Method and apparatus for non-destructive testing using eddy currents

The invention relates to a method of non-destructively testing a magnetisable conducting object surrounded by a magnetisable layer. The method comprises the step of abruptly changing a field strength of a primary magnetic field that is applied exterior to the magnetisable layer. Further, the method comprises the step of receiving a vanishing secondary magnetic field generated by eddy currents induced by the changed field strength of the primary magnetic field. The method also comprises the step of analyzing a temporal field strength of the received secondary magnetic field for deriving characteristics of the magnetisable conducting object. In addition, the method comprises the step of applying a transient tertiary magnetic field exterior to the magnetisable layer when the field strength of the primary magnetic field abruptly changes, wherein the orientation of the primary and tertiary magnetic field, respectively, are mutually opposite.