Test Coil Research Articles

Method for Quantifying Variation in the Resistance of Electronic Cigarette Coils.

In electronic nicotine delivery systems (ENDS), coil resistance is an important factor in the generation of heat energy used to change e-liquid into vapor. An accurate and unbiased method for testing coil resistance is vital for understanding its effect on emissions and reporting results that are comparable across different types and brands of ENDS and measured in different laboratories. This study proposes a robust, accurate and unbiased method for measuring coil resistance. An apparatus is used which mimics the geometric configuration and assembly of ENDS reservoirs, coils and power control units. The method is demonstrated on two commonly used ENDS devices—the ALTO by Vuse and JUUL. Analysis shows that the proposed method is stable and reliable. The two-wire configuration introduced a positive measurement bias of 0.086 (Ω), which is a significant error for sub-ohm coil designs. The four-wire configuration is far less prone to bias error and is recommended for universal adoption. We observed a significant difference in the coil resistance of 0.593 (Ω) (p < 0.001) between the two products tested. The mean resistance and standard deviation of the reservoir/coil assemblies was shown to be 1.031 (0.067) (Ω) for ALTO and 1.624 (0.033) (Ω) for JUUL. The variation in coil resistance between products and within products can have significant impacts on aerosol emissions.

Mechanical design of the magnet mirror structure for testing Nb3Sn sextupole coil of 45 GHz ECRIS

The new Nb3Sn superconducting magnet system for the fourth-generation 45 GHz ECR source is under development at the Institute of Modern Physics (IMP). A mirror structure of the Nb3Sn sextupole testing coil based on an aluminum shell-based structure and bladder & key technology is used for studying the coil's mechanical, thermal and quench performance under realistic conditions. This paper describes the mechanical analyses performed to estimate the sextupole’s preload. Based on the three-dimensional finite-element mechanical model, the stress analysis for the process of assembly, cooling down, and charging is carried out. The assembly and strain measurement results of sextupole mirror structure are also introduced in this paper.

An effective method for differentiating inside and outside defects of oil and gas pipelines based on additional eddy current in low-frequency electromagnetic detection technique

Accurate differentiation of whether the defect position is located on the inside or outside surface is necessary in the low-frequency electromagnetic detection technique (LFET) on oil and gas pipelines. We design a set of composite probe arrays that consisted of inductive magnetic coils (LFET coils) and eddy current testing (ECT) coils to accomplish comprehensive inspection, meanwhile, the theoretical calculation and analysis of the mutual interference mechanism between LFET and ECT coils were mainly implemented. Experimental result demonstrates that the ECT coils can effectively minimize the low-frequency magnetic field interference and allow low-frequency excitation coil setting parameters to be adjusted in a wide range (760 V Hz of voltage–frequency product in this experiment) to identify the inside defects above 1 mm depth while nothing found to detect outside defects. This circumstance enables the identification of the inside defect of 4 mm wide and 1 mm deep (10% wall thickness) at a lift-off value of 14 mm.

Probing interhemispheric dorsal premotor-primary motor cortex interactions with threshold hunting transcranial magnetic stimulation

ObjectiveTo characterise the effect of altering transcranial magnetic stimulation parameters on the magnitude of interhemispheric inhibition (IHI) from dorsal premotor (PMd) to primary motor cortex (M1). MethodWe used a fully automated adaptive threshold hunting paradigm to quantify PMd-M1 IHI across a range of conditioning stimulus (CS) intensities (90%, 110%, 130% of resting motor threshold, rMT) and interstimulus intervals (ISIs) (8, 10, 40 ms). M1-M1 IHI was examined with CS intensities of 110%, 120%, and 130% rMT and ISIs of 10 and 40 ms. Two test coil orientations (inducing posterior-anterior or anterior-posterior current) were used. ResultsPMd-M1 IHI was obtained consistently with posterior-anterior (but not anterior-posterior) test stimuli and increased with CS intensity. M1-M1 IHI was expressed across all conditions and increased with CS intensity when posterior-anterior but not anterior-posterior induced current was used. ConclusionsThe expression of PMd-M1 IHI is contingent on test coil orientation (requiring posterior-anterior induced current) and increases as a function of CS intensity. The expression of M1-M1 IHI is not dependent on test coil orientation. SignificanceWe defined a range of parameters that elicit reliable PMd-M1 IHI. This (threshold hunting) methodology may provide a means to quantify premotor-motor pathology and reveal novel quantitative biomarkers.

Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils

REBCO coated conductors are now being used for building very high-field magnets with large electromagnetic stresses, both expected ones due to transport current × stresses and additional stresses resulting from the large screening currents inherent in wide tapes. Post mortem analyses of several recent test coils operated above 40 T show that significant conductor plastic deformation occurs, even for JBR stresses well below the ∼1 GPa yield of the Hastelloy substrate of the conductor. To investigate these deformation mechanisms, conductors were unwound after coil test and carefully examined with respect to their length-wise Ic which revealed many areas of local damage. Regions of interest were examined by metallographic cross-section, Hall microscopy, magneto-optic imaging and scanning electronic microscopy. Important damage frequently occurred to the outer edges of pancakes in the coil ends, which were often plastically deformed over the whole turn circumference, especially when this outer edge was a slit edge. Internal conductor damage was also seen, especially delamination between the buffer and REBCO layers at slit edges. Careful sectioning of the tape at ∼10 mm intervals showed that the plastic deformation of the turns was complex and variable around the turn circumference, with tape cross-sections that exhibited continuous shape change in the outer turns. The bending center line of tapes often shifted from the tape center line toward the edge closest to the coil center, indicating asymmetric effects of transport and screening current stresses across the conductor width. A surprising and vital result is that damage was prevalent when the slit edge was also the edge at which transport current flowed. This damage was absent when the transport current flowed at the not-slit edge, implying great sensitivity of the effect of screening current stresses to localized conductor damage.

The vestibular implant: Opinion statement on implantation criteria for research.

This opinion statement proposes a set of candidacy criteria for vestibular implantation of adult patients with bilateral vestibulopathy (BVP) in a research setting. The criteria include disabling chronic symptoms like postural imbalance, unsteadiness of gait and/or head movement-induced oscillopsia, combined with objective signs of reduced or absent vestibular function in both ears. These signs include abnormal test results recorded during head impulses (video head impulse test or scleral coil technique), bithermal caloric testing and rotatory chair testing (sinusoidal stimulation of 0.1 Hz). Vestibular implant (VI) implantation criteria are not the same as diagnostic criteria for bilateral vestibulopathy. The major difference between VI-implantation criteria and the approved diagnostic criteria for BVP are that all included vestibular tests of semicircular canal function (head impulse test, caloric test, and rotatory chair test) need to show significant impairments of vestibular function in the implantation criteria. For this, a two-step paradigm was developed. First, at least one of the vestibular tests needs to fulfill stringent criteria, close to those for BVP. If this is applicable, then the other vestibular tests have to fulfill a second set of criteria which are less stringent than the original criteria for BVP. If the VI-implantation is intended to excite the utricle and/or saccule (otolith stimulation), responses to cervical and ocular vestibular evoked myogenic potentials must be absent in addition to the above mentioned abnormalities of semicircular canal function. Finally, requirements for safe and potentially effective stimulation should be met, including implanting patients with BVP of peripheral origin only, and assessing possible medical and psychiatric contraindications.

Theoretical and experimental investigation of R&W and W&R SMES coils wound with large-scale MgB2 Rutherford cables operated around liquid hydrogen temperature

We have developed the system called Advanced Superconducting Power Conditioning System (ASPCS) composed of a Superconducting Magnetic Energy Storage (SMES), a fuel cell and a water electrolyzer for effective use of renewable energy such as wind and solar power generation. We have been investigating about the SMES coil using the large-scale Rutherford-type conductors made of commercially-available MgB2 wires. Due to strain sensitivity even before heat treatment for MgB2 production, the design for large-scale Rutherford cables both in the wind and react (W&R) method, and the react and wind (R&W) method applied to coil fabrication has to be done cautiously to prevent the degradation of the IC by the optimizing design parameters such as the twist pitch and the cable compaction. Especially for the R&W method using heat-treated wires, other factors like handling during the coil production process which affect the conductor and coil IC should be also considered. To evaluate the applied strains during the manufacturing process, we conducted theoretical investigation on the strains applied to individual filaments caused by wire-bending. We developed a test coil designed for the R&W method based on analyzing those factors. Furthermore, we measured the coil IC-B-T characteristics and compared to those of other test coils made by the W&R method.

