Ideal Coil Research Articles

Influence of framing coil orientation and its shape on the hemodynamics of a basilar aneurysm model.

Aneurysms are bulges of an artery, which require clinical management solutions. Due to the inherent advantages, endovascular coil filling is emerging as the treatment of choice for intracranial aneurysms (IAs). However, after successful treatment of coil embolization, there is a serious risk of recurrence. It is well known that optimal packing density will enhance treatment outcomes. The main objective of endovascular coil embolization is to achieve flow stasis by enabling significant reduction in intra-aneurysmal flow and facilitate thrombus formation. The present study numerically investigates the effect of framing coil orientation on intra-aneurysmal hemodynamics. For the purpose of analysis, actual shape of the embolic coil is used, instead of simplified ideal coil shape. Typically used details of the framing coil are resolved for the analysis. However, region above the framing coil is assumed to be filled with a porous medium. Present simulations have shown that orientation of the framing coil loop (FCL) greatly influences the intra-aneurysmal hemodynamics. The FCLs which were placed parallel to the outlets of basilar tip aneurysm (Coil A) were found to reduce intra-aneurysmal flow velocity that facilitates thrombus formation. Involving the coil for the region is modeled using a porous medium model with a packing density of 20 . The simulations indicate that the framing coil loop (FCL) has a significant influence on the overall outcome.

An approach to improve the tension constancy of a TF coil shape

An ideal TF coil shape or centerline should be such that the TF coil is subjected to constant tension. The Princeton-D and the Modified-D are widely used as constant-tension centerlines for designing TF coil, however, our analyses show that their tensions are not fully constant. The reason is that the magnetic field used to calculate the centerlines is inaccurate. In this work, we propose an approach of calculating the Optimized-D shape with improved tension constancy. First, the Princeton-D and the Modified-D are introduced and their tension non-constancies are revealed. Then, a code is written to calculate the accurate toroidal fields. Next, the Optimized-D coil shape is obtained through a semi-analytical iteration process. Finally, for the three D shapes, the relationship between the TF coil parameters are discussed. Our results indicate that the Optimized-D shape realizes a noteworthy improvement in tension constancy.

Evaluation of the Properties of Eddy Current Sensors Based on Their Equivalent Parameters

This paper presents a practical way of using the method of evaluating the metrological properties of eddy current sensors. The idea of the proposed approach consists of employing a mathematical model of an ideal filamentary coil to determine equivalent parameters of the sensor and sensitivity coefficients of tested physical quantities. These parameters were determined on the basis of the measured value of the real sensor's impedance. The measurements were carried out with an air-core sensor and an I-core sensor while they were positioned at different distances from the surface of tested copper and bronze plates. An analysis of the influence of the coil's position in relation to the I core on the equivalent parameters was also carried out, and the interpretation of the results obtained for various sensor configurations was presented in a graphical form. When equivalent parameters and sensitivity coefficients of examined physical quantities are known, it is possible to compare even very different sensors with the employment of one measure. The proposed approach makes it possible to make a significant simplification of the mechanisms of calibration of conductometers and defectoscopes, computer simulation of eddy current tests, creating the scale of a measuring device, and designing sensors.

Compression and interpenetration of adsorption-active brushes.

Compression and interpenetration of two opposing polymer brushes formed by end-grafted adsorption-active chains are studied by the numerical self-consistent field approach and by analytical theory. For sufficiently strong polymer-surface attraction, a fraction of chains in the adsorption-active brush condenses into a near-surface layer, while the remaining ones form the outer brush with reduced effective grafting density. Analysis shows that the normal pressure in adsorption-active brushes can be understood in terms of the effective grafting density concept although the pressure at small separations is affected by the presence of the dense adsorbed phase. We propose a simple theory modification that accounts for this effect. We also formulate a procedure for extracting the value of the effective grafting density directly from the pressure vs separation curves by inverting the equation of state. In contrast to the normal pressure, the interpenetration of the two opposing adsorption-active brushes demonstrates a much more intricate behavior. At weak to moderate compressions, the effective grafting density concept works well but fails spectacularly at small interbrush separations. We identify two interpenetration regimes for adsorption-active brushes: (i) at separations larger than the ideal Gaussian coil size N1/2, the overlap of the two brushes is concentrated in the mid-plane region, in the same way as in brushes grafted onto non-attractive surfaces; (ii) at separations less than N1/2, the brush overlap is strongly enhanced in the wall regions where the attractive interaction plays an important role both in generating the dense layer for the "proper" brush and in attracting the "foreign" chains.

