A dc transformer

Although conventional transformers are ac, a device that may be termed a dc transformer has been constructed by using superconductors. To provide an understanding of how such a transformer would operate, some of the properties of type I and type II superconductors are reviewed. Since the dc transformer under discussion is constructed from thin superconducting films, the main emphasis is on these structures; the concept of flux motion is also explained. The result of the work described is a device in which a direct current or voltage can be transformed, and in which it is possible to extract power from the secondary circuit.