High-temperature Superconducting Quantum Interference Device Research Articles

Analyzer-to-Analyzer Variations in Assaying Ultralow Concentrated Biomarkers Associated with Neurodegenerative Diseases Using Immunomagnetic Reduction.

By utilizing a high-temperature superconducting quantum interference device (high-Tc SQUID) magnetometer, an alternating current (AC) magnetosusceptometer, referred to as an analyzer, was developed for ultrasensitive immunoassays. The analyzer has been applied to assay biomarkers in human plasma associated with Alzheimer's disease (AD) and Parkinson's disease (PD). The involved assay methodology is the so-called immunomagnetic reduction (IMR). Such an analyzer has been approved for clinical use in Taiwan and Europe. The mass production of the analyzer is needed for clinical utilities. The issue of exploring analyzer-to-analyzer variations in the performances becomes critical. Unfortunately, there is no standard characterization to determine the variations in performances among analyzers. In this study, key characterizations, such as output signal stability, signal-to-noise ratio, measured concentrations of a control sample, etc., are proposed. In total, three analyzers are characterized in this work. The detected biomarkers include amyloid peptides, total tau protein, phosphorylated tau protein, and α-synuclein protein for AD and PD. Through one-way ANOVA for any of the characterizations among the three analyzers, it was found that there was no significant difference in any of these characterizations among the analyzers (p > 0.05). Furthermore, the three analyzers are applied to assay biomolecules for AD and PD in reference samples. High correlations (r > 0.8) in measured concentrations of any of these biomarkers in reference samples were obtained among the three analyzers. The results demonstrate that the proposed characterizations are feasible for achieving consistent performance among high-Tc SQUID-based AC magnetosusceptometers for assaying biomolecules.

Scalp attached tangential magnetoencephalography using tunnel magneto-resistive sensors

Non-invasive human brain functional imaging with millisecond resolution can be achieved only with magnetoencephalography (MEG) and electroencephalography (EEG). MEG has better spatial resolution than EEG because signal distortion due to inhomogeneous head conductivity is negligible in MEG but serious in EEG. However, this advantage has been practically limited by the necessary setback distances between the sensors and scalp, because the Dewar vessel containing liquid helium for superconducting quantum interference devices (SQUIDs) requires a thick vacuum wall. Latest developments of high critical temperature (high-Tc) SQUIDs or optically pumped magnetometers have allowed closer placement of MEG sensors to the scalp. Here we introduce the use of tunnel magneto-resistive (TMR) sensors for scalp-attached MEG. Improvement of TMR sensitivity with magnetic flux concentrators enabled scalp-tangential MEG at 2.6 mm above the scalp, to target the largest signal component produced by the neural current below. In a healthy subject, our single-channel TMR-MEG system clearly demonstrated the N20m, the initial cortical component of the somatosensory evoked response after median nerve stimulation. Multisite measurement confirmed a spatially and temporally steep peak of N20m, immediately above the source at a latency around 20 ms, indicating a new approach to non-invasive functional brain imaging with millimeter and millisecond resolutions.

Automatic coregistration of MRI and on-scalp MEG

BackgroundRecent progress in optically pumped magnetometers (OPMs) and high-temperature superconducting quantum interference devices (SQUIDs) has facilitated the development of an on-scalp magnetoencephalography (MEG) system that offers high signal intensity and flexibility at a lower cost. While the on-scalp sensor array has high flexibility, it brings new challenges to accurate sensor-to-brain coregistration, which is essential for MEG source localization. New methodA novel automatic filtering algorithm based on plane segmentation was proposed to locate on-scalp MEG sensors in 3D images reconstructed from optical scanning. Global image registration was employed for the automatic alignment of anatomical images and sensor positions. ResultsSeventy-one sensor dummies on the scalp were located and registered to brain anatomical images. The deviations of the sensor location and orientation from the averaged result of 10 measurements were less than 1 mm and 0.6°, respectively. The entire process could be completed in less than 4 min. Comparison with existing methodsCompared with existing methods that involve various manual procedures, such as moving digitizers to fiducials and repeatedly pulling out sensors, our proposed coregistration method is more efficient and accurate. ConclusionAn automatic method for the coregistration of anatomical structure and on-scalp sensors that will have a large impact on the practical use of on-scalp MEG is developed.

