Wave control and development of anechoic systems in air are of major interest to improve acoustic comfort. Currently, passive control techniques, which consist in using absorbing materials are effective at high frequency, but the principal limitation of this approach is mass and volume, particularly in the low-frequency range. Active control techniques (like the use of antinoise, which uses interference of sound waves) have been successfully applied to reduce the noise level, but their main drawback is the complexity of the global system and global power requirements. Another approach is to reduce the noise transmission by a proper control of transmitting structure oscillations. The aim of this study is to develop a technique of noise reduction by using piezoelectric elements. The device considered is a large clamped plate, equipped with piezoelements. Sound transmission through this plate is strongly related to the various resonances. Vibration damping devices implemented on this plate results in the reduction of the plate resonances and therefore of the correlated transmitted sound. The synchronized switch damping technique (SSD) is implemented. In this semi-passive approach, the piezoelements are continuously switched from the open circuit state to a specific electric network synchronously with the strain. Owing to this switching mechanism, a phase shift appears between the strain induced by an incident acoustic wave and the resulting voltage, thus creating energy dissipation. As many techniques using piezoelements, in this non-linear process, damping performances directly depend on the electromechanical coupling coefficient of the system. An analytical model and a finite element model are proposed in this study to obtain optimal size and location of piezoelectric inserts. Using this design, an attenuation of 19 dB on the plate oscillations and 15dB on the transmitted wave pressure can be obtained.

This study focuses on the development of a piezoelectric device capable of generating feedback vibrations to the user who manipulates it. The objective here is to explore the possibility of developing a haptic system that can replace physical buttons on the tactile screen of in-car systems. The interaction between the user and the developed device allows completing the feedback loop, where the user’s action generates an input signal that is translated and outputted by the device, and then detected and interpreted by the user’s haptic sensors and brain. An FEM (finite element model) via ANSYS multiphysics software was implemented to optimize the haptic performance of the wafer structure consisting of a BaTiO₃ multilayered piezocomposite coated on a PET transparent flexible substrate. Several parameters relating to the geometric and mechanical properties of the wafer, together with those of the electrodes, are demonstrated to have significant impact on the actuation ability of the haptic device. To achieve the desired vibration effect on the human skin, the haptic system must be able to drive displacement beyond the detection threshold (~2 µm) at a frequency range of 100–700 Hz. The most optimized actuation ability is obtained when the ratio of the dimension (radius and thickness) between the piezoelectric coating and the substrate layer is equal to ~0.6. Regarding the simulation results, it is revealed that the presence of the conductive electrodes provokes a decrease in the displacement by approximately 25–30%, as the wafer structure becomes stiffer. To ensure the minimum displacement generated by the haptic device above 2 µm, the piezoelectric coating is screen-printed by two stacked layers, electrically connected in parallel. This architecture is expected to boost the displacement amplitude under the same electric field (denoted $E$) subjected to the single-layered coating. Accordingly, multilayered design seems to be a good alternative to enhance the haptic performance while keeping moderate values of $E$ so as to prevent any undesired electrical breakdown of the coating. Practical characterizations confirmed that $E=20 \mathrm{V}/\mathsf{\mu }\mathrm{m}$ is sufficient to generate feedback vibrations (under a maximum input load of 5 N) perceived by the fingertip. This result confirms the reliability of the proposed haptic device, despite discrepancies between the predicted theory and the real measurements. Lastly, a demonstrator comprising piezoelectric buttons together with electronic command and conditioning circuits are successfully developed, offering an efficient way to create multiple sensations for the user. On the basis of empirical data acquired from several trials conducted on 20 subjects, statistical analyses together with relevant numerical indicators were implemented to better assess the performance of the developed haptic device.