Planar Array Capacitive Imaging Sensor Design Optimization

Electrical capacitance tomography (ECT) is used in many industries as a non-invasive detection and measurement method, which works by finding permittivity changes in a viewing region. This usually consists of sensor electrodes surrounding a region of interest; however, this is not always possible as sometimes the viewing region is only accessible from a single side. In this case, a planar array ECT system can be used where the electrodes are all laid out on a co-planar surface. Initial simulation results indicated some features of sensor design which might aid image reconstructions. Five new electrode configurations were designed which incorporated these features in different ways. The designs were tested on their ability to reproduce a wooden block suspended in air and a water bottle buried in sand. Their performance was judged based on distance/depth detection of the block/water bottle, and the shape of the reconstruction. Singular value decomposition analysis was also performed on each sensor design to show their theoretical ability to reproduce the permittivity of the viewing region. Previously, similar work managed to reliably reconstruct objects at distances of 60 mm from the sensor. But in this paper, with a smaller sensor head, up to 90 mm was achieved with good accuracy. Combining the sensor designs together into a single sensor created the combined sensor, which was able to reconstruct objects with a much greater reliability, and was less susceptible to error or noise. With the right setup, the combined sensor was able to achieve up to 120 mm of depth detection. Also the combined sensor was able to detect a buried water bottle in sand up to 50 mm. Further simulation results on the combined sensor indicated that using up to 100 unique sensor configurations in the combined sensor was beneficial, but after 100 the amount of additional information gained was not significant. The results showed that the sensor head design can be optimized in order to produce improved reconstruction for planar array ECT. This improvement means that planar array ECT could potentially become a viable option for applications, such as landmine detection, particularly finding non-metallic objects, which cannot be picked up with conventional landmine detection techniques, such as metal detectors.