Acoustic attenuation characteristics of the muffler phononic crystal with hybrid resonators

Abstract

Aiming at achieving broadband and strong sound attenuation in the duct, this study proposes one compact and hybrid muffler phononic crystal. The two-dimensional (2D) transfer matrix method is applied to calculate the transmission loss (TL) of one unit cell validated by the numerical simulation and experiment. On this basis, the unit cell dispersion theory is employed to predict the bandgap properties of the infinite periodic mufflers. The sound reduction mechanism in the hybrid muffler is disclosed, while the effect of the period number on the acoustic performance is examined. It demonstrated that the acoustic resonant behaviors of the short-length mufflers are conducive to the continuous and superior attenuation band through the compact structure. The number of the TL domes and the boundary length of the short chamber could be evaluated by the cut-off frequency at the (0,1) radial mode and the first passing frequency for the muffler. Although each resonant-type component of the hybrid muffler is responsible for the TL peaks at different frequency ranges, via the coupling effect, they provide remarkably improved performance over a wide frequency range. The unit cell periodicity brings two types of bandgap, the locally resonant bandgap (LRG) and Bragg bandgap (BG), further enhancing the attenuation amplitude. Utilizing the different resonance mechanisms as well as the merging of the LRG and BG, the hybrid muffler phononic crystal is improved, which possesses a wide attenuation range with a tinier structure. The results develop new approaches for broadband and strong sound attenuation using the concept of the phononic crystal and offer a promising application in duct noise control.