Rauno Gordon

Model of an inductive sensor of cardiac activity attached to patient

An electric circuit model describing an inductive sensor of cardiac mechanical activity in its working condition has been developed. The sensor comprises a single-turn coil which is fed by 7.7 MHz constant current and induces probing eddy currents in the body. The inductor is considered to be attached to the thoracic surface of a normal human male, in front of the heart. A simple axial-symmetric model of the thorax, formed of tightly packed circular current tubes, has been used to calculate the resistances, self-inductances and mutual inductances within the human body. Then the inductor and the eddy currents in the body were reduced to a system of two inductively coupled coils; estimates of the parameters and frequency response of the system have been found; the active and reactive contributions of the human body to the resulting impedance of the inductor were calculated.

An overview of the impedance models of the thorax and the origin of the impedance cardiography signal for modelling of the impedance signals

This paper presents our work in the search for a realistic thorax impedance model that is suitable for the simulation of an impedance cardiography (ICG) signal model. The developed ICG signal model would be useful to evaluate the performance of e.g. algorithms for the separation of cardiac and respiratory signals. Five different impedance models of the thorax were studied to evaluate their suitability with respect to the development of the ICG signal model. We found out that none of the models would be accurate enough to imitate the real human thorax phenomena in the context of ICG. In addition, we also reviewed the generation of (bio-) impedance signal in order to understand the origin of the ICG signal waveform. It is found that although a consensus exists in the scientific community, several researchers have expressed doubts about the generally admitted origin of impedance signal waveform. The present study concludes that the ICG signal model could be mathematically derived from measured electrical bio-impedance (EBI) data obtained with a specific electrodes configuration.

Multi-electrode arc furnace technology with improved metal processing capability using current driven mixing

This paper presents a finite element solution for three-dimensional isothermal flow for DC arc furnace where low frequency AC component is added. Electrodes of the furnace are connected with independent supply sources. Current densities, magnetic flux densities, force densities and flow of molten metal are investigated in the case of two different furnace constructions. Methodology for supply source control described in this paper can be used in industrial applications for mixing molten metals or other conductive liquids.

Simulation of Intra-Cardiac Complex Impedance Signals for Developing Simple Bio-impedance Models for Cardio-Dynamics

In this study computer models are used for simulating electrical impedance signals from intracardiac catheter inserted to the bottom of the left ventricle of the heart. 3D dynamic heart is composed of dynamic spline surfaces. Impedance signals from the catheter electrodes are calculated with finite difference method using complex tissue impedance values at frequencies 1 kHz and 1 MHz. The results of the FDM modeling were compared with a simple 3-element equivalent circuit model where also a parameter change has been introduced. The impedance results exhibited significantly similar details once plotted on Nyquist real-imaginary plot. From those similarities we conclude, that it is worthwhile to continue research in this area and aim to develop a few-element electrical circuit model for whole organ impedance

On the possibility of detecting the electrical bioimpedance of human body by using non-contact electrodes in capacitive connection

In this paper, the characterization of electrodes with three different contact surfaces - aluminum foil, conductive metallized nylon fabric and copper plated printed circuit board - in non-contact measurement setup, is presented. The frequency responses are shown and self-resonant frequencies designated to suggest the excitation frequency for measurement of electrical bioimpedance. The conclusions are made concerning the influence of motion artifact through the change of the distance between the surfaces of the skin and electrode.

Eddy Current Testing Models for the Analysis of Corrosion Effects in Metal Plates

Direct method for the solution of eddy current testing problem for the case where an air core coil is located above a conducting two-layer plate with a flaw in the form of a cylindrical inclusion with reduced electrical conductivity is presented in the paper. Semi-analytical approach (the TREE method) is used to construct the solution of the system of equations for the components of the vector potential. The flaw is assumed to be symmetric with respect to the coil. Numerical calculations are performed using the proposed model and Comsol Multiphysics software. The obtained values of the change in impedance of the coil for both methods are found to be in a good agreement. The proposed model can be used for the assessment of the effect of corrosion in metal plates.

DIRECT EDDY CURRENT METHOD FOR VOLUMETRIC FLAWS OF CYLINDRICAL SHAPE

Abstract. A quasi-analytical method for the solution of direct eddy current testing problems for the case of cylindrical volumetric flaws is presented in the paper. The method is based on a simple physical assumption that the electromagnetic field induced by a coil carrying alternating current is exactly equal to zero at a sufficiently large radial distance from the coil. The axis of the coil concides with the axis of a cylindrical flaw. The method of truncated eigenfunction expansions is used to compute the change in impedance of the coil. Complex eigenvalues are computed numerically using the method which does not require initial approximation for the eigenvalue. Computations are presented for different values of the parameters of the problem. Calculated change in impedance is compared with numerical results obtained by means of Comsol Multiphysics software. Good agreement between quasi-analytical method and numerical solution is found.

Eddy Current Model for Nondestructive Testing of Electrically Conducting Materials with Cylindrical Symmetry

Eddy current method is widely used in practice for quality testing of conducting materials (examples include determination of electrical conductivity, thickness of metal coatings, identification of flaws in a conducting medium). In the present paper a semi-analytical method for solution of direct eddy current problems for the case of a conducting medium of finite size is considered. The method is applied to several eddy current problems with cylindrical symmetry. The following problem is analyzed in detail. Consider a coil with alternating current located above a conducting medium in the form of a circular cylinder (such a model can be used for design of coin validators which are based on the estimation of electrical conductivity of a coin). We assume that the electromagnetic field is exactly zero at a sufficiently large distance from the coil (the distance can be chosen on the basis of the required accuracy of the solution). The solution is constructed using the method of separation of variables which includes two steps where numerical calculations are necessary: (a) computation of complex eigenvalues without good initial guess for the roots and (b) solution of a system of linear algebraic equations. Computations of the change in impedance of the coil for different frequencies with the semi-analytical method are in good agreement with experimental data and results of numerical simulation with finite element method. Solution of other problems with cylindrical symmetry is also discussed (a flaw in the form of a circular cylinder in a conducting half-space or a plate). Such models can be used for the analysis of quality of spot welding (in case of a volumetric flaw) and estimation of the effect of corrosion (for surface flaws).

Fatigue Performance of Semiconductor Strain Gauges in GFRP Laminate

Semiconductor strain gauges have good potential for embedded structural health monitoring (SHM) applications. Silicon mechanical and thermal properties are similar to glass fiber. In this paper the high cycle loading of specimens with embedded and surface mounted semiconductor strain gauges is conducted. The base material is glass fiber laminate. Two different matrixes are used: polyester and epoxy resins. Hygrothermal loading is introduced to weaken the sensor-matrix interface and to imitate real application conditions.

Investigation of molten metal mixing in a DC electric arc furnace with added AC component on different frequencies

This paper describes flowing of molten metal in a novel electric arc furnace. Combined AC and DC components are used in the supply system for the furnace. Finite element method is used to investigate the impact of AC component frequency on the flowing of molten metal.