HIGH RESOLUTION EDDY CURRENT IMAGING WITH ATOMIC FORCE MICROSCOPE

Abstract

Eddy current testing is a widely used nondestructive evaluation technique of materials. This technique offers measurement of electrical conductivity and magnetic permeability of materials. Since the presence of defects significantly changes the electrical conductivity, eddy current testing is widely used to detect defects, cracks in materials. The resolution in eddy current imaging is mainly limited by the diameter of the sensor, which is most often greater than 500 μm. This paper presents development of an eddy current microscopy based on an Atomic Force Microscope (AFM) to image local variations in the electrical conductivity of materials with submicron resolution. The newly developed methodology has been used to characterize materials with varying electrical conductivities. Simultaneously acquired AFM surface topography images and eddy current images of the same region of the samples are presented. The contrast observed in eddy current images is explained based on the local electrical conductivity variations in the materials. The advantages and limitations of the AFM based eddy current imaging to study the electrically conductive materials are discussed.