Abstract: Thin film Josephson junctions are combined with a block of superconductive material to form a low inductance dc SQUID having very high sensitivity. The block has a toroidal cavity with a circular opening or gap between the cavity and one face of the block. A pair of Josephson junctions, using planar thin film technology, are formed on a substrate and clamped against the block so that the two junctions in series bridge the gap, the junctions and the block combining to form a superconductive closed loop with two junctions in the loop. Coils in the toroidal cavity are inductively coupled to this closed loop.

Abstract: A circuit for reducing low frequency noise in a direct current biased superconducting quantum interference device. A squarewave bias signal having no dc component is used to bias the two junctions of the dc SQUID. At the same time, the magnetic flux in the SQUID is modulated to heterodyne the input signals up to some convenient frequency where they may be amplified without concern for drift. Final demodulation automatically adjusts for the fact that the relative phase is reversed each time the squarewave bias changes polarity states.

Abstract: A thin film SQUID device in which one or two thin film Josephson junctions are positioned at the hub of a wheel-shaped conductive structure including an outer closed loop rim and a plurality of radial arms or spokes formed on a substrate. A first group of alternate arms connects to one side of the junctions and a second group of intermediate arms connects to the other side of the junctions, the two groups of arms being insulated from each other at the hub. An overlying conductive pattern forms a coil in which the conductive turns of the coil include portions extending parallel to each of the arms to provide inductive coupling to currents circulating through loops formed by the groups of radial arms and rim.

Abstract: A flux locked loop, employing a squid in connection with the production of the locked-loop error signal, includes circuitry which renders the locked loop more immune to disturbance inputs such as a ground-loop noise and interference transients and which facilitates a scale factor adjustment of a sub-carrier drive signal for the squid. To minimize ground-loop noise disturbance effects, a portion of the circuitry in the feedback path of the locked loop includes a voltage-responsive converter circuit arrangement providing a current-drive feedback signal for coupling to the squid. To minimize interference transient disturbance effects, a portion of the circuitry in the forward path of the locked loop includes a circuit arrangement having a non-linear transfer characteristic defining opposed substantial attenuation regions separated by a generally linear gain region.