A field diverter was a piece of technology used to divert baryon particles during a baryon sweep.
In 2369, a group of terrorists posing as baryon sweep engineers from Arkaria Base used a field diverter installed in engineering aboard the USS Enterprise-D to remain aboard the ship, which had been otherwise evacuated in advance of a sweep. After the terrorists captured Captain Jean-Luc Picard, they brought him to engineering. During his escape from the terrorists, Picard destroyed the field diverter, forcing the group to head toward Ten Forward, the last place on the ship that would be affected by the sweep. (TNG: "Starship Mine")