Progress in High-Speed Spin Testing of Superconducting Wire and Tapes for High-Field NMR Magnet Qualification

This paper summarizes the status of a 3-year, NIH-funded research project to study the strength of high temperature superconductors under high circumferential hoop stress, in order to qualify these materials for high-field (> 1 GHz-class NMR magnets. The unique approach presented here is to spin test coils at high rotational speeds, approaching 100,000 rpm, in order to induce the necessary hoop stress. Thermal strain compatibility between the Bi-2212 wire and Inconel wire has been qualified, including thermal cycling. Assembly and testing of the first low-speed (< 30,000 rpm) rotor is now in process, and the design of second, higher speed (> 60,000 rpm) rotor, is also underway.

Gentamicin Vestibulotoxicity: Further Insights From a Large Clinical Series.

To review insights gained from a 21-year experience with gentamicin-induced vestibulotoxicity including differences in vestibulotoxicity between single daily dosing (SDD) and multiple daily dosing (MDD) regimens. Retrospective case series. Tertiary care center. Patients with gentamicin vestibulotoxicity referred to the Hertz Multidisciplinary Neurotology Clinic between January 1993 and September 2014. None. Spectrum of vestibular dysfunction measured using videonystagmography, vestibular evoked myogenic potentials, video head impulse testing, and magnetic scleral search coil testing. Of 53 patients with gentamicin-induced vestibulotoxicity, 24 received SDD and 29 received MDD treatment. The most common indications for treatment were sepsis, endocarditis, and osteomyelitis. Angular acceleration receptor function (semicircular canals) was more commonly affected than linear acceleration receptor function (otolithic organ of the saccule; 100% vs. 62%). A significant proportion of patients (53%) developed vestibulotoxicity in the absence of nephrotoxicity and 40% experienced vestibulotoxicity in a delayed fashion up to 10 days posttreatment cessation (mean 3.9 ± 0.7). Therapeutic monitoring did not necessarily prevent delayed vestibulotoxicity. Nephrotoxicity was less common for SDD compared with MDD (60% vs. 35%, p = 0.01). However, the SDD group experienced vestibulotoxicity at a lower cumulative dose (6.3 vs. 7.0 g, p = 0.04) and shorter duration of therapy (20.7 vs 29.4 d, p = 0.02). Our study further highlights important insights regarding gentamicin-induced vestibulotoxicity. While SDD is associated with decreased risk for nephrotoxicity compared with MDD, it confers a higher risk for vestibulotoxicity.

Study on the Effect of Metal Protection Rings in No-Insulation HTS Coils

In this study, we propose the installation of multiple metal protection rings on the outermost turn of no-insulation (NI) coils to improve thermal, mechanical, and electrical stability. The current bypass characteristics in the transverse direction within an NI test coil wound with 10 turns of GdBCO wire and wrapped with 8 turns of Cu tape around the outermost layer were experimentally investigated for various amounts of heating by a heater and various heater positions. To confirm the electrical effectiveness of the metal protection rings, 8-turn Cu tape was used as the rings. A bypass current from the outermost part of the test coils to the Cu tape was observed. The local temperature increase due to thermal disturbance was suppressed.

Screening-Current-Induced Strain Gradient on REBCO Conductor: An Experimental and Analytical Study With Small Coils Wound With Monofilament and Striated Multifilament REBCO Tapes

Screening currents in REBCO conductors, induced by time-varying magnetic fields, not only affect the field quality of HTS coils but also cause strain gradients along REBCO tape width that may overstress REBCO conductors used in NMR and other high-field magnets. In this paper, we present results of an experimental and analytical study on screening-current-induced strain gradients, performed with small REBCO pancake coils. Because we believe that screening current effect is reduced in multifilament conductor, we have studied 2 test coils, φ150 mm, one wound with monofilament and the other with 3-striate/4-filament REBCO tapes. A 5-T/ 300-mm room-temperature bore magnet was used not only to excite a strong screening current but also apply the nonuniform Lorentz force to each coil at 4.2 K. Our experiment and analysis have quantitatively demonstrated that we can effectively suppress the screening-current effect on strain gradient, not surprisingly, by using striated multifilament REBCO conductor.

