Adhesion and air ionization in film-based electrostatic actuation: A case study

Electrostatic actuation (EA) plays an important role in applications like soft robotics and electrocaloric devices. With dielectric films, the interplay between adhesion and partial discharges plays a crucial role in the device losses and therefore represents a key challenge for optimizing the efficiency. Here, an advanced characterization method is used for measuring the position of the film during the actuation as a function of the applied voltage using, as a probe, the injection of a high-frequency voltage and the entailed capacitive response. This highly sensitive measurement of the film position during the actuation cycle reveals, on the one hand, the presence of a minimum voltage required for triggering the EA, and on the other, the appearance of charges on the film surface modifying the electrostatic force when the voltage exceeds a given threshold. The presence of surface charges is confirmed by fitting the electrostatic force and by current measurements before and after they appear. The study provides a new insight for discussing the fundamental trade-off between a lower working voltage bound defined by film adhesion, and an upper one imposed by the ionization of air, a very general issue all the EA devices will have to tackle in order to optimize their efficiency. As a case study, we analyze the losses on a zipping film-based electrostatic actuator using an m thick Polypropylene film as the moving part. • A position-sensing method to study in-depth electrostatic actuation. • Hysteresis cycle of the capacitance against the voltage. • Losses and speed of film-based zipping electrostatic actuation. • Low trigger voltage bound is related to film adhesion. • Upper voltage bound is related to the transfer of charges and to air ionization.