Coil Spacing Research Articles

A multimodal axial array resonator and its application in radiofrequency (RF) volume coil designs for low-field open magnetic resonance imaging (MRI).

Low-field open magnetic resonance imaging (MRI) systems, typically operating at magnetic field strengths below 1 Tesla, has greatly expanded the accessibility of MRI technology to meet a wide range of patient needs. However, the inherent challenges of low-field MRI, such as limited signal-to-noise ratios and limited availability of dedicated radiofrequency (RF) coils, have prompted the need for innovative coil designs that can improve imaging quality and diagnostic capabilities. In this work, we introduce a multimodal axial array resonator and its implementation in a volume coil, or referred to as a coupled stack-up volume coil, to address these challenges in low-field open MRI. A prototype coupled stack-up volume coil was designed with optimized coil spacing to improve B1 field homogeneity. Finite difference time-domain (FDTD) simulations were conducted to evaluate the coil's performance, including B1 field efficiency and specific absorption rate (SAR). Bench tests were performed to validate the simulated results using oil phantoms. Comparisons were made with a solenoid coil, a birdcage coil, and an equal gap coupled coil throughout the study. Numeral electromagnetic studies demonstrate the superior performance of the proposed coupled stack-up volume coil, achieving 47.7% higher transmit/receive efficiency and 68% more uniform magnetic field distribution compared to conventional birdcage coils. The results of the bench tests show that the achieved B1 field efficiency of the coupled stack-up volume coil is 11.48 , representing a 57.3% improvement in comparison to that of a conventional birdcage coil. A multimodal axial array resonator technique or coupled stack-up technique is successfully developed for the design of low field MR RF volume coils. The proposed coupled stack-up volume coil outperforms the conventional volume coils in terms of B1 efficiency, imaging coverage, and low-frequency operation capability. This design provides a robust and simple solution to the low-field MR RF coil design.

A Computational Framework to Optimize the Mechanical Behavior of Synthetic Vascular Grafts.

The failure of synthetic small-diameter vascular grafts has been attributed to a mismatch in the compliance between the graft and native artery, driving mechanisms that promote thrombosis and neointimal hyperplasia. Additionally, the buckling of grafts results in large deformations that can lead to device failure. Although design features can be added to lessen the buckling potential, the addition is detrimental to decreasing compliance (e.g., reinforcing coil). Herein, we developed a novel finite element framework to inform vascular graft design by evaluating compliance and resistance to buckling. A batch-processing scheme iterated across the multi-dimensional design parameter space, which included three parameters: coil thickness, modulus, and spacing. Three types of finite element models were created in FEBio for each unique coil-reinforced graft parameter combination to simulate pressurization, axial buckling, and bent buckling, and results were analyzed to quantify compliance, buckling load, and kink radius, respectively, from each model. Importantly, model validation demonstrated that model predictions agree qualitatively and quantitatively with experimental observations. Subsequently, data for each design parameter combination were integrated into an optimization function for which a minimum value was sought. The optimization values identified various candidate graft designs with promising mechanical properties. Our investigation successfully demonstrated the model-directed framework identified vascular graft designs with optimal mechanical properties, which can potentially improve clinical outcomes by addressing device failure. In addition, the presented computational framework promotes model-directed device design for a broad range of biomaterial and regenerative medicine strategies.

Experimental and Numerical Study of Newly Assembled Lightweight Radiant Floor Heating System

In this study, the heating capacity of a new prefabricated assembled hot water radiant modular heating system made from a recycled waste building masonry structure is investigated through experimental and numerical simulation methods. The heating capacity of the system in different working conditions (a water supply temperature of 48 °C, 51 °C, 56 °C, and 61 °C; a flow rate of 0.49 m3/h, 0.35 m3/h, and 0.21 m3/h) is analyzed and verified. A three-dimensional steady-state heat transfer numerical model of the floor heat transfer of the module is established, and the accuracy of the model is verified through the measured results to investigate the heating capacity of this system under different water supply temperatures, flow rates and coil spacings. The results show that the new prefabricated hot water radiant module heating system has a 0.9 °C higher air temperature and 2.1 °C higher average floor surface temperature than the traditional wet floor radiant heating system under the same experimental conditions, and the response time is 44% shorter. The water supply temperature can significantly change the heating capacity of the system, while the water supply flow rate has little effect on the system. The established three-dimensional steady-state numerical model can be in good agreement with the measured results. This study can provide an experimental and theoretical basis for the design and application of such systems.

