switching electric AC voltage

Hi, I'm rather new to COMSOL. Is there a way to model a switching AC field between two electrodes? That is, both electrodes are always applying an AC field of the same frequency, but one side is high and the other is lower but periodically, they switch potentials?

In the past, I've used the electric currents model and frequency domain to solve, but I need to include this switching effect in the model, which I'm not sure how to.

Also, why is there such a huge difference when I'm defining the electrodes as floating potentials versus terminals? The E-field map I got when using the floating potential resulted in no gradient in potential and thus the E-field was zero everywhere.

Any suggestions would be helpful.

Thanks,
Ed