A hybrid electro-acoustic nonlinear membrane absorber working as a nonlinear energy sink (here after named EA-NES) is described. The device is composed of a thin circular visco-elastic membrane working as an essentially cubic oscillator. One face of the membrane is coupled to the acoustic field to be reduced and the other face is enclosed. The enclosure includes a loudspeaker for the control of the acoustic pressure felt by the rear face of the membrane through proportional feedback control. An experimental set-up has been developed where the EA-NES is weakly coupled to a linear acoustic system. The linear acousticsystem is an open-ended tube, coupled on one side to the EA-NES by a box, and on the other side to a source loudspeaker by another box. Only sinusoidal forcing is considered. It is shown that the EA-NES is able to perform resonance capture with the acoustic field, resulting in noise reduction by targeted energy transfer, and to operate in a large frequency band, tuning itself passively to any linear system. We demonstrate the ability of the feedback gain defining the active loop to modify the resonance frequency of the EA-NES, which is a key factor to tune the triggering threshold of energy pumping. The novelty of this work is to use active control combined to passive nonlinear transfer energy to improve it. In this paper, only experimental results are analyzed.

We present the first real size evidence of targeted energy transfer in a concrete building, with an efficient action on low frequency noise reduction. It is achieved by the means of a hybrid Electro-Acoustic Nonlinear Energy Sink

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.

In this paper an electro-Acoustic Nonlinear Absorber (ANLA) is described. It is composed of a baffled nonlinear membrane with its front face coupled to an acoustic cavity and the other one enclosed. The enclosure includes a feedback loop composed of a microphone and a loudspeaker that control the acoustic pressure seen by the rear face of the membrane. Due to the nonlinear geometrical properties of the membrane, the ANLA can synchronize it resonance with one of the resonances of the cavity. It allows to bring out the energy transfer toward the ANLA and thus to reduce pressure in the cavity. The feedback loop tunes the resonance frequency of the ANLA at low level, wich is a key factor for the triggering threshold of the targeted energy transfer. An numerical study of the efficiency of the ANLA to reduce noise in a cavity is presented including the influence of the feedback loop parameters.