Here we report the fabrication and electrical characterization of high-transition temperature SQUIDs directly written by helium ion beam irradiation for use in Quantum Design's pulsed tube cooler ...based physical property measurement system. Our device consists of a SQUID with a direct coupled 300 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m diameter flux focusing pickup loop. When DC biased above the critical current, we observe a modulation in the voltage with a peak-to-peak amplitude of 500 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>V, while having periodicity of 275 nT per flux quantum. The SQUID chip was mounted to the temperature-controlled system equipped with optically aligned piezo scanners which allow the accurate positioning of the sample less than 100 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m from the sensor. The system functions as a magnetic properties characterization tool which can operate over a wide temperature range (1-50 K) without thermally isolating the SQUID from the sample.
Increasing the flux-to-voltage transfer coefficient of the SQUID output voltage is necessary to release the constraint on the preamplifier input noise. As one of the approaches to increase the ...transfer coefficient, we have been using a double relaxation oscillation SQUID (DROS) having a transfer coefficient of about 10 times larger than those of DC-SQUIDs. Traditionally, DC-SQUIDs were operated in the non-hysteretic condition with the Stewart-McCumber parameter (β c ) less than 1. In this study, we fabricated hysteretic DC-SQUIDs with the β c ranging from 2.5 and compared the transfer coefficient and the system noise of DC-SQUIDs and DROSs. Both DROS and DC-SQUID have the same structure and design parameters for the SQUID loop inductance, resonance-damping circuits in the SQUID loop, and input coil. All the SQUIDs were fabricated in the same wafer using the Nb/AlO x /Nb junction process. The transfer coefficients of DROSs were about 1 mV/Φ 0 , regardless of SQUID parameters. For DC-SQUIDs, the transfer coefficients were sensitive to the β c and the operating margin was narrower than that of DROS. The white noise of both SQUIDs in the flux-locked loop mode was around 1.5 μΦ 0 /√Hz at 100 Hz, measured with a preamplifier of input voltage noise of 1 nV/√Hz. DC-SQUIDs had mostly a narrower operating margin against the bias current, and the modulation voltage was smaller than DROS. In a near-optimized operating condition, both DROS and hysteretic DC-SQUID showed comparable noise performance.
Inductance is a key parameter when optimizing the performance of superconducting quantum interference device (SQUID) magnetometers made from the high temperature superconductor YBa2Cu3O7−x (YBCO) ...because lower SQUID inductance L leads to lower flux noise, but also weaker coupling to the pickup loop. In order to optimize the SQUID design, we combine inductance simulations and measurements to extract the different inductance contributions, and measure the dependence of the transfer function VΦ and flux noise S Φ 1 2 on L. A comparison between two samples shows that the kinetic inductance contribution varies strongly with film quality, hence making inductance measurements a crucial part of the SQUID characterization. Thanks to the improved estimation of the kinetic inductance contribution, previously found discrepancies between theoretical estimates and measured values of VΦ and S Φ 1 2 could to a large extent be avoided. We then use the measurements and improved theoretical estimations to optimize the SQUID geometry and reach a noise level of S B 1 2 = 44 fT/ Hz for the best SQUID magnetometer with a 8.6 mm × 9.2 mm directly coupled pickup loop. Lastly, we demonstrate a method for reliable one-time sensor calibration that is constant in a temperature range of several kelvin despite the presence of temperature dependent coupling contributions, such as the kinetic inductance. The found variability of the kinetic inductance contribution has implications not only for the design of YBCO SQUID magnetometers, but for all narrow linewidth SQUID-based devices operated close to their critical temperature.
Design Overview of DM Radio Pathfinder Experiment Silva-Feaver, Maximiliano; Chaudhuri, Saptarshi; Hsaio-Mei Cho ...
IEEE transactions on applied superconductivity,
2017-June, 2017-6-00, Volume:
27, Issue:
4
Journal Article
Peer reviewed
Open access
We introduce DM Radio, a dual search for axion and hidden photon dark matter using a tunable superconducting lumped-element resonator. We discuss the prototype DM Radio Pathfinder experiment, which ...will probe hidden photons in the 500 peV (100 kHz)-50 neV (10 MHz) mass range. We detail the design of the various components: the LC resonant detector, the resonant frequency tuning procedure, the differential SQUID readout circuit, the shielding, and the cryogenic mounting structure. We present the current status of the pathfinder experiment and illustrate its potential science reach in the context of the larger experimental program.
Magnetometer Calibration Methods Fagaly, R. L.; Paulson, Douglas N.; Wikswo, John P.
IEEE transactions on applied superconductivity,
2024-Sept., Volume:
34, Issue:
6
Journal Article
Peer reviewed
The use of a magnetometer or gradiometer as a quantitative instrument requires the proper calibration of the output voltage as a measure of the magnetic field. The methods used to calibrate the ...conventional and superconducting quantum interference device-based detection systems depend upon the configuration of the detection coils and the environment. Calibration procedures for a number of different detection coil designs and their mathematical foundations are addressed. Many of these procedures can be applied to a wide variety of magnetic measurement technologies.
The use of external pickup coils in a gradiometer based Superconducting Quantum Interference Device (SQUID) enhances the sensitivity of gradiometer. These pickup coils convert the coupled magnetic ...flux into a current that is transmitted to the input coil, establishing a secondary coupling with the SQUID and thus enabling the measurement of weak signals. The combination of inductance between the pickup antenna and input coil critically affects the magnetic field to voltage conversion coefficient and noise level of the entire gradiometer module. Through theoretical derivation, simulation, and practical testing, this study demonstrates that the optimal magnetic field to voltage conversion coefficient and noise levels are achieved when the inductance ratio of the detection to input coils is between 0.9 and 1.1. Moreover, for optimal inductance matching, the twisted pair lengths of the entire gradiometer are presented for axial second-order gradiometers of different radii and baselines in this paper. This guides the practical winding of sensor modules, and a gradiometer with 5 cm baseline and 9 mm radius was validated by experiment.
In this work, we investigate two-dimensional arrays of High-
T
C
superconducting quantum interference devices (SQUIDs) for optimization of their electrical transport characteristics. Specifically, we ...look at devices with different electrode configurations in between the series segments to gain insight into how the array spacing, in the direction of the bias current, affects the voltage magnetic field characteristics. Our results suggest that for spacing dimensions greater than the penetration depth interactions are minimal. Furthermore, comparisons of voltage field characteristics reveal higher modulation voltages and narrower peaks with as the numbers of SQUIDs in the parallel direction increases from 1 to 6. For larger numbers of SQUIDs in parallel greater than 6 little change is observed. These results suggest a pathway to SQUID array scaling for very large numbers of SQUIDs within in a small area.
The magnetoenterogram (MENG) utilizes the superconducting quantum interference device (SQUID) with ultrahigh sensitivity to detect magnetic signals emanating from the intestines. The magnetic field ...distribution reflects the ischemic condition of the mesentery to diagnose acute mesenteric ischemia. In practice, the intestinal magnetic signal is very weak and difficult to identify from noises, that is, the signal-to-noise ratio (SNR) is relatively low. An innovative magnetic flux concentrator (MFC) combined with the MENG is presented in the article to enhance the SNR. The specific work includes the selection of MFC material with suitable permeability and optimization of the diameters and heights. The enhancements for various directional magnetic signals were simulated. Finally, some preliminary experiments were conducted to test the MFC enhancements. The intestinal signal was simulated using a powered coil at low frequencies. Approximately a tenfold enhancement is achieved, remaining constant during the 0.2-1-Hz range.
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