SQUID Gradiometer Research Articles

Simulation and Parameter Optimization of Two-Dimensional SQUID Gradiometer

Simulation and Parameter Optimization of Two-Dimensional SQUID Gradiometer

A planar mounted SQUID full-tensor module for magnetoenterogram denoising detection

Magntoenterogram (MENG) is a functional imaging method with great clinical potential for non-invasive diagnosis of intestinal diseases. In measurements of MENG, the cardiac artifacts are a strong biological source of interference. Based on wire-wound SQUID gradiometers, we constructed a planar mounted full-tensor compensation module for MENG system, which can obtain cardiac artifacts while suppressing ambient noise, so as to denoise MENG signals without increasing external ECG recording channels. The cardiac artifacts are regressed out from the full-tensor compensation module outputs, which can denoise the MENG measurements. Using this module, the SNR is about 70 dB better than the raw data. At last, 36-point array MENG signals were detected successfully and the contour map of jejunal slow-wave frequency (SWF) was consistent with the jejunal area (one part of the small intestine). This method will save costs and avoid the new electromagnetic interferences introduced by ECG equipment. It will lay a good foundation for the rapid clinical application of the MENG system.

Optimization of High-Sensitivity SQUID Gradiometer for ARIADNE at CAPP

Optimization of High-Sensitivity SQUID Gradiometer for ARIADNE at CAPP

A Modeling Method for Synthetic SQUID Gradiometer With Optimized Baseline in Magnetocardiography Measurement

A Modeling Method for Synthetic SQUID Gradiometer With Optimized Baseline in Magnetocardiography Measurement

Inductance Matching in Axial SQUID Gradiometer and the Influence on Its Performance

Inductance Matching in Axial SQUID Gradiometer and the Influence on Its Performance

Design of a High-Tc SQUID Planer Gradiometer and Evaluation of Sensitivity Distribution

When using SQUID magnetic sensors to inspect metallic contaminants in magnetic matrices, such as battery components, it is advantageous to use a gradiometer rather than a magnetometer because a higher signal-to-noise ratio can be obtained. In this study, we reviewed the design of directly coupled SQUID gradiometers and optimized their pickup loops. Several gradiometers with pickup loops of different sizes were fabricated. To evaluate these gradiometers, we applied a small magnetic field produced by a magnetic field coil with a small diameter (effective diameter: 0.65 mm) to them. The sensitivity distribution of these gradiometers was evaluated using a special mechanism that allows for complete scanning over the device substrate. As a result, the magnitude of the peak value could be explained by an inductance imbalance between the pickup loop and the SQUID. Finally, we could find the optimal pickup coil design conditions. Furthermore, we could capture the sensitivity distribution of a small SQUID loop placed in the center of the device.

Лабораторный стенд на основе СКВИД-магнитометров для исследования магнитных свойств наноматериалов

The laboratory stand with the squid-based gradiometer was developed and tested in experimental studies of magnetic nanoparticles used in medicine. Two versions of the cryogenic probe were tested in investigations, the first of which included an additional XYZ squid-based magnetometer for "electronic" balancing of the input signal gradiometer in a uniform magnetic field. The second probe contained in its design movable trimmers with superconducting plates located in the area of the input loops of the gradiometer for its mechanical balancing. Both cryogenic probes demonstrated stable operation of the squid-based gradiometer at usual laboratory conditions without additional magnetic shielding. The stand was used to study the magnetization of aqueous suspensions of magnetite nanoparticles in various concentrations, which was induced using an uniform magnetic field with an amplitude of up to 15 milliTesla, created by a special system of Helmholtz coils at a frequency range of 4-12 Hz in the vertical and horizontal directions. The magnetic signals of nanoparticles were recorded using a second-order axial gradiometer in a «2:4:2» configuration with an input loop diameter of 8 mm and a base length of 29 mm. The experimental studies of the magnetization of aqueous suspensions of magnetite nanoparticles were aimed at estimating the limiting resolution of the SQUID gradiometer by the number of detected magnetic nanoparticles. The possibility of registering a magnetic signal from about 6 × 109 MNPs of magnetite 6 nm in size in a volume of 1 ml from a distance of about 20 mm from the receiving coils of the gradiometer was demonstrated. Dry liver extracts of small animals containing MNPs were also used as objects of study. Directions of further improvement the used instrumental elements and methods of magnetic measurements for increasing the sensitivity of squid-based gradiometers in experiments with MNPs are determined.

