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Fringe effect of electrical capacitance and resistance tomography sensors and its application in 3D imaging

Sun, Jiangtao

[Thesis]. Manchester, UK: The University of Manchester; 2014.

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Abstract

This PhD work is dedicated to investigating the fringe effect of electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) sensors systematically, exploring possible solutions and developing a novel 3D imaging technique by utilising the fringe effect of electrical tomography (ET) sensors.By referring to 2D simulation results, the fringe effect is investigated for 3D ERT and ECT sensor models with or without grounded guards, and with different axial lengths of electrodes. Simulation results reveal that increasing the electrode length or adopting grounded guards can reduce the fringe effect of ECT and ERT sensors.In this work, a voltage-excitation strategy is proposed and validated for ERT sensors instead of the conventional current-injection strategy. This approach enables ECT and ERT sensors to be integrated together as a common one to simplify the sensor design and reduce the interference between the ECT and ERT dual-modality measurements.For a conventional ERT sensor with the adjacent strategy, the fringe effect is evaluated for axially non-uniform central core and off-central core distributions at different axial positions and with different axial dimensions and conductivity contrasts. A method is proposed for compensating the fringe effect with the above typical distributions and a two-object distribution. A three-plane ERT sensor scheme is suggested for reducing the fringe effect induced by objects outside the sensor plane and the over-estimation by Landweber iteration. Both simulation and experiment have proved the effectiveness of the three-plane sensor scheme and the compensation method.Using the fringe effect, a novel 3D imaging method is proposed for ET with a single-plane sensor. It is explored to image metallic objects with ECT. The axial position of the object is derived by examining the corresponding fringe effect in a single-plane ECT sensor. Along with 2D imaging of the cross-sectional distribution, 3D imaging is achieved for a cylindrical metallic rod with known size. With this method, only the 3D position of the object needs to be calculated during the reconstruction which reduces the number of unknowns greatly and can improve the accuracy and stability of reconstruction.