ABSTRACT
This chapter discusses the possible use of self-compensated sensing coils to visualize conductive objects. Low-frequency magnetic fields can be used in the tomography of flat metal objects. The basis of its use consists in measurements of secondary magnetic fields generated by eddy currents induced on the object's boundaries. Magnetic and magnetic induction methods were almost entirely worked out in the twentieth century and offer a comprehensive range of feasible solutions. Metal detectors make use of the same physical phenomena as eddy current flaw detectors. It can differ in their design: some of them contain a source coil and a receiver coil, other use a single transmitter– receiver coil. Object detection is based on an analysis of the signal level in the receiver coil; or, in the case of a single transmitter– receiver coil, the coil is integrated into an oscillating LC circuit, whose frequency is known in the absence of inhomogeneities.