Dynamic Range Expansion Method of Three-component HTc SQUIDs Magnetometer

In view of the small dynamic range of the three-component high-temperature superconducting quantum interference device (HTc SQUID) magnetometer and it is easy to exceed the measurement range when working in the field without magnetic shielding environment. A dynamic range expansion method based on step compensation is proposed. By setting a magnetic compensation coil on each axis of the three-component HTc SQUIDs magnetometer probe, a current is passed to generate a magnetic field opposite to the direction of the external magnetic field to offset most of the magnetic field to be measured. The measured values are calculated and processed to obtain the magnetic field value to be measured. The test results show that the method can greatly improve the dynamic range without reducing the sensitivity of the magnetometer, which can work stably in a non-magnetic shielding environment and meet the requirements of field geophysical magnetic exploration.

Portable Cryostat With Temperature Control Function for Operation of HTS-SQUID at a Higher Slew Rate

We examined a portable cryostat utilizing liquid nitrogen with temperature control function for operation of high-temperature superconducting quantum interference devices (HTS-SQUIDs) to have a higher slew rate. To operate a non-destructive evaluation system with HTS-SQUID in city areas with serious environmental electromagnetic noise, we often need a higher slew rate. A glass Dewar is installed in an outer case made of aluminum, which is sealed hermetically. The temperature of liquid nitrogen is controlled by using a vacuum pump connected to a feedback circuit, which monitors the temperature of liquid nitrogen. The temperature of liquid nitrogen could be controlled in the range between 73 and 77.2 K with a 0.1 K step. For example, the temperature was kept at 75 K with precision of ±0.05 K for 9 hs and SQUID was operated stably for this period. The ΔV and the slew rate of a test SQUID were increased from 22 μV and 3.2 mT/s at 77.2 K to 37 μV and 5.9 mT/s at 73 K, respectively. The white noise was also improved from 48 fT/√Hz at 77.2 K to 32 fT/√Hz at 74 K. We believe that this technology is useful to extend application of HTS-SQUIDs in the fields.

HPCVD Thin Film MgB2 for Superconducting Magnetic Shielding

Superconducting magnetic shielding (SMS) is crucial for superconducting electronic devices such as superconducting quantum interference devices (SQUIDs). Current magnetic shielding devices suffer from high construction price, poor mobility, and flexibility. The MgB2 SMS with cryocooler could be the potential the solution. In this work, a hybrid physical–chemical vapor deposition system, which is capable of depositing on a long cylindrical surface, is demonstrated. A dense and robust MgB2 film has successfully been deposited on the inside wall of a Φ50 × 120 mm 304 stainless steel tube. A microscopic image indicated that the deposited MgB2 showed a dendritic structure with cracks on it. Sample with different B2H6 flow rates has been made, current result showed a better performance with higher B2H6 flow rate. However, safety issue should be taken into consideration as we further increase the B2H6 concentration. The sample deposited with 10 sccm 25% B2H6 showed the best performance so far with a TC of 34.4 K. A SQUID testing system specifically for high-temperature SQUID with MgB2 SMS with a liquid-helium-free cryogenic system has been design and under construction for the future researches.

Development of HTS-SQUID System for a Monitoring System of CO2 Enhanced Oil Recovery

We have tried to develop an induction logging system for oil fields utilizing a high-temperature superconducting quantum interference device (HTS-SQUID). Enhanced oil recovery (EOR) technology utilizing carbon dioxide (CO2 ) is a promising technique for efficient production of petroleum. To control the EOR, it is important to improve the accuracy of monitoring technique of CO2 injected into the oil reservoir. The HTS-SQUID has a potential to monitor CO2 behavior in crude oil reservoir because of its high sensitivity in a wide frequency range from dc to over 1 MHz. As the first step of the developments, we prepared a vessel for SQUID system by using carbon fiber reinforced plastic with pressure tightness of 70 MPa and thermal durability of 200 °C. By using the SQUID system placed at a depth of about 300 m in a steel-cased borehole filled with water, magnetic signals from a transmitter coil in another borehole were successfully measured.

