An inverted magnetic pulse was a form of electromagnetic field. In 2371, Lieutenant B'Elanna Torres modified the USS Voyager's main deflector to emit an inverted magnetic pulse in order to nudge a swarm of space-dwelling lifeforms out of the ship's path. However, the pulse caused the creatures to perceive Voyager as a potential mate, and they began to attach to the warp nacelles and drain power. (VOY: "Elogium")