Single Coil Research Articles

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil: External Field Dependence

The characteristics of no-insulation high-temperature superconducting (HTS) manet is dominated by the magnitude of the turn-to-turn contact resistance. A few techniques have been proposed to increase the turn-to-turn contact resistance. The relation between the turn-to-turn contact resistance and the magnet stability has also been investigated in simulations. Although the turn-to-turn contact resistance measurement was only the sudden-discharging method before, we proposed a low-frequency-AC current (LFAC) method. Using our proposed method, it is possible to measure the turn-to-turn contact resistance under various conditions. In a previous paper, we measured it when charging DC current to a single pancake coil. In this paper, the turn-to-turn contact resistance was measured by the LFAC method when an external field of 1-3 T was applied to a single pancake coil. The coil strain was also measured, and the relation of the turn-to-turn contact resistance and the coil strain was also discussed.

Fast Distributed Simulation of “Defect-Irrelevant” Behaviors of No-Insulation HTS Coil

This paper proposes a new equivalent circuit model to calculate current distribution in an NI (no-insulation) high temperature superconductor (HTS) coil that contains a defect. When the well-known defect irrelevant behaviors of an NI HTS coil are analyzed, the so-called partial element equivalent circuit (PEEC) technique has been commonly adopted. However, the PEEC technique often takes an extremely long time, days or even weeks, for just a single simulation depending on the number of internal elements within the target NI coil. Here we propose an alternative method that may substantially reduce computation time and load in distributed simulation of the defect-irrelevant behaviors of an NI HTS coil. We showed that the current sharing region of an NI coil containing a defect could be divided into 5 segments, and an equivalent circuit, which is named “B model” as the equivalent circuit resembles the alphabet “B,” could be constructed using circuit parameters in each segment. Using the proposed method that significantly simplifies the existing PEEC model, we successfully simulated the defect-irrelevant behaviors of an NI HTS single pancake coil, essentially the local current sharing between the defect spot and its healthy neighboring turns.

Measurements and Analysis of AC Losses in HTS Windings of Electrical Machine for Different Operation Modes

The article is devoted to the study of losses in devices based on high-temperature superconductors of the 2nd generation. The complexity of the devices under study increases from a single rack coil to a winding assembled from several coils, and finally to an electric machine operating in generator mode. This is the way to experimentally study the behavior of 2nd generation high temperature superconductor (2G HTS) carrying a transport current in various conditions: self-field, external DC, and AC magnetic field. Attention is also paid to the losses in the winding during its operation from the inverter, which simulates the operating conditions in the motor mode of a propulsion system.

Evaluation Analysis of Double Coil Heat Exchanger for Heat Transfer Enhancement

In order to maximize the thermal efficiency of shell and coil heat exchangers, substantial research has been done and geometrical modification is one way to improve the exchange of thermal energy between two or more fluids. One of the peculiar features of coiled geometry is that the temperature distribution is highly variable along the circumferential section due to the centrifugal force induced in the fluid. Moreover, most researchers are concentrated on using a shell and single helical coil heat exchanger to enhance the heat transfer rate and thermal efficiency at different operating parameters. Therefore, the aim of this study is to investigate temperature variation ((T-1, T-2, T-3 and T-4) across a shell and single/double coil heat exchanger at different coil pitches, hot water flow rate, and cold-water flow rate along the outer surface of the coil using experimental and numerical analysis. For single and double coil heat exchangers, Computational Fluid Dynamics (CFD) is carried out using pure water with a hot water flow rate ranging between 1-2 l/min for the coil side heat exchanger. For single coil heat exchangers, the numerical analysis findings showed a good agreement with experimental four-temperature measurement results (T-1, T-2, T-3 and T-4) with an error rate of 1.80%, 3.05%, 5.34% and 2.17% respectively. Moreover, in the current double coil analysis, the hot outlet temperature decreased by 3.07% compared to a single coil (baseline case) at a 2.5L/min hot water flow rate. In addition, increasing the coil pitch will increase the contact between the hot fluid and the coil at a constant hot water flow rate and thereby decrease the hot fluid outlet temperature. Finally, a computational analysis was carried out to examine the flow structure inside single and double coil heat exchangers, and the findings indicated that the effect of centrifugal forces in double coil heat exchangers at various coil pitches caused the secondary flow to be substantially reduced.

