Stanislaw Gratkowski

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.

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.

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.

Shielding from external magnetic fields by rotating magnetic 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.