Cédric Margo

Physical limitations on spatial resolution in electrical capacitance tomography

Electrical capacitance tomography (ECT) is an imaging technique providing the distribution of permittivity in a medium by means of electrodes. As for any imaging systems, the accessible spatial resolution is a key parameter. In this paper the physical limitations on the spatial resolution of ECT sensors are analysed in terms of the accuracy of an objects position and of the ability to distinguish between two close objects for any sensor geometry. Cylindrical geometry sensors are particularly studied and the example of a square geometry sensor is used to show how to apply the calculations to any other geometries. In cylindrical geometries, it is shown that a 50% gap between electrodes is a good compromise and that increasing the number of electrodes improves the spatial resolution near the electrodes but decreases the spatial resolution in the centre. The best spatial resolution at the centre of the sensor is obtained with 3 or 4 electrodes. In the square geometry studied, it is shown that a better distribution of the spatial resolution is obtained when there are electrodes in the corners.

Four electrode embedded bioimpedance measurement system

A new extension of the AD5933 impedance measurement chip is presented. It allows to use the chip in the four electrode configuration to reduce the artifact effects of interface impedance between the electrode and the sample to be measured. The measurement approach is validated on various test circuits, and the system has been able to measure small physiological samples (50 ul) in a four microelectrode configuration and with a low sensitivity to interface impedances. The system is a good candidate for any embedded bioimpedance measurement system which requires a low sensitivity to interface impedances.

Fast circular shapes detection in cylindrical ECT sensors by design selection and nonlinear black-box modeling

Purpose Within the framework of image reconstruction in cylindrical electrical capacitance tomography (ECT) sensors, the purpose of this study is to select the structure of a sensor in terms of number and size of the electrodes, to predict the radius and the position of a single circular shape lying in the cross-section defined by the sensor electrodes. Design/methodology/approach Nonlinear black-box models using a set of physically independent capacitances and least-square support vector machines models selected with a sophisticated validation method are implemented. Findings The coordinates of circular shapes are well estimated in fixed and variable permittivity environments even with noisy data. Various numerical experiments are presented and discussed. Sensors formed by three or four electrodes covering 50 per cent of the sensor perimeter provide the best prediction performances. Research limitations/implications The proposed method is limited to the detection of a single circular shape in a cylindrical ECT sensor. Practical implications This method can be advantageously implemented in real-time applications, as it is numerically cost-effective and necessitates a small amount of measurements. Originality/value The contribution is two-fold: a fast computation of a circular shape position and radius with a satisfactory precision compared to the sensor size, and the determination of a cylindrical ECT sensor architecture that allows the most efficient predictions.