Mapping and monitoring peatlands in the Belgian Hautes Fagnes: Insights from Ground-penetrating radar and Electromagnetic induction characterization

Peatlands are vital ecosystems providing crucial ecological services such as significant carbon storage in the context of climate change. These sensitive ecosystems are subjected to degradation due to land use change. In this context, it is important to understand the actual state of degraded peatlands and their recovery potential for regaining important functions. This study focuses on a disturbed peatland in the Belgian Hautes Fagnes, previously drained and planted with spruce, and characterized by a topographic gradient. We aimed to elucidate the use of Ground-penetrating radar (GPR) and Electromagnetic induction (EMI) techniques in characterizing such peatlands, with a specific focus on their implications for peat depth and electrical conductivity assessment, related to peatland degradation. The GPR revealed a high spatial heterogeneity in peat depth, ranging from 0.2 to more than 2 m on the site. In contrast, an EMI instrument used with single coil spacing proved to be unsuccessful to deduce peat depth but demonstrated potential for the delineation of zones of mineral soil. It is also shown that the links between soil physical and chemical properties and its bulk soil electrical conductivity (ECa) measured by EMI are complex in zones of shallower peat. Additionally, this study highlights the role of pore water conductivity in influencing temporal variations in ECa. Our findings explain the intricate interplay between peat depth, topography and ECa in disturbed peatlands. The results of this study may be of substantial societal interest, as it provides insights into techniques for the rapid non destructive characterization of the conditions of previously drained peatlands.

Wireless power transfer efficiency enhancement based on a negative permeability double‐helix metamaterial structure

SummaryIn wireless power transfer (WPT) systems, extended transmission distances significantly impede efficiency, posing a major challenge to their practical application. This paper presents a novel ortho‐octagonal double‐helix metamaterial that can effectively enhance the transmission efficiency of WPT systems. It has theoretically derived and experimentally verified the enhancement of evanescent wave transmission by this metamaterial dielectric plate. A WPT simulation system operating at 10.78 MHz is constructed by HFSS software, and the effects of adding passive relay coils and different shapes of metamaterials on the transmission efficiency are comparatively investigated. Simulated data converge to indicate that integrating variously shaped metamaterials at the transceiver's end distinctly elevates the WPT system's transmission efficiency. When the transceiver coil spacing of the WPT system is greater than 22 cm, the effect of metamaterials on the system transmission efficiency enhancement shows an increasing and then decreasing trend as the distance increases. The positive octagonal metamaterial improves 12% over the circular metamaterial in the mid‐range transmission distance due to its better magnetic coupling effect. When the transceiver coil spacing is 22 cm, the open‐circuit voltage of the receiving coil after loading the metamaterial is stabilized to be enhanced by nearly five times, and it has the best effect at 30 cm, and the transmission efficiency is enhanced from 30% to 60%, which verifies the effective enhancement of the metamaterial on the transmission efficiency of the WPT system.

Tailoring tokamak error fields to control plasma instabilities and transport

A tokamak relies on the axisymmetric magnetic fields to confine fusion plasmas and aims to deliver sustainable and clean energy. However, misalignments arise inevitably in the tokamak construction, leading to small asymmetries in the magnetic field known as error fields (EFs). The EFs have been a major concern in the tokamak approaches because small EFs, even less than 0.1%, can drive a plasma disruption. Meanwhile, the EFs in the tokamak can be favorably used for controlling plasma instabilities, such as edge-localized modes (ELMs). Here we show an optimization that tailors the EFs to maintain an edge 3D response for ELM control with a minimized core 3D response to avoid plasma disruption and unnecessary confinement degradation. We design and demonstrate such an edge-localized 3D response in the KSTAR facility, benefiting from its unique flexibility to change many degrees of freedom in the 3D coil space for the various fusion plasma regimes. This favorable control of the tokamak EF represents a notable advance for designing intrinsically 3D tokamaks to optimize stability and confinement for next-step fusion reactors.

