A multiphasic scan or multiphasic sweep is a type of sensor scan conducted by modifying the navigational sensors to operate on a multiphasic bandwidth. The result is a scan capable of penetrating intense electromagnetic radiation as well as ion radiation. (VOY: "Cathexis", "Dreadnought")
The USS Voyager utilized this method to scan a dark matter nebula in 2371. (VOY: "Cathexis")
In 2372, Captain Janeway ordered Tuvok to run a multiphasic scan on a group of ships projected by the Bothans, in order to find some evidence of defensive weakness. (VOY: "Persistence of Vision")
The same year, a multiphasic sweep was ran to locate the rogue Cardassian ATR-4107 discovered in the Delta Quadrant after it masked its warp trail with a randomized electromagnetic field. (VOY: "Dreadnought")
The following year, Janeway ordered Harry Kim to run a multiphasic scan on a Borg cube found adrift in the Nekrit Expanse, while ordering Tom Paris to "stand by to get us out of here in case they react." From Kim's scan, he was able to determine that the cube did not have any active energy signatures or life signs. (VOY: "Unity")