Leakage current as a predictor of failure in Dielectric Elastomer Actuators

Dielectric breakdown often leads to catastrophic failure in Dielectric Elastomer Actuator(s) (DEA). The resultant damage to the dielectric membrane renders the DEA useless for future actuation, and in extreme cases the sudden discharge of energy during breakdown can present a serious fire risk. The breakdown strength of DEA however is heavily dependent on the presence of microscopic defects in the membrane giving its overall breakdown strength inherent variability. The practical consequence is that DEA normally have to be operated far below their maximum performance in order to achieve consistent reliability. Predicting when DEA are about to suffer breakdown based on feedback will enable significant increase in effective DEA performance without sacrificing reliability. It has been previously suggested that changes in the leakage current can be a harbinger of dielectric breakdown; leakage current exhibits a sharp increase during breakdown. In this paper the relationship between electric field and leakage current is investigated for simple VHB4905-based DEA. Particular emphasis is placed on the behaviour of leakage current leading up to and during breakdown conditions. For a sample size of nine expanding dot DEA, the DEA that failed at electric fields below the maximum tested exhibited noticeably higher nominal power dissipation and a higher frequency of partial discharge events than the DEA that did not breakdown during testing. This effect could easily be seen at electric fields well below that at which the worst performing DEA failed.