L. Zilberti

INRIM Istituto Nazionale di Ricerca Metrologica, Torino, Piedmont, Italy

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Publications (27)22.83 Total impact

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    ABSTRACT: This paper investigates the effect of relevant physical parameters on transient temperature elevation induced in human tissues by electromagnetic waves in the terahertz (THz) band. The problem is defined by assuming a plane wave, which, during a limited time interval, normally impinges on the surface of a 3-layer model of the human body, causing a thermal transient. The electromagnetic equations are solved analytically, while the thermal ones are handled according to the finite element method. A parametric analysis is performed with the aim of identifying the contribution of each parameter, showing that the properties of the first skin layer (except blood flow) play a major role in the computation of the maximum temperature rise for the considered exposure situation. Final results, obtained by combining all relevant parameters together, show that the deviation from the reference solution of the maximum temperature elevation in skin is included in the coverage intervals from -30% to +10% at 0.1 THz and from -33% to +18% at 1 THz (with 95% confidence level). These data allow bounding the possible temperature increase against the spread of tissue properties that could be reasonably used for dosimetric simulations. Bioelectromagnetics © 2014 Wiley Periodicals, Inc.
    Bioelectromagnetics 02/2014; · 2.02 Impact Factor
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    ABSTRACT: The paper discusses the application of a hybrid Finite Element–Boundary Element technique to the electromagnetic dosimetric analysis of voxel based human models, with particular attention to the Magnetic Resonance Imaging appliances. A rational organization of the large amount of data involved by the voxel anatomy is presented to reduce the computational burden. The most suitable choice of the unknowns and the possible simplifying assumptions are also investigated. A hybrid Finite Element–Boundary Element approach is derived from the previous considerations, underlining the procedure for the system solution adopted when the whole algebraic matrix exceeds the RAM capabilities. The work is completed with some examples of applications.
    Engineering Analysis with Boundary Elements. 01/2014;
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    ABSTRACT: The electric current densities induced inside a human head by transcranial magnetic stimulations are evaluated through a hybrid finite-element–boundary-element method applied to an anatomical model based on voxel data set. The results of the computational procedure are first validated considering two model problems. Then, the induced E-field within the head of Duke model of the Virtual Family are simulated for two different transcranial magnetic stimulation coils, evaluating the impact of tissue properties variability and model resolution.
    IEEE Transactions on Magnetics 01/2014; 50(2):1033-1036. · 1.42 Impact Factor
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    ABSTRACT: The aim of this paper is the investigation of the numerical properties of the boundary element method (BEM) when applied to dosimetric analysis of human exposure to electromagnetic fields adopting high resolution voxel-based data sets. Some test problems are analyzed considering the neck region of the human body radiated by a loop antenna. Different strategies in the development of the problem equations are proposed and their effects on the conditioning of the BEM matrix are discussed. Several direct and iterative solvers are applied to the model problems and their efficiency is compared.
    IEEE Transactions on Magnetics 01/2014; 50(2):521-524. · 1.42 Impact Factor
  • O. Bottauscio, M. Chiampi, L. Zilberti
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    ABSTRACT: Boundary element and hybrid boundary element—finite element approaches are applied to the computation of induced electric field and specific absorption rate in voxel-based human models undergoing magnetic resonance imaging. Due to the very large size of the algebraic system, the procedure uses an iterative GMRES solver recalculating the element matrix at each iteration. A suitable processing of the Green integrals and a massively parallelized algorithm, based on the use of graphical processing units, leads to a strong reduction of the computational time.
    IEEE Transactions on Magnetics 01/2014; 50(2):1029-1032. · 1.42 Impact Factor
  • Luca Zilberti, Mario Chiampi
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    ABSTRACT: This paper deals with the electric field generated inside the bodies of people moving in proximity to magnetic resonance scanners. Different types of scanners (tubular and open) and various kinds of movements (translation, rotation, and revolution) are analyzed, considering the homogeneous human model proposed in some technical Standards. The computations are performed through the Boundary Element Method, adopting a reference frame attached to the body, which significantly reduces the computational burden. The induced electric fields are evaluated in terms of both spatial distributions and local time evolutions. The possibility of limiting the study to the head without affecting the accuracy of the results is also investigated. Finally, a first attempt to quantify the transient effect of charge separation is proposed.
