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Many devices for the smart mobility make use of low frequency magnetic sensors to determine the alignment of the device with respect to the earth field. In highly manned areas, the presence of meaningful disturbance fields must be expected and as much as possible counteracted. Typical sources of disturbances are metallic parts or AC power lines, possibly carrying spurious current harmonics induced by rectifiers. Numerical analysis is hard also when the environment is known since the numerical computation requires meshing of complex 3D structures and non-linear problems resolution. In this paper, a numerical model able to treat, in a fast but accurate way, such complex 3D nonlinear problems is applied to estimate the impact of disturbing fields on the magnetic measurement of the device alignment.

Due to unavoidable tolerances in components construction and assembly, the actual magnetic fi eld in Tokamak devices differs from the nominal one. The experimental studies nowadays available indicate a strong impact of the error fields on the plasma stability in next generation, large size, devices. Therefore, a careful preliminary analysis aimed at evaluating the impact of possible error field sources, to define tolerance ranges and assess the effect of current feeders, was envisaged before realization of ITER reactor. The paper discusses the tools used to perform ITER tolerance analysis, from the viewpoints of two possible approaches to tolerancing, which are statistical analysis and worst case analysis. The two methods aim to get different characterizations of devices performance, and a critical comparison of drawbacks and advantages of both methods is reported. 1. Error fields in tokamaks In magnetic confinement controlled thermonuclear fusion devices (Tokamaks), the confinement ca- pability of the machine is quite sensitive to discrepancies between the nominal magnetic field and the actual one (called "error fields"), resulting from several causes including non axi-symmetric sources (e.g. current leads for superconducting magnets) and mechanical inaccuracies in the manufacturing and assembly of magnets. The error fields are by their intrinsic nature quite complex to describe; an effective tool for their quantitative analysis is the Fourier toroidal and poloidal decomposition of normal field component on the nominal plasma surface at the start of flat top, when the impact of error fields is the highest. Experimental studies (1) have shown that only some specific Fourier components have the highest impact on plasma confinement. With reference to ITER Tokamak, the Three Modes Error Index (TMEI) hasbeenintroducedasaneffectiveindexto describetheamountoferrorfieldsinthethreemodesrelevant for confinement, namely field harmonic m = 2, n = 1 - with toroidal periodicity index n equal to one and poloidal periodicity index m equal to two - and the two side bands m = 1, n = 1a ndm = 3, n = 1. TMEI is based on the weighted average of normalized mode coefficients, that must remain below the fixed threshold of 5 × 10 −5 to guarantee expected performance (2)

Magnets for Nuclear Magnetic Resonance applications are designed to provide high level of magnetic flux density in a testing volume with the greatest level of field homogeneity. Anyway, the manufacturing and assembly tolerances cause unavoidable uniformity degradation, that is usually counteracted by correction coils. The measurement of the magnetic field is the final verification of the complex design and fabrication process of a magnetic system, aimed also at defining currents in correction coils to improve uniformity. Anyway, when seeking high accuracy, it is necessary to assess the effect on final uniformity of uncertainties in the measurement technique. In this paper, an approach is presented to assess impact of measurement error bars on final device performance, based on Worst Case Analysis, guaranteeing quick computational time.

PurposeThe purpose of this paper is to evaluate the performances of a resolution scheme able to follow the dynamics of brain tissue properties in combined ElectroEncefaloGraphic (EEG) – MagnetoEncefaloGraphic (MEG) techniques for the brain analysis, minimizing the computation burden.Design/methodology/approachThe estimation process in combined EEG‐MEG is performed by a Moore‐Penrose pseudo‐inverse computation. This is affected by the uncertain knowledge of the living tissues' electric properties. In principle, it is possible to estimate those properties from the EEG‐MEG signals. The estimation process becomes in this case non‐linear. A resolution scheme is proposed, based on the exploitation of the different dynamics characterizing sources and tissues properties.FindingsThe proposed resolution scheme provides a reasonable estimate of the sources for a computationally affordable frequency of non‐liner estimations.Research limitations/implicationsThe proposed approach has not been tested yet on experimental data, and as such, its sensitivity to environmental uncertainty is not known yet.Practical implicationsThe proposed strategy can be easily implemented to perform realistic measurement processing.Originality/valueThe paper presents a novel strategy to estimate tissues properties and EEG‐MEG signal sources based on the exploitation of their different dynamics, possibly taking advantages from an impedance tomography preliminary analysis for the tissue properties dynamics.

