Single-sided acoustic beam splitting based on parity-time symmetry

Unidirectional reflectionless resonance observed in parity-time-symmetric systems suggests a promising strategy to produce extremely asymmetric scattering. Inspired by such a unique feature, we propose a single-sided acoustic beam splitter that splits sound incident from a specific side but is totally transparent for sound incident from the opposite side. The unidirectional response is due to a parity-time-symmetric refractive index distribution. At the exceptional point when the real-part index and gain/loss modulations are balanced, it interacts with obliquely incident waves in a single-sided manner. In addition, by engineering the sidewall boundaries within an acoustic waveguide, we provide a general approach for obtaining the required complex refractive index, in which we show that the resistive or reactive component of the sidewall impedance can independently modulate the gain/loss or the real-part index. Based on this, a planar waveguide implementation of the single-sided acoustic beam splitter is demonstrated. Our study presents opportunities enabled by exploiting parity-time-symmetric systems in a higher-dimensional space and could find applications such as sensing and communication in a wide range of wave systems including but not limited to acoustics.