Abstract: A sealing apparatus is described for use with a container having an open end with a sealing rim therearound, a closure on the open end and a membrane in the closure disposed against the sealing rim, the membrane having at least a plastic layer adapted for being sealed to the sealing rim of the container and a layer formed of a high dielectric loss tangent material. Preferably, it includes a resonant cavity having first and second ends, a central axis and an inner peripheral surface located around the central axis, the first end of the resonant cavity having an opening for receiving the open end of the container having the closure thereon. It also includes an applicator electrode extending into the resonant cavity from the second end thereof and having an open end with a sealing rim therearound for supporting the container.