How to use multimodal neuroimaging to personalize rTMS parameters for depression treatment

Abstract Even though repetitive transcranial magnetic stimulation (rTMS) is already an FDA approved technique to treat depression, the overall clinical effectiveness is still rather modest. Overly general stimulation protocols that neither consider subject-specific depression symptomology nor individualized brain characteristics such as anatomy, or structural, and functional connections, may be the cause of the high inter- and intra-individual variability in rTMS response rates. This work gives an overview of ways of how we think that multimodal neuroimaging could provide insights into individual brain characteristics and therefore be used to personalize rTMS parameters; coil position, stimulation intensity, and timing. The optimal coil positioning could potentially be derived using a three-step process: 1) identification of the optimal (indirect) target area based on the symptom pattern; 2) derivation of the cortical (direct) target location based on functional and/or structural connectomes derived from functional and diffusion MRI data; 3) determination of the ideal coil position by computational modeling, such that the electric field distribution overlaps with the cortical target. TMS-induced electric field simulations require anatomical, and potentially diffusion, MRI data. Information about the induced field strengths can be used to derive optimal stimulation intensities. Besides MRI, EEG can provide complementary information regarding the ongoing oscillating brain-states. This information could be used to apply timely TMS pulse trains during preferred states or personalize the frequency of the stimulation. The added value of these personalized stimulation protocols is logically reasoned, but speculative. Randomized clinical trials will be required to compare clinical responses from standard rTMS protocols to personalized protocols. Ultimately, we hypothesize that optimized clinical response results from precision protocols derived from combinations of personalized stimulation parameters. Keywords: TMS, personalized medicine, MRI, EEG

Locating Defects in Conductive Materials Using the Eddy Current Model of the Filamentary Coil

This article presents an innovative technique for detecting flaws in conductive materials by using an ideal filamentary coil. To characterize such a coil accurately and explicitly, it is sufficient to be in possession of merely two parameters: the radius of the circle within which all the turns are located and the distance of the coil from the tested surface. The mathematical model derived using the truncated region eigenfunction expansion method enables the calculation of the changes in the components of the filamentary coil impedance that are the result of positioning the coil close to the conductive material with a hole. Because of this, the air-cored coil model can be replaced with a much simpler filamentary coil model. This solution makes it is possible to detect various types of holes (internal, surface, subsurface or through) occurring in both multilayer magnetic and non-magnetic materials. The derived results were verified by means of measurements and numerical calculations based on the finite element method. Very good agreement was observed in both cases. The paper contains the source code implemented in Matlab, which is used to for calculations.

A Method for Comparing the Metrological Properties of Eddy Current Probes

This article describes a method for comparing the metrological properties of air-cored and solid-cored coils designed as eddy current probes. The approach suggested in this article assumes that a pair of equivalent parameters of an ideal filamentary coil can be assigned to any contact coil so that the impedance variations in both coils are identical. These two parameters include the coil radius and its distance from the surface of a test piece. The experiments performed demonstrate that for equivalent parameters defined in such a way, impedance variations in a real and filamentary coil are the same for a broad frequency range of excitation current and conductivity of the material being tested. Therefore, comparisons between parameters of eddy current probes such as sensitivity, depth of penetration, or inspection coverage can be made with the use of a simple model of an ideal filamentary coil defined by only two parameters. The solution proposed in this article substantially simplifies the calibration process of the measuring instrument, the adjustment and optimization of parameters for newly designed probes, and the development of efficient and reliable mechanisms to eliminate undesired effects (e.g., lift-off).

Numerical Analysis of Eddy Current Induced by z-Gradient Coil in a Superconducting MRI Magnet

In magnetic resonance imaging (MRI), pulsed magnetic gradient fields induce eddy currents in surrounding conducting components of the MRI scanner. These eddy currents distort MRI image and introduce thermal load in cryostat. Ohmic heating of superconducting magnet due to eddy currents changes the operating temperature of magnet, which can lead to system quench. Numerical simulation of these eddy current is important to compensate/control their adverse effects. In this paper, a coupled circuit network method is outlined to model eddy currents in a superconducting magnet that induced by z-gradient coil. According to the axial symmetry, the cylindrical cryostat vessels are divided into several concentric slices with a finite thickness. Each slice is modeled as a series circuit composed of a resistor and an inductor, and inductively coupled with other slices and gradient coil. To improve the calculation efficiency, the Eigen matrix technique is used to simplify the coupled differential matrix equation. The undesired eddy current effects including time-varying secondary magnetic field and power losses are analyzed. In addition, the eddy current behavior due to mechanical errors of gradient coil is discussed. Compared with the simulation results of ideal gradient coil design, the misalignment between primary and secondary layer of z-gradient coil can cause asymmetric secondary magnetic field along z-axis and further introduce $B_{0}$ -shift in imaging area.

