Sandor Bilicz

Budapest University of Technology and Economics · Department of Broadband Infocommunicatons and Electromagnetic Theory

Litz wires consist of many individual, isolated conductor strands. Certain litz wires are fabricated by simply twisting the bundle of strands, hence a wire pitch is realized. In this paper, the ac resistance of coils made of such twisted litz wire are calculated by combining two-dimensional finite element simulation and circuit laws. In so doing, t...

The wall, made of ferromagnetic steel, of a nuclear reactor pressure vessel is covered by an austenitic (very weakly ferromagnetic) cladding. In this work, we investigated how the base material and the cladding can be inspected separately from each other by nondestructive magnetic measurements. It was found that with the proper choice of the magnet...

Purpose The purpose of this paper is the development of an analytic computational model for electromagnetic (EM) wave scattering from spherical objects. The main application field is the modeling of electrically large objects, where the standard numerical techniques require huge computational resources. An example is full-wave modeling of the human...

Purpose The purpose of this paper is performing a global sensitivity analysis for automotive electromagnetic compatibility (EMC) measurements related to the CISPR 25 setup in order to examine the effect of the setup uncertainties on the resonance phenomenon. Design/methodology/approach An integral equation formulation is combined with Darwin model...

Inverse scattering problems can be seen as an optimization problem in which a cost function has to be minimized. The cost function measures the discrepancy between a physical model written as a function of the sought parameters and the measured data. Due to the high computational cost of physical models, metamodels (also known as surrogate models)...

Darwin model is a reduced form of the Maxwell’s equations, where radiations are neglected, while inductive, resistive and capacitive effects are still taken into account. In this paper we propose a method for the efficient modeling of electrically long, thin wires using a Darwin-based integral equation approach, thus keeping the number of DoFs and...

The inverse problem of electromagnetic (EM) non‐destructive testing (NdT) consists of reconstructing material defect parameters invoking EM field measurements. Uncertainties of the configuration (e.g. imprecise constitutive and geometrical parameters) are inevitably present; hence, the reconstructed defect parameters are also uncertain. In this stu...

In this paper, we investigate a novel iterative antenna array synthesis method. The method is based on the iterative addition of antenna array elements. After defining the synthesis algorithm, we prove that the discrepancy between the goal and the synthesized pattern converges to the theoretical lower bound in the sense of a certain norm. The algor...

The subdomain perturbation (SDP) finite-element (FE) method is a very efficient numerical technique and it speeds up the analysis of magneto- and electroquasi-static problems significantly. In order to solve quasi-static Darwin models, the authors have recently developed a low-frequency stable FE A-V formulation that incorporates both capacitive an...

Purpose The purpose of this study is to introduce a novel method for the measurement of electromagnetic material parameters. Design/methodology/approach The main idea behind the approach is the fact that for slabs with elongated shapes, the intensity of the backscattered field and the electromagnetic resonance frequency corresponding to the length...

Integral equation (IE) methods have recently been proposed for the modeling of inductively coupled resonant wireless power transfer. These approaches usually result in a low number of degrees of freedom. However, their applicability is mostly limited to homogeneous background media. In the present contribution, integral formulations are extended to...

An efficient method is proposed for the numerical simulation of the bundle-level skin effect and its consequences arising in certain types of litz wires. The method is based on a probabilistic approach. The theory presented allows characterization of the repartition of currents between bundles and predicts some unexpected unique features. The metho...

Magnetic flux simulations were utilized in a novel magnetic measurement method performed for the detection of local thinning of ferromagnetic plates. It was shown by numerical simulation, how parameters affect detectability of the defects. Linear relationship was found between the evaluated parameters and size of the artificial slot. Good correlati...

The change in the two-port parameters of a wireless power transfer (WPT) chain is evaluated when an object (foreign object) with given material parameters is placed in the vicinity of the WPT transmitter and receiver. An integral formula for the change of the two-port parameters due to the presence of a foreign object has been derived by using the...

An integral equation method is used for the modeling of electromagnetic scattering from a rotating propeller, of which the length is about half a wavelength. This provides a convenient way of calculating its backscattering spectrum that is useful, for example, when radar detection capabilities are studied. This theoretical model is used to predict...

