Preliminary studies on the design principles of capacitive imaging probes for non-destructive evaluation

As a novel electromagnetic non-destructive evaluation (NDE) technique, capacitive imaging (CI) has been successfully used on a various types of materials, including concrete, glass/carbon fibre composite, steel, etc. In this work, studies on the design principles for the CI probes were presented. Firstly, measures for the evaluation of the CI probe performance are presented. The concept of volume of influence is then raised, to evaluate the imaging ability of a given CI probe. Examples of CI probe designs are then provided, namely symmetric and concentric geometries. Design factors, such as separation between electrodes, guard electrodes, and electrode shapes are also discussed and examined experimentally. CI scans were performed on two typical specimens, namely Perspex and aluminium, to evaluation the imaging performance of CI probes with different geometries.