PurposeThe purpose of this paper is to present a new approach to drive the excitation field sources in the eddy current testing (ECT) of tubular conductive structures.Design/methodology/approachThe magnetic field used for ECT is generated by pairs of counter‐series connected coils, driven by AC currents. The phase and amplitude of the currents is electronically controlled in order to shape the primary field map, allowing circumferential sweeps until the presence of defects is detected, and then “focusing” the field on the defective section of the tube, increasing in this way the sensibility of the ECT probes in the targeted area, in order to determine with higher precision, the position, and the shape of the defect.FindingsIf suitably designed, the field measurement system allows to enable/disable a number of probes to enhance the resolution in the defect area while keeping low the number of required data channels.Research limitations/implicationsThe analyzed geometry is limited to circular‐shaped tubes, of infinite extent. Future work should be on the extension of the methodology to general shapes, and to finite length cylinders.Practical implicationsThe proposed method allows to enhance resolution in ECT of tubes at the end of production lines, guaranteeing a first, simple yet effective quality assessment of tubes in industrial environments.Originality/valueThe paper presents a new technique to test conductive tubes using fixed excitation system, but allowing to focus magnetic field in defective regions. The method could be helpful for industrial diagnostics.

PurposeThis paper seeks to describe an approach to multi‐objective optimization problems (MOOPs) based on game theory (GT) and to provide a comparison with the more standard Pareto approach on a real design problem.Design/methodology/approachThe GT is first briefly presented, then a possible recasting of MOOPs in terms of GT is described, where players from GT are associated with single objectives and strategies to the choice of degrees of freedom. A comparison with the Pareto approach is performed on the optimized design of a superconducting synchronous generator.FindingsIt was shown that the GT can be applied to the optimized design of real world devices, with results that present a different viewpoint on the problem, yet with device performance comparable with those obtained by standard approaches.Research limitations/implicationsOnly the Nash approach to non‐cooperative games has been applied; the conditions for the solution found using GT to belong to the Pareto front have not been fully explored.Practical implicationsDesigners and engineers interested in optimal design are presented with a new design technique able to get a balance among conflicting partial objectives, that can also be used to select among different possible designs obtained in other ways (e.g. using the Pareto front approach).Originality/valueThe paper demonstrates the possibility of using GT in the design of real world electromagnetic devices, with reference to the optimal shape design of a high temperature superconducting single‐phase synchronous generator.

Power transformers based on High Temperature Superconductors (HTS) technology are an appealing promise for several practical applications. The present designs still leave wide margins of possible improvement in terms of both layout optimisation and introduction of new technologies. In the framework of a technical-scientific cooperation among scientific and industrial subjects, a 10 kVA single-phase transformer was designed and manufactured, using copper for primary windings and BSCCO-2223 HTS tape for secondary windings. The layout has been optimized taking into account the particular characteristics of BSCCO tapes, in particular their AC losses, and the usual figures (stray flux, Joule and iron losses, weight and overall footprint) considered in transformers design. The prototype has then been realized and characterized, using general as well as specific tests. The performance of the device has been evaluated and compared with numerical calculation. In the paper, an overview of the device design and manufacturing will be presented, together with a critical comparison between computed and measured performance.

The identification of plasma parameters from different sets of measurements is a key topic in the thermonuclear fusion research. Most of the information relevant to the plasma shape and position control is usually gained via external magnetic measurements, but information related to internal distribution of current density is not accessible in this way. Other possible measurements are available. In this paper a performance analysis is done with respect to the adoption of polarimetric measurements.

Purpose - The paper aims to illustrate a numerical technique to calculate fields and inductances of rotating electrical machines. Design/methodology/ approach - The technique is based on an integral formulation of the nonlinear magnetostatic model in terms of the unknown magnetization. The solution is obtained by means of a Picard-Banach iteration whose convergence can be theoretically proved. Findings - The proposed method has been used to build a model of a large turbine generator. In particular, the influence of end effects on flux linkages has been computed. It has been demonstrated that the 2D solution underestimates the flux linkages as well as the no load voltage of 2 per cent, while the leakage fluxes are computed by the 2D solution with errors as high as 20 per cent. Originality/value - The method is advantageous in comparison to standard methods.

The paper proposes an optimization procedure suited to design the shape and the current feed of active coils. A suitable spline-based basis is used for the coil geometry modeling, based on a rather limited number of optimization parameters. In order to simplify the constraints treatment, a set of knot points are introduced, linked with the design degrees of freedom.

