Losses in electrostatic actuation: a key challenge for electrocaloric cooling devices

Cooling plays a vital role in daily life, accounting for around 10% of global electricity consumption. Electrocaloric cooling is an emerging technology that offers a promising, energy-efficient alternative to traditional vapor compression technologies. The electrocaloric (EC) effect is a reversible temperature change triggered by the application or removal of an electric field. To achieve cooling, the EC material is alternately brought into contact with the hot and cold sides using electrostatic actuation (EA). However, EA currently entails significant losses caused by various interfacial and electrostatic effects. To study these detrimental effects, an experimental setup was built to characterize the electro-adhesion pressure (EAP) between the two films mimicking the EC device, with a focus on identifying the contribution of each loss component. Losses are characterized by comparing the maximum EAP before contact (actual force of EA) to the maximum post-contact EAP (losses of EA) under a DC voltage. Prior to this analysis, the triboelectric for PVDF was examined, and it was found to be a negligible contributor to losses. Results show that PVDF exhibits significantly higher losses than polypropylene (PP), while the similar pre-contact air gaps estimated for both materials confirm the theoretical model and validate the measurements. The contact adhesion forces have also been estimated, and unexpectedly, they are found to increase with applied voltage, confirming them as the primary loss mechanism in EA. This voltage-dependent behavior is attributed mainly to charge injection or diffusion bonding forces.