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Accurate tracking involuntary head movements is fairly a challenging problem in MR imaging of the brain. Though there are few techniques available to monitor the head movement of the subject for a prospective motion correction, it is still an unsolved problem in MRI. In this theoretical study, we aim to describe an analytical investigation to track head movement inside an MR scanner by calculating the change in induced voltage in the head-mounted coils during the execution of time-varying gradients. We derive an expression to calculate the change in induced voltage in a coil placed in a time-varying gradient. We also derive a general equation to investigate the changes in the induced voltage in a set of coils mounted onto the head for the planar position and orientation of the coils. Each coil is considered as a magnetic dipole with location and sensitivity vectors. The changes of the vectors can track the head movement in the MR scanner by measuring the changes in the induced voltage in the coils. The dipole concept is valid for a wide range of coils. The changes in induced voltage in the coils are linear due to small changes in pose of the head. Movement parameters are estimated from the induced voltage changes. If the random noise voltage is less than 100 μV, it does not significantly affect movement parameters because the change in induced voltage in the coils dominates over the small noise voltage. This method and array of the coils may provide a real-life solution to the long-standing problem of head motion during MRI. Enamul H. Bhuiyan gratefully acknowledge Professor Richard W. Bowtell, Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham for his scholastic discussion during preparation of the manuscript. Scopus

Recent developments, in the field of wireless charging, have led to increasing use of this technology across different areas of research. The search for improvement in Soldier Combat Systems has seen major investments in recent years, to find a standard architecture that can enhance military capabilities, such as in power management systems. This work is part of the C4I program of the Portuguese army, having had the primary objective of studying an alternative power supply option based on wireless technology, capable of charging man-portable devices in military vehicles. On this dissertation, it was conducted a study on the behavior of the components of a wireless power transfer, focusing on different configurations and geometries of the charging coils, as well as the optimization of key parameters in a wireless power module. For this, key operating principles and charging methods were approached. Using distance as a variable parameter, it was possible to study the variation in signal amplitude and compare the performances of each coil, reaching promising conclusions on which coil geometry is best suited in terms of shape, reach, and intensity of the generated magnetic field of the power transfer. Also, the matching outcomes from the theoretical deductions and the experimental work done in a controlled environment led to a strengthening of the obtained results. After fabricating and testing prototype 3D structures for the coils, a proposal for a wireless charging system was conceived. This proposal includes architecture, protocols, and its implementation taking into account the characteristics of the charging environment.

A recently developed compact 3 T (C3T) MRI scanner with high performance gradients [1, 2] has a dedicated radiofrequency (RF) transmit coil that exposes only the head, neck and a small portion of the upper body region during head-first scanning. Due to the unique coil geometry and patient positioning, the established SAR model used for a conventional whole-body scanner cannot be directly translated to the C3T. Here a specific absorption rate (SAR) estimation and validation framework was developed and used to implement a dedicated and accurate SAR prediction model for the C3T. Two different SAR prediction models for the C3T were defined and evaluated: one based on an anatomically derived exposed mass, and one using a fixed anatomical position located caudally to the RF coil to determine the exposed mass. After coil modeling and virtual human body simulation, the designed SAR prediction model was implemented on the C3T and verified with calorimetry and in vivo scan power monitoring. The fixed-demarcation exposed mass model was selected as appropriate exposed mass region to accurately estimate the SAR deposition in the patient on the C3T.

This paper reported an analytical formulation for the optimum geometry of a uniform pressure coil used in electromagnetic forming and welding. To characterize the energy efficiency of the coil, we defined the objective function as the ratio between the produced magnetic pressure and the required magnetic energy. We then deduced an analytical formulation of the objective function in terms of the geometry and electromagnetic parameters. Based on the analytical formulation, we finally deduced the optimum configuration of the coil geometry in analytical form. To validate the proposed analytical formulation, we analytically and numerically analyzed a uniform pressure coil fabricated in our laboratory, showing that the proposed analytical formulation can well reproduce the numerical results over a broad range of geometric parameters. In addition, it was found that the uniform pressure coil exhibits an optimum channel height, which can be analytically expressed in terms of the coil geometry. In summary, the present study provides an efficient method for designing a uniform pressure coil.

