Bifilar coil
（重定向自Bifilar transformer）
![Nikola Tesla's flat inductive bifilar coil.](/Images/godic/202412/24/TeslaBifilarColor.svg0759.png")
![Bifilar wound toroidal transformer.](/Images/godic/202412/24/Bifilar_wound_toroidal_transformer0759.jpg")
![Electrodynamometer with bifilar winding. A Page from Treatise on Electricity and Magnetism Volume 2.](/Images/godic/202412/24/A_Treatise_on_Electricity_and_Magnetism_Volume_2_3570759.jpg")
A bifilar coil is an electromagnetic coil that contains two closely spaced, parallel windings. In engineering, the word bifilar describes wire which is made of two filaments or strands. It is commonly used to denote special types of winding wire for transformers. Wire can be purchased in bifilar form, usually as different colored enameled wire bonded together. For three strands, the term trifilar coil is used.