Mechanical Damage Protection Method by Reducing Induced Current in NI REBCO Pancake Coils During Quench Propagation

The no-insulation (NI) winding technique has been attracting attention, because NI Rare-Earth Barium Copper Oxide (REBCO) pancake coils have high thermal stability. It is an indispensable technology to generate an ultra-high magnetic field. In 2017, using the NI winding technique a world-record high magnetic field, 45.5 T, was generated by 12 insert single pancake coils with an outsert magnet, and it showed a high potential to generate 14.4 T inside a background field of 31.1 T. After the experiment, the REBCO tapes were mechanically damaged, so that the critical currents were deteriorated. A large current was induced in NI REBCO coils next to the quenched coil when one of multi-stacked NI REBCO pancake coils quenched, resulting in tape property degradation and irreversible mechanical damage. Therefore, in order to protect NI REBCO pancake coils during quench, it is desired to reduce the amount of induced current. To suppress an induced current, the idea of “magnetic dam” has been proposed previously. The idea is to use a copper pipe installed at the outside of NI REBCO pancake coils. However, the copper pipe just slowed the quench propagation. In this paper, we extended the method to decrease an induced current much more by installing extra NI REBCO windings instead of the copper pipe. The electromagnetic and stress behaviors of 6-stacked NI REBCO coils with extra windings are simulated when one of the stacked NI REBCO coils transitions into a normal state. The ability of mechanical damage protection from a strong stress by an induced current during quench propagation is demonstrated through simulations.

Combination of temporary bridging device (Comaneci) and permanent stenting in the treatment of unruptured wide neck bifurcation aneurysms.

The double stent-assisted techniques for the treatment of wide neck bifurcation aneurysms (WNBAs) may be more complicating than single stent-assisted or balloon-assisted coiling. The Comaneci device (Rapid Medical, Yokneam, Israel) is a new temporary bridging device developed for covering the aneurysm neck during coiling. This new design enabled us to treat unruptured WNBAs with the use of single stent-assisted coiling instead of double stent in eight patients. At the 1-year angiographic follow-up, there was no filling in any aneurysm. There was no mortality or morbidity cases related to the procedure. In this study, we are reporting our experience of using single stent-assisted coiling combined with a Comaneci device in the treatment of unruptured WNBAs.

Investigation of a Novel Radial Partitioned Stator HTS-Excitation Flux-Switching Machine

This paper proposes and analyzes a novel radial partitioned stator HTS-excitation flux-switching (RPS-HTSFS) machine. The key is that the single ring-shaped HTS-excitation coil is independently placed in the coaxial claw-pole outer stator while the armature windings are wound around the U-shaped iron core on the inner flux-switching armature stator without permanent magnets. This solution has been explored to realize the physical isolation of armature winding and excitation winding, relieving the influence of armature field on the HTS-excitation coil. Moreover, only a single ring-shaped HTS-excitation coil is employed, therefore, reducing the HTS wires and the bending strain of the HTS-excitation coil. Also, the special refrigeration system can realize stationary seals of the double-layer ring-shaped cooling Dewar pattern, improving the cooling performance. By using the three-dimensional finite element analysis (3D-FEA), the machine performances are investigated and the validity of the proposed machine is verified.

Endovascular Treatment Strategy and Clinical Outcomes for Ruptured Blood Blister–Like Aneurysms of the Internal Carotid Artery Using Low-Profile Visualized Intraluminal Support Stent

It is challenging to safely treat blood blister-like aneurysms (BBAs) of the internal carotid artery. Endovascular surgery has been reported, but the optimal strategy is yet to be established. We report our endovascular treatment strategy using the Low-profile Visualized Intraluminal Support (LVIS) stent. Twelve patients with ruptured BBAs including 1 patient with 2 separate aneurysmal bulges were treated from December 2017 to January 2020. Single LVIS stent-assisted coil embolization was performed as the initial treatment. If the coil could not be placed in the aneurysm, or follow-up angiography showed persistent filling or regrowth of the aneurysm, a second LVIS stent was deployed as an overlapping stent. Clinical characteristics, treatment details, and clinical outcomes were retrospectively examined. Single stent-assisted coiling was performed in 8 patients (69%), 2 overlapping stents with coiling in 1 (8%), a single stent in 2 (15%), and 2 overlapping stents in 2 (15%). Three patients with persistent filling or regrowth of the aneurysm were re-treated with overlapping stents. Follow-up angiography confirmed complete occlusion in 12 aneurysms (92%). No re-rupture occurred. Postoperative symptomatic ischemia was confirmed in 4 patients (33%), and all 4 patients suffered severe subarachnoid hemorrhage. Modified Rankin scale was 0-2 in 8 patients (67%). LVIS stent-assisted coil embolization is effective in preventing re-rupture of BBAs. However, the morphology of the aneurysm may change within a short period, so careful angiographic follow-up is needed. Appropriate preoperative antiplatelet administration and optimal timing of the treatment may reduce the risk of postoperative ischemic complication.

