Enhanced semi-passive damping using continuous switching of a piezoelectric device on an inductor

The SSD technique proposed here addresses the problem of resonance damping on a mechanical structure. SSD stands for Synchronized Switch Damping. Apart from active techniques, passive ones consist in connecting a piezoelectric insert attached to the structure to a passive electric network in which the energy generated by the piezoelectric inserts is degraded. In the semi passive approach, the piezoelectric inserts are continuously switched from open circuit to short circuit synchronously to the structure motion. Due to this switching mechanism, a phase shift appears between the piezoelectric strain and the resulting voltage, thus creating energy dissipation. For the new technique proposed here, instead of discharging the piezoelectric inserts during a brief short circuit, they are connected on a small inductor, allowing the inversion of the voltage and then released to open circuit. In this case the voltage amplitude is optimized and is 90 degrees out of phase with the motion then enhancing the damping mechanism. The technique is applicable at any frequency without the need for a large tuned inductor, especially for low frequency applications. There is no need for external power supply unless for the low power circuitry of the switch device. The implementation of the switch drive with a very cheap micro-controller is described. Experimental results measured on cantilever beams made with different materials are proposed. Damping ability ranges from 6 dB on a very viscoelastic epoxy beam to nearly 20 dB on a steel beam. Harmonic excitation and transient results are both proposed and compared. Finally, an electromechanical model is proposed, giving an interpretation of the damping mechanism. Theoretical predictions are in good agreement with the experiments.