The research work is focused on conducting a feasibility study on a new “non-contact” single probe dual coil inductive sensor for sensing the proximity and thickness of Aluminum (Al) 3003 alloy metal sheets, which is a non-magnetic metal. A bulk of the research and development work has already been done in the area of non-destructive testing (NDT) using eddy current technology targeted to various applications like corrosion detection, material thickness, material conductivity, etc. The research work presented in this thesis uses the prior research and development work completed in NDT as a platform for conducting this study to estimate proximity and thickness of Aluminum 3003 alloy metal sheets, which is not considered a flaw detection application. Some of the current technologies in the area of eddy current NDT for proximity and thickness estimation, each with its own limitations, include single probe ‘contact' sensors for magnetic metals, single probe ‘non-contact' sensors with separation distance of less than 1 mm and dual probe sensors that requires probes on both sides of the metal sheet.
A swept multi-frequency scanning technique is used together with an automated data collection system to measure and collect output voltage and phase difference data over a wide range of frequencies. The skin effect in conductors and its associated property of skin depth is used to extract proximity and thickness information from the data collected, and then correlated with reference values to validate the results. Experimental results show the output voltage and phase difference of the sensor is dependent on the metal parameters (resistivity ‘ρ', permeability ‘μ', thickness ‘T') and coil parameters (diameter ‘D', frequency ‘F', lift-off ‘L'). Further, proximity is estimated from output voltage difference, and metal thickness (single/double) is estimated from phase difference independent of lift-off, which is a novel approach for thickness detection. The test sensor provides an accurate measure of proximity and thickness of Al 3003 alloy from a single sided measurement with varying lift-off, overcoming the limitations of other sensor configurations.