Experimental demonstration of negative refraction and subwavelength imaging by left-handed composite metamaterials
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0919-J03-06
Experimental demonstration of negative refraction and subwavelength imaging by lefthanded composite metamaterials Ekmel Ozbay1, Koray Aydin1,2, Gonca Ozkan1, and Irfan Bulu1,2 1 Nanotechnology Research Center, Bilkent University, Bilkent, Ankara, 06800, Turkey 2 Department of Physics, Bilkent University, Bilkent, Ankara, 06800, Turkey ABSTRACT We report a true left-handed (LH) behavior and focusing in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures. The magnetic resonance of the SRR structure is demonstrated by comparing the transmission spectra of SRRs with that of closed SRRs. We confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined left-handed transmission band with a peak value of -1.2 dB (–0.3 dB/cm) is obtained. We also report the transmission characteristics of a 2D composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement and the experimental results agree extremely well with the theoretical calculations. By measuring the refracted electromagnetic (EM) waves from a LHM slab, we found an effective refractive index of -1.86. A 2D scanning transmission measurement technique was used to measure the intensity distribution of the electromagnetic (EM) waves that radiate from the point source. The flat lens behavior of a 2D CMM slab was demonstrated for two different point source distances of ds = 0.5λ and λ. The full width at half maximum of the focused beams is 0.36λ and 0.4λ, respectively, which are both below the diffraction limit. INTRODUCTION Veselago predicted that a medium with negative permittivity, ε, and negative permeability, µ, will exhibit negative indices of refraction [1]. When both the permittivity and the permeability are negative the electric field, the magnetic field and the wavevector components form a lefthanded coordinate system, hence the name left-handed material (LHM) is used for description. Such a medium is expected to exhibit unusual physical properties such as negative refraction, reversal of Doppler shift, backward Cherenkov radiation. Materials that possess a negative index of refraction [1] have become a remarkable research area in recent years thanks to a number of possibilities for their realization. To realize a LHM, one approach is to construct a composite metamaterial (CMM) consisting of two components that have permittivity of ε(ω) < 0 [2] and permeability of µ(ω) < 0 [3] simultaneously over a certain frequency range, so that the resulting index of the refraction of the effective medium be
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