US Patent 9991680 Ignition plug and plasma generation device

To provide an ignition plug having low power loss even though iron is a main component of a center electrode thereof, to which a high frequency power such as a microwave is electrically supplied. A low impedance layer 6 composed of a material having magnetic permeability lower than iron is provided between an outer peripheral surface of a center electrode 2 and an inner peripheral surface of an axial hole 30 of an insulator 3. The low impedance layer 6 is in contact with at least the outer peripheral surface (surface) of the center electrode 2, thereby reducing power loss of an electromagnetic wave flowing on the surface of the center electrode 2. More particularly, the low impedance layer 6 is made of silver, copper, gold, aluminum, tungsten, molybdenum, titanium, zirconium, niobium, tantalum, bismuth, palladium, lead, tin, an alloy composed mainly of these metals, or a composite material of these metals.