    Health physics 12/2013; 105(6):498-511. · 0.92 Impact Factor
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    ABSTRACT: We investigated the efficiency in magnetic field mitigation of superimposed MgB2/Fe coaxial cups with cylindrical symmetry, subjected to an applied magnetic field parallel to their axis. The MgB2 cup was grown by a microwave-assisted Mg-liquid infiltration technique in a boron preform. This technique allows obtaining samples with a reduced amount of unreacted magnesium, shape chosen before the growth procedure, and easily scalable sizes. Local magnetic induction measurements were carried out by means of a cryogenic Hall probe mounted on a custom-designed stage moveable along the sample axis with micrometric resolution. The measurements were performed at 20 K and 30 K, in magnetic field up to 1.5 T, as a function of the external source field, of the position and of time. At higher magnetic fields the superposition of the Fe cup on the MgB2 one allows obtaining a shielding efficiency 3-4 times higher than that measured with the single superconducting cup. The magnetic induction relaxation rate is also strongly reduced. On the contrary, a decrease of the shielding efficiency of the hybrid system with respect to the MgB2 cup alone turns out at low magnetic field. Numerical simulations indicate a reduction of this worsening by a protrusion of the superconducting cup above the ferromagnetic one.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):8201305. · 1.20 Impact Factor
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    ABSTRACT: We studied the magnetic shielding properties of a MgB2/Fe hybrid structure consisting of two coaxial cups subjected to a magnetic field applied parallel to their axis. This study was performed to analyze the magnetic shield properties of a system contemporary exploiting the opposite magnetic properties of superconducting/ferromagnetic materials. The MgB2 cup was grown by a microwave-assisted Mg-infiltration technique that allows obtaining samples with different shapes and easily scalable sizes, meeting the requirements of different shielding applications. Measurements of mitigation of the magnetic induction were performed in applied magnetic field up to 1.5 T and in different positions along the cup axis at temperature T = 20 K. A decrease of the shielding factor (SF) of the hybrid system with respect to the MgB2 cup alone turns out at low magnetic field. On the contrary, at higher magnetic field the superposition of the two cups increases the SF of the hybrid system up to 3 times over that one of the single MgB2 cup.
    Journal of Superconductivity and Novel Magnetism 05/2013; 26(5):1513-1516. · 0.70 Impact Factor
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    ABSTRACT: This paper proposes a hybrid experimental-numerical technique, based on the boundary element method, able to reconstruct the magnetic field distribution in the free space outside the unknown field sources, without requiring the onerous process of source identification. The approach is validated by comparison with experimental data considering a Helmholtz coil system, where the connections of the coils and the supply currents can be controlled to generate different spatial distributions of the magnetic field. The presence of materials with high magnetic permeability, also involving eddy currents, is considered as well. An analysis on the reachable accuracy and on the related parameters is developed, with the final aim of obtaining a satisfactory compromise between result accuracy and experimental burden. Finally, the field values reconstructed by the proposed experimental-numerical technique are compared with the measured ones, showing a good agreement.
    IEEE Transactions on Magnetics 03/2013; 49(3):1143-1148. · 1.42 Impact Factor
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    ABSTRACT: The paper investigates the heating of tissues exposed to millimeter and sub-millimeter electromagnetic waves. The problem is faced by assuming a plane wave normally incident to the surface of a layered model of the human body and by solving analytically both the electromagnetic and thermal equations. The effect of a possible variability in the relevant parameters is put in evidence through a specific parametric analysis.
    Electromagnetics in Advanced Applications (ICEAA), 2013 International Conference on; 01/2013
  • Wencui Wang, M. Borsero, L. Zilberti
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    ABSTRACT: This paper introduces a Boundary Element reconstruction method to predict the electromagnetic fields generated by unknown sources. This procedure allows to calculate the field distributions in free space directly from a limited number of measurements carried out on a closed surface which contains all the radiating sources. The accuracy of the proposed procedure has been found to be satisfactory through two tests; the first involves four simple radiating elements, while the second considers a realistic comb generator.
    Electromagnetics in Advanced Applications (ICEAA), 2013 International Conference on; 01/2013
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    ABSTRACT: This paper is focused on the uncertainty estimate of a hybrid experimental-numerical procedure for the evaluation of the electric field induced in a human model radiated by a low-frequency magnetic field produced by unknown sources. The procedure is based on magnetic field measurements in a limited number of points around the field source and makes use of the boundary element method. The uncertainty contribution due to the measurement operations is taken into account by evaluating its propagation through the computational process using a Monte Carlo approach coupled to a discrete numerical technique. The procedure is then applied to the case of a body exposed to the field generated by a Helmholtz coil system. The results show that the relative standard uncertainty of the estimated induced electric field is within a few percent.
    IEEE Transactions on Instrumentation and Measurement 01/2013; 62(6):1436-1442. · 1.36 Impact Factor
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    ABSTRACT: The paper proposes and discusses a boundary element procedure able to predict the distribution of the electric field induced in a human body exposed to a low-frequency magnetic field produced by unknown sources. As a first step, the magnetic field on the body surface is reconstructed starting from the magnetic field values detected on a closed surface enclosing the sources. Then, the solution of a boundary value problem provides the electric field distribution inside the human model. The procedure is tested and validated by considering different non-uniform magnetic field distributions generated by a Helmholtz coil system as well as different locations of the human model.