Numerical investigation of helical coil tube bundle in turbulent cross flow using large eddy simulation

A realistic five-layered helical coil tube bundle in turbulent cross flow is numerically investigated using large eddy simulation (LES). The geometry of the helical coil tube bundle, which is a 1/45 sector of a helical coil steam generator design for an advanced small modular reactor, has three counterclockwise helical layers and two clockwise helical layers stacked in alternating fashion in the radial direction. A Reynolds number of 21,800 is considered based on the mean gap velocity, diameter of the coil tube, and kinematic viscosity of the working fluid. The WALE sub-grid scale model is employed for LES to resolve scale smaller than the grid size. Additionally, LES for an ideal five-layered coil bundle model without a helical geometry is utilized to generate comparison data. Instantaneous flow fields are explored by analyzing velocity magnitude, vorticity, static pressure, and vortical structures. The detachments of vortical structures from the coil tube surface are observed by visualizing vortical structures and wall shear stress distributions simultaneously. Various turbulent statistics at multiple monitoring locations are presented with an emphasis on feature difference between realistic and ideal coil bundle models. The results of spectral analyses, including the power spectral density and continuous wavelet transform analyses, are addressed from the perspective of flow-induced vibration. The key feature of this paper is the discussion of three-dimensional effects based on the helical geometry of a coil bundle.

Single Molecule Force Spectroscopy Reveals the Mechanical Design Governing the Efficient Translocation of the Bacterial Toxin Protein RTX.

The efficient translocation of the bacterial toxin adenylate cyclase toxin (CyaA) from the bacterial cytosol to the extracellular environment by the type 1 secretion system (T1SS) is essential for the toxin to function. To understand the molecular features that are responsible for the efficient translocation of CyaA, here we used optical tweezers to investigate the mechanical properties and conformational dynamics of the RTX domain of CyaA at the single molecule level. Our results revealed that apo-RTX behaves like an ideal random coil. This property allows the T1SS to translocate RTX without overcoming the enthalpic resistance. In contrast, the folded holo-RTX is mechancially stable, and its folding occurs in a vectorial, cotranslocational fashion starting from its C-terminus. Moreover, our results showed that the folding of holo-RTX generates a stretching force, which can further facilitate the translocation of RTX. Our results highlight the important role played by the Ca2+-triggered folding of RTX in the translocation of RTX and provide mechanistic insights into the mechanical design that governs the efficient translocation of RTX.

Fractional-order Modelling and Parameter Identification of Electrical Coils

Abstract The accurate modelling of an electrical coil over a wide range of frequency is the keystone for a precise modelling of an electrical machine. As a consequence of copper losses, eddy-current losses and hysteresis losses; electrical coils with conductive ferromagnetic core show different behaviour from that of an ideal coil. Throughout this paper, dynamic modelling and performance analysis of conventional as well as fractional-order models of an electrical coil with an interchangeable core are achieved. Measurement results are acquired through an integration between Matlab and the high-speed measurement system LTT24. In order to assess the accuracy of these models, simulation results are compared with experimental results whereas unknown parameters are identified through an optimization process that is based on the method of least squares. It is known that the parameters of fractional-order model (Lα , α, Cβ , β) can not be measured directly. Therefore, the paper proposes a possibility based on system analysis to derive these parameters (indirect measurement) from the parameters of the classical model. A frequency band beyond the self-resonant frequency of the electrical coil is explored, thus the parasitic capacitance between coils windings must be considered as an important part of the equivalent circuit. The dependency of model parameters on frequency due to skin-effect is also examined.

Note: Parametric tuning of the Helmholtz coil and its optimal designs with thick winding pairs

Thick winding pairs are generally utilized in high-power Helmholtz coil systems, where the coil-heating and insulation are usually of concern for their field uniformity. Beyond the ideal thin model, we discuss the field uniformity of thick Helmholtz coils and their optimal designs based on the numerical and experimental analysis. Furthermore, the design tuning parameters, i.e., ampere-turn configurations, are introduced to the numerical models to investigate their influence on the magnets’ field uniformity. The results show that different ampere-turn realizations of one ideal Helmholtz coil could induce up to ∼30% uniformity variation within the central region. Regardless of whether it is the conventional Helmholtz coil or its optimal designs, the increase in layer number and axial insulation gaps tends to improve the field uniformity. However, the increase in turns per layer results in a great reduction in their field uniformity. By optimizing the ampere-turn arrangement, it is possible to further improve the performance of a Helmholtz-coil-based magnet.

