Compact phononic crystal ducts with periodic helmholtz mufflers and integrated thin plates for low-frequency broadband noise control

This paper presents a compact phononic crystal featuring periodic Helmholtz mufflers with integrated thin plates for low-frequency broadband noise control in duct systems. Combining transfer matrix theory with rectangular plate modal analysis, the acoustic impedance model is developed for the Helmholtz mufflers that accounts for acoustic-structure coupling. The bandgap characteristics are systematically investigated through unit cell dispersion theory, with transmission loss predictions validated through both numerical simulations and experimental measurements. Afterward, the acoustic attenuation mechanism in the phononic crystal and the influence of different structure parameters on the acoustic attenuation characteristics are revealed. The research shows that introducing the thin plate brings a new peak of the transmission loss in the low-frequency range, which could generate one locally resonant bandgap. The existence of two bandgaps could widen the range of sound attenuation in the medium and low-frequency region. The thin plate is conducive to attenuating low-frequency noise with the help of small-size structures and various bandgap regulation factors. Moreover, the effect of the periodicity on the acoustic performance is investigated. Compared with the case of non-uniform distribution in the circumferential direction with the strict periodicity, the phenomenon of bandgap coupling is more obvious in the case of non-uniform axial distribution with the relaxation of periodicity. This research provides technical support for the low-frequency, broadband and large amplitude noise attenuation in pipelines using the concept of phononic crystals.