Patent GB-1196788-A (GB)
Title: Josephson Junctions.
Inventor: CLARK TERENCE DANIEL
IPC: H03B15/00
Filed: 1967-11-28
Abstract: 1,196,788. Superconductor devices. MULLARD Ltd. 14 Feb., 1969 [28 Nov., 1967 ; 11 April, 1968; 13 Dec., 1968], Nos. 54134/67, 17582/68 and 59371/68. Heading H1K. An array of Josephson junctions comprises a plurality of superconductive balls each of which is separated from a superconductive part of a substantially superconductive circuit by a thin non-superconductive barrier. When energized by a D.C. supply each junction emits radiation due to the A.C. Josephson effect and the array is arranged to concentrate and direct the radiation. The array may be used as a detector of incident radiation and to measure magnetic fields and hence electric currents. The superconductive part forming the junction with each ball may be a plate or strip or may be a further ball. A planar array of Sn balls with oxide coatings are arranged between two p.t.f.e. plates and are contacted at opposite sides of the array to provide a radiation generator, Fig. 2 (not shown). If the spacing of the junctions (i.e. the diameter of the balls) is half the wavelength of the radiation the emission pattern comprises a primary lobe at right angles to the plane of the array with no appreciable side lobes, Fig. 5 (not shown). The balls may be ellipsoidal instead of spherical. An array of spherical balls may be arranged to conform to the surface of a paraboloid and are covered on the outside by a Nb sheet coated with p.t.f.e., Fig. 3 (not shown). An arrangement for measuring the absorption spectrum of a specimen comprises identical generating and receiving arrays arranged in two legs of a specially shaped dewar flask so that the specimen may be placed in the radiation path between them but external to the flask, Fig. 4 (not shown). A generator comprises a plate to which are secured a plurality of balls for example by soft soldering or by using A1 loaded epoxy resin, a top plate being pressed against the balls which have an oxide coating, Fig. 7 (not shown). The emission is parallel to the plates and three sides may be shielded to direct the radiation. The top plate may also have a matching array of balls secured to it. One plate may be of frozen mercury, the balls being secured to the other plate and pressed into the surface of liquid mercury which is then frozen. The devices may be mounted in resonant cavities and the gaps between the balls may be filled with an impedance matching dielectric which may be granular or porous to allow the passage of coolant. A conductive cylinder having an axial rod of non-conductive material and having an irregular filling of superconductive balls from which it is insulated generates radiation which may be emitted through windows, e.g. slots, in the cylinder, Fig. 10 (not shown). The axial rod may be omitted, Fig. 11 (not shown). Detectors may be operated by biasing the array to a point at which they would just oscillate but maintaining the temperature marginally above the critical temperature. When illuminated with radiation the junctions become superconductive. A detector array may also be held at a constant temperature such that the working point is on the high slope part of the current-temperature characteristic near the critical temperature and when fed from a constant current source the resistance, and hence the voltage drop, decreases when subjected to radiation. A detector array may also be cooled to a temperature just below the steep part of the characteristic so that heating due to incident radiation increases the resistance. When an array is subjected to a suitably orientated magnetic field the current-magnetic flow characteristic exhibits a periodic structure Fig. 13A (not shown), so that changes in flux may be measured digitally by counting the number of oscillations produced in the current. The array may comprise two layers of balls contacted by plates, the layers being staggered so that each ball contacts a plurality of balls in the other layer. Current may also be measured digitally by arranging a wire close and parallel to the array and perpedicular to a biasing magnetic field. A plurality of arrays may be mounted in an oversize waveguide to act. as a generator Fig. 16 (not shown), or the arrays may be coupled to a correctly sized waveguide by means of horns, Fig. 17 (not shown). The use of such arrangements for frequency multiplication is also mentioned. The superconductor may be Sn, A1 or Nb and the insulating material may be the oxide of the superconductor or may be a normal metal such as Cu or Au.