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.

Electromagnetic Imaging Methods for Nondestructive Evaluation Applications

“…In the imaging system that he proposed, an electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents generated in the conducting sample are detected and measured with a magnetic tip attached to a flexible cantilever of an AFM [ 46 ]. The contrast in the image was explained based on the electrical conductivity and eddy current force between the magnetic tip and the sample, where the spatial resolution of the eddy current imaging system was determined by imaging carbon nanofibers in a polymer matrix.…”

New Trends in Non-Destructive Evaluation of Surface Hardened Layers and Coatings

“…The proposed one is eddy current imaging using an atomic force microscope (AFM). [21]. Usually the spatial resolution of eddy current flaw detectors is limited by the values 500 microns.…”