When the eddy current method is used to detect flaws inside conductive materials, different kinds of probes can be used. One probe is basically constructed with an excitation coil to apply a time-varying magnetic field, and a magnetic field detector to sense the perturbation field originated by the presence of flaws. In this work we focus on the invariance of the excitation field, under a probe rotation, when a solenoidal-type coil is used, or on the invariance under a probe translation, when a “constant field” probe is used.
In the case of a solenoidal axisymmetric coil, the excitation invariance can be used to infer the field along directions different from those acquired by measurements.
In the case of a constant field probe, that produces a spatially invariant field on a bounded area, the excitation currents inside the conductive material can be considered invariant under limited probe translations. Thus, the measurements taken on successive probe positions are identical to those that would be taken simultaneously with an array of sensors positioned on those grid locations.
In our present work we show that the experimental data acquired with the measuring system developed at our laboratory agree with the computed results obtained from the theoretical assumptions.