Perfect Absorption in Duct by Coupling Helmholtz Resonators

摘要

Perfect absorption in straight through ducts, resulting from coupling side-branched resonators, is always interesting highly desired. However, reaching the perfect coupling condition has remained difficult since there has not a clear instruction for perfect coupling design yet. In this research, the condition for perfect absorption of two-coupled Helmholtz resonators (HRs) will theoretically developed, which indicates explicit required values for acoustic impedance of the HRs. It theoretically points out that, at perfect coupling state, the volume velocities at two HRs' inlets have same amplitude but are nearly out-of-phase. The radiations from the coupled HRs are two-complement. A one-complement is absorbed by the first HR, while the other cancels out with the incident wave. A design of two HRs coupled at 1000 Hz has been proposed to validate the theoretical result, which shows excellent agreement with simulation. In addition, the perfect absorption peak exposes substantial Q-factor, 25.8%, and high transmission loss, at least 10 dB, is realized in a broadband region from 873 - 1808 Hz. The achieved coupling condition and proposed design can pave the way for designing and optimizing perfectly absorbing and highly blocking acoustic liners and silencers.