Optimal Design and Performance Analysis of Radial MR Valve with Single Excitation Coil

The main issue addressed in this paper involves the magnetorheological (MR) valve increasing the pressure drop by changing the internal structure, which leads to the increase of dimension sizes and the easy blocking of the internal channel. Optimizing the design of the traditional radial MR valve without changing the internal structure and whole dimension size is indispensable. Firstly, a radial MR valve with single excitation coil was proposed. The mathematical models of the field-dependent pressure drop and viscosity pressure drop in fluid flow channels were deduced, and the calculation formula of pressure drop was also established. Then, ANSYS software was used to simulate and analyze the distributions of the magnetic flux lines and magnetic flux densities of the proposed radial MR valve. Subsequently, the radial MR valve was simulated and analyzed by using the ANSYS first-order and zero-order simulation tools. In addition, the experimental test bench of the proposed MR valve was setup, the static performance of pressure drop was tested, and the change of pressure drop of the optimal radial MR valve under different loads was studied, furthermore, the response time with current of the initial and optimal radial MR valve were also investigated. Finally, the dynamic performances of the optimal radial MR valve controlled cylinder system under different currents, frequencies and amplitudes were tested, respectively. The experimental results indicate that the total pressure drop of the initial valve is 1.842 MPa when the applied current is 1.8 A, and the total pressure drop of the optimal valve is 2.58 MPa, the increase is 40.07%. Meanwhile, the maximum damping force of the optimal radial MR valve controlled cylinder system can reach about 3.6 kN at the current of 1.25 A, which shows a better optimization effect of the optimal radial MR valve.

Design, Fabrication, and Testing of a Full-Scale HTS Coil for a 10 MW HTS Wind Power Generator

The authors have proposed a performance evaluation system (PES) for large-scale high temperature superconducting (HTS) wind power generators, which produces strong electromagnetic force and high torque due to the high excitation current and the high magnetic load of the machine, based on the computer simulation results. The PES can physically test the structural stability of HTS coils and armatures against high torque and the effect of the magnetic field before mounting the HTS coil on the generator. This paper deals with the design, fabrication, and performance testing of a full-scale HTS coil to be installed in the PES, a performance analysis system for a 10 MW HTS wind power generator. The HTS coil with metal-insulation consists of four racetrack-type single coils with 310 turns per layer. The manufactured HTS coil was tested at 77 K with and without an iron-core. As a result, the critical currents of the tested HTS coils with and without the iron-core were 90 A and 106 A, respectively. Compared to the simulation results, it was found that the magnitude of the magnetic field was the same. These results will be effectively used to study and fabricate high magnetic field coils for HTS applications, as well as the PES being fabricated.

Design and analysis of DNA shaped antenna for terahertz and sub-terahertz applications

The article presents design and detailed analysis of DNA (Deoxyribonucleic Acid) shaped antenna for terahertz and sub-terahertz applications. The final antenna is designed in four steps starting with a single coil as a patch and by adding four fractal coils in DNA shape. The bandwidth of novel DNA shaped antenna is enhanced by altering full ground to partial ground. The antenna has dual-band characteristics with an impedance bandwidth in the sub-terahertz band (0.22−0.32 THz) and terahertz (1.38–2.89 THz) band and maximum gain of 9.03dBi at 2.71 THz.

Sudden Discharging and Overcurrent Simulations of REBCO Coils Coated With Conductive Epoxy Resin

In 2011, a no-insulation (NI) winding technique was first proposed. Rare-Earth Barium Copper Oxide (REBCO) pancake coils using the NI winding technique are promising to generate an ultrahigh magnetic field, because the NI winding technique drastically enhances the thermal stability. When a local hot spot appears on a turn of the NI REBCO pancake coil, the enforced current can bypass into the adjacent turns to suppress the Joule heat generation. Recently, different types of REBCO coils to enhance the thermal stability by escaping the current flow from a local hot spot have been researched and developed. A few years ago, a REBCO single pancake coil whose upper surface was coated with conductive epoxy resin was proposed as one kind of NI winding techniques. The high thermal stability of conductive-epoxy-resin-coated (CERC) REBCO single pancake coil was demonstrated through an overcurrent test. However, the current behavior in the coil is still unclear. Therefore, we have newly developed an equivalent circuit model for CERC REBCO pancake coils. The sudden discharging and overcurrent tests were simulated for CERC REBCO pancake coils, and the resistance parameters were varied to investigate the coil stability.

