Abstract: A bias wiring layer for supplying a bias current to a DC-SQUID is disposed above or below the superconductive ring of the DC-SQUID. The bias wiring layer is routed such that it passes through an axis of symmetry so that the center of the wiring layer passes through the middle of the superconductive ring. By providing a bias wiring layer rather than external bias wire, it is possible to prevent the generation of a magnetic flux caused by a bias current. Since no magnetic flux is produced by a bias current and the DC-SQUID and the vicinity thereof are not interfered with by a bias current, elements integrated on the same substrate are not adversely affected. It is thus easy to match the phases of the magnetic flux-voltage characteristics of plural DC-SQUIDs constituting a SQUID array, which is significantly effective in increasing the modulated voltage.

Abstract: An arrangement for coupling an rf-SQUID magnetometer to a superconductive tank circuit on a substrate is constructed in such a way that the two components are fully integrated into each other. Such integration increases the quality of the tank circuit by a factor of 2 to 3 as opposed to an arrangement obtainable by the flip-chip technology. Furthermore, the integrated arrangement permits simple assessment of coupling “k” between the SQUID and the tank circuit.

Abstract: This magnetic sensor comprises a flux transformer 2 having a superconducting thin film 2f formed on a sapphire substrate 2s, and a SQUID 1 disposed on the flux transformer 2 opposite thereto. In this magnetic sensor, since the sapphire substrate 2s, which can be obtained in a large size, is used for the flux transformer 2, even when the SQUID 1 is made smaller, the magnetic flux introduced from the flux transformer 2 into the SQUID 1 can be enhanced so as to increase the effective magnetic flux capturing area, whereby the detecting performance is improved, while the manufacturing cost can be reduced due to the smaller size of the SQUID 1.

Abstract: A SQUID (Superconducting Quantum Interference Device) magnetometer, by far the most sensitive means for detecting small magnetic field variations, is utilized to detect defects inadvertently produced in the manufacture and draw-down of wires. Detection is effected by moving any electrically-conducting wire directly under a shielded SQUID magnetometer with a small aperture to permit the sensing of the magnetic field associated with injected or induced alternating electrical current. Shielding may be provided either by a mu-metal cylinder with a small concentric bottom hole or an open superconducting cylinder strategically placed around the SQUID sensor. Initially, the position of the cryogenic containment vessel (dewar) is oriented to produce a null magnetic signal at the squid sensor location. Any phase-sensitive-detected) signal that appears after wire is spooled under the sensor must be related to non-concentric deviations of the current path in the wire.

Abstract: The operation of a planar geometry superconducting coil used in conjunction with a ground plane is improved by intracoil damping. This damping reduces coil resonances. The improvement consists of an intracoil shunt, which damps the resonances of the coil by connecting each turn, or loop, of the multiturn/multiloop coil with resistors. One example of a planar geometry superconducting coil which is effectively damped according to the present invention is the input coil to a superconducting quantum interference device (SQUID). The intracoil shunt may be added to the SQUID at the same time in the SQUID fabrication as the junction shunts.

Abstract: An asymmetric planar gradiometer for use in making biomagnetic measurements. The gradiometer is formed from a magnetometer which is inductively-coupled to the smaller of two connected loops patterned in a superconducting film which form a flux transformer. The magnetometer is based on a SQUID formed from a high T.sub.c superconducting material. The flux transformer and magnetometer may be formed on separate substrates, allowing the baseline to be increased relative to presently available devices.

Abstract: An apparatus for the qualitative and/or quantitative measurement of analytes, in particular in biological samples by means of receptor ligand binding and having a magnetizing device for the production of a magnetic field at the location of the sample and with a detection device for measurement of magnetic properties of the sample is characterized in that the magnetizing device is spatially disposed with respect to the detection device in such a fashion that the magnetic field produced by the magnetization device at the location of the magnetization is attenuated by at least a factor of 10, and preferentially by a factor of 1000 or more, at the location occupied by the sample during the measurement, or in that a switching device is provided for which, throughout a predetermined time duration and in particular during the measurement phase of the detection device can switch-off the magnetic field of the magnetizing device at the location of the sample.

Abstract: A SQUID magnetometer for low noise, stable measurement of magnetic fields. The magnetometer has a SQUID formed of two Josephson junctions connected in parallel in a superconducting ring. An external damping impedance is connected across the Josephson junctions. The damping impedance has a resistive component and a capacitive component. The damping impedance damps Josephson oscillations occurring at frequencies greater than the frequency response range of said magnetometer. An amplifier stage coupled to said Josephson junctions has a biasing impedance for damping the Josephson junctions in the frequency response range of the magnetometer.

