Coil Loop Research Articles

A numerical study of flow behavior in the shell and helical finned‐tube heat exchanger

AbstractExtended surfaces mostly aim to improve the heat transfer upon increasing the area of heat transfer. In this paper, the influence of using fins on flow behaviors and the heat transfer of the shell and tube heat exchanger has been investigated. In this regard, the present results are verified with available experimental data in the literature for a helical tube without fins. The effects of fin density (fin per inch), its height, and material have been studied on the heat transfer rate. In addition, the effects of radial pitch and the number of coil loops are studied. The results indicate that implementing extended surfaces significantly increases the heat transfer rate. The increase of fin density from 8 to 12 and the height from 11.5 to 13.5 mm enhances heat transfer up to 48% and 43% depending on Dean number, respectively. The rise of coil pitch augments the overall heat transfer, and it is more efficient at lower Dean numbers. The predicted results also show that the fin material does not have any significant effect on heat transfer.

Dual-Band Free-Positioning Transmitting Coil for Multiple-Receiver Wireless Power Transfer

In recent years, the requirement for a compact wireless power transfer (WPT) system that can supply power to multiple devices in various practical usage scenarios has been attracted many researchers. The receiver (Rx) misalignment problem is contributory to the power transfer efficiency (PTE) degradation. Moreover, in a multiple-output WPT system, the overall system efficiency is also affected by cross-coupling between receivers. This paper proposes a dual-band free-positioning transmitting coil (FPDB-Tx) for multiple-receiver WPT. A three-dimensional Tx structure is modeled by investigating the current direction on each coil loop to adapt the Rx angular and axial misalignment. The Tx configuration is designed following a wireless charging box concept, where multiple Rx devices can receive energy freely without a null efficiency point. The mutual inductance is examined by a mathematical method in various Rx orientations to verify the free-positioning characteristic. Furthermore, an equivalent circuit model of the WPT system is theoretically analyzed to obtain dual operating frequency bands and then maximized the PTE. The experimental results show that the proposed WPT system achieves a stable PTE in various Rx positions. Especially, the WPT system has a maximum PTE of 97.27% and 91% at 6.78 MHz and 13.56MHz, respectively.

Design Model of Null-Flux Coil Electrodynamic Suspension for the Hyperloop

The Hyperloop has been developed using various technologies to reach a maximum speed of 1200 km/h. Such technologies include magnetic levitation technologies that are suitable for subsonic driving. In the Hyperloop, the null-flux electrodynamic suspension (EDS) system and superconducting magnets (SCMs) can perform stable levitation without control during high-speed driving. Although an EDS device can be accurately analyzed using numerical analysis methods, such as the 3D finite element method (FEM) or dynamic circuitry theory, its 3D configurations make it difficult to use in various design analyses. This paper presents a new design model that fast analyzes and compares many designs of null-flux EDS devices for the Hyperloop system. For a fast and effective evaluation of various levitation coil shapes and arrangements, the computational process of the induced electromotive force and the coupling effect were simplified using a 2D rectangular coil loop, and the induced current and force equations were written as closed-form solutions using the Fourier analysis. Also, levitation coils were designed, and their characteristics were analyzed and compared with each other. To validate the proposed model, the analyzed force responses for various driving conditions and the changed performance trend by design variables were compared with analyzed FEM results.

Phase‐detection‐based metal objects and pick‐up coils detection scheme without malfunction in wireless power transfer system

Metal object detection (MOD) and detection of position (DoP) of pick-up coils are increasingly critical to the commercialisation of the wireless power transfer system. In this study, a detection scheme based on phase-detection, which can both realise the function of MOD and DoP, is newly introduced. The method is based on the principle that the presence of metal objects and pick-up coils both affect the impedance phase of the detection coil loop. Comparing with the traditional detection methods, which is based on measuring the absolutely value of impedance in detection loop, the malfunction is avoided by adopting phase difference as the criterion of the existence of metal objects and pick-up coils. An inexpensive and high-precision sensing circuit is newly designed to acquire the phase difference accurately. Simulation models and experiments are conducted to verify the feasibility of the proposed detection scheme. The of the detection coil circuit with a coin placed reaches −5.17, while the of other detection coils without metal objects keeps zero. In the meantime, the position of the pick-up coil is identified because the of these detection coils closer to the centre of the pick-up coil varies more significantly while other coils vary slightly.