Superconducting Wireless Power Transfer Beyond 5 kW at High Power Density for Industrial Applications and Fast Battery Charging

State-of-the-art wireless power transfer (WPT) systems, based on conventional copper coils, are known to exhibit efficiencies well above 90% when operated in the resonantly coupled mid-range regime. Besides full system efficiency, the area- and weight-related power densities of the transmission coils are key figures of merit for high power applications. This article reports on a fully functional WPT system, consisting of single pancake high-temperature superconducting (HTS) coils on the transmitter and the receiver side, which exceeds the power density of most conventional systems. Despite a compact coil size, a dc-to-dc efficiency above 97% is achieved at 6 kW output power. Next to the fundamental coil design, analytical and numerical simulations of the ac loss in the HTS coils are shown, taking into account both hysteresis and eddy current contributions. The results are validated by experimental ac loss measurements of single coils, obtained by a standard lock-in technique up to frequencies of 4 kHz. Finally, experimental results of the full system performance at different frequencies and load conditions are presented.

Electromagnetic Induction Imaging at Multiple Depths With a Single Coil

Electromagnetic induction imaging (EII) is an attractive imaging modality due to its contactless operation, low cost, and good penetration depth. To implement real-time imaging, in applications such as object tracking or functional biomedical imaging, fast data acquisition is required. To proceed toward this goal, in this article, we propose the use of a single coil for 3-D EII along with a fast inversion approach. To collect sufficient data that allow 3-D imaging, we propose two approaches: collecting data at multiple coil’s drive current levels and collecting data with multiple tank circuit’s capacitor values. We show that the use of such data when using a single coil allows for 3-D EII. For proof-of-concept experiments, we use a commercial data acquisition board, that is, LDC1614EVM module, and multilayer planar coils made by Texas Instruments.

Mirror aneurysm of ICA terminus associated with adult polycystic kidney disease

Introduction. Bilatereal saccular cerebral aneurysms (SCAs) that developed symmetrically on the same named vessels are defined as mirror aneurysms and account for a small subset of multiple cerebral aneurysms. The internal carotid artery (ICA) bifurcation is a rare location for mirror aneurysms. Aim. We aimed to present the importance of risk status assessment for SCAs and screening in all ADPKD patients for timely detection and managementof SCAs before catastrophic complications occur Description of the case. We present mirror aneurysms of bilateral ICA bifurcation that appear like a couple of dancing men on coronal computed tomography angiography (CTA) images, which were successfully treated with single stage coil embolization in a 45 year old female patient with medical history of autosomal dominant policystic kidney disease (ADPKD). Conclusion. SCAs are more frequent in patients with ADPKD than in general population and also these aneurysms are more likely to rupture at earlier ages. Mirror aneurysms of ICA terminus can be treated effectively and safely by single stage coil embolization.

An artificial intelligence approach for the in-line evaluation of steels mechanical properties in rolling

The large demand of high-performance steels to improve the safety and energetic performances in automotive is driving the increasing need of higher uniformity of mechanical properties of rolled products, both within a single coil and in large batch productions of multiple coils. To achieve these targets, we are witnessing an evolution of rolling towards the introduction of sensors and Artificial Intelligence (AI) algorithms to allow the real-time monitoring of both the strip tensile properties and the evolution of microstructure during the annealing process. The work described in the paper is part of a research work that is aimed at developing an AI framework that could allow the full real-time control of the entire mill rolling plant thanks to (i) innovative sensors applied at different steps of the coil processing, (ii) mixed analytical and numerical algorithms for the data computation and analyses, and (iii) IT infrastructure to collect and elaborate the data. The focus of the paper is on the tension-levelling operation which is one of the first that is performed in the rolling mill and can have a relevant influence on the strip mechanical characteristics. To reach this aim, a predictive model applicable to the tension-levelling process was developed, as this process is used to minimize flatness imperfections and residual stresses by means of plastic deformation. During the process, the material is subjected to cyclic tension-compression stresses, obtained with repeated and alternate bends under superposed tension. Consequently, the desired product standards, in terms of thickness and flatness, are achieved, while the mechanism of deformation changes the final mechanical properties of the material, increasing the yield strength and decreasing the maximum elongation. Finally, the predictive model is used to predict the coil mechanical characteristics, by using the data sampled from the sensors placed inside the tension-levelling machine.