Winding Configurations and AC Loss of Superconducting Synchronous REBCO Motors

We investigate effects of armature winding configurations on properties of fully superconducting synchronous motors using REBCO tapes. The effect of the configurations on ac losses in the winding tapes due to the changing transvers magnetic fields applied to the tapes in direction of perpendicular to the flat face of the tapes is important. In generally, it is effective to close winding factor to 1 for improvement of properties of motors. For the purpose, the shape of armature windings is better saddle-shaped winding than race-track winding. In this paper, numerical calculations on the properties of fully superconducting synchronous motors using REBCO tapes with 500 kW class were described. Operating temperature was 65 K. In order to demonstrate the feasibility of saddle-shaped winding, test coil with 5 turns were wound with YBCO tapes and then critical current measurements were carried out. The degradation of the properties has not observed.

Computing Strains Due to Screening Currents in REBCO Magnets

Screening currents have long been known to impact the stress state in tape-wound superconducting coils. In recent years the advent of REBCO tape has led to the development of tape-wound coils by a number of organizations. While several groups have been computing screening currents and ac losses in REBCO tape in a variety of applications for several years, little has been published about the stress due to the screening currents. This problem is challenging due to the need to analyze thousands of REBCO turns which are not bonded together. The T-A formulation of Maxwell's equations employing a homogenization technique enables efficient estimation of the current distribution while structural calculations employing contact elements allow conservative estimation of stresses. Computational results are compared with observed degradation in a test coil. Future coil designs that include the effects of screening current strains are proposed.

Fabrication and Test of Diameter 35 mm Iron-Based Superconductor Coils

Iron-based superconductor (IBS) is expected to be the next generation high temperature superconductor with their potential good properties for the high-field application. This study focus on exploration of the characteristics of IBS coils at high field and development of the IBS coil fabrication technology. A series of diameter 35 mm IBS coils including single pancake (SPC) and double pancakes (DPC) were designed and winded with the 7-filamentary Ba 1-x K x Fe 2 As 2 (Ba122) tape which was produced by the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE-CAS). The IBS coils were divided into 3 groups according to the different fabrication processes. The tests of the IBS coils were firstly carried out at 4.2 K and 10 T background field. The highest quench current of the coils at 10 T is 69.4 A, which is about 90% of the critical current of the short sample at 10 T. Then, two SPCs were selected and tested at 4.2 K at 24 T [1]. The highest quench current of the coils at 24 T is 25.6 A, which is about 39% of the quench current at self-field. The test results were presented and analyzed with respect to the different fabrication processes.

Preliminary Integration for Testing HTS Feather-M2 in the FRESCA2 Dipole Magnet

In 2018, FRESCA2 magnet, developed within a collaboration between CEA and CERN to provide a background field for tests of cables and small coils, reached a field of 14.6 T. This represents a new record field for dipole magnets with a clear aperture. As a continuity of the European project EUCARD-2, CERN aims at exploring accelerator magnet technology up to a 20 T operating field level. For that aim, Feather magnet 2, coils 3 and 4 (FM2.3-4) utilizing REBCO Roebel cable is planned to be inserted in FRESCA2 to reach a higher field. A new structure must be designed to accommodate the insert coils inside FRESCA2. The integrated design has to be capable to deal with several challenges. The magnetic forces in the coils of the insert magnet are high. FRESCA2 is pre-loaded by the so-called bladder-and-key concept, and a shrinking Al-alloy shell. The preload, however, decreases the diameter of the aperture at cryogenic temperature. The stiff external tube of FM2.3-4 is specifically designed for the background field operation. This component, made of 3D printed Inconel-based alloy, has a different thermal contraction with respect to the inner pole of FRESCA2. As a result, the thickness of the shell of FM2.3-4 needs to be maximized to guarantee mechanical support for the FM2.3-4, while simultaneously enabling the integration with FRESCA2.

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil at DC Current Operation

No-insulation (NI) (RE)Ba $_2$ Cu $_3$ O $_y$ (REBCO) magnets are very promising for practical applications to generate high magnetic field. The NI winding technique provides high thermal stability so that quench protection is unnecessary. However, the turn-to-turn contact resistance (sometimes called characteristic resistance) is an important factor to characterize the thermal stability and charging delay of NI REBCO pancake magnets. Although the conventional sudden-discharging method is widely used to measure the turn-to-turn contact resistance, it is not applicable to various conditions; e.g., the change of DC operating current and temperature. Therefore, we have previously proposed a turn-to-turn contact resistance measurement method using a low-frequency AC (LFAC) current. In this paper, we measured the contact resistance for different DC operating currents or change of DC current to confirm the validity of LFAC method. In addition, by heating a test coil, the contact resistances were also measured during the change of DC operating current. Since the electromagnetic stress is small enough not to change the contact condition, the change in contact resistance is negligible. The measured contact resistance was unchanged, so we could conclude that the LFAC method is effective in measurement of the contact resistance when DC operating current was applied.

