Eddy current testing has the advantage of non-contact and
fast test method over other non-destructive testing methods.
However, one of the disadvantages of eddy current testing is
that it tends to generate large noise generated by variations
of many factors such as probe lift-off and electromagnetic
characteristics of the test material. For the particular case of
welded zone testing the conventional eddy current
method [1] performance is strongly affected by shape
changes and variable electromagnetic characteristics on the
tested regions. In order to overpass these problems several
eddy current probe architectures are reported in the
literature [2] and are normally based on excitation and
detection coil sets [3]. Latest works on flaw and crack
detection in conductive plates underline the capabilities of
eddy current probes (ECP) based on single or multiple giant
magneto-resistance (GMR) sensors [4]. The use of GMRs is
a good tested choice for the present application.
When a GMR is used the obtained images represent one
component of the magnetic induction field along the sensing
axis. With these images it is possible to detect the presence
detection coils as depicted in Fig.1.b, and a pancake probe
(ECT-PP) with one excitation coil and a GMR sensor with
the sensing plane perpendicular to the coil axis as depicted
in Fig. 1.b.