Abstract: The present invention provides an improved and simplified voltage step-up circuit (2) for a SQUID magnetometric sensor (1), which provides step-up of a voltage signal generated by a SQUID element (11). The SQUID element is exited by a modulated signal using the FLL method. In an example, a step-up means (22) comprises only one step-up transformer (22T) working at room temperature and an electronic amplifier (22A). The voltage signal is first stepped up by the transformer. A signal processing means (23) processes the stepped up signal with the modulation signal to output a magnetic field measurement signal (V.phi.). In another example, a bias current source (21) is also connected to terminals between SQUID element (11) and the transformer (22). A series resistor is connected between the transformer and one of the terminals. This allows a reduction in the number of terminals between the SQUID sensor (1) and the circuit (2).

Abstract: A detecting coil of a SQUID is made of a superconductive film material having a critical temperature higher than a critical temperature of a superconductive film material composing a Josephson junction part. It is possible to measure the sample even when its temperature is higher than the critical temperature of the Josephson junction section by increasing the critical temperature of the detecting coil than that of the Josephson junction section.

Abstract: The present invention comprises a high-transition-temperature superconducting device having low-magnitude low-frequency noise-characteristics in magnetic fields comprising superconducting films wherein the films have a width that is less than or equal to a critical width, w.sub.C, which depends on an ambient magnetic field. For operation in the Earth's magnetic field, the critical width is about 6 micrometers (.mu.m). When made with film widths of about 4 .mu.m an inventive high transition-temperature, superconducting quantum interference device (SQUID) excluded magnetic flux vortices up to a threshold ambient magnetic field of about 100 microTesla (.mu.T). SQUIDs were fabricated having several different film strip patterns. When the film strip width was kept at about 4 .mu.m, the SQUIDs exhibited essentially no increase in low-frequency noise, even when cooled in static magnetic fields of magnitude up to 100 .mu.T.

Abstract: A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators, that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.

Abstract: A non-destructive testing equipment comprises a magnetic field generator for generating a uniform magnetic field, and a magnetic sensor accommodated in a thermal insulation container and filled with a liquid nitrogen. The thermal insulation container is located within a magnetic shield container having an opening. The magnetic sensor includes a SQUID that is a magnetic sensor having very high sensitivity. The magnetic sensor can detect, through the opening, an appreciable variation of the magnetic field that is caused by small impurities or minor defects contained in the object to be tested.

Abstract: A circuit device for driving a SQUID magnetometric sensor. This device includes an FLL magnetometer circuit for driving the SQUID with an AC signal as a magnetometric sensor, an evaluator circuit for evaluating the SQUID characteristics, and a selector circuit for selecting a sensor function or an evaluator function. When the selection circuit selects one of the sensor and evaluator functions, only one of magnetometer and evaluator circuits is activated. Therefore, the circuit device can act alternatively as either a sensor or an evaluator.

Abstract: A gradiometer for measuring magnetic field gradients has two SQUID loops lying in a SQUID loop plane with a flux concentrator lying in a flux concentrator plane parallel to the SQUID loop plane. The flux concentrator body is mirror symmetrical with respect to a plane of symmetry perpendicular to the SQUID plane and the flux concentrator plane along a basis line connecting the centers of the SQUID loops.

Abstract: A magnetometer using a plurality of superconducting quantum interference devices (SQUIDs) includes a detecting part composed of a plurality of SQUIDs each detecting external magnetic flux, converting the detected external flux into a voltage value, and outputting a differential voltage of the converted voltage value, a signal-processing part for modulating, amplifying, and demodulating the differential voltage outputted by the detecting part, and a feedbacking part for converting a signal outputted by the signal-processing part into magnetic flux to feedback the signal to the loop of the SQUIDs.

Abstract: A cryogenic apparatus for microscopy of physical properties of an object including a thin, stiff, transparent substrate or window within the outer wall of the vacuum space of a dewar and a cryogenic sensor within the vacuum space and spaced very close distances to the window. This construction allows for positioning a sample for measurement outside of the vacuum space, at room temperature or higher and for microscopy of physical properties of the sample by monitoring the output from the cryogenic sensor as it is scanned along the surface of the sample.

