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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.

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.

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.

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.

A balanced armature receiver (BAR) as a special type of electromagnetic acoustic transducers plays a significant role in reproduction of music and speech, active noise control in modern hearing aid and in contemporary in-ear monitors. This paper aims to present a static analysis of the balanced armature receiver based on the lumped network approach (LNA) and the finite element method (FEM).

In this paper, the LNA and two-dimensional FEM are applied to model deflections of the BAR’s armature from the equilibrium position. Results of calculations are compared with measurements.

The derived analytical formulas and developed procedure allow for calculation of the armature deflection.

Comparing to the previous papers, the reluctance’s nonlinearity of the armature has been considered.

This article has been withdrawn as it was published elsewhere and accidentally duplicated. The original article can be seen here: 10.1108/02644400910985206. When citing the article, please cite: Ryszard Palka, Stanislaw Gratkowski, Krzysztof Stawicki, Piotr Baniukiewicz, (2009), “The forward and inverse problems in magnetic induction tomography of low conductivity structures”, Engineering Computations, Vol. 26 Iss: 7, pp. 843 - 856.

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.

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.

It is possible to design in a relatively simple way an exciter for MIT under the given assumptions.

Detailed description of the multi‐objective optimization procedure has been presented.

This paper presents ‘infinite’ finite elements for magnetic field problems with open boundaries in r‐z and r‐φ geometries. The formulations of the elements are so simple that closed‐form expressions for the element matrix are obtained. In order to test the new elements, simple examples, for which analytical solutions exist, are analysed.

This paper describes numerical tests for a three dimensional infinite element suitable for finite element modelling of open boundary field problems. The infinite element has four nodes and is compatible with conventional cuboids. The effectiveness of the infinite element in the interior — finite element region is shown by comparing the accuracy and the CPU time when various boundary conditions are applied. The possibility of computing the external fields is also illustrated.

In many different engineering fields often there is a need to protect regions from electromagnetic interference. According to static and low-frequency magnetic fields the common strategy bases on using a shield made of conductive or ferromagnetic material. Another screening technique uses solenoids that generate an opposite magnetic field to the external one. The purpose of this paper is to discuss the shielding effect for a magnetic and conducting cylindrical screen rotating in an external static magnetic field.

The magnetic flux density is expressed in terms of the magnetic vector potential. Applying the separation of variables method analytical solutions are obtained for an infinitely long magnetic conducting cylindrical screen rotating in a uniform static transverse magnetic field.

Analytical formulas of the shielding factor for a cylindrical screen of arbitrary conductivity and magnetic permeability are given. A magnetic Reynolds number is found to be an appropriate indication of the change in magnetic field inside the screen. Useful simplified expressions are presented.

This paper treats in a qualitative way the possibility of static magnetic field shielding by using rotating conducting magnetic cylindrical screens. Analytical solutions are given. If the angular velocity is equal to zero or the relative permeability of the shield is equal to one the shielding factor has forms well known from literature.