Design of a Lightweight, Electrodynamic, Inertial Actuator with Integrated Velocity Sensor for Active Vibration Control of a Thin Lightly-Damped Panel C. Paulitsch § , P. Gardonio § , S.J. Elliott § , P. Sas * and R. Boonen * § University of Southampton, ISVR Highfield SO17 1BJ, Southampton, U.K. e-mail: cp@isvr.soton.ac.uk * Katholieke Universiteit Leuven, PMA Celestijnenlaan 300B, B-3001, Heverlee, Belgium Abstract This paper presents the design study of a lightweight inertial actuator, with integrated velocity sensor, for the implementation of velocity feedback control, i.e. active damping, in lightly-damped panels. The arrangement provides a collocated force actuator and velocity sensor device so that, in principle, an unconditionally stable direct velocity feedback loop could be implemented. However, this property is limited by the fundamental resonance due to the vibration of the inertial mass on the supporting spring. The main design issues are discussed starting from the characterization of the electromagnetic device which has been optimised using a Finite Element Analysis (FEA) to produce the maximum design force of 3N for a given weight of the inertial mass of 20g and input power constraints. The actuator suspension is designed so that important resonance frequencies lie outside the desired control bandwidth of 70Hz to 1kHz. Finally the design predictions are compared to measurements at a built up prototype actuator. 1 Introduction Large vibrations may lead to failure of mechanical structures or compromise the functionality of attached sensitive devices. Vibration suppression is especially important for lightweight structures since lightweight design usually leads to thin, lightweight, but stiff structures with low damping. Hence, despite good static properties under dynamic loads vibrations may be amplified at resonance. Moreover due to the reduced impedance of the structure outside the stiffened load path noise transmission may be enhanced. In order to prevent failure or reduce noise radiation active vibration damping may add a higher degree of damping than passive means of the same weight when actuators, sensors and the control scheme are properly chosen. Passive means are especially inefficient and heavy for low frequency noise attenuation [1]. Flexible structures have multiple resonance frequencies that all should be controlled when they are exposed to broadband excitation. But often these resonance and anti-resonance frequencies are not precisely known or change during operation. Therefore collocated absolute velocity feedback using a dual actuator-sensor pair [2] should be used so that in theory unconditional stability is guaranteed [3]. Point force actuators are more efficient than distributed actuators for the control of bending vibrations that are important for sound radiation [4]. In practical applications point force actuators often do not react relative to a solid ground, but against a reaction mass. Then the actuation force from the force generation mechanism is different from the force actually transferred onto the structure [5]. Additionally in practice internal resonance frequencies of the suspension are introduced that limit the control bandwidth at higher frequencies. The transmitted force is limited by the reaction mass and the actuator stroke. Typical force generation mechanisms are electromagnetic, electrodynamic or piezoelectric actuators. Piezoelectric 239