Electrostatic actuators with constant force at low power loss using matched dielectrics

Electrostatic multilayer systems, which often employ thin polymer films in combination with displaceable insulating fluids, can enable actuation in applications such as soft robotics. Driven by high electric fields, they provide strong performance in terms of power density, actuation strain and speed, but suffer from rapid force decay due to interfacial charging. High-frequency polarity inversion of driving voltages is a remedy, but involves large power consumption and unfavourable force oscillations. Here we report a theoretical and experimental framework for the force behaviour in generic solid/liquid-dielectric multilayer stacks independent of actuator design and solely based on their dielectric properties. We use this model to develop materials-based solutions, which rely on matching the bulk charge relaxation rates of the constituent dielectrics, for a variety of soft actuator systems: tunable lenses, artificial muscles and haptic devices. The approach provides indefinite, steady force output under constant-voltage operation, with up to 1,000-fold power loss reduction compared with unmatched material combinations.