Abstract: Apparatus for measuring weak magnetic fields includes a cryogenic vessel CR having a domed bottom D for accepting a human head, a plurality of magnetic sensor units 10 mounted upright on the inner surface of the bottom D of the cryogenic vessel CR, an interface device 20 for receiving output signals of the magnetic sensor units 10 through respective lead lines 4, a data processor device 30 for analyzing the output signals of the magnetic sensor units 10 to specify magnetic fields spread in the ambient space about the human head and calculating the activity of a brain B from the magnetic fields, and a display device 40 for displaying the brain activity. Each of the magnetic sensor units 10 is fed along its guide line G through a small opening OP of the cryogenic vessel CR and mounted upright on the bottom D. As the opening OP of the cryogenic vessel CR is relatively small, the evaporation loss of a coolant in the cryogenic vessel CR is minimized and the running cost of the apparatus will be decreased.

Abstract: An RF-SQUID magnetometer whose RF-SQUID has an operating frequency, is formed by a superconductive ring having a Josephson element. An electric resonant circuit in the form of a closed superconductive conductor is coupled with the ring and forms a superconductive microwave resonator at that frequency.

Abstract: A nondestructive inspection apparatus having a SQUID is made with compact configuration and is capable of detecting a metallic or non-metallic metal for defects, corrosion, and the like, by forming the SQUID and a magnetic field applying coil on the same substrate. The SQUID comprises two Josephson junctions, a washer coil connected to the Josephson junctions to form a superconducting loop, shunt resistors, a damping resistor, and a feedback modulation coil, all of which are formed from a superconducting thin film on a supporting substrate. A magnetic field applying coil is formed on the same supporting substrate with a superconducting thin film or a normal conducting metal thin film. The magnetic field applying coil, which generally has plural turns around the SQUID, applies a dc or ac magnetic field to a sample. The change in magnetic field caused by a defect in the sample is detected by the washer coil, and the position and size of the defect may thus be determined.

Abstract: A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators, that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.

Abstract: To provide a nondestructive inspection apparatus with a reduced distance between a superconducting magnetic sensor and an object under inspection, a cryostat for cooling the sensor to a superconducting state is provided with inner and outer vessels. The inner vessel has a baseplate on which the magnetic sensor is disposed, and has an inner wall defining a central chamber for containing a refrigerant for cooling the magnetic sensor. The outer vessel has an inner wall defining a central chamber for containing the inner vessel, the magnetic sensor and the stage. A gap between the inner and outer vessels is evacuated to insulate the inner chamber from the ambient atmosphere. To facilitate ease of transferring an object to and from the stage for inspection, a load lock area is provided adjoining the outer vessel.

Abstract: A superconducting loop is formed by two Josephson junctions connected to both ends of a washer coil which serves also as a pick-up coil. The washer coil which is a magnetic field detection portion is constituted by two coils, i.e., a coil having a radius r.sub.1 and a number of turns n.sub.1 and a coil having a radius r.sub.2 and a number of turns n.sub.2 which are in the form of concentric circular loops. The two coils are coupled in opposite directions and are designed so that effective areas n.sub.1 .pi.r.sub.1.sup.2 and n.sub.2 .pi.r.sub.2.sup.2 are equal to each other. Since a magnetic field is directly detected by the washer coil, sensitivity to a magnetic field is enhanced. This makes it possible to obtain sufficient sensitivity to a magnetic field even if the area of the magnetic field detection portion is reduced to improve spatial resolution.

Abstract: A measurement system for measuring material deterioration in accordance with a magnetic field of the material in the presence of radiation. The measurement system includes a detection circuit which detects a magnetic field of the material and generates a signal indicative thereof which signal includes noise due to the radiation, a signal processing circuit including semiconductor devices to process the signal generated from the detection circuit and a noise reducing circuit for at least reducing noise in the generated signal which is due to the radiation. The signal processing circuit is installed at a place where a dose equivalent of radiation is equal to or smaller than that of a place where the detection circuit is installed.

Abstract: The present invention provides a miniature three-axis instrument for measuring the actual magnetic field vector. The novel instrument of the invention has three magnetometers on a single chip configured such that their pickup elements are coplanar, colinear and in fairly close proximity to each other. The tip of the chip, with the three pickup elements, is fashioned to allow as close an approach to the surface to be scanned as is possible with current single magnetometer scanning microscopes. The different positions of the pickup elements on the chip is compensated for digitally after data acquisition. The z-axis magnetometer has a planar pickup coil structure as is known in the art while the x-axis and y-axis sensing elements have a novel multi-turn, thin-film structure in the form of a planar solenoid which is another novel aspect of the present invention.