Coil Inductance Design for Low Power Hybrid Wireless Power Transfer

This paper presents a coil inductance design for low power hybrid wireless power transfer (WPT). The proposed coil inductance design of transmitter and receiver circuits of 7.1 μH are designed using handmade copper wire structure. Several coils with the variations of wire diameters, coil loop radius, and numbers of loops are proposed to find optimum structure in the low power hybrid WPT. The optimum coil structure is obtained at wire diameter of 0.5 mm, 2.25-inch coil loop radius and 1 MHz operation frequency. The measured transceiver coil design has exhibited peak power transfer efficiency (PTE) of 33.1% at 1 cm distance between Tx and Rx. Therefore, the proposed coil design is applicable to low power hybrid wireless power transfer circuits.

A 16-channel loop array for in vivo macaque whole-brain imaging at 3 T

Non-human primates (NHPs) are vital models for neuroscience research. These animals have been widely used in behavioral, electrophysiological, molecular, and more recently, multimodal neuroimaging and neuro-engineering studies. Several RF coil arrays have been designed for functional, high-resolution brain magnetic resonance imaging (MRI), but few have been designed to accommodate multimodal devices. In the present study, a 16-channel array coil was constructed for brain imaging of macaques at 3 Tesla (3 T). To construct this coil, a close-fitting helmet-shaped form was designed to host 16 coil loops for whole-brain coverage. This assembly is mountable onto stereotaxic head frame bars, and the coil functions while the monkey is in the sphinx position with a clear line of vision of stimuli presented from outside of the MRI system. In addition, 4 openings were allocated in the coil housing, allowing multimodal devices to directly access visual cortical regions such as V1-V4 and MT. Coil performance was evaluated in an anesthetized macaque by quantifying and comparing signal-to-noise ratios (SNRs), noise correlations, and g-factor maps to a vendor-supplied human pediatric coil frequently used for NHP MRI. The result from in vivo experiments showed that the NHP coil was well-decoupled, had higher SNRs in cortical regions, and improved data acquisition acceleration capability compared with a vendor-supplied human pediatric coil that has been frequently used in macaque MRI studies. Furthermore, whole-brain anatomic imaging, diffusion tensor imaging and functional brain imaging have also been conducted: the details of brain anatomical structure, such as cerebellum and brainstem, can be clearly visualized in T2-SPACE images; b0 SNR calculated from b0 maps was higher than the human pediatric coil in all regions of interest (ROIs); the time-course SNR (tSNR) map calculated for GRE-EPI images demonstrates that the presented coil can be used for high-resolution functional imaging at 3 T.

Dual microcatheter technique for coil embolisation of irregular and wide-necked intracranial aneurysms: A case series

Background: The endovascular coiling of ruptured aneurysms with complicated geometry presents a significant treatment challenge, especially with the non-availability of adequate sized coils and balloon/stent. The dual microcatheter technique is an alternative treatment for stent-assisted coiling in acutely ruptured wide-necked aneurysms because of no antiplatelet therapy. Objective: We report our initial experience with the use of a dual microcatheter technique in seven patients. The technique provided an efficient strategy for treating aneurysms with complicated configurations and high risks. Patients and Methods: We describe a technique used to treat seven patients with irregular shaped and wide-necked aneurysms. In the initial attempts at embolisation, coil instability within the aneurysm or significant impingement of coil loops on the parent artery was observed. The advancement of a second microcatheter into the aneurysm allowed two coils to be braced across the aneurysmal neck before the detachment of either coil. This technique permitted successful coil treatment. Conclusion: The dual microcatheter technique is a safe and effective treatment for acutely ruptured wide-necked aneurysms due to few treatment-related complications and mortality rate.