Reduction of Magnetic Noises in Cryocooler Operated Multichannel SQUID System

We developed a low-vibrational-noise cooling configuration using continuous liquefaction of evaporated helium gas from a multi-channel SQUID gradiometer system for whole-head magnetoencephalography (MEG) measurements. The initial reduction of the vibration of the cryocooler was done by rigidly mounting the remote motor and cold head chamber on a concrete wall. This significantly reduces transmission of vibrations to the transfer tube, especially compared with mounting them on vertical aluminum frames. In addition, to reduce vibrations from a mechanical SQUID array insert, we completely eliminated it by mounting each SQUID gradiometer separately on the helmet surface within the vacuum space. Thus, vibrations from the boiling liquid helium and transmission from the transfer tube were both greatly reduced. Magnetic field noise of the 150-channel SQUID gradiometer system showed that the vibration-induced interference peaks are comparable in amplitude to those from a conventional MEG system without helium reliquefaction.

Towards Ultrasensitive SQUIDs Based on Submicrometer-Sized Josephson Junctions

We recently demonstrated a 1$^{\textrm{st}}$-order axial gradiometer SQUID system which is operated in a liquid He dewar with negligible noise contribution. The achieved close to SQUID limited measured coupled energy sensitivity $\varepsilon_{c}$ of $\sim$30$\,h$ corresponds to a white field noise below 180$\,$aT$\,$Hz${^{-1/2}}$. In order to further improve the SQUID noise performance, the junction capacitance was reduced by decreasing its lateral size to below $1\,\mu$m. This was realized by extending the fabrication process for sub-micrometer-sized Josephson Junctions based on the HfTi self-shunted junction technology to an SIS process with AlO$_{\textrm{x}}$ as the insulating layer. We achieved energy sensitivities of 4.7$\,h$ and 20$\,h$ at 4.2$\,$K for uncoupled and coupled SQUIDs, respectively. We also investigated the temperature dependence of the noise of the uncoupled SQUIDs and reached an energy sensitivity of 0.65$\,h$ in the white noise regime at 400$\,$mK.

A High-Balance Planar SQUID Gradiometer

We have developed and fabricated SQUID gradiometers in a Nb/Al-AlOx/Nb technology using an i-line stepper combined with a mask aligner lithography. The stepper and the aligner are used to fabricate fine-scale patterns such as the Josephson junctions and large-scale patterns such as pickup coil, respectively, on the same wafer with a 4-inch diameter. The SQUID is designed as a first-order gradiometer with a dual-washer configuration. Two sets of multiturn spiral input coils with opposite directions are integrated on the washer and connected to the pickup coil to form a flux transformer. In order to improve the balance of the gradiometer, a fully symmetric configuration is introduced with a mirrored SQUID. The pickup coil is a first-order gradiometric type with a base line of 3.5 cm. The size of each loop is 12.65 mm × 11.65 mm, which results in a gradient magnetic field sensitivity of 0.25 nT/(cm·Φ0). The measured gradient magnetic field noise is 75 fT/(m·√Hz) in the white noise region. Moreover, a sapphire holder is used to fix and package the chip in order to maintain the high intrinsic balance (typical 10−4). It makes the SQUID gradiometer more attractive for an unshielded operation in noisy environments.

Effect of Niobium Cylinder on Output of the Three-Dimensional SQUID Gradiometer

Because of the large ambient noise in biomagnetic measurements, it is usually necessary to use a gradiometer to reduce the environmental noise [A. Hayashi, Y. Hirata, and S. Kuriki, “Coil cancellation scheme with an electronic gradiometer for the reduction of magnetic field noise,” J. Magn. Soc. Jpn., vol. 29, no. 4, pp. 477-481, 2005.]. In order to prevent noise coupling into the SQUID from the on-chip input coil, it is also necessary to cover the chip with a niobium cylinder [S. L. Zhang et al., “A novel superconducting quantum interference device for biomagnetic measurements,” Sci. Bull., vol. 58, no. 24, pp. 2917-2919, 2013.], [J. R. Claycomb and J. H. Miller, Jr., “Superconducting magnetic shields for SQUID applications,” Rev. Sci. Instrum., vol. 70, no. 12, pp. 4562-4568, 1999.]. This paper focuses on the possible impact of introducing a niobium cylinder on the output of a SQUID gradiometer and how to reduce this effect. In this paper, the effect of the niobium cylinder on the output is equivalent to imbalance in simulation and measurement. Changing the relative position of the niobium cylinder makes the equivalent imbalance of the SQUID gradiometer coil less than 1%, which is caused by manual winding.

Defect Detection of Pipes using Guided Wave and HTS-SQUID

In this paper, we investigated ultrasonic guided wave measurements on aluminium pipes with defects using high temperature superconducting (HTS) SQUID gradiometer and magnetostrictive sensors (MsS), which utilized pre-magnetized nickel thin plates. One of the pipes was provided with an axial defect, and the other was provided with a circumferential defect. The MsSs were used by adhering them on circumferences of the pipes to generate ultrasonic guided waves and to receive the waves by converting them into the magnetic signals, which were measured by the HTS-SQUID gradiometer. Guided wave measurements using the MsSs and the gradiometer demonstrated that magnetic signals of about 3.3 mΦ0 due to reflected waves from both the defects were successfully detected. Reflected wave signals of about 1.4 mΦ0 from thin nickel plates of the MsS on the pipes were also detected.