    Radiation Protection Dosimetry 08/2012; · 0.91 Impact Factor
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    ABSTRACT: This paper focuses on the estimation of the Specific Absorption Rate (SAR) and temperature increase within an irradiated human body, starting from known values of the electric and magnetic fields around the body. The proposed approach, based on the Boundary Element Method (BEM) for the solution of the integrated electromagnetic/thermal problem, uses SAR values provided by the electromagnetic solution as input for the bioheat equation which includes the effects of the metabolic heat and of the blood flow. The validity of the BEM approach is proved in the analysis of a simplified human model by comparison with the results given by a different numerical method.
    IEEE Transactions on Magnetics 02/2012; 48(2):691-694. · 1.42 Impact Factor
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    ABSTRACT: The paper presents a Boundary Element procedure able to predict the emission radiated by unknown sources, starting from the knowledge of the electromagnetic field in a limited number of points placed on a surface surrounding the sources. The proposed approach is tested by analyzing the field distribution obtained as a superposition of the emissions produced by four different radiating elements. The influence of the number of points on the accuracy and the possibility of simplifying the measurement procedure are finally investigated.
    Electromagnetic Compatibility (EMC EUROPE), 2012 International Symposium on; 01/2012
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    ABSTRACT: The paper is focused on the estimate of the uncertainty of the results obtained by a hybrid experimental/numerical procedure for the evaluation of the electric field induced in a human body radiated by a LF magnetic field produced by unknown sources. The procedure is based on magnetic field measurements in a limited number of points around the field source and makes use of the Boundary Element. A method for the evaluation of the uncertainty contributions due to both the measurement process and the use of a discrete numerical technique is presented.
    Precision Electromagnetic Measurements (CPEM), 2012 Conference on; 01/2012
  • O. Bottauscio, M. Chiampi, L. Zilberti
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    ABSTRACT: This paper describes and discusses the use of the boundary element method to reconstruct the induced current density and specific absorption rate (SAR) distribution within a phantom of arbitrary shape, starting from field values on its external surface. The accuracy of the proposed approach is evaluated by comparison with the results given by other techniques in the solution of the whole electromagnetic problem, including also the sources. The influence of the parameters which could affect the reconstruction accuracy is deepened. The encouraging results obtained can open the way to a noninvasive experimental-computational procedure for the SAR evaluation.
    IEEE Transactions on Magnetics 12/2011; · 1.42 Impact Factor
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    ABSTRACT: This paper investigates the possibility of using superconductive elements as passive magnetic shields, in order to mitigate the magnetic field in limited regions around magnetic resonance scanners where medical staff could operate. The analysis is performed through the Finite Element Method by assuming a relative permeability close to zero to simulate the behavior of superconductive materials. Some shielding solutions employing superconductive sheets are proposed, also evaluating the disturbance on the field homogeneity in the center of the superconducting MRI. Possible synergies between the superconductive shields and the ferromagnetic elements, employed as hybrid shields or field concentrators, are finally discussed.
    IEEE Transactions on Magnetics 11/2011; · 1.42 Impact Factor
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    ABSTRACT: This paper proposes a numerical technique, based on the boundary element method, for the reconstruction of the specific absorption rate in 3-D human phantoms. The method intends to relate electric and magnetic field measurements on the surfaces of a virtual box surrounding the considered phantom with the SAR values within the body. After a description of the adopted boundary element approach, an analysis of the influence on the SAR reconstruction accuracy of several parameters, such as size and shape of the virtual box, or position and number of the measurement points, is presented. The effect of the field source and supply frequency is also investigated. Finally, an extension of the approach to non-homogeneous phantoms is discussed.
    Engineering Analysis With Boundary Elements - ENG ANAL BOUND ELEM. 01/2011; 35(4):657-666.
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    ABSTRACT: The thin-shell formulation is applied to a combined finite element-boundary element technique to study the magnetic shielding efficiency of superconducting layers and hybrid superconducting-ferromagnetic sandwich structures in 3-D domains. The behavior of the superconducting material, assumed to be in a Meissner-like state, is here described by the London model. The numerical simulations are validated by comparison with the experimental results obtained for magnesium diboride (MgB2) samples having different shapes (i.e., disk, cup) and immersed in uniform low dc magnetic fields.
    IEEE Transactions on Magnetics 01/2011; 47(10):4266-4269. · 1.42 Impact Factor