Abstract:

We have designed and fabricated three types of high- SQUID (superconducting quantum interference device) magnetometers based on step-edge Josephson junctions using three different concepts of coupling magnetic flux into the SQUID: (i) a single pickup loop galvanically coupled to the SQUID, (ii) a flux transformer inductively coupled to the SQUID and (iii) a multiloop pickup loop used directly as the SQUID inductance. On a substrate we achieved an effective flux capture area of and for the inductively coupled and multiloop devices, respectively. Due to the low white noise levels of for the inductively coupled magnetometer and for the multiloop device high quality magnetocardiograms were recorded inside a magnetically shielded room without signal averaging.

Abstract:

A multi-layer technology, based on YBaCuO as the superconducting material and SrTiO3 as the insulating material, is described. Patterning is performed by photolithography and Ar-ion-beam etching under fiat incidence. Using a resist bake-out prior to the etching, step angles in the patterned lower film of less than 20 degrees are obtained. Superconducting 10-turn thin-film coils have been fabricated with transition temperatures of up to 83 K and critical current densities at 77 K of 2*105 A cm-2. Furthermore we have fabricated a thin-film flux transformer and combined it in flip-chip configuration with a low-noise YBCO step-edge DC SQUID. We measured a magnetic field resolution of the complete magnetometer of 200 fT Hz-1/2 at 1 Hz, dominated by the SQUID noise itself.

Abstract:

NbN/MgO/NbN Josephson tunnel junctions have been prepared using various barrier preparation conditions. The energy of the sputtered MgO particles arriving at the substrate was found to be the most important parameter. Tunnel junctions (10*10 mu m2) with Vm values of up to 23 mV have been fabricated. The optimized NbN/MgO/NbN junction process is extended to a reliable whole-wafer process for DC SQUID fabrication.

Abstract:

Ziel dieses neuen medizinischen Diagnoseverfahren ist es, mit sog. supraleitenden Quanten-Intererenz-Detektoren (SQUIDs), die durch neuronale Ströme im Gehirn hervorgerufen magnetischen Felder außerhalb des menschlichen Kopfes zu messen, um so ein Bild von der Funktion des Gehirns zu erstellen.

Abstract:

The noise of two integrated YBa2Cu3O7-SrTiO3-YBa2Cu3O7 multilayer magnetometers in static magnetic fields up to 110 µT is investigated: An inductively coupled magnetometer with integrated flux transformer and a multiloop magnetometer. In both samples, only a moderate increase of the low frequency flux noise is found in high fields, due to the high epitaxial quality of the involved multilayer films. So for moderately shielded or unshielded applications in the earth's magnetic field, high-quality integrated YBa2Cu3O7 magnetometers can be operated with low excess noise.

Abstract:

Three magnetometers based on dc superconducting quantum interference devices (SQUIDs) fabricated from YBa2Cu3O7 x have been operated in a magnetically shielded room using a flux-locked loop involving additional positive feedback with bias current reversal. Two of these devices, integrated multiloop dc SQUIDs with outer diameters of 7 mm, achieved white noise levels of 10 fT/√Hz for bicrystal junctions and 30 fT/√Hz for step‐edge junctions. The third magnetometer involved a flux transformer with a 10×10 mm2 pickup coil connected to a 16-turn input coil which was inductively coupled to a bicrystal SQUID. This device achieved a white noise of 16.2 fT/√Hz. High quality magnetocardiograms were obtained without signal averaging.

Abstract:

We have fabricated YBa2Cu3O7 ramp-type junctions incorporating a barrier layer of NdGaO3 with a nominal thickness of 2 nm. The junctions exhibit pronounced Josephson effects and operate up to 82 K. The characteristics are well described within the resistively shunted junction model. We observe large hysteresis parameters βc even at elevated temperatures. The output voltage of a high-Tc dc SQUID is found to benefit from the intrinsic junction capacitance.

Abstract:

We have fabricated ramp-type Josephson junctions and SQUIDs (superconducting quantum interference devices) using an ultrathin barrier layer of NdGaO3 as weak contact between the YBa2Cu3O7 electrodes. The junctions operate up to 82 K, exhibiting current-voltage characteristics of the resistively-hunted-unction type. A normal-state resistance of up to....

Abstract:

A modular multichannel SQUID-system, in which every single channel can be optimized or replaced individually, is presented. The DC-SQUIDs based on the materials NbN/MgO are prepared by thin film technology and show noise values below 10μΦ0/√Hz. A simplified way of coupling the modulation and feedback current directly to the coupling coil is realized The complete SQUID module including the superconducting shield was miniaturized down to a diameter of 5mm. The gradiometers are wire wound and an as made balancing better than 10−3 is achieved. The cryogenic system was optimized with respect to low vibrations and low helium boil off rate. Simple conductive paint with precisely adjusted surface resistivity is used for RF-shielding. The complete SQUID-electronic of one channel has been realized on one single board and uses a new bias modulation scheme to completely suppress intrinsic 1/f noise. The noise level of the complete system is below 10fT/√Hz. Biomagnetic measurements of the human heart and brain are presented. Single current dipole reconstructions and current density imaging techniques can be used to find the underlying sources. Using a special coil positioning system an overlay of the functional current images with morphological MR-images can be carried out.

