Non-destructive control of metallic plate with magnetic techniques

Magnetic inspection techniques are nowadays widely used in system for Non-destructive Test (NDT) of various type of application. One of the most important application is the magnetic inspection of metallic object, that use family of sensor (Hall, GMR and coils) sensible to the magnetic flux (Hall and GMR are sensible to intensity of flux, and coils are sensible to the variation of the flux). System based on this techniques, in general, are able to read the sensor and, applying a proper software processing to the data collected, give information about the external an internal state (damage, presence of inclusion) of the object under test. An example of this method is the magneto-inductive inspection of metallic rope, widely used for the inspection of cableways. In this paper we will present a different application of this techniques, were the object that we want to test is a metallic plate (or sheet) and the output of a sensor designed ad-hoc for the application is combined to numerical techniques that can give a visual representation of the state of the objec