Alex I. Braginski

The SQUID Handbook: Fundamentals and Technology of SQUIDs and SQUID Systems

Volume I.Preface.1 Introduction.1.1 The Beginning.1.2 Subsequent Developments.1.3 The dc SQUID: A First Look.1.4 The rf SQUID: A First Look.1.5 Cryogenics and Systems.1.6 Instruments: Amplifiers, Magnetometers and Gradiometers.1.7 Applications.1.8 Challenges and Perspectives.1.9 Acknowledgment.2 SQUID Theory.2.1 Josephson Junctions.2.2 Theory of the dc SQUID.2.3 Theory of the rf SQUID.3 SQUID Fabrication Technology.3.1 Junction Electrode Materials and Tunnel Barriers.3.2 Low-temperature SQUID Devices.3.3 High-temperature SQUID Devices.3.4 Future Trends.4 SQUID Electronics.4.1 General.4.2 Basic Principle of a Flux-locked Loop.4.3 The dc SQUID Readout.4.4 The rf SQUID Readout.4.5 Trends in SQUID Electronics.5 Practical DC SQUIDS: Configuration and Performance.5.1 Introduction.5.2 Basic dc SQUID Design.5.3 Magnetometers.5.4 Gradiometers.5.5 1/f Noise and Operation in Ambient Field.5.6 Other Performance Degrading Effects.6 Practical RF SQUIDs: Configuration and Performance.6.1 Introduction.6.2 Rf SQUID Magnetometers.6.3 Rf SQUID Gradiometers.6.4 Low-Frequency Excess Noise in rf SQUIDs.6.5 Response of rf SQUIDs to High-frequency Electromagnetic Interference.6.6 Characterization and Adjustment of rf SQUIDs.6.7 The rf SQUID versus the dc SQUID.6.8 Concluding Remarks and Outlook.7 SQUID System Issues.7.1 Introduction.7.2 Cryogenics.7.3 Cabling and Electronics.7.4 Data Acquisition and Rudimentary Signal Processing.7.5 Characterization, Calibration and Testing.7.6 Conditions Imposed on SQUID Systems by the Environment and Applications.7.7 Noise Suppression.7.8 Signal and Noise Implications forthe SQUID System Design.7.9 Concluding Remarks and System Trends.Appendix 1: Basic Properties of Superconductivity.Appendix 2: Abbreviations, Constants and Symbols.Index.Volume II.Preface.List of Contributors.8 SQUID Voltmetersand Amplifiers (J. Clarke, A. T. Lee, M. Mck and P. L. Richards).8.1 Introduction.8.2 Voltmeters.8.3 The SQUID as a Radiofrequency Amplifier.8.4 Microstrip SQUID Amplifier.8.5 SQUID Readout of Thermal Detectors.8.6 NuclearM agnetic and Quadrupole Resonance and Magnetic Resonance Imaging.8.7 The Axion Detector.9 SQUIDsfor Standardsand Metrology (J. Gallop and F. Piquemal).9.1 Introduction.9.2 SQUIDs in Voltage Metrology.9.3 Cryogenic Current Comparator (CCC).9.4 Other Current Metrological Applications of SQUIDs.9.5 Future Trends and Conclusion.10 The Magnetic Inverse Problem (E. A. Lima, A. Irimia and J. P. Wikswo).10.1 The Peculiarities of the Magnetic Inverse Problem.10.2 The Magnetic Forward Problem.10.3 The Magnetic Inverse Problem.10.4 Conclusions.11 Biomagnetism (J. Vrba, J. Nenonen and L. Trahms).11.1 Introduction.11.2 Magnetoencephalography.11.3 Magnetocardiography.11.4 Quasistatic Field Magnetometry.11.5 Magnetoneurography.11.6 LiverS usceptometry.11.7 Gastromagnetometry.11.8 Magnetic Relaxation Immunoassays.12 Measurements of Magnetism and Magnetic Properties of Matter (R. C. Black and F. C. Wellstood).12.1 Introduction.12.2 The SQUID Magnetometer-Susceptometer.12.3 Scanning SQUID Microscopy.13 Nondestructive Evaluation of Materials and Structuresus ing SQUIDs (H.-J. Krause and G. Donaldson).13.1 Introduction.13.2 Detection of Magnetic Moments.13.3 Magnetic Flux Leakage Technique.13.4 Static Current Distribution Mapping.13.5 Eddy Current Technique.13.6 Alternative Excitation Techniques.13.7 Conclusion and Prospects.14 SQUIDsfor Geophysical Survey and Magnetic Anomaly Detection (T. R. Clem, C. P. Foley, M. N. Keene).14.1 Introduction.14.2 Magnetic Measurements in the Earths Field.14.3 Operation of SQUIDs in Real World Environments.14.4 Data Acquisition and Signal Processing.14.5 Geophysical Applications of SQUIDs.14.6 Magnetic Anomaly Detection Systems using SQUIDs.14.7 Future Prospects.15 Gravity and Motion Sensors (Ho J. Paik).15.1 Introduction.15.2 The Superconducting Accelerometer.15.3 Superconducting Transducer for Gravitational-Wave Detectors.15.4 Superconducting Gravity Gradiometers (SGGs).15.5 Applications of the SGG Technology.15.6 Outlook.Appendix: Physical Constants, Abbreviations and Symbols.Index.