The magnetic flux density in the magnetizing coil during the hysteresis measurement was calculated. The influence of a slot, machined in a ferromagnetic plate was simulated. The size of the magnetizing yoke was changed and the influence of this modification was studied on the detectable flux density. The size of the slot and the thickness of the ai...

A full-wave surface integral equation method is used for modeling coils in a wide frequency range. This is of high importance in the analysis of resonant wireless power transfer (WPT) links, for example. The paper presents a non-local generalization of the impedance boundary condition concept by incorporating a 2D model (using the finite element me...

Purpose The electromagnetic modeling of inductively coupled, resonant wireless power transfer is dealt with. A numerically efficient simulation method is presented in this paper. Design/methodology/approach Recently, integral equation formulations have been proposed, using piecewise constant basis functions for the series expansion of the curren...

A full-wave integral equation scheme for modeling resonant coils applied in wireless power transfer systems is presented. An A − formulation is applied with current and charge densities on the wire surface as unknowns. The method overcomes the limitation of the “thin-wire approximation” as it enables the unknowns to vary on the wire surface. Thus,...

In Non-Destructive Testing, model selection is a common problem, e.g, to determine the number of defects present in the inspected workpiece. Statistical model selection requires to approximate the marginal likelihood also called model evidence. Its numerical approximation is usually computationally expensive. Nested Sampling (NS) offers a good comp...

In this paper, the uncertainty of electric properties of wireless power transfer systems due to uncertain geometric design parameters is analyzed. An electromagnetic simulation tool, based on an integral formulation, is coupled with a stochastic method that quantitatively determines the contribution of each uncertain design variable to the output u...

Sparse grids make possible the interpolation-based approximation of the output of computer experiments, even for a high number of independent input parameters. In this contribution, the sparse grid interpolation technique is shown to apply well to eddy-current non-destructive testing and simulations thereof. Once such interpolation is obtained –bei...

Purpose – The purpose of this paper is to discuss a numerically efficient simulation method for the study of the high-frequency behaviour of air-cored coils. The self-resonance phenomenon of coils can be studied which is important, e.g., in wireless power transfer (WPT). Design/methodology/approach – A full-wave and a quasi-stationary integral f...

A conductor moving in a stationary magnetic field often rises crucial issues at the courses on electromagnetics for electrical engineering students. The correct use of Faraday's induction law can sometimes be harder than one would think for the first sight. In this paper, we revisit two simple examples of eddycurrents by means of numerical field co...

A sparse grid surrogate model (or metamodel) is proposed to reduce the computational time involved by accurate electromagnetic (EM) simulators. Sparse grids have already been used in many applications for interpolation and integration. The method can treat a high ber of independent parameters that are intractable for many other techniques due to th...

With resonant WPT (wireless power transfer) systems in operation, objects and/or humans having divers material properties come into the vicinity of the resonant coils. To model such systems efficiently a novel full-wave multi-solver is developed where the TVFE (tangentially continuous vector finite element) method is coupled with a MoM (method of m...

A full-wave integral formulation has recently been proposed for the simulation of magnetically coupled resonant wireless power transfer (WPT) arrangements in homogeneous medium. In this paper, the formulation is extended to the case where two different types of dielectrics are separated by a planar interface. This configuration has extensive practi...

The aim of this paper is, on one hand, to give an overview of the fast developing and diversified field of wireless power transfer (WPT) from the point of view of the inevitable numerical modeling of electromagnetic fields. On the other hand, we propose a fast method by which the full WPT system based on inductive resonant coupling (IRC) can be ana...

In this contribution, the inverse problem of electromagnetic nondestructive evaluation is targeted. The inverse problem is formalised as an optimisation task which is to be performed over a small number of parameters of a defect model, in order to fit the simulated data to the measurement as much as possible. A well-known drawback of this classical...

Typical Pulsed Eddy Current Testing (PECT) signals, resulting from the inspection of canonical structures affected by flaw(s), consist in magnetic field variations above the conductor or in coil impedance change, both as functions of time. Calculation of specimen response to Time-Dependent (TD) excitation signals can be obtained through an inverse...