Ultra-low field MRI food inspection system prototype

We develop an ultra-low field (ULF) magnetic resonance imaging (MRI) system using a high-temperature superconducting quantum interference device (HTS-SQUID) for food inspection. A two-dimensional (2D)-MR image is reconstructed from the grid processing raw data using the 2D fast Fourier transform method. In a previous study, we combined an LC resonator with the ULF-MRI system to improve the detection area of the HTS-SQUID. The sensitivity was improved, but since the experiments were performed in a semi-open magnetically shielded room (MSR), external noise was a problem. In this study, we develop a compact magnetically shielded box (CMSB), which has a small open window for transfer of a pre-polarized sample. Experiments were performed in the CMSB and 2D-MR images were compared with images taken in the semi-open MSR. A clear image of a disk-shaped water sample is obtained, with an outer dimension closer to that of the real sample than in the image taken in the semi-open MSR. Furthermore, the 2D-MR image of a multiple cell water sample is clearly reconstructed. These results show the applicability of the ULF-MRI system in food inspection.

Magnetorelaxometry of few Fe3O4 nanoparticles at 77 K employing a self-compensated SQUID magnetometer

Magnetic nanoparticles (MNPs) are of great interest for industrial and medical applications. Therefore, the properties of the particles have to be well controlled. Several magnetic measurement schemes have been developed in order to determine particle parameters such as size distribution and structural properties. In general, systems are designed either for the analysis of large amounts of MNP (≫1000) or for single particle investigation. Up to now, the region in between has been less studied. However, small and well defined amounts of MNPs are of high interest, e.g. for the systematic investigation of particle–particle interactions. In this paper, we present a method using electron beam lithographic preparation of small amounts of MNPs directly on a self-compensating high-temperature superconducting quantum interference device (SQUID) with micrometer dimensions which is insensitive to homogeneous fields and first order gradients but very sensitive to internal magnetic dipole fields. Magnetorelaxometry (MRX) measurements were carried out at 77K sample temperature in a magnetically shielded room in order to analyze the dynamic behavior of MNP samples and to evaluate the detection limit of our SQUID sensors. Calculations based on the magnetic moment superposition model (MSM) and finite element simulations (FEM) indicate that the MNP samples can be fabricated in a well-defined way by the presented method. Based on MRX measurements of a sample with 200 single-core magnetite MNPs with core diameters of 12nm, we estimate the detection limit of our SQUID MRX setup as 70 MNPs.

Numerical Simulation of DC SQUID Taking Into Account Quantum Characteristic of Josephson Junction

High-temperature superconducting quantum interference devices (HTS SQUIDs) have been developed as an extremely sensitive magnetic sensor. The HTS SQUIDs are required to have high robustness with respect to the magnetic noise for stable operation in an unshielded environment and also reduced cost to widen the application range. It is, therefore, necessary to clarify the quantum magnetic behavior of the HTS SQUID. However, a simulation tool, which can consider the quantum magnetic behavior, has not been developed yet. In this paper, an equivalent circuit of a Josephson junction comprising the HTS SQUID is more properly considered to represent the quantum behavior. It can consider the ac and dc Josephson effect. The obtained results are compared with an ordinary simulation using a simplified circuit model, and the results agree well with each other. Using the proposed simulation method instead of the ordinary simulation, the current path is more accurately simulated, so this new method will be used to evaluate the robustness of the SQUID.

Development of Non-destructive Evaluation System Using an HTS-SQUID Gradiometer with an External Pickup Coil

We are developing a new eddy-current non-destructive evaluation (NDE) system using a high-temperature superconducting quantum interference device (HTS-SQUID) gradiometer with the aim of applying it to power plants. Electric power facilities such as ducts and vessels are generally untransportable because of their size, and thus it is difficult to apply a conventional SQUID NDE system. The new NDE system employs an external Cu pickup coil which is supposed to be driven flexibly by a robot arm at room temperature and an HTS-SQUID chip which is placed in a magnetically shielded vessel. In the present research, we investigated the performance of an HTS-SQUID sensor connected with external pickup coils before mounting them to a robot arm. By varying the Cu coil conditions such as their sizes, the number of turns, and the diameter of wire, we qualitatively evaluated the frequency dependence of the effective area and the cutoff frequency.

