Oblique incidence sound absorption of a hybrid structure using a micro-perforated panel and a planar actuator

An ultra-thin hybrid sound absorber consisting of a micro-perforated panel and a planar actuator (MPP-PA) is proposed. With the optimization of excitations on the PA plate, the absorber, almost half the thickness of a conventional passive MPP structure, can realize broadband oblique-incidence sound absorption from 100 to 1000 Hz due to the strong plate-cavity coupling. Particularly at frequencies dominated by the zeroth cavity mode and lower-order plate modes (100 to 300 Hz), extraordinary absorption is achieved and barely changes with the incident angle. Consequently, the hybrid MPP-PA provides an ultra-thin solution for the broadband high absorption in low-and-mid frequency ranges.