2 x 2 and 3 x 2 inhomogeneous arrays which contain columns of different types of metamaterial unit cells. We have shown that these inhomogeneous arrays provide two or three different frequency bands of operations due to the use of different magnetic resonators together. The number of additional micro-splits in a given MSSRR cell can be interactively controlled by various switching technologies to modify the overall metamaterial topology for the purpose of activating different sets of multiple resonance frequencies. In this context, use of electrostatically actuated RF MEMS switches is discussed, and their implementation is suggested as a future work, to control the states of micro-splits in large MSSRR arrays to realize tunable multi-band metamaterials.