Highly effective leakage magnetic field suppression by using a reactive coil in perfectly aligned EV wireless charging systems

Using a reactive coil to suppress the leakage magnetic field (LMF) in wireless power transfer is practical, but the suppression capability reported in the literature is still limited. This paper proposes several methods for improving the suppression capability of this scheme. Three conditions are required to realize this goal, namely (1) a good LMF proportionality, (2) an equation regarding the LMF coefficients and mutual inductances, and (3) an equation regarding the impedance of the reactive coil loop. Coil geometry optimization is performed to meet condition (2), and coil reactance is compensated by a capacitor to meet condition (3). Given the trade-off between LMF suppression capability and efficiency, a control strategy based on a switching capacitor array is adopted. In the experiments, a 97.5% reduction in the LMF strength is achieved on the measurement point with slight effects on efficiency.

Thermal performance of helical coils with reversed loops and wire coil inserts

Flow and heat transfer characteristics of water in a newly designed helical coil heat transfer device were investigated in this experimental study. The conventional helical coil configuration was structurally modified aiming to improve its heat transfer performance. Specifically, 360° plastic tubing with or without wire coil inserts was added after each 180° of the main helical coil loop to enhance fluid mixing and redistribute the flow, which should have a direct effect on the thermal performance of the helical coil heat transfer device. Experimental results show that the structural modifications of the conventional helical coil configuration led to enhanced heat transfer in the test section while the pressure drop penalty increased slightly. Furthermore, the heat transfer performance of the overall test section improved by using wire coil inserts in the plastic tubing after every 180° of the main helical coil loop. The results reveal that the modified helical coil section offers a good trade-off between heat transfer enhancement and pressure drop penalty.

Plasma Wave Observation in Space Via Scientific Satellites

Space plasmas are essentially collisionless. Kinetic energies of plasmas are transferred through wave-particle interactions. Since plasmas are dispersive media, plasma waves show various features depending on how and which plasma wave modes interact with particles. Plasma wave observations via scientific satellites have a key role in knowing physical processes in space. Plasma wave investigation systems on board satellites are dedicated to the observations of electric field and magnetic field components of plasma waves. They consist of sensors, receivers and an onboard digital processing unit. While dipole antennas are used for electric field sensors, search coil magnetometers or loop antennas are used for magnetic field sensors. Plasma wave receivers are a kind of sophisticated radio receivers. The recent plasma wave receiver is designed as a waveform receiver that can save its mass and size. In addition to waveforms, the waveform receiver provides frequency spectra which are calculated in the digital processing unit from the observed waveforms. The present paper introduces plasma wave observation by scientific satellites on the basis of the latest design of plasma wave investigation systems.

A novel approach involving a microcatheter tip during aneurysmal coil embolization: The Γ (gamma) tip method.

Complete and secure occlusion of the entire aneurysmal neck remains a problem despite major advances in the treatment of intracranial aneurysms using endovascular coil embolization. Here, we present our initial clinical experience using a novel strategy for endovascular coil embolization involving a microcatheter tip, known as the "Γ (gamma) tip method," and compare the invitro results of this technique with those of conventional straight microcatheters. The microcatheters were bent at a right angle starting 1-2 mm from the length of the tip using a catheter-shaping mandrel and a hot air gun. The tiny right-angled tip is the "Γ tip." In aneurysm models, we assessed the efficacy of shaping during coil deployment. The Γ-tipped microcatheters demonstrated better movement and oscillation during insertion of the coil into the aneurysm compared with the straight-tipped catheters. Moreover, the Γ-tipped microcatheter provided less coil protrusion into the parent artery and less microcatheter kickback compared with the straight tip. With the Γ-tipped microcatheter, even if the first coil loop migrated into the parent artery, its subsequent dynamic movement routed it back into the aneurysm. The Γ tip method enabled smooth movement of the microcatheter into the aneurysm, demonstrating the safety and security of coil insertion using the Γ tip compared with the conventional straight tip.

