Asymmetric acoustic absorption realized by a ventilation meta-window

Acoustic insulation windows with ventilation feature can maintain the quietness of the indoor environment while ensuring airflow. Some specific scenarios including music theaters, home cinemas, and gymnasiums have unique demand for windows that simultaneously satisfy the suppression of outdoor noise and create reverberation of indoor sound. Therefore, it is necessary to construct an acoustic window system with excellent ventilation abilities as well as asymmetric absorption behaviors. In this work, we present a meta-window that designed by a non-Hermitian acoustic system composed of annular coiling-up structures (ACSs) with dual-port and spatial rotational symmetry. By adjusting the lengths of the two internal pipes, the ACS can operate at the exceptional point (EP) and achieve extremely asymmetric absorption. In addition, the length and width of ACS are only 1/28.8 and 1/32.2 of the working wavelength, which has advantages of deep sub-wavelength scale and compact configuration. Meanwhile, the meta-window consisting of 8 ACSs can further increase the ventilation rate. The measured wind velocity ratio is above 0.59, and the absorptivity of forward and backward absorptivity are 0.99 and 0.08, respectively. Moreover, we further verify that the meta-window cascaded by 8 ACSs with different parameters can work in a broadband from 408 Hz to 572 Hz. The meta-window proposed in this work balanced the ventilation performance, asymmetric absorption capacity and configuration scale. Our work contributes to the development and application of noise control in the field of architectural acoustics.