Abstract: A low-noise directly coupled dc SQUID magnetometer is disclosed. The magnetometer provides for single layer fabrication and is particularly applicable to high-T.sub.c superconductors operating at 77 Kelvin. A pair of dc SQUIDs are connected and biased in series such that the output voltage modulation with applied flux of the dual SQUID magnetometer, is double that of a single SQUID magnetometer. The bias current is applied to one SQUID and removed from the second SQUID of the pair. The magnetometer pick-up coil is directly coupled to the SQUID pair, providing for coherent modulation of the series-connected SQUIDS and a reduction of flux density noise of the device by a factor of 1/.sqroot.2.

Abstract: Flux of magnetic field generated from an object P of magnetic measurement, which links with the pick-up coils of the fluxmeters, where the flux is converted into electrical signals by each of the SQUID chips driven by the FLL circuits. The electrical signals are sent to the data collection unit via the signal processing circuit. In the data collection unit, the electrical signals are converted into digital data by the A/D converter. The converted digital data are recorded on a hard disk or a magnet-optical disk or the like, of the data recording section. The digital data recorded on the data recording medium are compensated with use of a crosstalk compensation matrix so as to remove the interference due to crosstalk for each channel, by the crosstalk compensation section. The compensated data are displayed directly on the display in the form of a magnetic field distribution or time waveform, and sent to the data analysis section.

Abstract: In case of cooling a SQUID magnetometer by a cryogenic refrigerator, a tubular resinous bobbin of the SQUID magnetometer around which a pick-up coil is wound is arranged so as to have wires, in the body of the bobbin, which are each coated with a resinous film, made of non-magnetic material with high thermal conductivity such as copper, and netted in a grid pattern substantially in an axial direction of the bobbin and a circumferential direction of the bobbin. According to the arrangement, thermal conduction characteristic of the bobbin is improved, thereby enhancing efficiency of cooling the pick-up coil made of a superconducting wire. This accomplishes an effective cooling of the SQUID magnetometer by the refrigerator.

Abstract: A multiple loop dc SQUID configuration with input and modulation circuitry configured for high-symmetry and low-noise operation is disclosed. The configuration is adaptable to implementation using standard thin film circuit fabrication technology. The SQUID inductance is defined by a plurality of washer-shaped thin superconducting films symmetrically oriented on a substrate and connected in series through a pair of Josephson junctions to form a multiple-washer gradiometric structure. The series connection arrangement also minimizes the number of required input and output terminal pads. Bias and modulation conductors are configured so as to prevent magnetic fields produced by currents flowing therethrough from coupling to the SQUID, and the modulation and input coil portions of the SQUID circuit are symmetrically configured to minimize signal coupling therebetween.

Abstract: A Josephson signal detector is presented which includes (1) a sensor with at least one Josephson junction (e.g., a SQUID) and (2) a comparator (e.g., an analog-to-digital converter); a measurement system using such detector; and a method of using such detector and measurement system. The detector can be, e.g., a digital SQUID. The detector can also include a readout circuit for reading out the output of the comparator. In one aspect of the invention, the sensor, or both the sensor and readout circuit, are powered by a DC current source. Through use of the DC current source, it is possible to provide, e.g., a digital SQUID, having reduced crosstalk and reduced fluctuation of ground potential, and which is kept from an increase in noise or a miss operation.

Abstract: A high temperature T.sub.c SQUID chip magnetometer has a flux-locked loop circuit including an independent feedback coil having an internal diameter greater than the maximum SQUID chip dimension. The feedback coil is mounted in close co-axial proximity to the SQUID chip to produce a substantially uniform feedback field over the entire area of the SQUID chip to cancel applied fields which penetrate the superconducting material.

Abstract: A magnetic telescope utilized to detect flaws in underground articles such as underground piping, implements multiple stages in the form of geometric and electronic configurations to enhance noise suppression. The geometric configuration includes a differential configuration of two pair of source coils which generate the magnetic flux, and gradiometers which pick-up the magnetic flux. A superconducting quantum interference device (SQUID) is utilized to detect the magnetic flux. The electronic configuration includes circuitry to adjust the current in the source coil pairs to minimize the signal seen by the SQUID when no underground article is present. The electronic configuration also includes feedback circuitry to feed back magnetic flux to the SQUID based on the signal detected by the SQUID. Combining the geometric and electronic configurations provides enhanced noise suppression so that the SQUID is capable of detecting smaller flaws in the underground piping for the same amount of source magnetic flux.

