Temperature Superconducting Quantum Interference Device Research Articles

Magnetic Detection of Neural Activity by Nanocoil Transducers.

Electrophysiological recordings from brain cells are performed routinely using implanted electrodes, but they traditionally require a wired connection to the outside of the brain. A completely passive, wireless device that does not require on-board power for active transmission but that still facilitates remote detection could open the door for mass-scale direct recording of action potentials and transform the way we acquire brain signals. We present a nanofabricated coil that forms a neuroelectromagnetic junction, yielding a highly enhanced magnetic field transduction of electrophysiology. We show that this micrometer-scale device enables remote magnetic detection of neuronal fields from the center of the coil using room temperature superconducting quantum interference device (SQUID) microscopy. Further, time-locked stimulation in conjunction with magnetometry demonstrates thresholding behavior that affirms the viability of the technology for detection with no requirement for wires or on-board power. This strategy may permit unprecedented detection of electrophysiology using magnetoencephalography and magnetic resonance imaging.

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.

Apparent Ferromagnetism in Exfoliated Ultrathin Pyrite Sheets

Experimental evidence for ferromagnetic ordering in isotropic atomically thin two-dimensional crystals has been missing until a bilayer Cr2Ge2Te6, and a three-atom thick monolayer CrI3 are shown to retain ferromagnetic ordering at finite temperatures. Here, we demonstrate successful isolation of a non-van der Waals type ultra-thin nanosheet of FeS2 derived from naturally occurring pyrite mineral (FeS2) by means of liquid-phase exfoliation. Structural characterizations imply that (111) oriented sheets are predominant and is supported theoretically by means of density functional theory surface energy calculations. Spin-polarized density theory calculations further predicted that (111) oriented three-atom thick pyrite sheet has a stable ferromagnetic ground state different from its diamagnetic bulk counterpart. This theoretical finding is evaluated experimentally employing low temperature superconducting quantum interference device measurements and observed an anomalous ferromagnetic kind of behavior.

On-scalp MEG sensor localization using magnetic dipole-like coils: A method for highly accurate co-registration

Source modelling in magnetoencephalography (MEG) requires precise co-registration of the sensor array and the anatomical structure of the measured individual’s head. In conventional MEG, the positions and orientations of the sensors relative to each other are fixed and known beforehand, requiring only localization of the head relative to the sensor array. Since the sensors in on-scalp MEG are positioned on the scalp, locations of the individual sensors depend on the subject’s head shape and size. The positions and orientations of on-scalp sensors must therefore be measured at every recording. This can be achieved by inverting conventional head localization, localizing the sensors relative to the head - rather than the other way around.In this study we present a practical method for localizing sensors using magnetic dipole-like coils attached to the subject’s head. We implement and evaluate the method in a set of on-scalp MEG recordings using a 7-channel on-scalp MEG system based on high critical temperature superconducting quantum interference devices (high-Tc SQUIDs). The method allows individually localizing the sensor positions, orientations, and responsivities with high accuracy using only a short averaging time (≤ 2 ​mm, < 3° and < 3%, respectively, with 1-s averaging), enabling continuous sensor localization. Calibrating and jointly localizing the sensor array can further improve the accuracy of position and orientation (< 1 ​mm and < 1°, respectively, with 1-s coil recordings).We demonstrate source localization of on-scalp recorded somatosensory evoked activity based on co-registration with our method. Equivalent current dipole fits of the evoked responses corresponded well (within 4.2 ​mm) with those based on a commercial, whole-head MEG system.

Measurement of Magnetic Nanoparticles Using High Transition Temperature Superconducting Quantum Interference Devices

Superconducting quantum interference device (SQUID) based sensors hold promise for magnetic detection of magnetically tagged biological cells. In this work, a high transition temperature (high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) direct-coupled SQUID micro-magnetometer was fabricated from a 30-nm-thick YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) thin film. The SQUID was directly written with irradiation from a finely focused helium ion beam without milling or etching any material. An experiment estimating the sensitivity of the magnetometer to magnetic nanoparticles was conducted that revealed the magnetic moment calculated based on the measurement of the SQUID magnetometer is consistent to that obtained from susceptibility measurements.

