Conformal cloak for waves
  Conformal invisibility devices are only supposed to work within the validity range of geometrical optics. Here we show by numerical simulations and analytical arguments that for certain quantized frequencies they are nearly perfect even in a regime that clearly violates geometrical optics. The quantization condition follows from the analogy between the Helmholtz equation and the stationary Schrodinger equation. 
Huanyang Chen, Ulf Leonhardt, Tomas Tyc
physics.optics