Nonreciprocal localization of ultrasound in a viscous medium with asymmetric scatterers
A two-dimensional phononic crystal with asymmetric scatterers is used for the study of Anderson localization of sound along one-dimensional disorder produced by random orientation of metallic rods. An exponentially weak transmission of ultrasound is demonstrated for the waves propagating along the direction of disorder. In the perpendicular direction where the scatterers are ordered, sound propagates as extended wave. The {\it PT}-symmetry of the system is broken by dissipative viscous losses and asymmetric shape of the scatterers. Nonreciprocal transmission of sound is observed for both, ordered and disordered, directions. In the localized regime, the nonreciprocity is manifested through different values of localization length for sound propagating in the opposite directions.