Noise properties of HTS-SQUID gradiometer in an elevated magnetic field

Abstract Stability of a high-temperature superconducting quantum interference device (HTS-SQUID) gradiometer with ramp-edge Josephson junctions against application of magnetic fields was investigated. The gradiometer with a SQUID inductor having a 5-μm-wide line and pickup coils of 0.5x1.5 mm for one side was used. Noise spectra were measured for the gradiometer in zero field after cooled in dc magnetic fields up to 300 μT. no increase in noise level was observed until 95 T, being higher than the earth field. Noise spectra in elevated magnetic fields up to 320 μT were also measured for the gradiometer cooled in zero field. No appreciable increase in noise was observed until 150 μT. By decreasing the applied field from 320 μT to zero, the gradiometer recovered the original low noise level. These results indicated that the examined gradiometer had a good durability against magnetic fields and could be used without a magnetic shield for various applications.

A Superconducting Magnetic Tensor Gradiometer for Underwater UXO Detection

Magnetic surveys are routinely used for detection of discrete magnetic targets, such as unexploded ordnance (UXO). Gradient tensor measurements have a number of benefits over measuring total field intensity or its vector gradient: they provide detailed information about a target in a single pass, without necessarily passing directly over the target; they determine the location of the target using a direct method, rather than the indirect inversion method required with other measurements; and they determine directly the magnitude and orientation of the magnetic moment, as well as the location of the target, aiding discrimination between sources and characterization of the munitions. The CSIRO is building a magnetic tensor gradiometer, designed for underwater deployment, based on high temperature superconducting quantum interference devices (SQUIDs). Technical challenges for the project include: designing a high temperature SQUID device that can achieve the required gradient sensitivity in motion; developing a gradiometer housing that can deal with the boil-off gas from the liquid nitrogen cryogen while underwater; identification and removal of wave-induced magnetic noise; compensation for magnetic noise caused by motion and the platform itself; and developing a dipole-tracking algorithm for gradient tensor measurements that is both robust and computationally undemanding. This paper presents the progress to date on this project including an evaluation of gradiometer performance in laboratory conditions, and describes some simple methods for localization and characterization of compact magnetic sources using gradient tensor measurements.

Low-frequency nondestructive analysis of cracks in multilayer structures using a scanningmagnetic microscope

The use of a scanning magnetic microscope (SMM) with a high temperaturesuperconducting quantum interference device (SQUID) for quantitative measurements ineddy current nondestructive analysis (NDA) is presented. The SQUID has been used todetect the weak magnetic field variations around a small defect, close to a structural partgenerating an intensive magnetic field. The experimental data for a deep crack close to arivet in a multilayer conducting plate have been taken in a RF-shielded environment anddiscussed in the light of the theoretical predictions. The results show that eddycurrent NDA can distinguish subsurface crack signals from wider structural signals,with defects located 10 mm below the surface. Moreover, in order to visualizethe structure of the probing current when a circular induction coil is used, thesimulation of eddy currents in a thick unflawed conducting plate has been carriedout.

Metallic Contaminant Detection using a High-Temperature Superconducting Quantum Interference Devices Gradiometer

We develop magnetic metallic contaminant detectors using high-temperature superconducting quantum interference devices (HTS-SQUIDs) for industrial products. Finding ultra-small metallic contaminants is an important issue for manufacturers producing commercial products such as lithium ion batteries. If such contaminants cause damages, the manufacturer of the product suffers a big financial loss due to having to recall the faulty products. Previously, we described a system for finding such ultra-small particles in food. In this study, we describe further developments of the system, for the reduction of the effect of the remnant field of the products, and we test the parallel magnetization of the products to generate the remnant field only at both ends of the products. In addition, we use an SQUID gradiometer in place of the magnetometer to reduce the edge effect by measuring the magnetic field gradient. We test the performances of the system and find that tiny iron particles as small as 50 × 50 μm2 on the electrode of a lithium ion battery could be clearly detected. This detection level is difficult to achieve when using other methods.

Application of SQUID to magnetic contaminant detection

We have developed a magnetic metallic contaminant detector using a high-temperature superconducting quantum interference device (HTS-SQUID) gradiometer for industrial products such as lithium ion batteries. Finding ultrasmall metallic contaminants is a critical issue for manufacturers producing commercial products such as lithium ion batteries. When contamination occurs, the manufacturer incurs a great loss in recalling the tainted products. We employed a permanent ring magnet for magnetizing the products in order to generate remnant fields only at the ends of the products, thereby reducing their impact in masking the field from a contaminant. For practical applications, the detection width of a sensor must be sufficiently large to identify an inclusion from above the product during inspection. Here, we made a large SQUID gradiometer 8mm in width and compared its detection width with that of a conventional small sensor 3mm wide. We found that the effective detection width of the 8mm sensor was 11.6mm. It was 1.8 times larger than that of the small sensor. Finally, a test of the system’s performance revealed that iron particles as small as 50μm×50μm on the electrode of a lithium ion battery could be detected clearly.