Measuring MEG closer to the brain: Performance of on-scalp sensor arrays

Optically-pumped magnetometers (OPMs) have recently reached sensitivity levels required for magnetoencephalography (MEG). OPMs do not need cryogenics and can thus be placed within millimetres from the scalp into an array that adapts to the individual head size and shape, thereby reducing the distance from cortical sources to the sensors. Here, we quantified the improvement in recording MEG with hypothetical on-scalp OPM arrays compared to a 306-channel state-of-the-art SQUID array (102 magnetometers and 204 planar gradiometers).We simulated OPM arrays that measured either normal (nOPM; 102 sensors), tangential (tOPM; 204 sensors), or all components (aOPM; 306 sensors) of the magnetic field. We built forward models based on magnetic resonance images of 10 adult heads; we employed a three-compartment boundary element model and distributed current dipoles evenly across the cortical mantle.Compared to the SQUID magnetometers, nOPM and tOPM yielded 7.5 and 5.3 times higher signal power, while the correlations between the field patterns of source dipoles were reduced by factors of 2.8 and 3.6, respectively. Values of the field-pattern correlations were similar across nOPM, tOPM and SQUID gradiometers. Volume currents reduced the signals of primary currents on average by 10%, 72% and 15% in nOPM, tOPM and SQUID magnetometers, respectively. The information capacities of the OPM arrays were clearly higher than that of the SQUID array. The dipole-localization accuracies of the arrays were similar while the minimum-norm-based point-spread functions were on average 2.4 and 2.5 times more spread for the SQUID array compared to nOPM and tOPM arrays, respectively.

Weakly Damped SQUID Gradiometer With Low Crosstalk for Magnetocardiography Measurement

In a multichannel magnetocardiography system, the problem of crosstalk is serious due to mutual inductances between the pickup coils of adjacent channels. In this paper, a superconducting quantum interference device gradiometer module based on weakly damped Josephson junctions with large $\beta _{c}\;(\approx 5)$ is presented. An external feedback design is also adopted to suppress the crosstalk between different channels. With a special superconducting connection between input coil and pickup coil, an axial first-order gradiometer with baseline of 70 mm and diameter of 18 mm is fabricated. Using a direct readout circuit with equivalent flux noise of $1.8\;\mu \Phi _{{0}}{\rm{/ \surd Hz}}$ , the flux noise of this gradiometer is measured to be $6.5\;\mu \Phi _{{0}}{\rm{/ \surd Hz}}$ in a white noise range, corresponding to a field sensitivity of ${\rm{0.5\;fT/ (cm\bullet \surd Hz)}}$ . The crosstalk rates in external feedback mode and internal feedback mode are both successfully simulated with MAXWELL software. The results by experimental measurements using these gradiometers are in coincidence with the simulated ones; both simulation and experimental results show a substantial suppression of crosstalk in the external feedback design.

Volcanic ash in bare ice south of Sør Rondane Mountains, Antarctica: geochemistry, rock magnetism and nondestructive magnetic detection with SQUID gradiometer

Nondestructive magnetic detection of tephra layers in ice cores will be an important method to identify and correlate stratigraphic horizons of ice bearing volcanic ash particles. Volcanic ash particles were extracted from tephra-bearing ice samples collected from Nansen Ice Field south of the Sor Rondane Mountains, Antarctica. Particles are fresh glassy volcanic ash with diameters of ~50 μm, and chemical composition of the matrix glass belongs to a low-K basaltic andesite group, ranging from SiO2 60–62 wt% and K2O 0.40–0.50 wt%. Considering the grain size of ash particles and chemical composition of volcanic glass, the ash in tephra-bearing ice samples might be originated from the South Sandwich Islands located 2800 km northwest of the sampling sites. Correlations on major element concentrations with tephra layers associated with South Sandwich Islands in EPICA-Dome C, Vostok, and Dome Fuji ice cores show high similarity. Rock magnetic experiments show that the magnetic mineral is pseudo-single-domain titanomagnetite with ulvospinel content of 0.2–0.35 mixed with single-domain to superparamagnetic (titano)magnetite. Small blocks of the tephra-bering ice were measured with a SQUID gradiometer at 1-mm intervals with a spatial resolution of ~3 mm. With DC magnetic field of 25 mT, magnetic signal could be enhanced and detected for all the samples including the one with invisible amount of tephra particles. In order to simulate a thin ash layer in ice core, volcanic ash particles extracted from the tephra-bearing ice were used to fabricate a thin ash layer, which were subsequently magnetized, measured with the gradiometer. The noise level for Z axis gradiometer was about 0.6 pT. Detection limit for a half-cylinder with 29 mm radius and a thickness of 1 mm uniformly magnetized in X axis direction is ~9 × 10−5 A/m, which could be improved down to ~2 × 10−6 A/m by reducing the sensor-to-sample distance to 0.5 mm.

