Subspace field emitter

From Memory Alpha, the free Star Trek reference

You may also be looking for field emitters, or force field emitters.

Subspace field emitters are 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, can cause a distortion of a ship's power signature to resemble malfunctioning phase modulators in the ship's subspace field emitters. (DS9: "The Homecoming")