Location

Santa Cruz, CA

Start Date

1-1-1984 12:00 AM

Description

Surface eddy current probes are widely used for measuring crack depth, coating thickness and corrosion effects in metals. In most applications, single (absolute) coils are used, and the coil impedance is monitored. Information concerning inhomogeneities is extracted from changes in the coils impedance. Double probes consist of a driving coil and a smaller concentric pickup coil. In this case the induced voltage in the pickup coil is measured. This work describes the application of the finite element method to the analysis and design of both single and double coil surface probes. Double coil probes are shown to be superior for the applications mentioned above because of better linearity of the lift off curve and wider useful range. The rate of change of the induced voltage in a double coil probe is shown to be larger than the rate of change of the impedance in single coil probes for given parameter changes. This clearly indicates a higher sensitivity. Moreover, in the case of corrosion depth measurement, the noise generated by lift off changes can be suppressed by use of an appropriate double coil. The results presented are also verified experimentally.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

3A

Chapter

Chapter 3: Eddy Currents

Section

Probes

Pages

675-682

DOI

10.1007/978-1-4684-1194-2_64

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Finite Element Analysis of Eddy Current Surface Probes

Santa Cruz, CA

Surface eddy current probes are widely used for measuring crack depth, coating thickness and corrosion effects in metals. In most applications, single (absolute) coils are used, and the coil impedance is monitored. Information concerning inhomogeneities is extracted from changes in the coils impedance. Double probes consist of a driving coil and a smaller concentric pickup coil. In this case the induced voltage in the pickup coil is measured. This work describes the application of the finite element method to the analysis and design of both single and double coil surface probes. Double coil probes are shown to be superior for the applications mentioned above because of better linearity of the lift off curve and wider useful range. The rate of change of the induced voltage in a double coil probe is shown to be larger than the rate of change of the impedance in single coil probes for given parameter changes. This clearly indicates a higher sensitivity. Moreover, in the case of corrosion depth measurement, the noise generated by lift off changes can be suppressed by use of an appropriate double coil. The results presented are also verified experimentally.