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International audience; Controlling low-frequency vibration of structures is still a challenge in modern industries. Metamaterials with local resonators present bandgaps at sub-wavelength frequencies. Propagative waves are not supported within the bandgaps. Therefore, metamaterials are widely proposed for vibration reduction or isolation at low frequencies. However, metamaterials with passive resonators suffer narrow effective frequency band and lack of adaptivity. In this talk, a new type of smart metamaterial with online controllable bandgaps is presented. The studied metamaterial is composed of piezoelectric actuators and digital synthetic impedance circuits (digital circuits). The digital circuit contains a micro-controller. By programming the micro-controller, the circuit can establish any desired impedance between the terminals of the connected piezoelectric patch, therefore to program the dynamical behaviours of the designed metamaterial. In this sense, a programmable metamaterial is studied. Experiments are performed to study its programmable dynamical behaviours, with a particular focus on isolation of vibration transmission. Results demonstrate that the proposed smart metamaterial can be flexibly programmed online to isolate vibration transmission in beam structures at desired frequencies or within a large frequency band. The proposed programmable metamaterial conception can be naturally extended to other kinds of structures like plates and shells, they are promising components in the future adaptive structures.

An Electroacoustic Resonator consists of a loudspeaker used as a membrane resonator, through anacoustic pressure-based controlled electrical current, in order to vary its vibrating velocity in re-sponse to an exogenous sound field. This way, the loudspeaker membrane can be turned, for example,into an effectively broadband sound absorber. However, the effectiveness and stability conditions ofsuch an active device are intrinsically dependent on the accurate knowledge of its electromechanicalconstituents and the whole control chain, and any mismatch might impair significantly the controlperformance. In this paper, we propose a new method for identifying the Thiele-Small parametersof a loudspeaker to be used as an active electroacoustic resonator through a digitally-implementedcontrol architecture. Then, numerical and experimental investigation are undertaken to show how theapplication of Impedance Control laws affects the stability of the electro-mechano-acoustical system.An experimental verification of the acoustic performance of the proposed control strategy is provided,leading to concluding discussion on further developments.