A flexible printed-circuit coil for scanning transversal magnetic-fields errors in accelerator magnets

The proof of principle of an induction coil sensor for scanning transverse magnetic-field errors is presented. This sensor allows to build a rotating-coil transducer that is not sensitive to the axial magnetic field component in the magnets. The main design objective is to optimize the positions of each coil loop in the sensor's transverse cross-section, to guarantee the desired sensitivity factors to the specific field-harmonic components. After illustrating the magnetic measurement principle, the design and the manufacturing technology of the flexible circuit board are presented. Then the metrological characterization, the calibration and the functional tests are discussed.

An Institutional Retrospective Study of Coil Loop Herniation and its Management.

Endovascular coiling is a method of aneurysm embolization. Sometimes coil loops herniate in the lumen after deployment of the coil. It is usually seen in wide-necked aneurysms. It can cause migration of the coil and thromboembolic complications. There are different methods such as the use of a balloon, stent, and coil retriever to treat coil loop herniation. There are very few case series on coil loop herniation management. Most series are about the use of a stent/balloon for reposition. We are going to describe simple, novel techniques to treat coil loop herniation. In the last five years, 13 aneurysms out of 325 coiled aneurysms had coil loop herniation. We used three different techniques in these patients according to our selection criteria. The first technique was loop trap with another coil, the second was balloon and coil-plasty to trap, and the third was rescue stent and flow control. The first, second, and third techniques were successfully used in five, five and three patients, respectively. There was a complete reposition of herniated coil and thus embolization of aneurysm in all cases. All patients recovered completely without any thromboembolic complications. We recommend the use of these techniques according to the proper selection criteria.

Commentary on An Institutional Retrospective Study of Coil Loop Herniation and Its Management.

Commentary on An Institutional Retrospective Study of Coil Loop Herniation and Its Management.

Self-decoupled radiofrequency coils for magnetic resonance imaging

Arrays of radiofrequency coils are widely used in magnetic resonance imaging to achieve high signal-to-noise ratios and flexible volume coverage, to accelerate scans using parallel reception, and to mitigate field non-uniformity using parallel transmission. However, conventional coil arrays require complex decoupling technologies to reduce electromagnetic coupling between coil elements, which would otherwise amplify noise and limit transmitted power. Here we report a novel self-decoupled RF coil design with a simple structure that requires only an intentional redistribution of electrical impedances around the length of the coil loop. We show that self-decoupled coils achieve high inter-coil isolation between adjacent and non-adjacent elements of loop arrays and mixed arrays of loops and dipoles. Self-decoupled coils are also robust to coil separation, making them attractive for size-adjustable and flexible coil arrays.

Thermal and flow characteristics of helical coils with reversed loops

In this experimental study, flow and heat transfer characteristics of water through a newly designed helical coil heat transfer test section were investigated. A structural modification of the traditional helical coil has been implemented to improve its thermal effectiveness. Specifically, a 360° plastic reversed loop was added after each 180° of the main helical coil loop to redistribute the flow’s velocity profile, which should have a direct effect on the thermal performance of the helical coil heat transfer test section. Results reveal that reversed loops do enhance heat transfer rates by more than 20%, while pressure drop penalty also increases but not at the same rate. The curvature of the reversed loops with respect to the main coil is a critical factor in terms of thermal performance. Furthermore, as the size of the reversed loop decreases, the heat transfer enhancement and pressure drop penalty increment for the modified helical coil test section increase as well. Accordingly, it is suggested that there may exist an optimum helical coil structural modification for which the best tradeoff between pressure drop penalty and heat transfer enhancement can be found.

Direct matching methods for coils and preamplifiers in MRI

In this paper, direct matching methods for coils and preamplifiers in receiver arrays are presented. Instead of compensating the reactance of the input impedance of preamplifiers, in our method, the reactance was used to resonate with the coil matching networks and thus to decouple the coils. Furthermore, coil matching networks and preamplifier input matching networks were combined, meaning the coil loop can be matched to the transistor in the preamplifier directly. These matching methods and, for comparison, the conventional matching method were implemented with custom-made preamplifiers and coils. Decoupling and noise-matching performance were compared between these three configurations. Phase shifting networks between coils and preamplifiers are not necessary in our matching methods. With fewer components, these matching networks showed lower noise factors, while similar preamplifier-decoupling performance was found for all three methods.

