Using self-sensing in an electrodynamic actuator for broadband active vibration damping requires compensation of the actuator resistance and of the self-inductance of the actuator with an appropriate shunted circuit. In order to reduce power consumption the actuator resistance should be small, but for robustness of self-sensing and a large bandwidth a large resistance is required. A high transducer coefficient is important to get high sensitivity of the induced voltage that is proportional to the vibration velocity of an attached mechanical structure. However, a large transducer coefficient implies a strong magnetic field that also increases the self-inductance so that the measurement bandwidth potentially is reduced. In this study, in order to eliminate the first trade-off between power consumption and robustness, an actuator with a primary driving coil and a secondary measurement coil is proposed. The primary coil is optimized for driving by choosing a small resistance, whereas the secondary coil is optimized for sensing by choosing a large resistance. It has been shown that the transformer coupling between the two coils could be reduced by decreasing the cross section of the secondary coil, but there is a geometric limit on the reduction of the cross section of the secondary coil. Therefore an analogue electronic compensation scheme is proposed to compensate for the transformer coupling between the primary and the secondary coil. Feedback of the sensed velocity in the secondary coil is implemented and experimental vibration damping results at a plate are presented. Results are compared to self-sensing vibration damping, active vibration damping using a velocity sensor and passive damping means of the same weight as the actuator.
Shunt damping for piezoelectric actuators has been extensively studied using passive, tuned or negative capacitance components. Recently it has been noted that a capacitor together with a negative resistance amplifier can also be used for shunt damping using electrodynamic actuators with a low cut-off frequency. However simulations presented in this study indicate that this method is not appropriate for electrodynamic actuators with a high electrical cut-off frequency. This study compares experimental and simulation results of three control approaches obtained with a simple electrodynamic shaker that has a high electrical cut-off frequency: first, proportional current feedback; second, induced voltage feedback estimated with a Wheatstone bridge and third, induced voltage feedback estimated with an Owens bridge which compensates for the inductance of the shaker. The study shows that induced voltage feedback using an Owens bridge results in a negative inductance component that is an appropriate means to obtain vibration damping of a single degree of freedom system. Imperfect tuning to the magnetic parameters and interaction with power amplifier dynamics limit the bandwidth.