An antimatter constrictor coil was a vital component of warp cores on NX-class vessels in the 2150s. In 2154, an illusion of T'Pol told a halluncinating Phlox that the antimatter constrictor coil was online when Phlox planned to take Enterprise NX-01 to warp speed while the ship was inside a trans-dimensional disturbance. (ENT: "Doctor's Orders")