Management of space loss in mixed dentition using open coil space Regainer: A case report

Management of space loss in mixed dentition using open coil space Regainer: A case report

Radiation damping at clinical field strength: Characterization and compensation in quantitative measurements.

In any MR experiment, the bulk magnetization acts on itself, caused by the induced current in the RF receiver circuit that generates an oscillating damping field. This effect, known as "radiation damping" (RD), is usually weak and, therefore, unconsidered in MRI, but can affect quantitative studies performed with dedicated coils that provide a high SNR. The current work examined RD in a setup for investigations of small tissue specimens including a quantitative characterization of the spin-coil system. A custom-made Helmholtz coil (radius and spacing 16 mm) was interfaced to a transmit-receive (Tx/Rx) switch with integrated passive feedback for modulation or suppression of RD similar to preamplifier decoupling. Pulse sequences included pulse-width arrays to demonstrate the absence/ presence of RD and difference techniques employing gradient pulses or composite RF pulses to quantify RD effects during free precession and transmission, respectively. Experiments were performed at 3T in small samples of MnCl2 solution. Significant RD effects may impact RF pulse application and evolution periods. Effective damping time constants were comparable to typical T2 * times or echo spacings in multi-echo sequences. Measurements of the phase relation showed that deviations from the commonly assumed 90° angle between the damping field and the transverse magnetization may occur. Radiation damping may affect the accuracy of quantitative MR measurements performed with dedicated RF coils. Efficient mitigation can be achieved hardware-based or by appropriate consideration in the pulse sequence.

Numerical study of heat transfer characteristics of organic heat carrier furnace chamber

The heat transfer oil in the organic heat carrier furnace (OHCF) is prone to deterioration and deterioration at higher operating temperatures, resulting in overheating of the furnace tube and bursting of the tube, resulting in safety accidents. Therefore, it is necessary to study and analyze the flowing heat transfer characteristics of organic heat carriers in the furnace tube. The paper takes YY(Q)W-180(15) OHCF as the research object, mainly through ANSYS CFX numerical simulation method, to analyze the influence of influencing factors: inner and outer spiral tube spacing R, oxygen content, air preheating degree T and excess air coefficient on the temperature field, velocity field and NOx concentration inside the OHCF, and found that the organic heat carrier in the oxygen concentration of 25%, air preheating The thermal efficiency of the furnace is higher and the pollutant content emitted at the exit of the furnace is lower when the oxygen concentration is 25%, the air preheating temperature is 498 K and the excess air coefficient is 1.10. Also, the smaller the inner coil spacing R1 and the outer coil spacing R2 from the furnace wall, the higher the overall furnace chamber temperature.

Frequency domain electromagnetic calibration for improved detection of sand intrusions in river embankments

Sand intrusions pose significant risks to river embankments due to potential flow pathways that can lead to instability during flood events. Visual inspection is a first step to recognize critical segments, but it does not deliver information about the subsurface. In this context, the electromagnetic induction (EMI) technique is a useful method for preliminary zoning at regional scale while the electrical resistivity tomography (ERT) method, widely used for hydrological purposes, is considered among the most reliable techniques for local subsurface imaging. A major sand intrusion within the levees of the Brenta River, located near Venice (northern Italy), resulted in water seeping during seasonal floods and posed severe threats to embankment stability. ERT and EMI techniques, along with geotechnical investigations, were the best survey choices to address the problem. Resistivity profiling successfully imaged the sand body geometry within and underneath the levee, and results correlated nicely with borehole stratigraphy. A first multiarray EMI device, which represented a faster and less expensive survey, was deployed to map further anomalies along nearby levees, but results were not satisfactory because the inverted profile failed to image the known intrusion. A second multiarray EMI device, with larger coil spacing, was also tested. Although it performed better in detecting the intrusion, results were still below expectations. A calibration procedure based on Pearson's coefficients and using ERT as a reference was then devised and implemented to correct the EMI data prior to carrying out inversion. The procedure was successful for both EMI data sets, leading to realistic subsurface resistivity in the inverted sections. EMI measurements could then be recovered and interpreted correctly to estimate subsurface textures. The possibility of calibrating EMI data and obtaining subsurface resistivity images comparable to standard ERT profiling is an important improvement for cost-effective EMI surveying of river embankments to mitigate flood hazards.

