An imaging system with planar PCB-coil sensor array

To detect hidden metallic objects, an imaging system with a planar PCB-coil sensor array has been developed. The sensor array consists of a driving board and a pickup board, with square spiral coil elements connected in series. Fast scan can be achieved by row-excitation and column-detection. Mutual inductance between the driving-pickup coil pairs is measured by an HP4192-based multi-channel measurement system. Using sensitivity coefficients, an image presenting conductivity/ permeability distribution can be obtained by interpolation and pixel-averaging from the normalised measurements. Initial tests show that the system can image both conductive and magnetic objects with an imaging depth of 10 mm and a spatial resolution of one coil element. The issues with cross-talk and image errors due to object covering multiple sensing elements should be compensated to improve image fidelity.