Microcoils provide significant applications in biomedical microdevices. Lab-on-chip systems make use of electromagnetic microactuators for controlling fluid flow within microscopic devices. Microcoils are inevitable components in electromagnetic microactuators. The effect of the geometrical parameters of a coplanar microcoil on the electromagnetic force of a microactuator is analysed and presented in this work. An optimized coil geometry is also presented to produce required electromagnetic force for the microactuating applications.

In the SAE J2954 standard for stationary wireless charging of electric vehicles, two different coil geometries are proposed: The circular (C) and the double-D (DD) coil system. In the future, electric vehicles are expected to be equipped with the vehicle assembly (VA) coil geometry as proposed in the standard. This can be used as a design criterion for an electrified road, where the installed primary coils have to be compatible to the vehicle coil. In this paper, the two SAE systems are compared to each other regarding the coupling factor stability with a compatible primary side for dynamic wireless charging, i. e., charging while in motion. Therefore, two coil designs have been built up in laboratory, each consisting of three identical primary air coil pads compatible with the corresponding SAE secondary side. The results indicate that the coupling factor for the double-D coil system shows lesser variation along the path than for the circular coil system, but the absolute coupling factor is greater for the circular coil system.

This paper presents a versatile tool for the self-inductance calculation of planar coils. Due to the growing interest in planar coils in the past few years, the possibility of using an analytical model as a valid alternative to FEM simulations, regarding versatility and result reliability, would be of great interest. The ideal scenario would be to combine speed, precision, easy interaction and understanding, while adding versatility in terms of geometry. To achieve that, a tool, based on Grover equations, that calculates the self-inductance of planar coils with a general geometry has been developed. The results achieved using this method, considering different coil geometries and dimensions, were compared with the main analytical methods that can be found in the literature, proving the reliability of the proposed method. This model has the novelty of not having any limitation on the coil geometry or dimension, which is not the case for the other existing methods., This work has been supported by FCT – Fundação para a Ciência e Tecnologia with in the R&D Units Project Scope: UIDB/00319/2020 and European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COM-PETE 2020) [Project nº 037902; Funding Reference: POCI-01-0247-FEDER-037902].

An experimental study is done to study the convection heat transfer from the outer surface of a group of helical coils that have the same external surface area which is 0.1 m2. These coils are wrapped to form different helical coils with different geometrical dimensions. Five pipe diameters are used in this study also; the pipes are wrapped by different values of coil diameter ranges 75–300 mm. The effect of the coil pitch on the heat transfer process has been studied, to reach the value that gives the best performance for each coil. The heat source is steam flowing inside the coil. These coils are tested at different airspeeds inside the wind tunnel, which made the Reynolds number (Re) changes from 239 to 3990. The obtained results showed that the Nusselt number enhances with the increase of D/do and P/do to reach the maximum value at the optimum values of D/do and P/do, and then, the Nusselt number begins to decrease. The Nusselt number increases with the increase of Reynolds number under all conditions. A correlation for Nusselt number as a function of Reynolds number and the other studied operating parameters is reported. By comparing this work with literature, one can find an acceptable agreement in the results.

A novel traveling-wave Zeeman decelerator based on a double-helix coil geometry capable of decelerating paramagnetic molecules with high efficiency is presented. Moving magnetic traps are generated by applying time-dependent currents through the decelerator coils. Paramagnetic molecules in low-field-seeking Zeeman states are confined inside the moving traps which are decelerated to lower forward velocities. As a prototypical example, we demonstrate the deceleration of OH radicals from an initial velocity of 445 m s-1 down to various final velocities. The experimental results are analyzed and numerically reproduced with the help of trajectory simulations confirming the phase-space stability and efficiency of the deceleration of the molecules in the new device.

Finite element modelling of high frequency inductive coils and metal plates was used to investigate the impedance response to a narrow gap between the plates. The model was used to predict distance ...

The problem of variation of the output characteristics (voltage, current, power) of inductive powering systems for implantable medical devices is considered. The variation is primarily caused by relative misalignment of transmitting and receiving coils. A classification of misalignments is proposed. Main approaches to coil misalignment compensation are: mechanical fixation of the coils; evaluation of the relative position of the coils for elimination of misalignment or further tuning of the transmitting part of the system; optimization of the coil geometry providing stability within the given misalignment range; tuning the working frequency of the transmitting part of the system. It is shown that the compensation method should be selected with due regard to the implantable device parameters (first of all, the coil implantation site and the power consumption of the device).

