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High sensitivity electromagnetic testing of hi-tech and safety critical metal components
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To, Amanda Lin (2021) High sensitivity electromagnetic testing of hi-tech and safety critical metal components. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3879849
Abstract
Eddy current testing is widely used to inspect safety-critical components, where it is important to find surface-breaking defects and fatigue cracks at their earliest stage of growth. This requires finding sub-millimetre defects, which usually means the electromagnetic skin depth of the eddy current must be < 1mm. To achieve skin depths of < 1mm on low conductivity metals such as Ti and TiAl, the frequency of the excitation current needs to be greater than several MHz. Eddy current sensor frequencies of up to 40MHz, which provide good signal-to-noise ratios, have been achieved by positioning circuitry directly behind the coils [1]. However, even when locating the electronics close to the coils, increasing frequency will always lead to an increase in electrical noise as inductance in the wires increases and stray capacitances become more significant. As an alternative, lower frequency (< 1MHz) Parametric approaches have been investigated [2], where the magnitude and phase of the eddy current signal are independently measured.
In this thesis, a combination of these approaches is used. A two coil transmitreceive eddy current sensor was built that operates at 1MHz where the sensor electronics were located behind the coils and simultaneously measure magnitude and phase of the eddy current signal. The approach can improve sensitivity to defects in experimental 2D scans of the sample surface.
In addition, work has been performed that involves changing various parameters such as defect orientation and the lift-off of the eddy current coils. Through this, it was found that this new approach can improve lift-off performance and the ability to measure defects close to the edge of a sample. Experimental results and finite element modelling are presented to support these findings. The standard experimental approach was one where software-based digital signal processing was used to measure the magnitude and phase difference of various signals, which is relatively time-consuming. A new approach was designed and tested using a low-cost, specialised chip to measure phase difference. This new meter is capable of measuring both the magnitude and phase of the signal using an inexpensive AD8302 chip, which produces good results from eddy current signals, decreasing system complexity and cost whilst also reducing measurement time.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General) T Technology > TK Electrical engineering. Electronics Nuclear engineering |
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Library of Congress Subject Headings (LCSH): | Eddy current testing, Electromagnetic testing, Metals -- Fatigue, Metals -- Defects, Signal processing -- Digital techniques | ||||
Official Date: | August 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Dixon, Steve M. | ||||
Sponsors: | Rolls-Royce Ltd. ; European Development Fund | ||||
Format of File: | |||||
Extent: | xvii, 185 pages : illustrations (colour), charts (colour) | ||||
Language: | eng |
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