Issue 45

S. Harzallah et al, Frattura ed Integrità Strutturale, 45 (2018) 147-155; DOI: 10.3221/IGF-ESIS.45.12 149   A   .   i i s N d N J d      ∮ ∮ (4)    [ . V ] 0 i i J N A d         (5) S ENSOR IMPEDANCE CALCULATION he detection of change of the resulting magnetic field is based on two basic methods: the NDT differential mode represented by two separate coils linked magnetically and supplied by the same current and the NDE absolute mode which makes use of only one coil. The impedance variation is obtained from comparison with the reference impedance. The impedance variation Z is a complex number. The imaginary part is computed with the magnetic energy (WM) in the whole meshed domain and the real part is computed with the Joule Losses in the conductive media and the imaginary part is computed with the magnetic energy in the whole meshed domain [12]. The coil impedance with an excited current I at a frequency F is obtained by the following expression;       2 2 2 1 C f JL Re Z I Re Z J J d              and       2 2 2 1 c M f W Im Z I Im Z B B               (6)   2 2 1  (   2    .  Z R j X J Z d j F B H d I                 (7) where J, B, and H are the induced magnetic induction, and the magnetic field, respectively [13]. Figure 1 : Vector of induction B. Figure 2 : Density of the induced current. A PPLICATIONS or the application, we chose to test a magnetic plate without any crack and characterized by a high conductivity 10 7 Sm-1 with a magnetic permeability μ of 1.2 10 -6 H/m. The plate is excited by a sinusoidal current of density J = 2.67 10 6 A/m and a frequency of 10 Khz. EC testing problem deals with a Pancake coil placed above a flat plate, as T F