Characterization and demonstration results of a SQUID magnetometer system developed for geomagnetic field measurements

We characterized a low temperature superconducting quantum interference device (SQUID) magnetometer system developed for high-sensitivity geomagnetic field measurement, and demonstrated the detection of weak geomagnetic signals. The SQUID magnetometer system is comprised of three-axis SQUID magnetometers housed in a glass fiber reinforced plastic cryostat, readout electronics with flux locked loop (FLL), a 24-bit data logger with a global positioning system and batteries. The system noise was approximately 0.2 pT √Hz−1/2 in the 1–50 Hz frequency range. This performance was determined by including the thermal noise and the shielding effect of the copper shield, which covered the SQUID magnetometers to eliminate high-frequency interference. The temperature drift of the system was ∼0.8 pT °C−1 in an FLL operation. The system operated for a month using 33 l liquid helium. Using this system, we performed the measurements of geomagnetic field in the open-air, far away from the city. The system could detect weak geomagnetic signals such as the Schumann resonance with sixth harmonics, and the ionospheric Alfvén resonance appearing at night, for the north–south and east–west components of the geomagnetic field. We confirm that the system was capable of high-sensitivity measurement of the weak geomagnetic activities.

Development of a Rigid One-Meter-Side and Cooled Coil Sensor at 77 K for Magnetic Resonance Sounding to Detect Subsurface Water Sources.

Magnetic resonance sounding (MRS) using the Earth’s magnetic field is a noninvasive and on-site geophysical technique providing quantitative characteristics of aquifers in the subsurface. When the MRS technology is applied in a mine or tunnel for advance detecting the source of water that may cause disastrous accident, spatial constraints limit the size of coil sensor and thus lower the detection capability. In this paper, a coil sensor for detecting the weak MRS signal is designed and the signal to noise (SNR) for the coil sensor is analyzed and optimized. The coil sensor has a rigid structure and square size of 1 m for deploying in a narrow underground space and is cooled at a low temperature of 77 K for improving the SNR. A theoretical calculation and an experimental test in an electromagnetically shielded room (EMSR) show that the optimal design of coil sensor consists of an 80-turn coil and a low-current-noise preamplifier AD745. It has a field sensitivity of 0.17 in the EMSR at 77 K, which is superior to the low temperature Superconducting Quantum Interference Device (LT SQUID) that is the latest application in MRS and the cooled coil with a diameter of 9 cm when detecting the laboratory NMR signal in kHz range. In the field experiment above the Taipingchi Reservoir near Changchun in China, the cooled coil sensor (CCS) developed in this paper has successfully obtained a valid weak MRS signal in high noise environment. The field results showed that the quality of measured MRS signal at 77 K is significantly superior to that at 298 K and the SNR is improved up to three times. This property of CCS makes the MRS instrument more convenient and reliable in a constricted space underground engineering environment (e.g., a mine or a tunnel).

Development of integrated AC-DC magnetometer using high-Tc SQUID for magnetic properties evaluation of magnetic nanoparticles in solution

We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-Tc SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The flux-transformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibrating-sample and harmonic detection techniques were used to reduce interference from excitation magnetic fields in the static and dynamic magnetization measurements, respectively. Static and dynamic magnetization measurements were performed on commercially available iron oxide nanoparticles in diluted solutions. The magnetic responses increased with the increase in concentration of the solutions in both measurement results. The magnetization curves showed that the diamagnetic signal due to the carrier liquid of the iron oxide nanoparticles existed in a dilute solution. Biasing with a proper DC magnetic field in the dynamic magnetization measurement resulted in improved signals of the second and third harmonics. Therefore, highly sensitive magnetic characterizations of MNPs utilizing the static and dynamic magnetization measurement are possible via the developed system.

