Nondestructive Surface Profiling and Inspection by Using a Single Unit Magneto-Eddy-Current Sensor

Abstract

This paper presents a novel nondestructive testing system, magneto-eddy-current sensor (MECS), to enable surface profiling of dissimilar materials by combining magnetic sensing for ferromagnetic materials and eddy-current sensing for nonferromagnetic materials. The interactions between an electromagnetic field and nonferromagnetic surface and between a magnetic field and ferromagnetic surface were measured by the MECS. The MECS consists of a conic neodymium magnet and a copper coil wound around the magnet. Aluminum and steel surfaces bonded together were prepared to test nondestructive surface profiling of dissimilar materials by the MECS. The interactions between an electromagnetic field and aluminum surface were characterized by monitoring the impedance of the coil, and the interactions between a magnetic field and steel surface were characterized by using a force sensor attached to the neodymium magnet. The magnetic and electromagnetic effects were numerically analyzed by the finite element model. The developed MECS showed the following performance: measurement spot size 5 mm and 10 mm, dynamic measurement bandwidth (eddy-current sensing 1 kHz and magnetic sensing 200 Hz), measuring range 25 mm and 17 mm, polynomial fitting error 0.51% and 0.50%, and resolution 0.655 µm and 0.782 µm for nonferromagnetic and ferromagnetic surface profiling, respectively. This technique was also applied to surface profiling and inspection of the rivet joining sheet materials. The results showed that the MECS is capable of nondestructively monitoring and determining the riveting quality in a fast, large-area, low-cost, convenient manner.