Location

Seattle, WA

Start Date

1-1-1996 12:00 AM

Description

The operation of the Flux Focusing Eddy Current Probe has been found to yield critical information on the thickness of the material being inspected [1–2]. The design of the probe forces the low frequency magnetic fields to diffuse through the sample in order to link with the pickup coil. An attenuation of the magnetic field results such that the pickup coil output is inversely related to the material thickness [2]. In extending the technique to thicker and/or layered materials, however, an apparently anomalous behavior is sometimes seen in which a small increase in the probe output occurs with increasing material thickness. This paper will clarify the underlying principles involved with the probe during low frequency operation and explain the apparent anomaly in terms of the phase shifting of the magnetic field with diffusion depth. A phasor addition model will be presented which accounts for the observed experimental results, and implications of the phenomena on material testing will be discussed.

Volume

15A

Chapter

Chapter 1: Standard Techniques

Section

Eddy Currents

Pages

417-423

DOI

10.1007/978-1-4613-0383-1_53

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Effect of Phase Delay on Low Frequency Operation of Flux Focusing Eddy Current Probe

Seattle, WA

The operation of the Flux Focusing Eddy Current Probe has been found to yield critical information on the thickness of the material being inspected [1–2]. The design of the probe forces the low frequency magnetic fields to diffuse through the sample in order to link with the pickup coil. An attenuation of the magnetic field results such that the pickup coil output is inversely related to the material thickness [2]. In extending the technique to thicker and/or layered materials, however, an apparently anomalous behavior is sometimes seen in which a small increase in the probe output occurs with increasing material thickness. This paper will clarify the underlying principles involved with the probe during low frequency operation and explain the apparent anomaly in terms of the phase shifting of the magnetic field with diffusion depth. A phasor addition model will be presented which accounts for the observed experimental results, and implications of the phenomena on material testing will be discussed.