Visualizing multi-physical spatiotemporal evolution of dielectric breakdown in high-performance polymeric capacitors

Pulse power has many important technological applications, for which the dielectric capacitors are essential. It is imperative to understand the breakdown mechanism to improve the dielectric energy storage density, yet the breakdown process involves multi-physical coupling spanning multiple spatial and temporal scales, making its characterization very challenging. Recognizing local field concentration results in local strain concentration through Maxwell's stress, we develop an effective method to visualize the dielectric breakdown process via optic strain measurement. Utilizing high-performance biaxially oriented polypropylene as a demonstration, we find dielectric breakdown is an ultrafast process with breakdown current rising and dropping in just tens of nanoseconds. Rapid temperature rise is observed after breakdown as well due to Joule heating, though both current measurement and temperature mapping offer little insight before breakdown actually occurs. Nevertheless, substantial strain concentration is observed before breakdown, reflecting electric field concentration that eventually leads to breakdown. A well-defined upper bound on the electric field concentration is also noted.