Purpose – The purpose of this paper is to present a novel eddy-current modeling technique of volumetric defects embedded in conducting plates. This problem is of great interest in electromagnetic non-destructive evaluation and has already been exhaustively studied. Design/methodology/approach – The defect is modeled by a volumetric current dipole...

The inverse problems of electromagnetic nondestructive testing are often solved via the solution of several forward problems. For the latter, precise numerical simulators are available in most of the cases, but the associated computational cost is usually high. Surrogate models (or metamodels)—which are getting more and more widespread in electroma...

We present a new method for forest characteristics inversion, based on a surrogate model derived from a full wave electromagnetic simulator using kriging techniques. To illustrate the feasibility of this method, we consider a simple configuration for the forest and we use the polarimetric backscattering coefficients to retrieve both the age of the...

Electromagnetic Nondestructive Evaluation (ENDE) is applied in various industrial domains for the exploration of hidden in-material defects of structural components. The principal task of ENDE can generally be formalized as follows: an unknown defect affects a given host structure, interacting with a known electromagnetic field, and the response (d...

A classical way to solve the inverse problem of defect characterization is to construct an iterative loop which tries to achieve the best resemblance between the measured data and the output of an appropriate simulator of the considered experiment. If the similarity of these signals is best, one can say that a solution for the defect characterizati...

Eddy-current testing (ECT) is a widely used nondestructive evaluation technique. The numerical simulation of ECT methods involves high complexity and computational load. However, one needs reliable solutions (within a reasonable CPU time) for these problems to be able to solve the related inverse problem. One possible approach is to build a configu...

In this paper, the characterization of electromagnetic inverse problems is addressed. As it is well known, an inverse problem can be ill-posed, i.e., its solution is not necessarily unique and might be quite sensitive to the measured data. To characterize such an inverse problem a combination of a surrogate model -based on an optimal database- and...

Accurate numerical simulation of Eddy-Current Testing (ECT) experiments usually requires large computational efforts. So, a natural idea is to build a cheap approximation of the expensive-to-run simulator. This paper presents an approximation method based on functional kriging. Kriging is widely used in other domains, but is still unused in the ECT...

Metamodeling is getting more and more widespread in the domain of electromagnetics to replace the often computationally expensive, time-consuming numerical simulations. This paper presents a novel method of metamodeling based on the kriging interpolation. The input-output function (realized by a numerical simulator) is interpolated using a set of o...

Numerical methods are used to simulate mathematical models for a wide range of engineering problems. The precision provided by such simulators is usually fine, but at the price of computational cost. In some applications this cost might be crucial. This leads us to consider cheap surrogate models in order to reduce the computation time still meetin...

One of the main challenges in Eddy Current Testing (ECT) is the solution of the inverse problem, i.e., the determination of the defect properties knowing the measured data. To this end, many approaches and mathematical tools have been proposed. The so-called adaptive database-method has recently been developed. Its main idea is to store correspondi...

In this paper, we apply a fast method using an optimal database to estimate the impact of some radar sensor characteristics on two quantities: the polarimetric scattering coefficient and the interferometric height of the forested area under study.

Purpose - The purpose of this paper is to provide a new methodology for the characterization of a defect by eddy-current testing (ECT). The defect is embedded in a conductive non-magnetic plate and the measured data are the impedance variation of an air-cored probe coil scanning above the top of the plate. Design/methodology/approach - The inverse...

This paper presents an inverse problem methodology in the domain of non-destructive testing, and more precisely eddy-current testing. Our objective is to use a precise but expensive-to-evaluate model of the electromagnetic induction phenomenon in a conductive material and to estimate the characteristics of a flaw by minimization of a regularized cr...

This paper presents an inverse problem methodology in the domain of non-destructive testing, and more precisely eddy-current testing. Our objective is to use a precise but expensive-to-evaluate model of the electromagnetic induction phenomenon in a conductive material and to estimate the characteristics of a flaw by minimization of a regularized cr...

The accurate numerical simulation of the eddycurrent testing (ECT) experiments usually requires large computational efforts. To avoid the time-consuming computations, the idea – which is new in the domain of ECT –of using databases appeared recently. The database consists of well-chosen pairs of input-output samples of a specified ECT experiment. O...