Abstract: The disclosed complex SQUID circuit achieves a high signal gain and high sensitivity for detecting a weak magnetic field. It is characterized by concentric loops of superconducting material, each loop incorporating preferably a pair of Josephson Junctions, the Josephson Junctions all aligned in a diameter generally transverse to the diameter defined by the connectors interconnecting the loops.

Abstract: A coupling structure for coupling a feedback signal to a superconducting quantum interference device (SQUID) by mutual inductance. In one embodiment the SQUID loop (A) is shielded from external magnetic fields perpendicular to it by a superconducting ground plane (B) at all points except for the pick-up loop (C). A feedback signal is coupled to the SQUID loop (A) by a feedback loop (D) which has a mutual inductance with the SQUID loop (A). During operation, the feedback loop (D) conducts a current in only one direction around the SQUID loop (A). This geometry ensures that the SQUID loop (A) is shielded from external magnetic fields, except at the pick-up loop (C), by the ground plane, and is balanced against fields parallel to the ground plane. The magnetic field produced by the current in the feedback coil (D) is small far from the SQUID (A). The feedback loop (D) is connected to exterior feedback electronics.

Abstract: A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the array, and electrically coupled to the active SQUIDs for eliminating the edge effects on the active SQUIDs. A magnetic flux transformer may be used in combination with a feedback assembly for increasing the sensitivity and linear dynamic range of the active antenna.

Abstract: DC-SQUID includes an input coil for transmitting an external magnetic field signal as a signal current from a detection coil, a washer coil to which the signal current is input as a signal magnetic flux, two Josephson devices for converting the signal magnetic flux transmitted to the washer coil to a signal voltage, shunt resistors and a damping resistor which are connected to each of the Josephson devices in parallel and in series respectively to extinguish the hysteresis of the current-voltage characteristic, and a feedback modulation coil to which a feedback and modulation current is transmitted from an external control circuit. The feedback modulation coil is arranged so as to linearly traverse over the upper portion or lower portion of the washer coil.

Abstract: A sensitive detector and detector system with multi-state element or elements employing the phenomenon of stochastic resonance to enhance signal-to-noise ratio (SNR) and detector sensitivity. Signal output is enhanced by the addition of external noise at the input. A single detector element has these improved outputs. Several stochastic resonance elements may be connected in arrays to further increase SNR of the output, increase detector sensitivity, and linearize the relation between input and output.

Abstract: The SQUID device consists of a loop of superconducting film material applied to the face of a substrate, the loop having a first width. A Josephson Junction is formed in the loop of the superconducting film material by pads of superconducting film material overlying one another and separated by a layer of insulating material. The pads have a second width larger than the first width. To increase the gain and improve the signal-to-noise ratio, the SQUID device may include a plurality of SQUID loops connected to one another in parallel. These loops may be overlie one another, or be adjacent to one another, or both, and may be either conventional SQUID loops or the improved SQUID loops with wide pads.

Abstract: A DC SQUID has a first washer coil for forming a superconducting ring, Josephson junctions and a dampening resistor coupled to both ends of the first washer coil, and a shunting resistor connected in parallel to the Josephson junctions. An input coil is magnetically coupled with the first washer coil, and a first modulation coil is also magnetically coupled with the first washer coil. A ground plane comprising a superconducting film is disposed to cover an area of the Josephson junctions without covering the first washer coil for shielding the Josephson junctions from a magnetic noise. The ground plane prevents a magnetic flux trap from occurring, thus enabling stable operation of the DC SQUID. A washer cover comprising a superconducting film is disposed to cover only a slit portion of the first washer coil to prevent leakage of a magnetic field from the slit portion. The ground plane and the washer cover are simultaneously formed in a same layer of the DC SQUID.

Abstract: SQUID control apparatus for controlling multiple SQUID probes includes a plurality of head units each corresponding to a respective SQUID probe, each of the head units including a non-cryogenic modulated flux-locked loop feedback circuit operating at a respective modulation frequency. The apparatus also includes a base unit coupled to all of the head units, the base unit providing control signals to control the multiple head units. Means are also provided, such as through the use of a daisy chain topology, for synchronizing the modulation frequency of all of the modulated flux-locked loop feedback circuits.

Abstract: Improved probes for miniaturized scanning magnetometers (scanning microscopes), particularly those utilizing superconducting quantum interference devices (SQUIDs), are provided by the invention. The improved probes can have sub-.mu.m.sup.2 effective pickup loop areas and enhanced shielding through the use of progressively wider double groundplane structures which result in improved probes having high spatial resolution.

