Efficiency of an absorber involving a nonlinear membrane driven by an electro-acoustic device

Great attention has been recently paid to employing nonlinear energy sink (NES) as an essential nonlinear acoustic absorber rather than Helmholtz absorbers. NES are based on the principle of the “Targeted Energy Transfer” (TET) that allows to transfer the energy from a primary acoustic field to the NES. In this paper, an hybrid electro-acoustic NES (hNES) is described. It is composed of an latex membrane with one face (exterior) coupled to the acoustic field (to reduce) and the other one enclosed. The enclosure includes a feedback loop composed of a microphone and a loudspeaker that control the pressure difference at the level of the membrane. Due to the hardness behavior of the membrane in non-linear deformation, the hNES can synchronize its resonance with one of the resonances of the acoustic field greater than the linear resonance of the hNES. It allows to bring out the TET toward the hNES and thus reduce noise. The feedback loop tunes the linear resonance frequency of the hNES at low level, which is a key factor for the triggering threshold of the TET. An experimental study of the hNES will be presented including TET regime characterization and influence analysis of the feedback gain.