Location

Brunswick, ME

Start Date

1-1-1997 12:00 AM

Description

Eddy currents can be used to characterize the conductivity and thickness of coatings on metals. However, when the same techniques were applied to magnetic metals, some uncertainties were found. We have discovered that the broadband behavior of eddy current coils in proximity to ferromagnetic surfaces depends dramatically upon very thin surface layers. For nickel, we found a 10∼100 micrometers thick dead layer at the surface that reduces the apparent relative magnetic permeability substantially [1]. Conversely, this extreme sensitivity to surface conditions means that measurement methods can be devised that will be sensitive to very thin surface coatings, on the order of a few micrometers thick or less.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

16B

Chapter

Chapter 6: Material Properties

Section

Coatings and Layers

Pages

1593-1600

DOI

10.1007/978-1-4615-5947-4_207

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Characterization of Coatings on Magnetic Metals Using Swept-Frequency Eddy Current and Transient Eddy Current Methods

Brunswick, ME

Eddy currents can be used to characterize the conductivity and thickness of coatings on metals. However, when the same techniques were applied to magnetic metals, some uncertainties were found. We have discovered that the broadband behavior of eddy current coils in proximity to ferromagnetic surfaces depends dramatically upon very thin surface layers. For nickel, we found a 10∼100 micrometers thick dead layer at the surface that reduces the apparent relative magnetic permeability substantially [1]. Conversely, this extreme sensitivity to surface conditions means that measurement methods can be devised that will be sensitive to very thin surface coatings, on the order of a few micrometers thick or less.