Split ring resonator-coupled enhanced transmission through a single   subwavelength aperture
  We report the enhanced transmission of electromagnetic waves through a single subwavelength aperture by making use of the resonance behavior of a split ring resonator (SRR) at microwave frequencies. By placing a single SRR at the near-field of the aperture, strongly localized electromagnetic fields are effectively coupled to the aperture with a radius that is twenty times smaller than the resonance wavelength. We obtained 740-fold transmission enhancement by exciting the electric resonance of SRR. A different coupling mechanism, through the magnetic resonance of SRR, is also verified to yield enhanced transmission. Good agreement is obtained between the microwave measurements and numerical simulations. 
Koray Aydin, A. Ozgur Cakmak, Levent Sahin, Z. Li, Filiberto Bilotti,   Lucio Vegni, and Ekmel Ozbay