Fractional-Order Impedance Modeling and Parameter Identification of an Electrical Coil with Interchangeable Core

The accurate modelling of an electrical coil over a wide range of frequency is essential for a precise modelling of an electrical machine. As a consequence of copper losses, eddy-current losses and hysteresis losses; electrical coils with conductive ferromagnetic core show different behaviour from that of an ideal coil. Throughout this paper, dynamic modelling and parameter identification of fractional-order models of an electrical coil with interchangeable core are achieved. In order to assess the accuracy of these models, simulation results are compared with experimental results whereas unknown parameters are identified through an optimization process that is based on the method of least squares. It is well known that the parameters of fractional-order model can not be measured directly. Therefore, the paper proposes a possibility based on system analysis to derive these parameters from the parameters of the classical model.

Anti-cooperative Nearest Neighbor Coupling Determines the Statistical Coil State of Peptides and Proteins at High Temperatures

The interest in the unfolded state of peptides and proteins stems partially from the observation that conformational distributions of amino acid residues are more restricted and residue specific than expected for an ideal random coil. Moreover, multiple lines of evidence suggest that contrary to the isolated pair hypothesis the conformational propensity of a distinct residue depends on the properties of its neighbors. We analyzed the recently reported conformational propensities of the two guest residues of GxyG peptides in terms of a statistical thermodynamics model that allows for cooperative as well as anti-cooperative interactions between adjacent residues adopting either a polyproline II (pPII) or a β-strand conformation. Our analysis revealed that the nearest neighbor interactions between most of the central residues in the investigated GxyG peptides is anti-cooperative. Interaction Gibbs energies become significant at high temperature (350 K) at which most proteins undergo thermal unfolding. At room temperature, these interaction energies are less pronounced. We utilized the obtained interaction parameters in an Ising-type approach to calculate the temperature dependence of the UV circular dichroism (CD) of the so-called MAX3 peptide that is predominantly built by KV-repeats. The agreement between simulation and experimental data is very good. Finally, we analyzed the temperature dependence of the CD spectra and selected 3J(HNHα ) parameters of the Aβ(1-9) fragment. The results corroborated the occurrence of anti-cooperative nearest neighbor interactions. A comparison of CD spectra of unfolded and intrinsically disordered proteins with predictions of our model suggests that anti-cooperative interactions govern their experimentally obtained temperature dependence. Generally, our results suggest that unfolded peptides and proteins behave like antiferromagnetic systems in the presence of a magnetic field of intermediate strength.

Micro PCB Rogowski coil for current monitoring and protection of high voltage power modules

We have developed a printed circuit board Rogowski coil for monitoring of current and protection of high-voltage power modules and packages. It is small, thin, and inexpensive current sensor and is almost the ideal Rogowski coil because of its fishbone pattern. For noise reduction under high-voltage/-current conditions in a module, shield layers and coaxial connector are employed. In addition, a new, fast simulation tool was developed to optimize the main coil pattern for realization of arbitrary printed circuit board geometry in specific, limited spaces.

Experimental and numerical study of error fields in the CNT stellarator

Sources of error fields were indirectly inferred in a stellarator by reconciling computed and numerical flux surfaces. Sources considered so far include the displacements and tilts of the four circular coils featured in the simple CNT stellarator. The flux surfaces were measured by means of an electron beam and fluorescent rod, and were computed by means of a Biot–Savart field-line tracing code. If the ideal coil locations and orientations are used in the computation, agreement with measurements is poor. Discrepancies are ascribed to errors in the positioning and orientation of the in-vessel interlocked coils. To that end, an iterative numerical method was developed. A Newton–Raphson algorithm searches for the coils’ displacements and tilts that minimize the discrepancy between the measured and computed flux surfaces. This method was verified by misplacing and tilting the coils in a numerical model of CNT, calculating the flux surfaces that they generated, and testing the algorithm’s ability to deduce the coils’ displacements and tilts. Subsequently, the numerical method was applied to the experimental data, arriving at a set of coil displacements whose resulting field errors exhibited significantly improved agreement with the experimental results.