Microstructure of epitaxial YBa2Cu3O7 films on step-edge SrTiO3 substrates

Abstract The microstructure of YBa 2 Cu 3 O 7 films epitaxially grown on step-edge (100) SrTiO 3 substrates has been characterized by means of high resolution transmission electron microscopy. The results indicate a relationship between the microstructure of the film acreoss a step and the angle step makes with the substrate plane. On a steep, high-angle step, the film grows with its c -axis perpendicular to that of the film on the substrate surface so that two grain boundaries are formed. On a low-angle step, the film grows without any change in c -axis orientation across the step and without grain boundaries. Epitaxial second phases intergrowths across the steps have been found in some cases which may act as barrier layers when they cut through th YBa 2 Cu 3 O 7 film.

The microstructure of epitaxial YBa2Cu3O7 films on steep steps in LaAlO3 substrates

Abstract The microstructure of YBa 2 Cu 3 O 7 grown on steep steps in (001 pseudocubic LaAlO 3 substrates was studied by high-resolution electron microscopy of cross-sectional and plan-view samples. Steps with angles of about 80° were obtained by ion milling. On the substrate plane, the films grew with the c -axis parallel to [001] while on the flank of a step the c -axis was parallel to the [100] direction of the substrate. As a result, two [010] tilt axis grain boundaries were formed at which the YBa 2 Cu 3 O 7 lattice changed orientation by approximately 90°. In the upper grain boundary, a [100] tilt axis and, on the average, a (013) habit plane alternated with a [010] tilt axis and a (1 0 3) habit plane. This alternating structure was caused by twinning in the orthorhombic film structure. The lower grain boundaries were found to be rather irregular and consisted of a chain of (0 1 3)(0 1 3) and (0 1 0)(0 0 1) type segments exhibiting a tendency to tilt the whole habit plane toward the a-b plane of the flank film. Dislocations, stacking faults and misfit strains were also observed in or close to the boundaries. Grain boundary modeling indicated a good agreement with the experimental image and permitted us to determine the atomic plane of a boundary.

Biomagnetism using SQUIDs: status and perspectives

Biomagnetism involves the measurement and analysis of very weak local magnetic fields of living organisms and various organs in humans. Such fields can be of physiological origin or due to magnetic impurities or markers. This paper reviews existing and prospective applications of biomagnetism in clinical research and medical diagnostics. Currently, such applications require sensitive magnetic SQUID sensors and amplifiers. The practicality of biomagnetic methods depends especially on techniques for suppressing the dominant environmental electromagnetic noise, and on suitable nearly real-time data processing and interpretation methods. Of the many biomagnetic methods and applications, only the functional studies of the human brain (magnetoencephalography) and liver susceptometry are in clinical use, while functional diagnostics of the human heart (magnetocardiography) approaches the threshold of clinical acceptance. Particularly promising for the future is the ongoing research into low-field magnetic resonance anatomical imaging using SQUIDs.

Sensitive RF-SQUIDs and magnetometers operating at 77 K

Large 6-mm*6-mm and 8-mm*8-mm flux-focusing washer structures with inductances L/sub S/ between 25 pH and 500 pH were fabricated from epitaxial, c-axis YBa/sub 2/Cu/sub 3/O/sub 7/ films. Double step-edge junctions having a low 1/f noise were incorporated in these washers to form RF-SQUIDs (superconducting quantum interference devices). A high tank circuit frequency near 150 MHz was chosen to reduce noise and improve the sensitivity of the SQUIDs. At 77 K, a transfer function exceeding 100 mu V/ Phi /sub 0/ and a white flux noise of 3*10/sup -5/ Phi /sub 0// square root Hz down to below 0.3 Hz were attained with L/sub S/=25 pH. A magnetometer with L/sub S/=190 pH was demonstrated. The best magnetic field and energy resolutions were 170 fT/ square root Hz and 5*10/sup -29/ J/Hz respectively, over a signal frequency range to below 1 Hz. The magnetometer was used to record human magnetocardiograms and auditory evoked human brain responses.<<ETX>>

A second-order SQUID gradiometer operating at 77 K

We describe a portable second-order electronic SQUID gradiometer cooled with liquid nitrogen and capable of operating in unshielded space. The measured magnetic-field resolution is <300 fT Hz-1/2 and <170 fT Hz-1/2 When operating in the first-order mode. The gradiometer was successfully used for the recording of screening magnetocardiograms of over 200 human subjects at four different geographic locations.

