Marco Bullo

A Coupled Thermo-Electromagnetic Formulation Based on the Cell Method

Two discrete approaches for 3-D weakly coupled thermo-electromagnetic, magnetically linear, quasi-static problems in bounded domains are presented and compared. Both approaches are based, as far as the electromagnetic equations are concerned, on discrete potentials to model both conducting and nonconducting regions, whereas the thermal problem is solved by direct use of the temperature as unknown. The code implementing the formulations is validated by comparing results with those obtained by a commercial axisymmetric package with similar space and time discretizations.

Isotropic and anisotropic electrostatic field computation by means of the cell method

The Cell Method (CM) is an approach to the numerical solution of field physical problems that has been recently applied to the electromagnetic computation. It is gaining more and more interest as it allows easy formulations based on integral (finite) quantities, with no need to resort to local quantities related by differential equations to be suitably regularized in numerical form. The paper deals with an application of the CM to the solution of electrostatic problems. Two formulations are presented: The first is suitable for isotropic electrostatic media, and the second is specifically suited for the anisotropic ones. The main items of the method and the structure of the two algorithms are described, and some results obtained for reference cases are reported. A comparison is also shown with the results from a first-order finite element method (FEM) algorithm.

Coupled electrical and thermal transient conduction problems with a quadratic interpolation cell method approach

The Cell Method is an approach to the numerical calculation of fields that has been recently applied to the coupled computation of electric and thermal conduction using a linear interpolation of both the electric and temperature fields. In this paper a quadratic interpolation approach is presented. It is aimed at the achievement of an accurate field distribution computation particularly in complex domains such as biological structures. Such condition are encountered in the prediction of the thermal distribution obtained in hyperthermic treatments. Some results for a real case are presented in the paper

Electric field computation and measurements in the electroporation of inhomogeneous samples

Abstract In clinical treatments of a class of tumors, e.g. skin tumors, the drug uptake of tumor tissue is helped by means of a pulsed electric field, which permeabilizes the cell membranes. This technique, which is called electroporation, exploits the conductivity of the tissues: however, the tumor tissue could be characterized by inhomogeneous areas, eventually causing a non-uniform distribution of current. In this paper, the authors propose a field model to predict the effect of tissue inhomogeneity, which can affect the current density distribution. In particular, finite-element simulations, considering non-linear conductivity against field relationship, are developed. Measurements on a set of samples subject to controlled inhomogeneity make it possible to assess the numerical model in view of identifying the equivalent resistance between pairs of electrodes.

A 3D Cell Method Formulation for Coupled Electric and Thermal Problems b)

A formulation is presented for the solution of coupled problems of steady-state electric and transient thermal conductions in three dimensional regions. The model is based on the cell method approach, taking advantages of the very agile algebraic formulations that it can provide for field theories

A 2-D formulation for eddy current anisotropic problems with the cell method

The paper presents a formulation for two-dimensional anisotropic eddy current problems developed both in the time and the frequency domains. It is based on the cell method, that makes use of integral electromagnetic quantities related to each other through algebraic constitutive and structure equations. This formulation directly assembles both the so-called stiffness and mass matrices by means of an inspection approach with no need to use topological incidence matrices, thus providing an agile construction of the fundamental system and requiring to compute only the primal cell complex, not the dual one. The formulation is compared with an equivalent finite element method method based on the Galerkin and Crank-Nicolson schemes, both being used for simulating an experimental induction-heating apparatus.

Efficiency optimization of a two-port microwave oven: a robust automated procedure

Purpose – In the paper, a single-objective optimization problem characterized by high-frequency field analysis is investigated: the optimal design of a two-port microwave (MW) oven, taking into account the possibility of two independently controlled sources, with the aim of improving the efficiency is considered as the case study. The paper aims to discuss these issues. Design/methodology/approach – A high-frequency field analysis has been coupled to a robust evolutionary-computing algorithm in order to create an appropriate procedure for the optimal design of a MW oven based on a cascade optimization: in the first step the optimized geometry has been identified, while in the second step the optimized electrical supply values have been synthesized. In particular, the direct problem has been faced by means of a 3D-FEM approach in order to obtain realistic results; the inverse problem has been faced by means of a derivative-free robust algorithm based on evolutionary strategy in order to get a fast converge...

Electrical resistance in inhomogeneous samples during electroporation

In electrochemotherapy (ECT), electric field is applied by means of needle pairs to the tumor tissue in order to permeabilize cell membranes and, as a consequence, enhance the effects of chemotherapeutic drugs. The target tissue is not homogeneous and the electric field, generated by the needle pairs, is strongly affected by the specific electrical characteristics of different tissues. This paper analyzes the effect of tissue in homogeneity by means of numerical models and suitable experiments.

Effect of tissue inhomogeneity in soft tissue sarcomas: From real cases to numerical and experimental models

Electrochemotherapy is an established treatment option for patients with superficially metastatic tumors, mainly malignant melanoma and breast cancer. Based on preliminary experiences, electrochemotherapy has the potential to be translated in the treatment of larger and deeper neoplasms, such as soft tissue sarcomas. However, soft tissue sarcomas are characterized by tissue inhomogeneity and, consequently, by variable electrical characteristic of tumor tissue. The inhomogeneity in conductivity represents the cause of local variations in the electric field intensity. Crucially, this fact may hamper the achievement of the electroporation threshold during the electrochemotherapy procedure. In order to evaluate the effect of tissue inhomogeneity on the electric field distribution, we first performed ex vivo analysis of some clinical cases to quantify the inhomogeneity area. Subsequently, we performed some simulations where the electric field intensity was evaluated by means of finite element analysis. The results of the simulation models are finally compared to an experimental model based on potato and tissue mimic materials. Tissue mimic materials are materials where the conductivity can be suitably designed. The coupling of computation and experimental results could be helpful to show the effect of the inhomogeneity in terms of variation in electric field distribution and characteristics.

Electroporation of inhomogeneous samples: From conduction field to equivalent resistance

Electrochemotherapy (ECT) is a local therapy used in clinical practice. This therapy improves the drug uptake of tumor tissue since it permeabilizes cell membranes by means of an electric field. Nevertheless, the tumor tissue could be characterized by inhomogeneity areas and needle electrodes could be implanted in tissue with different values of conductivity. The authors investigate by means of numerical simulations and experimental tests the effect of tissue inhomogeneity which can affect the current density distribution.