Improvements in or relating to electrical switching devices

1,068,325. Superconductor devices. INTERNATIONAL COMPUTERS & TABULATORS Ltd. July 21, 1964 [July 25, 1963 (4)], Nos. 29508/63, 29509/63, 29510/63 and 29511/63. Heading H1K. In a switching device comprising a superconductor gate conductor magnetically coupled to an element of ferromagnetic material, means are provided for applying at least two different values of magnetic field to the ferromagnetic element so that it assumes different values of effective permeability thus altering the value of the self-inductance of the gate conductor. As shown, a controlled inductance device comprises a substrate 1 carrying a superconductive ground plane 2 of niobium on which is deposited a thin ferromagnetic element 3, which may be of a nickel-iron alloy and is preferably anisotropic with mutually perpendicular hard and easy directions of magnetization. A gate conductor 4 and a control conductor 5, both of superconductive material such as niobium or lead, are deposited over element 3 parallel to its easy axis of magnetization. Insulating layers (not shown) are provided between conductors 4 and 5 and between conductor 4 and ground plane 2. In operation, element 3 increases the self-inductance of gate conductor 4, but on application of a control current sufficient to magnetically saturate element 3 this self-inductance is reduced. An inductive branch circuit 7 is connected in parallel with gate 4 and the signal current divides between them in the inverse ratio of their self-inductances so that the change in inductance of gate 4 switches the major part of the signal current from circuit 7 to gate 4. Branch circuit 7 may be a simple superconductive loop or may be the gate conductor of a second controlled inductance device. Circuit elements to be controlled by the switching device may be included in circuit 7 and/or connected in series with gate conductor 4. All the conductors remain in the superconductive state throughout the operation of the device. In a second embodiment, Fig. 2 (not shown), the magnetic element is in the form of a circular area over which the gate and control conductors cross one another at right angles. Either the gate or the control conductor may be parallel to the easy axis of magnetization of the ferromagnetic element, the inductance of the gate in the absence of control current being high in the first case and low in the second. A plurality of control conductors may be provided for a single gate conductor. If full control currents are used the device