Yes, if it is electromagnetic. A form of mosquito-netting that would create a Faraday cage would be similarly effective depending on where the source(s) were.

What is perhaps even more interesting, eddy currents on the boundaries of the cave could be used to indicate that you were being broadcast at.

I think we've just solved detection and prevention in one go

Tin foil suits with bell bottom pants and afros + sideburns should be the first aid in such cases. Add some lightning rods headbands to the mix and this ultrasonic weapon is rendered incapable of any harm