Effects of structural design including cellular structure precision controlling and sharp holes introducing on sound absorption behavior of polyimide foam

This paper aims to effectively improve acoustic property of polyimide foam (PIF) by regulating cellular structure of PIF on a large scale and introducing sharp hole structure simultaneously, adopting a special mold with split structure in a closed-mold foaming route. In this work, PIF with same split structure but different pore cell sizes, density, and windows opening rate were produced in the first time. Due to the stepwise transition principle, the impedance of the air acoustic medium and the acoustic material was well matched. In addition, the characterization results showed the effectively effects of microporous structure and split structure characteristics of PIF on the acoustical absorption coefficient. For PIF-4, sound absorption coefficient kept around 0.9 from 900 to 6300 Hz. Especially, the resonance sound absorption characteristics was basically eliminated, which ensured the high efficiency sound absorption behavior of PIF in the broadband range from 600 to 6300 Hz region.