Active-passive piezoelectric absorbers for systems under multiple non-stationary harmonic excitations

Previous research has shown that piezoelectric materials can be shunted with electrical networks to form devices that operate similarly to a mechanical vibration absorber. These systems can be tuned to provide modal damping (modal tuning) or to attenuate a harmonic disturbance (tonal tuning). Semi-active piezoelectric absorbers have also been proposed for suppressing harmonic excitations with varying frequency, a scenario that cannot be easily controlled using passive devices. However, these semi-active systems have limitations that restrict their applications. In a previous study, the authors have developed a high performance active-passive alternative to the semi-active absorber that uses a combination of a passive electrical circuit and active control actions. The active control consists of three parts: an adaptive inductor tuning action, a negative resistance action, and a coupling enhancement action. This new device has been shown, both analytically and experimentally, to be very effective for the suppression of harmonic disturbances with time-varying frequency. In the present paper, the adaptive active-passive piezoelectric absorber configuration is extended so that it can track and suppress multiple harmonic excitations. A new optimal tuning law is derived, and the stability conditions of the system are investigated. The effectiveness of this new multi-frequency absorber design is demonstrated by comparing its performance and control power requirement to the popular Filtered-x adaptive feedforward control algorithm. (C) 2002 Published by Elsevier Science Ltd.