This company builds pulsejets for UAV / RPV, like the one that delivers 350 lbf of thrust. They are designed by Matthew Travis of Florida, USA. These engines have no moving parts.

“Schematic drawing of the working principle”

"A complete prototype"

-This is a valveless engine, and the return of gases towards the front is reversed in the opposite direction to add to the main nozzle's thrust. There are quite a few engines with this type of operation and they are described in this A-Z edition.