Appl Phys A (2011) 103:989–994 DOI 10.1007/s00339-011-6376-2 Investigation of negative index properties of planar metamaterials based on split-ring pairs Yong Zhi Cheng · He Lin Yang · Yan Nie · Rong Zhou Gong · Zheng Ze Cheng Received: 27 October 2010 / Accepted: 15 March 2011 / Published online: 6 April 2011 © Springer-Verlag 2011 Abstract A low losses broadband planar negative refrac- tive index metamaterial based on split-ring resonator (SRR) pairs is proposed and investigated experimentally and nu- merically at microwave frequency range. The transmission spectra of the single-layer SRR pairs were measured, and exhibited left-handed (LH) transmission passband clearly. The metal-dielectric-metal structure exhibits strong mag- netic and electric responses simultaneously, and leads to negative permeability and negative permittivity. To further verify the LH properties of planer structure metamaterials, effect media parameters were retrieved, a refraction phe- nomenon based on a wedge-shaped model and negative phase advance between consecutive numbers of layers were also demonstrated. Y.Z. Cheng · Y. Nie · R.Z. Gong Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China Y.Z. Cheng e-mail: cyz0715@126.com Y. Nie e-mail: nieyan@yahoo.cn R.Z. Gong e-mail: rzhgong@mail.hust.edu.cn Y.Z. Cheng · H.L. Yang ( ) College of Physical Science and Technology, Huazhong Normal University, Wuhan 430079, China e-mail: emyang@mail.ccnu.edu.cn Z.Z. Cheng The School of Electronic and Information Engineering, XianNing University, Xianning 437100, China e-mail: czz8986my@163.com 1 Introduction Metamaterials with simultaneous negative effective permit- tivity (ε eff ) and negative effective permeability (μ eff ) are known as left-handed metamaterial (LHM) or negative re- fractive index metamaterial (NIM); they cannot be found in nature. The first artificial NIM composed of split ring resonators (SRRs) and metal rods was demonstrated exper- imentally by Smith et al. [1]. The NIMs usually exhibit exotic physics properties, such as negative refraction phe- nomenon, radiation effects of inverse Cerenkov, effects of inverse Doppler and so on. The research in metamaterials has ushered in a new field of science research, which has been growing rapidly in recent years [2–7]. The metamate- rials which composed of shaped elements are much smaller than the incident electromagnetic (EM) wavelengths, there- fore, treated as homogeneous media with EM constitutive parameters. At early stage, various kinds of artificial NIMs were proposed and investigated in microwave regime. These typical structures such as S-shaped [8], L-shaped [9], - shaped [10], and dendrites structure [11] are similar to the SRRs for achieving a negative magnetic permeability. For these metamaterials, incident EM waves must be paralleled to the substrate plane, and many layers NIMs have to be pro- duced and stacked in experiments, which make it quite trou- blesome to fabricate and use. Furthermore, the fabrication of NIMs at the optical frequency range is also rather difficult. Recent years, planar slab structures such as short wire pairs [12, 13], double fishnet pairs [14, 15] have been proposed and demonstrated negative refraction properties. Only sin- gle slab layer metamaterial, which could also exhibit the LH properties for normal incident EM wave, is much easier to fabricate and measure. Generally, there are four methods used by researchers to demonstrate a designed metamaterial with LH properties