Backscattering reduction in a twisted water wave channel

We study experimentally and numerically the propagation of water waves along a channel with two perpendicular turns. When the wave reaches the first turn, there is naturally a reflected wave. We show that it is possible to reduce almost completely the backscattering in such geometries, in agreement with a recent theoretical prediction. In order to avoid the reflection that naturally arises at that point of the waveguide, a simple metamaterial made of closely-spaced thin vertical plates is used. This metamaterial acts like a negative-refraction index media, producing a waveshift across it. This phenomenon is not restricted only to surface waves but also applies to any type of waves. Furthermore, the efficiency of this arrangement does not depend on the frequency of the incident wave, as long as its wavelength is much larger than the spacing between the plates.