Mach's Principle drive. Does it have to be electrons?...

[TDPerk]

...For purposes of pushing & pulling against the structure of the universe/rest of the universe?

Or does energy work for it?

Picture stacked thin discs of doped aluminum oxide (very high Q) excited by PZT's, with much smaller discs of ALOx in between. like large washers with small washers between, all on the same bolt.

As the overhanging edges of the discs oscillate, they are alternately charging and discharging photons, in phase such that they are moving rearwards when charged.

Since the Mach principle drive effect is related to acceleration and not translation, the relatively* minimal movement should be more than compensated for by the Hz rate, and it's a much more robust system mechanically than the capacitors now under discussion.

*No that is not meant to be a pun. It's a freebie.

[TDPerk]

Then wouldn't similarly assembled discs of semiconductors with rectennas on/in them, bathed in resonant EM fields such that they are alternately charged and discharged from axial periphery into the relatively not accelerated core (and the adjacent EM field) and back be a better solution?

I mean rectennas can see fairly high voltages which with a low resistance should see fast charge movement. And potentially* it could be very cold and employ high temp superconductors as rectenna elements.

*This one's the pun.