Design and optimization of superconducting CUSP electromagnetic field structure based on a COMSOL-GMDH-MOSO hybrid strategy

As the semiconductor industry gains momentum, there is a significant focus on producing high-quality silicon wafers with larger diameters. However, the preparation of major-diameter, high-quality silicon single-crystal has encountered challenges such as intense convection inside the melt and high oxygen impurity concentration at the interface between the fluid and solid phases. To tackle these problems, the external superconducting CUSP electromagnetic field structure was designed to optimize the crystal growth parameters. A hybrid strategy of the multiphysics field coupling method, Group Method of Data Handling (GMDH) type neural network identification, and the Multiple Objective Snake Optimizer (MOSO) algorithm was proposed to optimize the superconducting CUSP electromagnetic field structure. A two-dimensional axisymmetric model was established for 18-inch silicon single-crystal preparation using the Magnet system Applied Czochralski (MCZ) method. The amount of longitudinal plies of superconducting CUSP electromagnetic field coils, coil spacing, and the thickness of magnetic shields were selected as design variables, and the radial electromagnetic induction intensity at the graphite crucible inner wall and the superconducting magnet volume were used as dual objective functions. The required samples for GMDH training were provided by COMSOL Multiphysics (COMSOL) numerical calculations, and polynomial mathematical equations were established with the radial electromagnetic induction intensity at the graphite crucible inner wall and the superconducting magnet volume as the dual objective functions. Then the Pareto optimal solution for the electromagnetic field structure design variables was obtained using the dual objective function optimized by MOSO. With the hybrid strategy, numerical simulations and theoretical analysis of the crystal preparation process parameters under the effect of the superconducting electromagnetic field with the optimal structure were carried out. The results displayed that the added superconducting CUSP electromagnetic field reduced the crystal radial and axial thermal gradients and greatly suppressed the melt convection. As a result, the heat distribution inside the hot fused silicon was more even, the thermal gradient at the solid–liquid interface was reduced by 68.4%, and the oxygen impurity content was reduced by 82.1%, which effectively improved the crystal quality. The thermal field simulation results verified that the proposed hybrid strategy provided a new numerical calculation method for obtaining the optimal superconducting electromagnetic field structure.

Performance evaluation of a novel horizontal ground heat exchanger: Coil-column system

Horizontal ground heat exchangers (GHEs), which are used for heating/cooling buildings, have garnered significant attention in recent years owing to their low construction cost and ease of installation. However, they require a large installation area due to their low efficiency. In this study, a new horizontal GHE type, named a coil-column system (CCS), is proposed, and its feasibility is investigated. CCS is expected to increase the total heat exchange rate of the GHE, thus reducing the required installation area. First, the heat exchange performance of the CCS is investigated and compared with existing exchangers using COMSOL Multiphysics. The numerical model was validated using an in-door thermal response test in a 5 m × 1 m × 1 m mock-up steel box. Afterward, a parametric study was conducted to evaluate the effect of coil pitch, installation depth, and space between the coil-column on the heat transfer efficiency of the CCS. Finally, the feasibility of the CCS was comprehensively evaluated by considering the heat transfer performance and economic parameters. From the results, it was found that the heat exchange rate of CCS was double and triple that of the spiral-coil and the straight-line types. The parametric study reveals that the pitch between the coil and the space between the coil-column affect the short- and long-term heat exchange performance of CCS, whereas the installation depth influences both short- and long-term performances. The economic analysis of the CCS indicates that at an installation depth of 4 m, a space between the coil-column of 0.2 m, and a pitch of 0.15–0.2 m have the highest internal rate of return because they offer a trade-off between the construction cost and heat transfer performance. Furthermore, using a controlled low-strength material as a thermal-enhanced grouting material increased the annual heat exchange rate by 25% and resulted in a notable increase in the internal rate of return (19.5% compared with 15.6% when using soil).

