A new optical technique for detection of defects in ferromagnetic materials and components

In this paper, we present the details of a new optical technique to detect the defects present in a ferromagnetic material or component, using a ferro fluid emulsion. This new flux leakage probe consists of monodispersed ferro fluid confined between two thin transparent glass slides or in a cuvette an d a white light source for illumination. By employing ferrofluid droplets o f suitable size and surfactant concentration, one can qualitatively identif y the region where the defect is located in the test specimen by visually o bserving a color change in the ferrofluid cell, in the vicinity of a crack or defect in the test specimen. The origin of this color change in the back scattering direction is due to Bragg scattering from the droplet chains, f ormed by the leaked magnetic flux in the presence of a defect. We discuss i n detail the procedure, the merits and potential uses of this new technique for non-destructive testing and evaluation (NDT and E) applications. (C) 2 000 Elsevier Science Ltd. All rights reserved.