Magnetic properties of N‐doped multi‐walled carbon nanotubes

AbstractThe magnetic properties of nitrogen‐doped multi‐walled carbon nanotubes (N‐MWCNTs) were studied in the temperature and magnetic field range of (4.2–290) K and (0.05–30) kOe, respectively. Also magnetic properties of the reference MWCNTs without nitrogen doping were investigated on the same footing for comparison. The presence of iron‐based particles inside N‐MWCNTs was detected. The low temperature SQUID (Superconducting Quantum Interference Device) magnetization measurements were supplemented with thermogravimetric analysis. The magnetic characterization provided the saturation magnetic moment MS and residual magnetization MR of N‐MWCNTs to be, respectively, 4.5 emu/g and 0.9 emu/g, whereas for the reference MWCNTs the corresponding parameters are found to be about twice higher. The coercive field value amounts to 800 Oe for both systems at low temperatures, then decreasing to about 450 Oe at 200 K.

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.

Application of LTS-SQUIDs in Nuclear Measurement Techniques

Low temperature superconducting quantum interference devices (LTS SQUIDs) are used to make precision measurements of electromagnetic fields in applications ranging from biomedicine to high energy physics. We have previously described an LTS SQUID-based device for nuclear physics which employs the Cryogenic Current Comparator principle (CCC). The CCC consists of a high-performance LTS DC SQUID system, a toroidal pick-up coil, and a meander-shaped superconducting niobium shield. Theoretical investigations show that as external noise decreases, improvements in performance depend on the properties of the ferromagnetic core material embedded in the pick-up coil. Here we present the temperature- and frequency-dependence of several candidate ferromagnetic and nanocrystalline materials. We discuss these results in light of the optimization of the CCC sensor performance.

Design and construction of a top loading dilution refrigerator probe for a superconducting quantum interference device DC magnetometer

A commercially available SQUID (Superconducting QUantum Interference Device) DC magnetometer is often limited by its relatively high temperature (≥ 1.9 K) and low magnetic field (≤ 7 T) operating environment. The need for the lower temperature and higher field DC magnetization measurements keeps growing as more materials show interesting physical phenomena with relevant energy scales that require millikelvin temperatures. To meet these needs we have developed a SQUID DC magnetometer which operates in the top loading dilution refrigerator of a 16 T superconducting magnet. An essential part of this low temperature and high field SQUID magnetometer is a specialized probe which can adapt the SQUID electronics and low friction mechanical sample shaft. The details of magnetometer probe and preliminary testing results are described in this paper.

A case study of deep electromagnetic exploration in conductive cover

This paper describes the survey design, data collection and results from a geophysically driven exploration program in Northern Australia. The exploration project was a joint venture between Falcon Minerals NL and Anglo American. It was focussed on finding massive to net textured nickel sulphides associated with a mafic intrusive body. The extent of the intrusive body was inferred from interpretation of a significant 14mgal gravity anomaly. Limited previous exploration indicated any drill targets were likely to be covered by 400 to 500m of mesozoic and recent sediments. These sediments are estimated to have a conductance of 200Siemens, making it difficult to use conventional electrical geophysics for effective exploration. Anglo American, together with its research partner IPHT of Germany have developed a low temperature superconducting quantum interference device (LTS) that can be used as a sensor in transient electromagnetic (TEM) surveys. The LTS is a ?B field? sensor with significant advantages in noise levels over other ?B field? sensors and the ability to detect targets with time constants up to 3 orders of magnitude larger than conventional dB/dt coils (Le Roux et al 2007). The LTS sensor is particularly suited to finding highly conductive targets beneath conductive cover. After forward modelling and survey design, the JV completed some 270km of reconnaissance moving loop ground electromagnetic surveys. Selected anomalies identified with this survey were then followed up with more detailed moving loop and some fixed loop surveys. These results were then modelled using a variety of software packages to try and fit the late time TEM field data. Drilling of selected targets and some downhole TEM surveys are in progress.

