Determination of the conductivity and thickness of conductive layers on conductive base materials

John Burkhardt

doi:10.1177/1687814019854234

Abstract

An eddy current technique for the simultaneous determination of the layer thickness and conductivity of a uniform conductive layer on a known conductive base material is presented. Layer thickness and conductivity are determined by fitting apparent conductivity measurements taken on the surface of the part at a discrete set of frequencies to a calibration volume. The calibration volume is constructed from apparent conductivity measurements taken on a set of known layer materials, of various known thicknesses, as a function of frequency. Experimental results that support the technique are presented.

Highlights

The addition of coatings, platings and surface layers, or the modification of near-surface material properties plays an important role in the industrial application of metals
In many applications, including the current one, the varying magnetic field is produced by an eddy current transducer composed of a solenoid-like coil, created from wound wire, that is held with its primary axis perpendicular to the surface of the test article
A calibration-based technique for determining the conductivity and thickness of conductive layers placed on a conductive base material has been presented

Summary

Introduction

The addition of coatings, platings and surface layers, or the modification of near-surface material properties plays an important role in the industrial application of metals The purposes of these modifications include improved corrosion resistance, wear resistance, electrical conduction, thermal isolation, and appearance. Eddy current techniques[2] are attractive for the characterization of surface layers and treatments because they are nondestructive, potentially noncontact, and, importantly, have frequency-dependent penetration depth. These related inspection methods rely on the principle of magnetic induction, in which currents are generated in a conductor when in the presence of a varying magnetic field. The Mechanical Engineering Department, US Naval Academy, Annapolis, MD, USA

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Results

Conclusion