Concentric transmon qubit featuring fast tunability and an anisotropic magnetic dipole moment

We present a planar qubit design based on a superconducting circuit that we call concentric transmon. While employing a straightforward fabrication process using Al evaporation and lift-off lithography, we observe qubit lifetimes and coherence times in the order of 10 μs. We systematically characterize loss channels such as incoherent dielectric loss, Purcell decay and radiative losses. The implementation of a gradiometric SQUID loop allows for a fast tuning of the qubit transition frequency and therefore for full tomographic control of the quantum circuit. Due to the large loop size, the presented qubit architecture features a strongly increased magnetic dipole moment as compared to conventional transmon designs. This renders the concentric transmon a promising candidate to establish a site-selective passive direct Ẑ coupling between neighboring qubits, being a pending quest in the field of quantum simulation.

HfTi-nanoSQUID gradiometers with high linearity

We have developed a family of HfTi nanoSQUID gradiometers for different applications. These Nb-based nanoSQUIDs contain overdamped superconductor–normal conductor–superconductor (SNS) Josephson junctions with HfTi as a normal conducting barrier. The lateral dimensions of the junctions are about 200 nm × 200 nm, and the barrier thickness is nominally 30 nm. In order to enhance their practical use, the nanoSQUIDs are implemented with gradiometric SQUID and feedback loops, gradiometric transformers, and rf filters. The devices can be operated in an excitation field of up to a few mT with very low levels of nonlinearity. Due to the small loop size and the resulting low loop inductance, a white noise level down to 110 nΦ0/√Hz was achieved. The 1/f noise with a typical corner frequency below 1 kHz is dominated by critical current fluctuations. It can be reduced by applying bias reversal. A noise level of 600 nΦ0/√Hz was achieved at 1 Hz in a two-stage flux locked loop with bias reversal.

Baseline optimization of SQUID gradiometer for magnetocardiography**Project supported by the “Strategic Priority Research Program (B)” of the Chinese Academy of Sciences (Grant No. XDB04020200) and the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KGCX2-EW-105).

SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements. An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance. By placing several magnetometers at different heights along the vertical direction, we could simultaneously obtain the synthetic gradiometers with different baselines. By using the traditional signal-to-noise ratio (SNR) as a performance index, we successfully obtain an optimal baseline for the magnetocardiography (MCG) measurement in a magnetically shielded room (MSR). Finally, we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR. The SNR about 38 dB is obtained in the recorded MCG signal.

Effects of Ru Addition on the Superconducting Properties of the Eu-123 System

E ects of the Ru addition on the structural and superconducting properties of the Eu-123 system were studied. Samples of the nominal composition EuBa2Cu3−xRuxO7−δ with x ranging from 0.0 to 0.7 were prepared by the solid state reaction technique from Eu2O3, BaCO3, CuO and RuO2 precursors at the temperature of 1050 ◦C for 72 h in owing oxygen and oxygen-annealed at 580 ◦C for 24 h. X-ray di raction data show the presence of another Ba Eu Ru O phase, for x ≥ 0.03, in addition to the main superconducting phase. AC and DC magnetization characteristics were measured by the compensation method using the second-order SQUID gradiometer at ≈ 77 K and the QD SQUID magnetometer MPMS XL-7 at 20 K. The superconducting properties, Tc, ∆Tc, change only weakly up to x = 0.2, and magnetization M(H) deteriorates with an increasing Ru content.

Magnetic Studies of EuBa2Cu3-xRuxO7-δCompounds

E ects of Ru addition on magnetic properties of EuBa2Cu3−xRuxO7−δ compounds were studied. Samples of EuBa2Cu3−xRuxO7−δ with x from 0.00 to 0.70 were prepared by the solid state reaction technique from Eu2O3, BaCO3, CuO and RuO2 precursors. Temperature dependences of the zeroeld cooled (ZFC) and the eld cooled (FC) DC magnetic moment at low and high applied magnetic eld Ha were measured by the QD SQUID magnetometer MPMS XL-7 and AC magnetization MAC(H) curves at 77 K by the compensation method using the second-order SQUID gradiometer. The molar susceptibility χ of the samples was corrected to the e ects of the sample holder and diamagnetism and χ∗ also was corrected to the temperature independent paramagnetic/diamagnetic contribution χ and tted by the Curie Weiss relation. The values of the Weiss temperature and the e ective magnetic moment have been estimated at low and high value of applied magnetic eld.