This paper presents new developments in the area of nondestructive evaluation of defects in metallic non-magnetic materials. Two probes, one circular and another with a parallelepiped shape, are used to detect and analyze cracks in an aluminum plate. The geometrical characteristics of these probes are used to improve the interpretation of the image signals obtained when a plate is scanned. A quite simple direct model based on a conformal mapping is obtained and used to seek for the solution of the inversion problem, when the parallelepiped probe is under use. The steps carried out in the processing algorithms are illustrated using experimental data acquired in the detection of a crack in an aluminum plate.