Interlayer Parallel Connection of Multiple Helmholtz Resonators for Optional Broadband Low Frequency Sound Absorption

The Helmholtz resonance acoustic metamaterial is an effective sound absorber in the field of noise reduction, especially in the low-frequency domain. To overcome the conflict between the number of Helmholtz resonators and the volume of the rear cavity for each chamber with a given front area of single-layer metamaterial, a novel acoustic metamaterial of interlayer parallel connection of multiple Helmholtz resonators (IPC-MHR) is proposed in this study. The developed IPC-MHR consists of several layers, and the Helmholtz resonators among different layers are connected in parallel. The sound absorption property of IPC-MHR is studied by finite element simulation and further optimized by particle swarm optimization algorithm, and it is validated by standing wave tube measurement with the sample fabricated by additive manufacturing. The average sound absorption coefficient in the discrete frequency band [200 Hz, 300 Hz] U [400 Hz, 600 Hz] U [800 Hz, 1250 Hz] is 0.7769 for the IPC-MHR with four layers. Through the optimization of the thickness of each layer, the average sound absorption coefficient in 250-750 Hz is up to 0.8068. Similarly, the optimized IPC-MHR with six layers obtains an average sound absorption coefficient of 0.8454 in 300-950 Hz, which exhibits an excellent sound absorption performance in the low-frequency range with a wide band. The IPC-MHR can be used to suppress obnoxious noise in practical applications.