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2 Zeszyty Naukowe. Elektryka / Politechnika Łódzka

2 2009

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Limits of the weakly coupled field assumption for low conductivity electromagnetic induction tomography

Yin W., Peyton A. J., Zysko G., Dekdouk B.

Zeszyty Naukowe. Elektryka / Politechnika Łódzka

2009

z. 114

75-79

In medical or low conductivity electromagnetic induction tomography, a low frequency approximation (i.e. neglecting the diffusion effect) can significantly simplify the forward and inverse solutions. However, this approximation normally leads to the over prediction of the amount of eddy currents induced by the transmitter coil, and hence to an overestimation of the secondary voltage measured on the receiver coil. The reason is because the penetration of the field into the object is not correctly described and the skin effect is ignored. In effect, the theory assumes that the signal is coming from a larger-than-actual volume. This paper uses an exact analytical solution for a coil(s) near a stratified media derived from a full wave theory to evaluate the skin effect at a range of frequencies and compares it with a simple model which omits the skin effect. The error due to the approximation is evaluated and the highest frequency at which the approximation holds valid to within a defined error range is ascertained.

Application of the impedance method for computing the current density inside a 3D conductor for low conductivity Magnetic Induction Tomography

Dekdouk B., Ktistis C., Armitage D. W., Peyton A. J.

Zeszyty Naukowe. Elektryka / Politechnika Łódzka

2009

z. 114

81-86

An algorithm is presented to calculate the current density (J) in a 3D conductor. This is a key part in the forward model for magnetic induction tomography (MIT). The conductor is discretised into a Cartesian grid consisting of a network of interconnected resistors. Circuit analysis e.g. branch current method in combination with sparse matrix techniques were used to solve the system. The method is formulated based for the low conductivity case, such as a weak diffusion effect. The results show the method is capable of producing accurate solution with less memory and computation time requirements than Maxwell, a commercial Finite Element simulator.