Riccardo Scorretti

Identification of Jiles–Atherton Model Parameters Using Particle Swarm Optimization

This paper presents the use of the multiobjective particle swarm optimization (PSO) technique for the identification of Jiles-Atherton model parameters. This approach, implemented for the first time in order to solve this kind of problem, is tested for two magnetic materials: NO 3% SiFe and NiFe 20-80. The results are compared with those obtained with a direct search method and a genetic algorithm procedure. Experimental measures performed on both samples of materials allow us to complete and argue the validation for the PSO method.

Electromagnetic fields and human body: a new challenge for the electromagnetic field computation

The electromagnetic fields have a great influence on the behaviour of all the living systems. The as low as reasonably achievable (ALARA) principle imposes, in case of long exposures to low (i.e. power systems) or high frequency (i.e. microwave systems or cell phones) fields, some limitations to the radiated fields by the industrial equipment. On the other hand, some benefits can be taken from the effects of the electromagnetic fields on the living being: the hyperthermal technique is well known for the treatment of the cancer. Either we want to be protected from the fields, or we want to take benefit of the positive effects of these fields, all the effects thermal as well as genetic have to be well known. Like in any industrial application, the electromagnetic field computation allows a better knowledge of the phenomena, and an optimised design. Hence, there is a very important challenge for the techniques of computation of electromagnetic fields. The major difficulties that appear are: (1) related to th...

Speech auditory brainstem response (speech ABR) characteristics depending on recording conditions, and hearing status An experimental parametric study.

Speech elicited auditory brainstem responses (Speech ABR) have been shown to be an objective measurement of speech processing in the brainstem. Given the simultaneous stimulation and recording, and the similarities between the recording and the speech stimulus envelope, there is a great risk of artefactual recordings. This study sought to systematically investigate the source of artefactual contamination in Speech ABR response. In a first part, we measured the sound level thresholds over which artefactual responses were obtained, for different types of transducers and experimental setup parameters. A watermelon model was used to model the human head susceptibility to electromagnetic artefact. It was found that impedances between the electrodes had a great effect on electromagnetic susceptibility and that the most prominent artefact is due to the transducers electromagnetic leakage. The only artefact-free condition was obtained with insert-earphones shielded in a Faraday cage linked to common ground. In a second part of the study, using the previously defined artefact-free condition, we recorded speech ABR in unilateral deaf subjects and bilateral normal hearing subjects. In an additional control condition, Speech ABR was recorded with the insert-earphones used to deliver the stimulation, unplugged from the ears, so that the subjects did not perceive the stimulus. No responses were obtained from the deaf ear of unilaterally hearing impaired subjects, nor in the insert-out-of-the-ear condition in all the subjects, showing that Speech ABR reflects the functioning of the auditory pathways.

A survey of parallel solvers for the finite element method in computational electromagnetics

This paper presents new trends in parallel methods used to solve finite element matrix systems: standard iterative and direct solving methods first, and then domain decomposition methods. For example, the current status and properties of two prevailing programming environments (PVM and MPI) are finally given and compared when implemented together with a finite element time domain formulation.

Thermal activation of rupture and slow crack growth in a model of homogeneous brittle materials

Slow crack growth in a model of homogeneous brittle elastic material is described as a thermal activation process where stress fluctuations allow to overcome a breaking threshold through a series of irreversible steps. We study the case of a single crack in a flat sheet for which analytical predictions can be made, and compare them with results from the equivalent problem of a 2D spring network. Good statistical agreement is obtained for the crack growth profile and final rupture time. The specific scaling of the energy barrier with stress intensity factor appears as a consequence of irreversibility. In addition, the model brings out a characteristic growth length whose physical meaning could be tested experimentally.

Failure time in the fiber-bundle model with thermal noise and disorder.

The average time for the onset of macroscopic fractures is analytically and numerically investigated in the fiber-bundle model with quenched disorder and thermal noise under a constant load. We find an implicit exact expression for the failure time in the low-temperature limit that is accurately confirmed by direct simulations. The effect of the disorder is to lower the energy barrier.

Modeling of induced current into the human body by low-frequency magnetic field from experimental data

The induced currents into the human body by a low-frequency magnetic field are computed using three-dimensional finite elements and a special /spl phi/-A formulation. This magnetic field is generated by a real (possibly unknown) power system. The stray field is characterized by an equivalent multipole, fitted from some local measurements of the field, which is a good compromise between accuracy and number of degrees of freedom. The methodology is validated on a test-device using the software FLUX3D.

Computation of the induced current density into the human body due to relative LF magnetic field generated by realistic devices

A three-dimensional finite-element formulation to compute induced currents into the human body due to relative low-frequency magnetic field is described. Magnetic source field and induced currents are computed separately, allowing to handle sources due to realistic devices. This method is validated using analytical solutions over a sphere. The limit of validity of the formulation is established. Computations using an accurate model of the human body are presented.

Stochastic Uncertainty Quantification of Eddy Currents in the Human Body by Polynomial Chaos Decomposition

The finite element method can be used to compute the electromagnetic fields induced in the human body by environmental extremely low frequency (ELF) fields. However, the electric properties of tissues are not precisely known and may vary depending on the individual, his/her age and other physiological parameters. In this paper, we account for the uncertainties on the conductivities of the brain tissues and spread them out to the induced fields by means of a nonintrusive approach based on Hermite polynomial chaos, with the finite element method as a black box. After showing the convergence of the method, we compute the probability to be over the thresholds defined by the international guidelines for limiting exposure to electromagnetic fields published by ICNIRP.

Numerical Dosimetry of Induced Phenomena in the Human Body by a Three-Phase Power Line

We computed by finite element the fields induced in an heterogeneous model of the human body by both the electric and magnetic field generated by a three-phase power line. Results were partially validated and analyzed by comparison with existing data with uniform magnetic field. Induced currents due to both E and B were developed inside the body in an asymmetrical manner.