Outcomes of Microsurgical Clipping of Recurrent Aneurysms After Endovascular Coiling.

The outcomes of microsurgery of previously coiled aneurysms have been poorly described, and little is known about the factors predictive of poor outcome. Here we aimed to identify predictors of poor outcome following microsurgery for previously coiled recurrent aneurysms. In this retrospective cohort study of a prospectively maintained vascular database, we reviewed presentations, recurrent aneurysm measurements, surgery, and outcomes of microsurgical clipping of recurrent previously coiled intracranial aneurysms. Our series comprised 39 patients (mean age, 49 years; range, 22-70 years) who underwent microsurgical clipping of 40 previously coiled intracranial aneurysms. One patient suffered seizures, 1 patient experienced transient neurologic worsening, and 1 patient developed hyponatraemia, none of whom had long-term sequelae. Two patients sustained postoperative infarcts, for an overall incidence of permanent morbidity of 5.1%. There were no deaths or rebleeds on follow-up. In 3 patients, including the 2 patients with infarct and 1 patient with a transient deficit, an attempt was made to remove the coil ball. These patients had larger aneurysms (1106 mm3 vs. 135 mm3; P= 0.005), with larger coil balls (257 mm3 vs. 52 mm3; P= 0.01) and wider necks (7.09 mm vs. 2.69 mm; P= 0.02) but smaller remnant heights (1.59 mm vs. 1.99 mm; P= 0.04). They were also more likely to have prolapsing coil loops (3/3 vs. 3/27; P= 0.016). Our study demonstrates good clinical outcomes from microsurgical clipping of recurrent aneurysms. In the vast majority of cases, clips can be applied primarily. Coil ball removal is associated with increased morbidity, and thus should be considered only as a second-line option, with the likely need identified before the initiation of surgery.

Study of blood flow inside the stenosis vessel under the effect of solenoid magnetic field using ferrohydrodynamics principles

In this paper, biomagnetic blood flow in the stenosis vessel under the effect of the solenoid magnetic field is studied using the ferrohydrodynamics (FHD) model. The parabolic profile is considered at an inlet of the axisymmetric stenosis vessel. Blood is modeled as electrically non-conducting, Newtonian and homogeneous fluid. Finite volume and the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm are utilized to discretize governing equations. The investigation is studied at different magnetic numbers ( $ Mn_{F}=164$ , 328, 1640 and 3280) and the number of the coil loops (three, five and nine loops). Results indicate an increase in heat transfer, wall shear stress and energy loss (pressure drop) with an increment in the magnetic number (ratio of Kelvin force to dynamic pressure force), arising from the FHD, and the number of solenoid loops. Furthermore, the flow pattern is affected by the magnetic field, and the temperature of blood can be decreased up to $1.48 {}^{\circ}{\rm C}$ under the effect of the solenoid magnetic field with nine loops and reference magnetic field ( $ B_{0}$ ) of 2 tesla.

Modified Rogowski coil for the detection of fast plane currents

Rogowski coils are used to diagnostic currents of cylindrical configuration, therefore they are known to have a toroidal geometry. Nowadays, also linear transmission lines can be developed to get planar beams. Therefore, linear Rogowski coil to detect current pulses inside the linear conductors are necessary. For large devices, the theory necessary to study the system is that of the transmission lines, especially if the pulse width is comparable to the propagating time of signal inside the detector. The device we developed is able to record pulses more than 80ns long with rise time near 500ps. The former depends on the inductance value, load impedance and resistance of the coil; while the second on the mechanical configuration of coil loops. Theoretically, the attenuation coefficient depends exclusively on the turn number of the coil, while experimentally it is found to depend also on the current distribution inside the line.