Least squares reconstruction of non-linear RF phase encoded MR data

PurposeThe numerical feasibility of reconstructing MRI signals generated by RF coils that produce B1 fields with a non-linearly varying spatial phase is explored. TheoryA global linear spatial phase variation of B1 is difficult to produce from current confined to RF coils. Here we use regularized least squares inversion, in place of the usual Fourier transform, to reconstruct signals generated in B1 fields with non-linear phase variation. MethodsRF encoded signals were simulated for three RF coil configurations: ideal linear, parallel conductors and, circular coil pairs. The simulated signals were reconstructed by Fourier transform and by regularized least squares. ResultsThe Fourier reconstruction of simulated RF encoded signals from the parallel conductor coil set showed minor distortions over the reconstruction of signals from the ideal linear coil set but the Fourier reconstruction of signals from the circular coil set produced severe geometric distortion. Least squares inversion in all cases produced reconstruction errors comparable to the Fourier reconstruction of the simulated signal from the ideal linear coil set. ConclusionMRI signals encoded in B1 fields with non-linearly varying spatial phase may be accurately reconstructed using regularized least squares thus pointing the way to the use of simple RF coil designs for RF encoded MRI.

Construction and comparison of the statistical coil states of unfolded and intrinsically disordered proteins from nearest-neighbor corrected conformational propensities of short peptides.

Assessing the influence of nearest neighbors on the conformational ensemble of amino acid residues in unfolded and intrinsically disordered proteins and peptides is pivotal for a thorough understanding of the statistical coil state of unfolded proteins as well as of the energetics of the folding process. Research aimed at exploring nearest neighbor interactions has mostly focused on the analysis of restricted coil libraries that reflect conformational distributions in loops connecting more regular secondary structure segments. Recently, however, Toal et al. reported an experimentally based structural analysis of selected xy-pairs in GxyG tetrapeptides, which revealed quantitative information about conformational changes induced by nearest-neighbor interactions (Eur. J. Chem., 2015, 21, 5173-5192). Here, we perform analyses of Ramachandran plots of xy-pairs in GxyG and in coil libraries (Ting et al., PLOS CompBiol, 2010, 6, e1000763) using Hellinger distances as a quantitative measure of dissimilarities between Ramachandran distributions. Our analysis reveals that nearest-neighbor effects inferred from the above coil library are much less pronounced than corresponding structural changes observed for GxyG peptides. To determine whether nearest-neighbor induced conformational changes observed for GxyG can be utilized for the analysis of unfolded proteins, we analyzed sets of 3J(HHHα) coupling constants of three different unfolded proteins, namely the 130-residue fragment of the Staphylococcus aureus fibronectin-binding protein (FnBPc), denatured hen lysozyme, and the htau40 protein. For the first two proteins we found statistically meaningful correlations between predicted nearest-neighbor induced changes of 3J(HHHα) and experimentally observed deviations from corresponding coupling constants of GxG peptides in water, which we used as reference system with minimal nearest-neighbor interactions. This observation is in line with the NMR based understanding of these proteins being predominantly statistical coils. For htau40, however, which is known to exhibit residual structure and large deviations form statistical coil expectations, these correlations are weak or absent. Our results thus underscore the importance of nearest-neighbor interactions for a complete physical description of an ideal statistical coil state of a protein.

Thermal Behavior of an Integrated Square Spiral Micro Coil

We present in this paper a study on the thermal behavior of a square micro coil that will be integrated in a DC-DC micro converter. The first, we calculate the value of inductance. The second, we descript our micro coil; dimensioning, electrical model, and formula of loss. A buck micro converter schematic simulation coupled with ideal and integrated micro coil was presented. This conceptual model of the buck is best understood in terms of the relation between current and voltage of the inductor. Finely, we determinate a mathematical expression giving the evolution of temperatures in an integrated micro coil using the separation of variables method and a visualization of the thermal behavior is determined in 2D and 3D space dimension using the finite element method. DOI: http://dx.doi.org/10.11591/telkomnika.v14i2.7361

Development and optimization of hardware for delta relaxation enhanced MRI

Delta relaxation enhanced magnetic resonance (dreMR) imaging requires an auxiliary B0 electromagnet capable of shifting the main magnetic field within a clinical 1.5 Tesla (T) MR system. In this work, the main causes of interaction between an actively shielded, insertable resistive B0 electromagnet and a 1.5T superconducting system are systematically identified and mitigated. The effects of nonideal fabrication of the field-shifting magnet are taken into consideration through careful measurement during winding and improved accuracy in the design of the associated active shield. The shielding performance of the resultant electromagnet is compared against a previously built system in which the shield design was based on an ideal primary coil model. Hardware and software approaches implemented to eliminate residual image artifacts are presented in detail. The eddy currents produced by the newly constructed dreMR system are shown to have a significantly smaller "long-time-constant" component, consistent with the hypothesis that less energy is deposited into the cryostat of the MR system. With active compensation, the dreMR imaging system is capable of 0.22T field shifts within a clinical 1.5T MRI with no significant residual eddy-current fields.