Tissue variability, as well as human movement, can affect the mutual arrangement of coils during the energy supply of implantable medical devices. This can affect the geometry of optimized coils. This paper considers the resulting geometry of the coils, optimized for axial distances of 10, 15 and 20 mm with lateral displacements of up to 15 mm and 30 mm at operating frequencies of 0.1, 1 and 10 MHz. It was found that with increasing axial distance, the optimal size of the transmitting coil increase at an operating frequency of 0.1 MHz and decrease at 1 MHz. Using an operating frequency of 10 MHz makes it possible to obtain small optimal sizes of the receiving coil. At the end of the work, recommendations were given on the design of coils, depending on the expected displacements and operating frequency.

The appropriate design of a WPT charger encompasses multiple decisions, which include the coil geometry and the configuration of the power converters. This chapter proposes 8 phases to follow when approaching this kind of design. After an in-depth analysis of the application requirements and their impacts on the design, an iterative algorithm should be executed to determine the coil geometries and the topologies of the compensation networks. This chapter includes a description of the proposed approach. Through an illustrative example, we show how the design procedure can be applied.

Wireless power charging includes interesting physics from low frequencies and RF analysis which tends to be complex and tedious to model and simulate. Full wave simulations has been performed in order to evaluate the wireless power efficiency. A square coil was used to perform this analysis and simulations shows pick values of efficiency of 70% around 5 MHz, which is higher than most found at this frequency. The method has been proved, it is simple to implement in a commercial electromagnetic simulator. Then, it can easily be replicated and optimized to find optimal geometries of coil for specific applications such mobile phones, wearable devices or even electric car charging.

We evaluated the influence of 3T magnetic resonance imaging whole body birdcage coil modeling on electromagnetic exposure estimation using a human model. Simplification of coil geometry, realistic tuning and capacitor losses had a relevant impact on the estimated electric distributions. Variety of the generated electric field has to be carefully considered for reliable RF safety assessment of a patient with a passive or active implant undergoing magnetic resonance imaging.

Maintaining maximum power transfer efficiency (PTE) is one of the main challenges in resonant inductive power transfer (IPT) systems. Maximum PTE can be achieved if the coupling between transmitter and receiver coils is strong. One way of achieving this is to geometrically optimise a coil by employing small ohmic resistance combined with high self-inductance. In this paper a design method for an optimum coil geometry which offers maximum PTE has been introduced. The proposed technique, in addition to minimising the system’s physical size, provides high level of PTE for both strongly- and loosely-coupled links. A design example for a typical IPT system is presented that shows, with a proper selection of strong coupling factor (e.g.: C = 220.), the designed coil geometry can provide maximum PTE of 95.4% for coupling coefficient K = 1. Also, for a loose inductive link with K = 0.215, maximum calculated and measured PTE values are 89% and 86%, respectively.

In this paper, the influence of the inductive power transfer (IPT) coil geometry on the performance factors efficiency, power density, and stray field is studied for a public transport electric vehicle battery charging system. IPT coil geometries with rectangular winding and with double-D winding are compared based on the Pareto fronts obtained from a multi-objective optimization. In order to study the effect of the winding layout experimentally, two full-scale 50 kW/85 kHz hardware prototypes with the same outer coil dimensions ( $410\times 760\times 60$ mm3) and ferrite core structure are constructed. For both the prototypes, the measured dc–dc efficiency is approximately 95.5% at 50 kW with a 160 mm air gap and ideally positioned coils, which confirms the calculations. The positioning tolerance of the double-D prototype is inferior, because with coil misalignment the efficiency decays faster than for the rectangular winding prototype. Flux density measurements show that both the prototypes fulfill the ICNIRP 2010 standard at 800 mm lateral distance from the coil center. However, the measured magnetic stray field is a factor of two lower for the double-D prototype, which is a key advantage in high-power applications.

In inductive heat treatment, the induction coil design plays an important role in the localization of heat generation. Therefore, the combination of an optimized coil geometry and frequency choice determines the workpiece properties and applicability of close-to-contour hardening for small parts or thin hardened layers. Additive manufacturing of copper alloys in the Selective Laser Melting (SLM) process offers a method to build coils with high design flexibility and precision. Conventional coil manufacturing methods are reaching their limitations due to the conflicting geometry specifications at the applied frequency range. In the present work, a characterization is presented and the performance of an SLM manufactured coil in MHz induction application of small surface hardened wires of steel is examined.