Abstract: A magnetometer comprises a magnetic field pickup coil and a magnetic field detector that receives electrical signals from the pickup coil and produces an electrical detector output responsive thereto. The pickup coil and detector, which are preferably made of high temperature superconductors, are enclosed in an insulated enclosure having no vacuum insulation structure. Preferably, the enclosure is made of a foamed polymer material such as styrofoam. A coolant is provided to the interior of the enclosure, to cool the pickup coil and detector to a temperature below their superconducting transition temperature. A number of such modular magnetometers may be connected together to form an array.

Abstract: A magnetic flux microscope that measures the magnetic field about a sample surface. The apparatus uses a thin-film superconducting quantum interference device (SQUID) as the scanning device. Magnetic shielding is provided about the SQUID and is held stationary relative to the SQUID. The apparatus and method provides a very high magnetic image of the sample with a very high spatial and field resolution.

Abstract: The invention relates to a method and apparatus for processing the output signal of a low-noise sensor, particularly a squid. According to the invention, the output signal is coupled back to the sensor input by means of a resistance is set to be suitable by adjusting the rate of the resistor from room temperature, for instance by means of voltage.

Abstract: A shielding sleeve (19) for SQUID-magnetometers which serves to shield from electromagnetic interference fields, consists of an electrically conductive shielding material so as to obtain adequate RF shielding in conjunction with a low noise contribution, completely envelops a non-shielding cryostat (10), has a predetermined sheet resistance and consists of at least one layer of the shielding material in order to avoid an increase of the magnetometer overall noise.

Abstract: At least five planar gradiometers on at least three non-parallel surfaces are used to determine five, linearly independent components of a gradient tensor of a magnetic field.

Abstract: A SQUID system provides for tracking small input signals to a SQUID. A digital flux tracking loop provides for independently providing orthogonal error signal for signal and modulation feedback errors effective to form a flux tracking loop with the SQUID. A current source biases the SQUID with a current effective to cause the SQUID to output a periodic junction voltage V.sub.j having a period .PHI..sub.o, the V.sub.j having an amplitude as a function of magnetic flux .PHI. within the SQUID. A first processor modulates the magnetic flux within the SQUID to output at least three junction voltages. A second processor combines the at least three junction voltages and outputs first and second signals functionally related to flux tracking errors arising from the signal and modulation lock errors, respectively, the first and second signals forming feedback signals effective to form a flux tracking loop with the SQUID.

Abstract: A superconducting magnetic sensor includes a SQUID for interlinking with an external magnetic flux, an A.C. bias circuit for driving the SQUID with an A.C. bias current having a first frequency, a feedback circuit supplied with output voltage pulses from the SQUID for calculating a difference between the total number of positive output voltage pulses and the total number of negative output voltage pulses and for producing a feedback magnetic flux in response thereto such that the external magnetic flux is canceled out by the feedback magnetic flux, and a modulation current source for supplying a modulation current having a frequency substantially smaller than the frequency of the bias current and for producing a modulation magnetic flux in response to the modulation current such that the modulation magnetic flux interlinks with the SQUID.

Abstract: A magnetism sensor is disclosed that includes a substrate, a SQUID including a washer of an oxide superconductor thin film formed on a principal surface of the substrate, a hole shaped a similar figure to the washer at the center of the washer, a slit formed between one side of the washer and the hole and a Josephson junction by which portions of the washer at the both sides of the slit are connected across the slit. The magnetism sensor further includes a superconducting flux transformer of an oxide superconductor thin film including an input coil arranged on the SQUID but isolated from the SQUID and a pickup coil arranged on the principal surface of the substrate far from the SQUID, which are connected in parallel and a magnetism shield which excludes flux penetrating into the Josephson junction of the SQUID.

Abstract: A miniaturized SQUID module (10), notably for multi-channel magnetometers, for measurement of varying magnetic fields in a field strength range below 10.sup.-10 T, includes superconducting and shielded connections between a SQUID chip (19) and a gradiometer (12). The module can be mounted in the lower part of a cryostat and enables a large number of measurement points per unit of surface area. The SQUID chip (19) is arranged on a fully shielded supporting plate (18) which has a width of only a few millimeters and which is provided with electronic circuitry (23), the SQUID chip (19) being connected in a superconducting manner, at least by soldering, to the wires (11) of the gradiometer (12) via a superconducting, solderable and bondable intermediate support (27).