Non-reciprocal Sound Transmission in Electro-acoustic Systems with Time-Modulated Circuits

Non-reciprocal sound transmission is demonstrated in an electro-acoustic system consisting of two shunt loudspeakers with time-modulated circuits. The shunt circuit is modulated by periodically varying the resistance in time sequence, and a phase difference of time modulation is set between two sets of loudspeakers to produce a spatial bias. The spatiotemporal modulation of acoustic properties is thus formed to break the reciprocity. The theoretical model based on the transfer-matrix method is developed to predict acoustic scatterings of electro-acoustic systems. Acoustic asymmetric transmission in opposite directions is disclosed by the model and is verified by time-domain simulation results based on the finite-difference time-domain method. Asymmetric transmission in multiple frequency bands can be created by tuning circuit parameters, showing their ability in regulating acoustic non-reciprocal behavior. This study may provide a platform for the design of compact and non-reciprocal acoustic devices with applications to efficient noise control.