This study deals with the simplex optimization of a shield coil geometry for improving the magnetic shielding performance of fully air-cored superconducting generators. The superconducting generator in this study has a 10 MW-3000 rpm class, fully air-cored, rotating armature structure designed for electric propulsion aircraft applications. The magnetic flux radiated to the outside of the machine is shielded by the shield coil, and the shielding performance is determined by the shape of the shield coil. In this study, the design of the shield coil is developed using simplex optimization to improve the shield performance. The shape optimization is conducted using the simplex optimal design method, and the validity of the designed shield coil is verified by comparing the shielding performance of the initial and the optimized models.

The interrelation between coil geometry and operating frequency in the inductive powering unit is complex and can be assessed in several ways. In this paper, a pair of LC-circuits with series compensation is investigated in the following manner. The flat circular coil is optimized in order to obtain self-inductance to provide resonance of the pair of LC-circuits. The operating frequency is changing in the range of 1…10 MHz. The dependence of the coil geometric parameters (outer and inner radii, the number of turns) on the operating frequency is evaluated. A method for reducing the size of the coils has been proposed.

To clarify the mechanism of aneurysmal recanalization, it is necessary to understand the characteristics of the blood flow inside the aneurysm in particular the flow resistance generated by the coil. In studies using computational fluid dynamics (CFD), mainly two approaches have been used to model the coil embolized aneurysm; modeling the coils as porous media or by real coil geometries. In this study, we calculated the pressure drop along a vessel through a coiled region modeled as porous media or by real coil geometry and compared the pressure drop generated by the two coil models. The porous media model was described by Darcy's law and Ergun's equation, while the real coil geometry was generated using finite element method (FEM) structural analysis. We calculated the pressure drop for inlet velocities from 0.1 m/s to 1.0 m/s in steps of 0.1 m/s. Our results indicated that the porous media model may produce larger pressure drops than the real coil geometry model under low packing density. The value of the pressure drop was also changed due to the difference of coil distribution even if the packing density was the same.

Voltage stress due to steep impulses during switching operations of e.g. vacuum circuit breakers and ongoing harmonics caused by converters are a well-known but still increasing problem in the field of transformer design and operation [1]. In order to investigate the behavior of transformers during such impulses and oscillations, several models have been developed [2,3]. However, with increasing complexity of the coils, all studies show minor to major deviations in computation, compared to the corresponding measurements. Due to a high number of turns in the high voltage coils of transformers, the errors caused by simplifications or inaccurate data of the interwinding geometry can be tremendous. Hence, it is necessary to know which parameters are influencing the resonance behavior significantly and need to be represented accurately, while other parameters may be neglected. Therefore, a parameter study has been carried out, in order to analyze the resonance behavior of a simple coil geometry, based on FEM computations.

Carbon microcoils could be synthesized using a thermal chemical vapor deposition process in which C 2 H 2 /H 2 is used as the source gas and SF 6 as an additive gas. We investigated the formation of carbon microcoils as a function of reaction time to study the growth mechanism of coil-type carbon microcoils, particularly under long reaction time. After the first 5 min of the reaction, wave-like carbon nanocoils were formed along with carbon microcoils at certain positions on the sample. An increase in reaction time (60 min) led to the formation of double helix-type carbon microcoils. Further increase in the reaction time (120 min) led to the formation of twist-type carbon microcoils with occasional growth of the coil-type carbon microcoils on the sample. However, at the longest reaction time (180 min) investigated in this work, we observed a decrease in the density of the carbon microcoils. Based on these results, we determine the optimal reaction time for the growth of double helix-type carbon microcoils and suggest the growth mechanism of the coil-type carbon microcoils with a focus on long reaction time.

Magnetohydrodynamic (MHD) flow will be produced in liquid aluminium by gradients in the Lorentz forces created by the interactions of induced currents and the time-varying magnetic field of an induction coil. The magnitude of the velocity field is driven by the curl of the Lorentz forces. Practical coils are “Short” and produce magnetic fields having both lower flux densities and Lorentz forces than very “Long” or infinite coils. Unlike infinite coils, the magnetic fields of “Short” coils contain both axial and radial components, which vary with position and thereby produce powerful MHD mixing. When such a coil is used with the objective of achieving non-conductive particle migration in a liquid metal by electromagnetophoresis, the obtained mixing effects can be highly detrimental. In the present study different coil geometries and induced Lorentz forces with resulting MHD mixing are modelled (COMSOL® 4.4), and the obtained Lorentz forces compared to analytical results.