Experimental Study on Quench Protection of HTS Magnet Composed of Multiple Pancake-Coils by Use of Auxiliary Resistive Shunt Loop Method

In the authors' previous work, a new quench protection method to reduce hot-spot temperature and increase quench detection voltage was proposed to protect an HTS magnet composed of multiple pancake sub-coils from quench damages (Toriyama et al., 2019). In the method, a current of a quenching sub-pancake coil is transferred to the other sub-coils of the magnet forming auxiliary resistive shunt loop (ARSL) by resistively shorting the other sub-coils. In this work quench behaviors of the pancake sub-coils of a model magnet was investigated by a simulation experiment using small scale test pancake coils wound of YBCO wire. Current patterns of the sub-pancake coils of a model magnet at a quench event were calculated for the case that ARSL method was applied, and in the experiment, the same patterns of the calculated currents were applied to the quenching test coils by a controllable current supply. Experimental results show effectiveness of the new method.

HTS synchronous machine critical current modelling and comparison with tests

Superconducting rotating machines generate high magnetic fields and for economic application of these machines and to ensure safe and reliable operation accurate assessment of the critical current of the superconductor is required. This paper describes a process to assess the critical current for a HTS synchronous machine with a superconducting rotor using a self-consistent numerical model. The model is used to study the critical current of first generation (1G) Bi-2223 pancake coils under self-field conditions for coil tests as well as within a machine magnetic field under full load conditions. Model results are compared against test measurements on individual HTS pancake coils as well as a double pancake coil in an operating synchronous machine at the Queensland University of Technology (QUT) test facility. Results obtain show that the self-consistent model is fast and accurate in determining the effective critical current of superconductors in such applications. Insights from the modelling assist with the design and optimisation process of the superconducting coils, selection of coil voltage sensing locations to detect the risk of quench and establish safe margins for the superconductor operating current.

FRA Diagnostics Measurement of Winding Deformation in Model Single-Phase Transformers Made with Silicon-Steel, Amorphous and Nanocrystalline Magnetic Cores

The power transformer is a key object in the electrical power system. The working principle hasn’t changed since its discovery. The main work nowadays is focused on the rising of the reliability of transformers and lowering power losses. The replacement of new materials instead of conventionally used ones can provide a solution. This procedure can improve factors, like a reduction of power losses, but also influence others normally neglected, like proper work in higher frequencies. The article presents the measurement results of the frequency characteristics of model test coils made with different magnetic materials cores (silicon steel, amorphous material, and nanocrystalline material), the measurements based on the sweep frequency response analysis (SFRA) method used for the determination of chosen frequency characteristics. The analysis presents the impact of different coil deformation levels on frequency characteristics. Results show that the replacement of conventional silicon steel with thinner high permeability materials can modify the state-of-the-art frequency response analysis (FRA) interpretation guidelines. The replacement of a new type of magnetic material as a magnetic core in the existing design of power transformer should lead to a full analysis of its behavior in the high-frequency domain.

Electric Field Probe Used for Gradient Coil-Induced Field Measurements During Medical Device Testing: Design, Calibration, and Validation

In this article, an ultralow-frequency electric field probe capable of measuring time-varying gradient coil induced electric fields in a tissue-mimicking material was constructed, calibrated, and validated. This probe consisted of a 2 cm short dipole antenna followed by an instrumentation amplifier. The designed amplifier had a gain of 100 and a cutoff frequency of 31 kHz. The probe was fabricated on a four-layer printed circuit board (PCB), FR4 of thickness 1.57 mm and a copper thickness of $35~\mu \text{m}$ . A waterproofed 3-D probe holder was used to cover the electronics and expose the dipole tip to the saline solution. To calibrate this probe in a known environment, a parallel-plate conductor was used. The calibrated probe was validated by measuring the electric field in a saline-filled cylindrical phantom placed within a cylindrically symmetric test coil. In order to do the validation, simulations were performed using an in-house tool developed in MATLAB and a validated tool in Sim4Life.