EM Drive
"The EmDrive is a relatively simple device: It's an empty cavity that isn't perfectly symmetrical. According to proponents of the EmDrive, by bouncing electromagnetic radiation within the cavity, the tapering in the cavity results in a net thrust of the engine, despite nothing leaking from the drive. In 2016, a team at NASA's Eagelworks lab reportedly measured a net thrust from their EmDrive experiment, which they claimed was a revolution in our understanding of physics and the future of spaceflight."
https://phys.org/news/2021-04-comprehensive-emdrive.html
"EmDrive works (or not) by pumping microwaves into an asymmetrical closed chamber."
https://www.popularmechanics.com/science/a35991457/emdrive-thruster-fails-tests/
Inertial Mass Reduction Device
"The microwave emitters create high frequency electromagnetic waves throughout the resonant cavity causing the resonant cavity to vibrate in an accelerated mode and create a local polarized vacuum outside the outer resonant cavity wall."
"the resonant cavity is filled with a noble gas."
https://patents.google.com/patent/US10144532B2/en
High frequency gravitational wave generator
"A high frequency gravitational wave generator including a gas filled shell with an outer shell surface, microwave emitters, sound generators, and acoustic vibration resonant gas-filled cavities. The outer shell surface is electrically charged and vibrated by the microwave emitters to generate a first electromagnetic field. The acoustic vibration resonant gas-filled cavities each have a cavity surface that can be electrically charged and vibrated by acoustic energy from the sound generators such that a second electromagnetic field is generated. The two acoustic vibration resonant gas-filled cavities are able to counter spin relative to each other to provide stability, and propagating gravitational field fluctuations are generated when the second electromagnetic field propagates through the first electromagnetic field."
https://patents.google.com/patent/US10322827B2/en