Smart sensing architectures based on inductive readout are very intriguing solutions to perform measurements in industrial and in general in harsh environments. The proposed system is based on a primary coil as fixed sensing element and in front of it, a movable and battery less receiving sensor coil. The architecture measures the misalignment, with a non-destructive approach, between two objects and offers a high flexibility to perform the measurements also in presence of humidity, dirtiness, debris, oils or other non-homogeneous surfaces. Furthermore, it is easy to be implemented at low cost and it presents a wide operative range. For data acquisition, a low energy Bluetooth board is used, which starts automatically as soon as a minimum voltage value is reached. The system has been designed and studied; a laboratory prototype has been realized and experimentally validated. The results demonstrate the suitability of the proposed method.

Wireless Power Transfer (WPT) uses electromagnetic fields to transmit power due to which WPT systems have faced many challenges on the way of its adoption. This manuscript reviews the two aspects of its adoption. Firstly, the technical progress, development and applications and the state of the art progress in various technologies used in Wireless Power Transfer (WPT). Secondly, the sustainable performance. The technical part contains system performance factors like coil geometry, frequency, misalignment and compensation topologies which have been discussed. The sustainable perspective contains energy, environmental and health issues. Finally, the paper presents a state of the art development in WPT, understand the technical as well as health challenges of WPT and leave some unanswered questions to be answered related to the contribution of WPT for sustainable mobility.

The subject of this contribution is a description of accurate numeric calculation of a lap winding coil geometry, in particular preformed coil for armature winding. A method of calculation of the geometry in cylindrical coordinate system is proposed and it considers both radial extension of winding overhangs as well as bevelling of winding overhang loop. The results obtained by proposed calculation are compared with fifteen samples of coils used in mass produced traction machines, whose coils are manufactured with both mentioned modifications – radial extension of winding overhangs and bevelling of the coil loop.

Purpose The aim of this study was to evaluate the effect of integrated high-permittivity materials (HPMs) on excitation homogeneity and global specific absorption rate (SAR) for transmit arrays at 7T. Methods A rapid electrodynamic simulation framework was used to calculate L-curves associated with excitation of a uniform 2D profile in a dielectric sphere. We used ultimate intrinsic SAR as an absolute performance reference to compare different transmit arrays in the presence and absence of a layer of HPM. We investigated the optimal permittivity for the HPM as a function of its thickness, the sample size, and the number of array elements. Results Adding a layer of HPM can improve the performance of a 24-element array to match that of a 48-element array without HPM, whereas a 48-element array with HPM can perform as well as a 64-element array without HPM. Optimal relative permittivity values changed based on sample and coil geometry, but were always within a range obtainable with readily available materials (er = 100-200). Conclusion Integration of HPMs could be a practical method to improve RF shimming performance, alternative to increasing the number of coils. The proposed simulation framework could be used to explore the design of novel transmit arrays for head imaging at ultra-high field strength. Magn Reson Med 80:391-399, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Background/aims: Increasing signal-to-noise ratio for skin spectroscopy means increasing area, but increased area usually means resorting to Fourier window techniques to prevent overwhelming muscle contamination. The aim of this work was to develop a simple coil that would allow large areas of skin to be sampled while limiting muscle contamination simply by the coil's geometry. Methods: The coil design was arrived at by using simulations that were calibrated by phantom tests with prototype units. It was then fabricated by using an etched circuitboard technique and tested on three volunteers for comparison with predicted performance. Results: The new coil acquires magnetic resonance signals from a 140 cm2 contoured layer of surface tissue with sufficient selectivity that 81% of the signal comes from tissue less than 1.9 mm deep. For skin and fat thicknesses of 1.1 and 3.1 mm, respectively, tending toward a worst case in-vivo situation, muscle contamination is only 3.3%. With the new coil, in 1 h, it was possible to directly acquire 31P skin spectra comparable to those formerly obtained in 4 h in two separate acquistions that then had to be subtracted to obtain the desired skin spectra. Conclusion: Increasing the area of skin sampled while maintaining selectivity to limit muscle contamination, relying simply on coil geometry, is practical using a parallel configuration of long narrow strip coils.