Extremely Sub-Wavelength Negative Index Metamaterial

We present an extremely sub-wavelength negative index metamaterial structure operating at radio frequency. The unit cell of the metamaterial consists of planar spiral and meandering wire structures separated by dielectric substrate. The ratio of the free space wavelength to unit cell size in the propagation direction is record breaking 1733 around the resonance frequency. The proposed metamaterial also possesses the most extreme refractive index of -109 that has been recorded to date. Underlying magnetic and electric response originate from the spiral and meandering wire, respectively. We show that the meandering wire is the key element to improve the transparency of the negative index metamaterial.