YBa2Cu3O7 thin film SQUID gradiometer for biomagnetic measurements

Low‐noise rf SQUID washers fabricated from YBa2Cu3O7 epitaxial thin films have been used to construct a first‐order electronic gradiometer operating at 77 K and suitable for biomagnetic measurements. Mechanical adjustment of the two‐SQUID gradiometric setup made it possible to attenuate signals due to far magnetic field sources by three orders of magnitude. A magnetic field resolution of ≤280 fT/Hz1/2 above 2 Hz was attained through the use of large flux focusers. The fine structure of human heart magnetocardiograms was recorded in unshielded space. In a shielded room, magnetoencephalograms were obtained. The system was used to obtain new data on auditory evoked cortical response.

Characterization of YBa2Cu3O7 step-edge Josephson junctions

The authors have fabricated and characterized thin film YBa2Cu3O7 step-edge microbridges for application in SQUIDS. Epitaxial YBCO films were pulsed-laser-deposited on SrTiO3 and had Tcs of 88-90 K. Sharp steps in SrTiO3 were obtained by photolithographic techniques and Ar ion milling with step heights (h) between 100 and 250 mm. They investigated step-edge junctions (SEJ) with different film thicknesses (d) from 100 to 250 mm but with a constant ratio d/h=1. The width of the microbridges was 2-2.5 mu m. The Tcs of the bridges were 65-85 K, depending on film thickness and the duty cycle during ion milling. The I-V curves were RSJ-like and clear Shapiro steps were observed. The junction normal resistance was independent of temperature. With applied magnetic field the critical current Ic showed a T-dependent modulation, indicating that there was self-shielding and Ic non-uniformity in the junctions. Low-frequency noise measured in RF SQUIDS was relatively low. They showed that it was generated predominantly in the junctions.

Correlation of YBa2Cu3O7 step‐edge junction characteristics with microstructure

Current‐voltage characteristics, Josephson radiation spectra, and critical current versus magnetic‐field dependences were measured in epitaxial, c‐axis YBa2Cu3O7 step‐edge Josephson junctions (SEJs) on SrTiO3 and LaAlO3 substrates with various step angles α. The results were correlated with microstructural data to determine the origin of the observed weak‐link behavior. It was shown that on steps with α≳45° the SEJ is a series connection of two weak links unambiguously correlated with the occurrence of two 90° tilt grain boundaries. On steep steps, α≥70°, the boundary at the upper step edge has, on average, the (103) symmetry, while the lower one is predominantly of the basal‐plane‐faced (010)(001) type. Correspondingly, one link is weaker than the other, with the weaker link originating on the (010)(001) boundary. However, others have shown that analogous grain boundaries in planar (103) and biepitaxial a‐axis/c‐axis films do not exhibit a strong magnetic‐field dependence of critical current, which is ch...

Aircraft wheel testing with machine-cooled HTS SQUID gradiometer system

For eddy current detection of deep-lying flaws in large aircraft wheels, an automated airplane wheel inspection system using a HTS SQUID gradiometer sensor is being developed. Wheel drums made of aluminum alloys have to be tested frequently since they are subject to enormous dynamic loads and very high braking temperatures at landing. For economic reasons, testing should be performed from the outside without removing the inner ferromagnetic keys which fit the brake system. In order to operate the sensor in hostile environments such as airport maintenance hangars, a planar rf double hole SQUID gradiometer was used. SQUID cooling is performed by a closed cycle Joule-Thomson cryocooler, equipped with flexible plastic gas lines. The wheel testing is being performed on an automated test stand with the wheel slowly rotating and a robot with the SQUID enclosure scanning stepwise along the wheel axis. Additional signals due to inner cracks of 10 mm length, penetrating 25 percent of the 10 mm thick wall, are easily identifiable in the periodic signal background due to the presence of ferromagnetic keys. In comparative measurements, the prototype SQUID system clearly exhibited advantages over conventional techniques, with optimization reserve still at hand.