Patent GB-997787-A (GB)
Title: Electrical circuits including one or more superconductive elements
IPC: H03F19/00
Filed: 1961-09-14
Abstract: 997,787. Super-conductive amplifier. RADIO CORPORATION OF AMERICA. Sept. 14, 1961 [Oct. 5, 1960], No. 33075/61. Heading H3B. [Also in Division H1] An electrical device comprises a cooled element of super-conductor material having controllable different conditions for superconductivity along its length and means for generating excess ohmic heat in a region of the element so that an adjacent portion is in the resistive state while the remainder is in the superconductive state. Fig. 1 shows a superconductor element 10 of tin or tantalum in the form of a tapered film to provide an element of variable cross-sectional area, positioned in an environment having a temperature less than the transition temperature of the element. The element 10 is separated from a heating element consisting of a gold film 24 by a thin insulating layer 26 of silicon monoxide. The gold film rests on a glass support or aluminium oxide film on a support 30 of tetrafluoroethylene polymer. Source 38 which may be variable, provides current to heat film 24 to heat element 10 uniformly along its length. A current source 14 passes current through element 10. The arrangement and conditions are such that a portion of element 10 is in the normal resistive state and a portion is in the superconductive state. Assuming the resistive-superconductive interface to be in a certain position, any increase in current from source 14 will increase the joule heating in the resistive portion which will tend to make the adjacent superconductive portion go resistive; thus the interface moves farther into the superconductive region. Stability is achieved due to the tapering of the superconductive element which reduces the current density and therefore the joule heating effect as the interface moves to the right in Fig. 1. The operation requires a portion on the left-hand side of the element to be resistive initially and this is achieved either by providing a magnetic field by magnet 40 or by having a small portion of the element with higher current density (produced for example by a notch). The operation depends on whether or not the temperature of a particular section of the element 10 is above or below its transition temperature and thus movement of the interface may be controlled by variation of current from source 14, or of heat produced indirectly by source 38, or by varying the shape of the wedge-shaped element 10. If source 14 is a constant current source, variations of current from source 38 control the position of the interface and thus the voltage across element 10 which can be detected in output device 20. In this way the device constitutes an amplifier; if source 14 is also varied the device operates as a modulator. Shaping of the element 10 can be used to provide a function generator. In place of the heating effect provided by film 24, a magnetic field which is uniform along the length of element 10 may be used. The magnetic field may be constant or variable corresponding to a variation of source 38. In a further alternative a magnetic field which decreases along the length of element 10 may be used instead of varying the shape (i.e. tapering) element 10. This produces a similar mode of operation and in this case the magnetic field may also be varied by an input signal. Similarly this magnetic field can be replaced by a heat field whereby the temperature of the element decreases along its length.