Abstract:

Current sources in the human body can be localized by measuring the biomagnetic fields with multichannel SQUID systems. Important system aspects are the noise level, the ambient field suppression, the dynamic range, the reliability, the number of channels, and the arrangement of gradiometers. From the users point of view the most important quality factor is the accuracy with which a current dipole can be localized. A test procedure is proposed to determine the localization power of the system. A 31-channel-SQUID system is presented together with the results of the test. The crucial parts of the system determining the accuracy are pointed out.

Abstract:

We have designed and fabricated a thin-film flux transformer by a YBa2Cu3O7/SrTiO3 (YBCO/STO) multilayer process. The flux transformer consists of a 20-turn input coil of.....

Abstract:

We have fabricated Y1Ba2Cu3O7-x step-edge junction dc superconducting quantum interference devices (SQUIDs) and characterized their noise performance. The current-voltage characteristics of our SQUIDs are of resistively shunted junction type with critical current densities jc of about 104 A/cm2 and maximum flux to voltage transfer functions...

Abstract:

A 19-channel SQUID system for biomagnetic measurements has been developed. This system differs from standard instruments in its modular approach. Various gradiometers can be coupled to the SQUIDs, the cryogenic system allows the exchange of single channels and the electronics is based on a cassette system. Problems with thermal insulation, vibrations of the gradiometers and tilted gradiometer geometries are discussed and solutions are presented.

Abstract:

Papers from the 4th International Conference on Superconducting and Quantum Effect Devices and their Applications held in Berlin, Germany, June 18-21, 1991.Detailliertere InformationenSuperconducting devices and their applications: proceedings of the 4th international conference SQUID '91 (session on superconducting devices), Berlin, Fed. Rep. of Germany, June 18-21, 1991Von Hans Koch, H. LübbigMitwirkende Personen Hans KochEdition: illustratedVeröffentlicht von Springer-Verlag, 1992Original von University of MichiganDigitalisiert am 10. Dez. 2007ISBN 0387553967, 9780387553962603 Seiten

Abstract:

A modular, 9-channel high-Tc SQUID system for magnetocardiography (MCG) was developed and tested in an unshielded environment. Galvanically-coupled magnetometers made from Y-Ba-Cu-O films, with intrinsic white noise levels as low as 70 fT/√Hz, are used as SQUID sensors. In an unshielded environment, a noise level of about 1 pT/√Hz for each channel was achieved using an active noise compensation system. A new digital planar gradiometer is proposed. First magnetocardiograms recorded in an unshielded environment are presented

Abstract:

Ziel des Forschungsvorhabens ist die Herstellung von SQUID-Anordnungen aus Hochtemperatur-Supraleitern (HTSL), mit denen die Messung biomagnetischer Signale möglich ist. Dazu werden Magnetometer bestehend aus Flußantennen und dc-SQUID-Sensoren aufgebaut, und zu elektronischen Gradiometern zusammengefaßt. Rauscharme dc-SQUIDs, basierend auf einer zuverlässigen Josephsonkontakt-Technologie und eine HTSL-Mehrlagentechnologie sind dafür eine notwendige Voraussetzung. Neben den routinemäßig verwendeten YBa2Cu3O7 (YBCO)-Stufen-Kontakten wurden SIS-Rampen-Kontakte entwickelt, die NdGaO3 als Barrierenmaterial verwenden

Abstract:

A modular multichannel superconducting quantum interference device (SQUID) system, in which every channel can be optimized or replaced individually, was further improved. The number of channels was increased to 31. The noise level is better than 10 fT/√Hz. A novel way of RF shielding using conductive paint avoids degradation of the SQUID characteristics due to RF interference without introducing significant extra noise, so that the system works without any Faraday cage. A simplified way of coupling the modulation and feedback signal directly to the SQUID was developed and tested successfully. The SQUID module with superconducting connections to the gradiometer and its superconducting shield was miniaturized to an outer diameter of 5 mm, so that it can be placed near the gradiometer without introducing significant unbalance. Tests have demonstrated that the accuracy of the system with respect to the localization of a single current dipole is better than 2 mm

Abstract:

A modular low-noise seven-channel SQUID-magnetometer for biomagnetic measurements was developed. The DC-SQUIDs are prepared by thin film technology based on the materials NbN-MgO-NbN, and show a flux noise below 10 μΦ0/√Hz. The signal is picked up with first-order wire-wound gradiometers of 2-cm diameter and coupled to the SQUIDs by integrated coupling coils. Individual channels can be replaced from the system, and various gradiometers can be used giving a flexible modular system. The electronics are based on the flux-locked-loop method extended by a bias modulation technique to reduce 1/f noise. The overall system noise is below 20 fT/√Hz. Biomagnetic measurements on auditory evoked fields have been carried out