Effects of Substrate Parameters on the Resonance Frequency of Double-sided SRR Structures under Two Different Excitations

Abstract

In this study, we numerically investigate the efiects of substrate parameters (i.e., the thickness and the permittivity) on the resonance frequency of the double-sided SRR (DSRR) structure under two difierent excitation conditions. This includes either electric or magnetic excitations which are two common techniques to obtain a resonant efiective permittivity or per- meability, respectively. The numerical calculations are performed using CST Microwave Studio. The numerical results reveal a similar trend in the DSRR response as the substrate permittivity values are varied for either electric or magnetic excitation while an opposite behavior is observed for changes of the substrate thickness. 1. INTRODUCTION The split-ring resonator (SRR) is a well-known metamaterial structure used to obtain negative values of the permeability or permittivity, depending on the type of electromagnetic excitation (1{ 5). When a time-varying magnetic fleld is applied through the axis of this special structure, a magnetic resonance frequency together with a -negative (MNG) region can be obtained (2). This property makes SRRs special, because existing materials in nature typically yield only positive values for the permeability. Besides having special magnetic properties, SRRs can also be utilized as an electrical resonator, when a time-varying electric fleld is applied perpendicular to the gaps of the structure thereby providing an -negative (ENG) region (3,5). At terahertz (THz) frequencies and above, electrical excitation is common since magnetic excitation is not practical due to the limitations of measurement systems and fabrication techniques. Double-sided SRR (DSRR) structures take an important place in metamaterial applications. They are nothing but two identical SRR structures printed over both faces of the substrate, but in an inverted fashion (6,7). The special case with the single ring SRR on both faces is called the broadside coupled SRR (BS-SRR) structure (6). The most recent applications reported in the literature on these structures are related to miniaturization (7) and structural tunability (8). In this study, we investigate the efiects of the substrate thickness and substrate permittivity on the resonance frequency of the DSRR structure under electrical and magnetic excitation.