LAUSR

Illustrated with a magnetic field based eddy-current (EC) sensor which utilizes an anisotropic magneto-resistive sensor to directly measure the magnetic flux density (MFD) generated by the EC induced in a non-ferrous metal plate, this paper presents a material-independent method for multi-objective estimation of the plate geometrical parameters and/or electrical conductivity using frequency response analysis. The model, which agrees well with a 2-D axis-symmetric finite-element analysis, relates the measured (EC-generated) MFD to three dimensionless parameters (skin depth, plate thickness, and sensor-plate distance) normalized relative to a specified coil design. Data in the material-independent model that provides the basis to investigate the parametric effects on measured MFD can be regrouped in 2-D maps for simultaneously measuring any two of the three parameters. Experimental measurements were conducted on three different materials (Aluminum, Titanium, and Titanium alloy) with different thicknesses and sensor-plate distances between 1 and 5 mm operating in the frequency range from 100 Hz to 42.8 kHz. Experimental results show that the maximum difference between the analytically computed and experimental data is in the order of 5%, and demonstrate that the method has the capability of simultaneously measuring two unknowns out of three geometrical and/or material properties using a material-independent 2-D map.