The effect of non-uniform pitch length and spiraling pathway on the mechanical properties of coiled carbon nanotubes

Coiled carbon nanotubes (CCNTs) exhibit exceptional mechanical, electrical, and thermal properties, making them suitable for diverse applications such as nanoelectromechanical devices. Here, classic molecular dynamics (MD) simulations were employed to investigate the coil morphology and the uniaxial tensile characteristics of thirteen CCNTs that were constructed by twisting carbon nanotube (CNT) segments of toroid formed by six identical CNT segments, with intricate effects of coil spacing and twist-induced spiraling pathway. The MD results showed that the coil morphology and stretching properties of CCNTs are greatly dictated by pitch length and spiraling pathway. All CCNTs showed unique characteristics of sawtooth-like patterns in the tensile stress-strain curves, originating from the separation of van der Waals (vdW) attracted coils, strain-induced buckling of CNT segments and nanohinge-like plastic deformations. Depending on the non-uniform pitch length and spiraling pathway of twisted CCNT segments, CCNTs exhibit different mechanical properties including Young's modulus, elastic limit, tensile strength, fracture strain, stiffness coefficient and distinguishing deformation mechanisms. Particularly, the fracture strain and tensile strength are significantly dictated by the pitch length and spiraling pathway, respectively. The elastic proprieties of finite element (FE) models scaled to CCNTs were established for comparison with the case of CCNTs with symmetrical spiraling. Moreover, CCNTs show high toughness that can be controlled by the pitch length and spiraling pathway. This study provides new insights and perspectives into the mechanical properties of nanocoils, which is of help to designing optimal nanocoils for nano-device systems.

The Study of a Magnetostrictive-Based Shading Detection Method and Device for the Photovoltaic System

When the photovoltaic (PV) system suffers shading problems caused by different degrees and areas, the shaded PV cells will consume electricity and generate heat, the corresponding bypass diode operating at a certain current will conduct, and a special magnetic field will be generated in space. In this study, a magnetostrictive-based shading detection method and device for the PV system are developed from theoretical, simulation, and physical experimental aspects. This study aims to detect the special magnetic field using magnetostrictive material with a certain response pattern under the magnetic field to detect and locate the shading problem of each module in the PV system. Theoretically, the analysis is carried out from the on–off situation of the bypass diodes of PV modules under different shading conditions and the response mechanism of magnetostrictive materials under the action of the magnetic field. During simulation, the finite element magnetic field simulations are performed for the diode and the series magnetic field coil, and the structural parameters of the magnetic field coil are designed based on the simulation results. After establishing the validation idea of the detection method in this study, the experimental platform is built and the experimental steps are designed. Finally, the feasibility of the method proposed in this study is verified, the detection range of the method is calculated, and the minimum spacing of adjacent magnetic field coils is determined by experimental validation. This study provides a novel magnetostrictive-based detection method, as well as a theoretical and experimental basis, for identifying and localizing PV system shading problems, and discusses the feasibility of shading detection at the system level.

An optimal load indirect matching method without parameter identification and system efficiency optimization

In some wireless charging applications where the coil spacing varies in real time, such as UAV, electric boat and tram, etc., the traditional direct impedance matching method is difficult to identify the mutual inductance timely and accurately, thus affecting the efficiency optimization effect of the system. In this paper, an indirect impedance matching method without parameter identification is proposed, this method is based on the characteristic that the optimal voltage gain of the resonator is only related to its inherent parameters, and impedance matching can be achieved by controlling the voltage gain in real time. To further improve the efficiency of the system, a single-sided detuning design method is used to achieve soft switching of the inverter. Based on the optimal voltage gain expression derived by using both the indirect impedance matching method and the single-sided detuning design method, a compound control strategy for a series-series-compensated topology with dual-side power control is proposed to improve efficiency and stabilize the output voltage. A hardware prototype is built and a peak DC-to-DC efficiency with the optimal output resistance RL at about 28.9 Ω is 91.58%. When the output resistance RL is 100 Ω, the efficiency improved by 7% after using the proposed strategy.

Transient Electromagnetic Flaw Detection and Casing Wall Thickness Measurements in Multi-String Wells

The transient electromagnetic method is the most effective in the studying of multi-string wells. First, the nonstationary field is measured after the current is turned off (without the primary field) that reduces the coil spacing to zero, i.e. combine the generator and receiver coils. This significantly improves the vertical characteristic of the probe, allows the probe to register small defects. Second, the non-stationary mode allows separating signals from the first, second, third, etc. strings much easier than the harmonic mode. It improves the accuracy of thickness estimation and defect detection. The paper proposes an algorithm for interpreting the measurement results.