Browse Conference Publications > Electromagnetic Field Computa ... Flexible measures in magnetic Active Shielding .This paper appears in: Electromagnetic Field Computation (CEFC), 2010 14th Biennial IEEE Conference on Date of Conference: 9-12 May 2010 Author(s): Formisano, A. Dip. Ing. dell'Inf., Seconda Univ. di Napoli, Aversa, Italy Lupoli, M.C. ; Martone, R. Page(s): 1 Product Type: Conference Publications 5481633 searchabstract .Abstract The reduction in protected regions of low frequency magnetic fields is a complex problem when the sources are not known. The paper proposes a procedure able to choose the best currents able to mitigate the disturbance field. The magnetic field is represented by suitable series of eigenfunctions in the domain of interest. The procedure includes a field identification step starting from a set of measurements and a current design step, possibly based on a preliminary design of specialized shimming coils sets.

The optimal design of electromagnetic devices is often performed by balancing conflicting objectives, including performance and other relevant quality figures such as cost and robustness. The balance of conflicting partial objectives can be tackled with the Pareto approach. Unfortunately, assessment of robustness typically implies a relevant increase in the computational cost of optimization procedures; in the paper, it is proposed an approach allowing to include robustness in Pareto optimization with a reduced increase in the computational cost.

Purpose – The purpose of this paper is to propose the optimal allocation and alignment of probes for current distribution measurement (CDM) in the case of twin cable in conduit conductor (CICC) cables with equal and opposite current. Design/methodology/approach – The most effective approach to CDM in CICC cables is to perform indirect measurements starting from magnetic field map measured externally to the cable. A number of approaches have been proposed to optimize the layout of magnetic field probes external to the cable, but all dealing with single cables. In this paper, an approach to the optimized design of measurement system for twin cables will be proposed, based on the minimization of a suitable cost function. Findings – A method for the optimal allocation of probes both in terms of rejection of the background field and of condition number of the Green matrix has been defined. Research limitations/implications – The method is valid only in the hypothesis of linear relationship between currents and magnetic field. Practical implications – The proposed approach allows to design more robust CDM systems, with increased noise and background field rejection capability. Originality/value – The problem of optimal design of CDM systems has been previously tackled in literature, but typically with reference to single cables. In the paper, an approach able to explicitly deal with twin cables is proposed.

Air-core superconducting transformers incorporate the function of shunt reactors, thus they can be used in high- voltage high-capacity applications. They result lighter than their traditional counterpart while requiring heavy metallic shields. However they may represent an effective alternative to traditional transformers only if the weight and clearance reduction is accompanied by acceptable values of magnetizing current and leakage fluxes. The reduction of the leakage fluxes allows the reduction of the metallic shield size leading to an enhancement of the weight advantage. In addition the value of the mutual inductance should fit the shunt reactor action requirement. These objectives can be achieved by the active shielding technique. The paper proposes to properly design both the transformer and its active shield by means of a combined optimization stochastic algorithm. The procedure outlined is applied to a three-phase transformer layout.

PurposeTo present a robust optimal design technique in the presence of system parameters uncertainties.Design/methodology/approachThe properties of normally distributed random variables are exploited, together with surface response fitting techniques, with the aim to reduce the computational cost in assessing the effect of uncertainties.FindingsA fast approximate method for computing statistical average is presented together with its implementation for the design of magnets for magnetic resonance imaging.Research limitations/implicationsFuture research will be focused to multi‐dimensional problems and to the best choose of closed form expressions to evaluate statistical moments fitting.Practical implicationsRobust optimal design methodologies are receiving an increasing interest in both academic and industrial research, due to their capability of coping with construction uncertainties and tolerances.Originality/valueThe effectiveness of the simplified method has been demonstrated for an analytical example and on a simplified superconducting magnet design. The proposed strategy is quite general and it can be applied to a wide class of optimal design problems.

PurposeElectrical resistive tomography (ERT) is a non‐destructive testing technique based upon the reconstruction of the electrical conductivity profile inside a body from measurement made on its boundary. In the literature about the inverse problems the ERT is considered still challenging being both non‐linear, ill‐posed and very limited in resolution. Purpose of the paper is to assess the performances of an approach exploiting the circuital behaviour of a particular class of problems, highlighting its advantages in terms of simplicity and reduction of the computer burden.Design/methodology/approachIn this paper, an electrical property of a particular class of problems is pointed out; the same property is used to formulate in terms of a circuital model the ERT problem. The proposed methodology consists basically of combining properly simplified data previously evaluated and collected. The overall procedure is presented with reference to an underground structure diagnostics problem.FindingsThe effectiveness of the proposed approach has been evaluated quantitatively by comparing the simplified procedure results with the ones obtained by performing fully 3D FEM analysis.Originality/valueThe consistently low errors obtained state the convenience of the method also taking into account that the reconstruction process consists merely in post‐processing previously collected data.