Marcin Ziolkowski

Analysis of the magnetic field in the end region of induction motor

In this paper a useful approach to the analysis of magnetic fields in the end region of induction motors has been shown. There has been applied numerical FEM as well as an analytical approach based on the separation of variables method. The computations have been done in Cartesian and cylindrical coordinates systems.

Solution of three dimensional inverse problem of magnetic induction tomography using Tikhonov regularization method

Magnetic induction tomography, highly promising imaging technique for medical purposes, applies a magnetic field from an exciter to induce eddy currents in the object of low conductivity, and the magnetic field from these is then detected by a sensor. The induced eddy currents are proportional to the conductivity distribution. This paper deals with the solution of the fundamental inverse problem existing in magnetic induction tomography, which consists in the reconstruction of the eddy currents distribution basing on the magnetic field measurements. The problem has been solved by the Tikhonov regularization method. The choice of the regularization parameter and the accuracy of the proposed method have also been discussed.

Genetic algorithm‐based multi‐objective optimization of an exciter for magnetic induction tomography

Purpose – The purpose of this paper is to present the methodology of designing an exciter for magnetic induction tomography (MIT). The design of the exciter must satisfy following requirements: maximize MIT system sensitivity and minimize harmful influence on electronic MIT equipment.Design/methodology/approach – Two objective functions are considered, namely: a magnetic flux density in the protected regions and a module of the eddy current density vector in the object under test in the vicinity of a sensor. The paper demonstrates a multi‐objective optimization technique (based on the e‐constrained method) which, by coupling the finite‐element method with a genetic algorithm (GA), supports the design of the exciter.Findings – It is possible to design in a relatively simple way an exciter for MIT under the given assumptions.Originality/value – The paper is of value in presenting a detailed description of the multi‐objective optimization procedure.

A comparison of two formulations for magnetic field synthesis on a cylindrical solenoid's axis

In various engineering and biomedical disciplines often there is a need to design an electromagnetic arrangement which is able to generate a magnetic field of demanded distribution. Such a problem also takes place in magnetic field active shielding designing. In this case solenoids that generate an opposite magnetic field to the external field in the region of interest are used. This paper discusses the problem of finding the shape of a solenoid which produces a given magnetic field magnitude on the axis. Two different methods are used and compared: iteratively regularized Gauss-Newton method and genetic algorithm based method with the use of Bezier curves.

Shielding From External Magnetic Fields by Rotating Nonmagnetic Conducting Cylindrical Shells

The common strategy for reducing static and low-frequency magnetic fields in a specific region consists of surrounding the volume of interest with a layer of material with high magnetic permeability. However, if for some reasons, ferromagnetic materials are undesirable, rotating conducting nonmagnetic screens could be applied. In this paper, we discuss such a possibility in a quantitative way. Analytical solutions are obtained for infinitely long cylindrical shells rotating in a uniform, static, and time-harmonic external magnetic field. Useful simplified expressions for the shielding factors are given. Numerical results are shown for screens of finite length.

Full wave numerical modelling of terahertz systems for nondestructive evaluation of dielectric structures

Purpose – The purpose of this paper is to describe the full‐wave modelling of pulsed terahertz systems utilized in non‐destructive testing.Design/methodology/approach – At the outset, some basic information on the terahertz NDT are outlined and then, general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness.Findings – It is possible to model in a relatively simple way a terahertz system for nondestructive evaluation of dielectric materials. In contrast to other published work, the entire measuring setup is modelled, including photoconductive antenna with hemispherical lens, focusing lens and evaluated material with exemplary defect.Originality/value – This paper gives a description of the terahertz non‐destructive testing system with comparison of simulated and measured results.

Topology optimization of magnetic field in three-dimensional finite region

This article describes the method of magnetic field topology optimization in an axisymmetric three-dimensional finite region. It is assumed that the region of interest is surrounded by a cylindrical solenoid with an electrical current. The solenoid’s inner and outer surfaces are built-up by rotating plane Bezier curves around the symmetry axis. As a global minimizer a genetic algorithm method is used. Optimal configurations are provided under given constraints.

Optimum exciter design for Magnetic Induction Tomography (MIT)

Purpose – The purpose of this paper is to present the methodology of designing an exciter for Magnetic Induction Tomography (MIT). The design of the exciter must satisfy the following requirements: maximize MIT system sensitivity and minimize harmful influence on electronic MIT equipment.Design/methodology/approach – Two objective functions are considered, namely: a magnetic flux density in the protected regions and a module of the eddy‐current density vector in the object under test in the vicinity of a sensor. The paper shows a multi‐objective optimization technique (based on the weighted sum method) which, by coupling the finite‐element method with a genetic algorithm, supports the design of the exciter.Findings – It is possible to design in a relatively simple way an exciter for MIT under the given assumptions.Originality/value – Detailed description of the multi‐objective optimization procedure has been presented.

Numerical modelling of terahertz systems for nondestructive evaluation of dielectric materials

In this paper we deal with full-wave modelling of pulsed terahertz systems utilized in non-destructive testing. At the outset, some basic information on the terahertz NDT and next general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness.

Analytical and numerical models of the magnetoacoustic tomography with magnetic induction

Purpose Electrical properties of biological tissues are known to be sensitive to physiological and pathological conditions of living organisms. For instance, human breast cancer or liver tumor cells have a significantly higher electrical conductivity than a healthy tissue. The paper aims to the new recently developed magnetoacoustic tomography with magnetic induction (MAT-MI) which can be deployed for electrical conductivity imaging of low-conductivity objects. Solving a test problem by using an analytical method is a useful exercise to check the validity of the more complex numerical finite element models. Such test problems are discussed in Chapter 3. The detailed analysis of an electromagnetic induction in low-conductivity objects is very important for the next steps in the tomographic process of image reconstruction. Finally, the image reconstruction examples for object’s complex shapes’ have been analyzed. The Lorentz force divergence reconstruction has been achieved with the help of time reversal algorithm. Design/methodology/approach In given arrangements the magnetic field and eddy current vectors satisfy the Maxwell partial differential equations. Applying the separation of variables method analytical solutions are obtained for an infinitely long conducting cylindrical segment in transient magnetic field. A special case for such a configuration is an infinitely long cylinder with longitudinal crack. The analytical solutions are compared with those obtained by using numerical procedures. For complex shapes of the object, the MAT-MI images have been calculated with the help of the finite element method and time reversal algorithm. Findings The finite element model developed for a MAT-MI forward problem has been validated by analytical formulas. Based on such a confirmation, the MAT-MI complex model has been defined and solved. The conditions allowing successful MAT-MI image reconstruction have been provided taking into account different conductivity distribution. For given object’s parameters, the minimum number of measuring points allowing successful reconstruction has been determined. Originality/value A simple test example has been proposed for MAT-MI forward problem. Analytical closed-form solutions have been used to check the validity of the made in-house finite element software. More complex forward and inverse problems have been solved using the software.