Suppression of ringing in the tuned input circuit of a SQUID detector used in low-fieldNMR measurements

In low-field NMR measurements, we employ a high temperature superconductingquantum interference device (SQUID) as a detector with an inductively coupledliquid-nitrogen-cooled LC tuned input circuit. However, ringing across the LCcircuit appears after the sudden switch-off of the prepolarizing magnetic field. Thisringing leads to instability of the SQUID readout and prevents the acquisition ofshort-relaxation-time signals. We developed and tested two simple and effective FET-basedQ switch circuits with adjustable parameters which suppress the ringing. Each of theseQ switches makes it possible to record free induction decay signals with a Larmor frequencyof 1.2 kHz and an effective relaxation time constant of 30 ms. A gradually changing currentcaused by the release of charges stored in the p–n junction of the FET, which delays theQ value recovery of the LC circuit, can only be observed by the SQUID because of itsfrequency-independent sensitivity.

Application of high-temperature superconductor SQUIDs for ground-based TEM

Superconducting quantum interference devices (SQUIDs) are intrinsically very sensitive detectors of magnetic flux. Flux sensitivities of one millionth of a flux quantum per root Hz (1μφ0/√Hz) may typically be realized in low-temperature superconductor (LTS) materials, while sensitivities of ∼5μφ0/√Hz may be realized in high-temperature superconductor (HTS) materials. LTS devices are typically cooled with liquid helium (4 K) while HTS devices are typically cooled with liquid nitrogen (77 K). Coupling the magnetic field into a SQUID via a flux-transformer can result in a very sensitive magnetometer with, depending on the type of superconducting material used and the effective area of the flux-coupling transformer, achievable magnetic field sensitivities ranging from fT/√Hz to pT/√Hz over typical bandwidths that span hundreds of kHz. SQUID applications include NDE, biomagnetism and magnetic microscopes.

High-temperature superconducting quantum interference device with cooled LC resonant circuit for measuring alternating magnetic fields with improved signal-to-noise ratio

Certain applications of superconducting quantum interference devices (SQUIDs) require a magnetic field measurement only in a very narrow frequency range. In order to selectively improve the alternating-current (ac) magnetic field sensitivity of a high-temperature superconductor SQUID for a distinct frequency, a single-coil LC resonant circuit has been used. Within the liquid nitrogen bath, the coil surrounds the SQUID and couples to it inductively. Copper coils with different numbers of windings were used to cover the frequency range from <1 to nearly 100 kHz. A superconducting coil made of YBa(2)Cu(3)O(7-delta) tape conductor was also tested. With the LC circuit, the signal-to-noise ratio of measurements could be improved typically by one order of magnitude or more in a narrow frequency band around the resonance frequency exceeding a few kilohertz. The best attained equivalent magnetic field resolution was 2.5 fT/radicalHz at 88 kHz. The experimental findings are in good agreement with mathematical analysis of the circuit with copper coil.

Superconducting quantum interference device instruments and applications

Superconducting quantum interference devices (SQUIDs) have been a key factor in the development and commercialization of ultrasensitive electric and magnetic measurement systems. In many cases, SQUID instrumentation offers the ability to make measurements where no other methodology is possible. We review the main aspects of designing, fabricating, and operating a number of SQUID measurement systems. While this article is not intended to be an exhaustive review on the principles of SQUID sensors and the underlying concepts behind the Josephson effect, a qualitative description of the operating principles of SQUID sensors and the properties of materials used to fabricate SQUID sensors is presented. The difference between low and high temperature SQUIDs and their suitability for specific applications is discussed. Although SQUID electronics have the capability to operate well above 1MHz, most applications tend to be at lower frequencies. Specific examples of input circuits and detection coil configuration for different applications and environments, along with expected performance, are described. In particular, anticipated signal strength, magnetic field environment (applied field and external noise), and cryogenic requirements are discussed. Finally, a variety of applications with specific examples in the areas of electromagnetic, material property, nondestructive test and evaluation, and geophysical and biomedical measurements are reviewed.