Reflectionless Sharp Bends and Corners in Waveguides Using   Epsilon-Near-Zero Effects
  Following our recent theoretical and experimental results that show how zero-permittivity metamaterials may provide anomalous tunneling and energy squeezing through ultranarrow waveguide channels, here we report an experimental investigation of the bending features relative to this counterintuitive resonant effect. We generate the required effectively-zero permittivity using a waveguide operating at the cut-off of its dominant mode, and we show how sharp and narrow bends may be inserted within the propagation channel without causing any sensible reflection or loss. 
Brian Edwards, Andrea Alu, Mario G. Silveirinha, Nader Engheta