Subspace field emitter
You may also be looking for field emitters, or force field emitters.
Subspace field emitters were typically integrated into the warp nacelles on Federation starships. 

Modifications to a starship's engine's power emissions, in conjunction with the installation of field buffers around the emitter coil, could cause a distortion of a ship's power signature to resemble malfunctioning phase modulators in the ship's subspace field emitters. ()

de:Subraumemitter
field emitter
Warp