Transient and harmonic eddy currents: Lift-off point of intersection

Mandache, Catalin; Lefebvre, J. H. V.

doi:10.1016/j.ndteint.2005.06.003

Cited by 85 publications

(40 citation statements)

References 2 publications

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“…Further, Lefebvre and Mandache [72] recorded LOI phenomenon by covering a conductive but nonferrous layer on a ferromagnetic substrate. Also, Mandache and Lefebvre [73] made an attempt to disclose the physics of the LOI phenomenon. It is found that the LOI phenomenon is a general characteristic of the eddy currents, not only to transient eddy currents.…”

Section: Lift-off Problemmentioning

confidence: 99%

Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review

Sophian

Tian

Fan

2017

Chin. J. Mech. Eng.

215

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Pulsed eddy current (PEC) non-destructive testing and evaluation (NDT&E) has been around for some time and it is still attracting extensive attention from researchers around the globe, which can be witnessed through the reports reviewed in this paper. Thanks to its richness of spectral components, various applications of this technique have been proposed and reported in the literature covering both structural integrity inspection and material characterization in various industrial sectors. To support its development and for better understanding of the phenomena around the transient induced eddy currents, attempts for its modelling both analytically and numerically have been made by researchers around the world. This review is an attempt to capture the state-of-the-art development and applications of PEC, especially in the last 15 years and it is not intended to be exhaustive. Future challenges and opportunities for PEC NDT&E are also presented.

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Section: Lift-off Problemmentioning

confidence: 99%

Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review

Sophian

Tian

Fan

2017

Chin. J. Mech. Eng.

215

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“…2). The Fourier series expansion of this signal is given by (1), where n represents the harmonic order, and f 0 is the fundamental frequency [7].…”

Section: The Modeled Systemmentioning

confidence: 99%

“…On the other hand, the Fourier series expansion is commonly used for these signals reconstitution [7]. As this reconstitution is based on the summation of a set of steady state frequency responses of the eddy current sensor, it does not take account of the sub-transient regime which corresponds to the time of the diffusion of the electromagnetic field in the system, and thus some important features of the signal are lost.…”

Section: Introductionmentioning

confidence: 99%

Contribution to the modeling of a voltage driven pulsed eddy current sensor for the characterization of conductive plates

Menana¹,

Féliachi²

2011

Analog Integr Circ Sig Process

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We highlight some physical phenomena occurring in pulsed eddy current testing, through the modeling of the response of a voltage driven pulsed eddy current sensor for the characterization of the thickness and conductivity of a metallic conductive plate. We use the finite element time domain method coupled to the electric circuit equation in the eddy current sensor which consists of an air cored coil. The characterization parameters are obtained from the current variation in the coil. The effects of the thickness and conductivity are clearly distinguished by considering three metallic plates of different conductivities. Time and frequency approaches are considered. We show that the reconstitution of the coil response signal from its Fourier series expansion leads to a loss of important features of the latter, limiting thus the characterization parameters, since this reconstitution does not take account of the subtransient phenomena, i.e., the time of diffusion of the electromagnetic field in the conductive plate. The numerical results are supported by measurements.

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“…10,13 For eddy current methods, an important factor limiting the response interpretation is the lift-off effect on the signals because the lift-off variation changes the mutual inductance between the excitation coil and the target. Reduction of the liftoff effect has been attempted with some successes by using the lift-off point of intersection (LOI), 16,17,20 using multi-sensor coil, 2,21 and optimization of the sensor structure. LOI is an experimentally observed fixed point where the time-domain transient eddy current signals intersect as the lift-off solely changes.…”

Section: Introductionmentioning

confidence: 99%

Non-contact online thickness measurement system for metal films based on eddy current sensing with distance tracking technique

Wang

Feng

2016

Review of Scientific Instruments

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This paper proposes an online, non-contact metal film thickness measurement system based on eddy current sensing. The slope of the lift-off curve (LOC) is used for characterizing target thickness. Theoretical derivation was conducted to prove that the slope is independent of the lift-off variation. In practice, the measurement has some immunity to the lift-off, but not perfect. The slope of LOC is still affected at some extent by the lift-off. Hence, a height tracking system was also proposed, which could stabilize the distance between the sensor and the target and significantly reduce the lift-off effect. The height tracking system contains a specially designed probe, which could vibrate rapidly to obtain a fast measurement speed, and its height can be adjusted up and down continuously to stabilize the lift-off. The sensor coil in the thickness measurement system was also used as the height sensor in the height tracking system. Several experiments were conducted to test the system performances under static and dynamic conditions. This measurement system demonstrated significant advantages, such as simple and clear conversion between the slope of LOC and target thickness, high resolution and stability, and minimized effect of lift-off variation. Published by AIP Publishing. [http://dx

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Transient and harmonic eddy currents: Lift-off point of intersection

Cited by 85 publications

References 2 publications

Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review

Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review

Contribution to the modeling of a voltage driven pulsed eddy current sensor for the characterization of conductive plates

Non-contact online thickness measurement system for metal films based on eddy current sensing with distance tracking technique

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