Effective properties of split-ring resonator metamaterials using measured scattering parameters: Effect of gap orientation

Abstract

This paper presents experimental S-parameter data (amplitude and phase) in the 8–26GHz range for split-ring resonator (SRR) metamaterial samples exhibiting electric (E) and/or magnetic (H) resonances at 10.4GHz depending on the orientation of the gaps of the SRRs with respect to the E and H fields. Use of a thru, reflect, line (TRL) calibrated focused plane wave, free space microwave system permits inversion of the complex permittivity, permeability, and refractive index of planar metamaterial samples from measurement of the reflected and transmitted S parameters of the system. Samples were prepared by patterning concentric SRRs on a dielectric substrate. Three different orientations of the SRR have been used in the experimental study; (i) SRRparallel—gaps in the split rings parallel to the incident E field to realize a dielectric resonance; (ii) SRRrandom—randomly oriented gaps to realize simultaneous dielectric and magnetic resonances; and (iii) SRRperpendicular—gap oriented perpendicular to the E-field to realize a strong magnetic resonance. The experimentally extracted material properties show very good agreement with numerical simulations of effective properties giving rise to a negative magnetic permeability. A second resonance at 23GHz clearly establishes a passband between 10.4 and 23GHz for all samples. The extraction of effective properties from measured S parameters is a useful development in metamaterials research and the study of random orientations of gaps with respect to the E field is an interesting design for metamaterials that may lead to negative index behavior with further optimization.