Comparative Analysis of Coil Structures and Orientations of Single Transmitter and Multi Receivers Wireless Power Transfer System

Single transmitter and multi receiver (STMR) based WPT system is used to power multiple loads at a time. It consists of some limitations like long distance power transfer, mutual inductance between receiver coils and misalignment of receiver coils. this paper is going to give a detailed information about different designs of STMR, which are going to overcome the limitations of STMR. Different designs proposed by different authors are wireless power repeater system with single coil in each repeater, wireless power repeater system with two coils in each repeater, spherical strongly coupled magnetic resonant, square shape coils, maglev train IPT system and cube shaped unidirectional flux transmitter type. The above-mentioned designs are analysed and concluded a best design from it, depending up on applications and discussed about the control systems used in STMR.

A novel concept of SMES-based interline DC dynamic voltage restorer

The fast-response feature from a superconducting magnetic energy storage (SMES) device is favored for suppressing instantaneous voltage and power fluctuations, but the SMES coil is much more expensive than conventional battery energy storage device. In order to improve the energy utilization rate and reduce the energy storage cost under multiple-line power distribution conditions, this paper investigates a new interline DC dynamic voltage restorer (IDC-DVR) scheme with one SMES coil shared among multiple compensating circuits. In this new concept, an improved current-voltage (I/V) chopper assembly, which has a series of input/output power ports, is introduced to connect the single SMES coil with multiple power lines, and thus to satisfy with independent energy exchange requirement of any line to be compensated. Specifically, if two or more power lines have simultaneous compensating demands, the SMES coil can be selectively controlled to compensate the preferable line according to the priority order of the line. The feasibility of the proposed scheme is technically verified to maintain the transient voltage stability in multiple-line voltage swell and sag cases caused by either output voltage fluctuations from external power sources or power demand fluctuations from local sensitive loads. The simulation results lay some technical bases to develop a cost-effective SMES-based IDC-DVR for the use in various DC distribution networks.

A Multiarray Electromagnetic Instrument for Shallow Surface Real-Time Detection

A multiarray shallow surface electromagnetic detection instrument is presented in this article. The basic module of the instrument is an array system with a single transmitter coil and five receiver coils. In order to realize a modular array system and ensure the consistency of each array, a time slice overlapping method is proposed to solve the interference problem between neighboring arrays. The work process of a single array detection system is divided into three time slices, including simultaneous transmitting and receiving, data processing, and data uploading. The simultaneous transmitting and receiving procedure of each array is carried out sequentially with no interval. The data processing and uploading procedures are overlapped. To suppress environmental noise and electromagnetic interference, a cross correlation method based on a sliding window is designed to achieve real-time data processing. A four-array electromagnetic instrument prototype is implemented. Results of the field tests show that the time slice overlapping method eliminates mutual interference. Also, the electromagnetic response of the target is highlighted. It has been demonstrated that the cross correlation analysis improves the signal-to-noise ratio (SNR).

Efficiency Enhancement in a Multi-coil Wireless Power Transfer System

Wireless power transfer technology via magnetic resonance coupling now has significant interest in industry and research with many applications. This paper proposes a linear multiple transmitter coil array (5 coils) for wireless power transfer for added gain and hence higher transfer efficiency in comparison to a single transmitter coil. The frequency splitting effect as a result of the coupling between the resonant transmitter coils due to their close proximity is shown to reduce the transfer efficiency to a receiver. The effect of the array spacing on splitting effect suppression is verified. It is shown that the splitting effect is sup-pressed as the distance between the coils is increased leading to a higher received signal and hence higher efficiency. Proposed horizontal displacement of the middle transmitter coils (2nd and 4th coils) in the coil array is shown to suppress frequency splitting. To further suppress the splitting effect due to the magnetic coupling between the transmitter coils, a multiple transmitter array is proposed with different coil turns. Thus it is shown that designing the multiple coil array with mixed number of coil turns (the 2nd and 4th coils are designed to have different number of turns as compared to the other three coils) causes uniform coupling among the coils reducing and eventually eliminating the splitting effect. Also to increase the efficiency at the receiver coil, displaced stacked coils are introduced on top of the coil array. The pro-posed stacked coil array is demonstrated to improve the transfer efficiency. Using the techniques, the proposed linear array structure achieves a transfer efficiency of 36.9% for a receiver coil at the boresight of the array at a transfer distance of 40 cm.