Effect of Doping Concentration on Zn1-XMnxO Thin Films Grown by RF Magnetron Sputtering

We have investigated the effect of doping concentration on structural, optical and magnetic properties of Mn-doped ZnO thin films deposited on Si (100) substrate by RF magnetron sputtering. The films have been characterized by X-ray diffraction (XRD), photoluminescence (PL) and superconducting quantum interference device (SQUID) magnetometry. It is observed from XRD, that the increase of Mn content increases the FWHM which indicates the degradation of crystalline quality. The photoluminescence spectrum reveals that the incorporation of Mn ions suppresses the deep level emissions considerably in comparison to those observed in pure ZnO. The near band edge (NBE) emission of Mn-doped films is shifted to the lower energy side (red shift) in comparison to pure ZnO film. The room temperature SQUID magnetometer results reveal that all the films show paramagnetic behaviour due to the lack of interactions among Mn moments.

Synthesis of High Coercivity Cobalt Nanotubes with Acetate Precursors and Elucidation of the Mechanism of Growth

Cobalt nanotubes (CoNTs) with very high longitudinal coercivity were prepared by electrodeposition of cobalt acetate for the first time by using anodized alumina (AAO) template. They were then characterized with X-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), and a transmission electron microscope (TEM). Formation of a highly ordered hexagonal cobalt phase is observed. Room temperature SQUID (superconducting quantum interference device) magnetometer measurements indicate that the easy axis of magnetization is parallel to the nanotube axis. These CoNTs exhibit very high longitudinal coercivity of ∼820 Oe. A very high intertubular interaction resulting from magnetostatic dipolar interaction between nanotubes is observed. Thick-walled nanotubes were also fabricated by using cobalt acetate tetrahydrate precursors. A plausible mechanism for the formation of CoNTs based on mobility assisted growth is proposed. The role of the hydration layer and the mobility of metal ions are elucidated in the case of the growth mechanism of one-dimensional geometry.

Sensitivity and resolution of using magneto-telluric gradient method for detecting buried objects

The feasibility of using magneto-telluric gradient measurements at the surface of the earth for detecting buried objects is examined. A modified quasi-static version of the finite-difference time-domain method is used to examine the sensitivity and resolution of this approach. Buried objects with varying sizes, conductivities and depths were simulated. The use of high temperature superconducting quantum interference devices (SQUID) for carrying out this magneto-telluric measurement is discussed.

Magnetophoresis and cytometry with magnetic microparticles

Abstract We are developing a bioassay technique utilizing superparamagnetic and ferromagnetic microparticles, with the aim of using these in biological labeling. The technique uses two independent pieces of instrumentation; a magnetophoresis instrument and a magnetic flow cytometer. The former consists of a microfluidic sorting chamber that incorporates standard flow techniques and a permanent magnet. The particles are deflected into different outlet collection bins, with the degree of deflection determined by the particle's magnetic moment. We report on microparticle sorting and discuss the hydrodynamics of the chamber in relation to reproducibility. Once the microparticles have been sorted, the different populations will then be sequentially analyzed both optically and magnetically (while in flow). The magnetic analysis is presently performed with the aid of a LN 2 -cooled high temperature superconducting quantum interference device (HTS SQUID) array. We are currently also evaluating the use of giant magnetoresistive (GMR) sensors. In this paper we will discuss the sorting and resorting of microparticles and present preliminary results for the magnetic detection of the microparticles both with HTS SQUID and GMR sensors.

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.

High slew rate, ultrastable direct-coupled readout for dc superconducting quantum interference devices

A very fast and thermostable readout electronics for dc superconducting quantum interference devices (SQUIDs) is presented. The authors have applied a concept which gives them the opportunity to combine several, at first sight contradictory, important parameters for the SQUID system user. With their flux-locked-loop electronics they could reach more than 16MΦ0∕s slew rate while using a 1.3m cable between the electronics and a conventional low transition temperature SQUID (with a maximum peak-peak voltage of the flux-to-voltage transfer function of ⩾63μV). By making use of thermocurrent compensation in the first stage of the amplifier they have achieved a thermal drift of about 5nV∕K for a temperature range between 0 and 65°C. The system demonstrated a white noise voltage level of ∼0.32nV∕Hz1∕2, with a flicker noise corner frequency of about 0.1Hz.

Present situation and future prospects of food contaminant detection system using high temperature superconducting quantum interference device

Present situation and future prospects of food contaminant detection system using high temperature superconducting quantum interference device