Effects of curvature radius on flexible eddy current array sensors for the curved surface of metal components

The flexible eddy current array sensor owns the advantages of high sensitivity and strong adaptability, but the results are always affected by the curvature radius of complex curved surfaces. The relationship between the curvature radius of the curved surface and detection signals for surface-breaking cracks is mainly discussed. The change of magnetic field caused by the curved surface in the present eddy current testing is specially pointed out, which manifest themselves in the compression or enhancement of the testing signal in its peak value and the baseline drifts. Simulation and experimental results indicate that the concave surface weakens the signal, while the convex surface enhances the signal. The signal amplitude decreases with the decrease in the curvature radius for the concave surface, while it is the opposite for the convex surface. Meanwhile, coil spacing significantly affects the amplitude–curvature radius curve. Furthermore, the fluctuation characteristic affected by the curvature radius under different coil spacing is analyzed. The discovery and results will benefit the quantitative evaluation of flexible eddy current array testing.

Magnetic Permeability Sensor Array Prototype to Evaluate Reservoir Phase Permeability in situ Downhole

A measurement system capable of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> measurements of formation permeability is described. The measurement method relies upon imaging the distribution of magnetic permeability fluid injected into a wellbore system through mutual inductance measurements between pairs of coils and relating the change in distribution of this fluid over time to a direct measurement of formation phase permeability. Analysis of the mutual inductance measurement method shows a unique response to distributions of magnetic permeability for various coil spacings and insensitivity to other confounding electrical parameters. The lower bound of measurement variance for this system is modeled for a continuum of coil spacings and radii of investigation for a perturbation in magnetic permeability.

Study on Remote Field Eddy Current Testing Technology for Crack-like Defects in Long Truss Structure of Aircraft.

Detection of hidden defects of aircraft long truss structures (aluminum alloy) is a challenging problem. The shape of the aircraft truss structure is complex, and the crack defects are buried in a large depth. Without the restriction of skin effect, remote field eddy current (RFEC) has great advantages in detecting buried depth defects. In this paper, in order to detect the hidden defects of the aluminum alloy aircraft long truss structure, the remote field eddy current probe is improved from two aspects of magnetic field enhancement and near-field signal suppression using the finite element method. The results show that indirect coupling energy is greatly enhanced when the connected magnetic circuit is added to the excitation coil. By adding a composite shielding structure outside the excitation coil and the detection coil, respectively, the direct coupling energy is effectively restrained. As a result, the size of the probe is reduced. By optimizing the coil spacing and probe placement position, the detection sensitivity of the probe is improved. The simulation is verified by experiments, and the experimental results are consistent with the simulation conclusions.

Antibody-powered lighting-up fluorescence immunosensor based on hemin/G-quadruplex-quenched DNA-hosted dual silver nanoclusters as emitters

Immunosensors with many merits such as simplicity, high sensitivity and selectivity are intriguing for the detection of antibodies, especially bivalent antibody (e.g. anti-digoxin antibody, DigA). In this work, we report a sensitive immunosensor for DigA based on the switchable fluorescence of DNA-templated silver nanoclusters (AgNCs) modulated by hemin/G-quadruplex (hGq). To explore the fluorescing performance of one hGq-quenching dual-AgNCs (d-AgNCs), here we design a functional hosting DNA strand (HGH) encoding with one centered G-rich segment for forming hGq complex in the presence of hemin and K+, two terminated C-rich template sequences for the identical clustering of d-AgNCs, and two flanked symmetric domains for specific recognizing and linking. Because of the photoexcited electron transfer process to the stacked hGq, the originally presynthesized d-AgNCs colocalized in two ends are non-emissive, which are retainable after complementarily hybridizing with two recognizable single strands that are both tagged with a digoxigenin hapten, a Fab fragment. Upon introducing DigA, the steric strain associated with the affinity binding of two haptens results in the opening and stretch of hGq in a coil spacer, thereby lighting-up the d-AgNCs fluorescence. Based on one-step signal switch stimulated by targeting antibody, this label-free immunosensor strategy is of high specificity and sensitivity with low picomolar detection limit, as well as simplification, rapidness and cost-effectiveness.