Electromagnetic localization of defects in carbon epoxy composite materials

When an imperfectly conductive structure is illuminated by an electromagnetic wave, its response, on the magnetic component, is comparable to a first order integrator, if the skin effect is negligible at the wave frequency. Using this model, we have developed a method and a magnetic probe allowing to build <<electric images>> of the defects present in carbon epoxy composite materials, by measurement of magnetic field transmission (or reflection) in these materials. After a presentation of the theory of electromagnetic scattering in a non perfectly conductive materials from M.A. Bethe(1) and K.F. Casey(2), we demonstrate that it is not necessary to perform the magnetic field attenuation measurement by transmission; we can proceed on one face of the sample, by reflection, obtaining the same results. We present the experimental set up and the magnetic probe developed, we show several images achieved on samples having induced defects (impact, local burning, etc.) and we compare these images with the images achieved by a classical ultrasonic method on the same specimens. Furthermore we present images produced by integration in a structure of a <<sensor-network>>, based on the principle used by the probe.