Abstract

Magnetic particle and other Magnetic Flux Leakage (MFL)-based methods typically use high-strength (> 0.7 T) low-frequency (? 50 Hz) magnetic fields [1] for practicality purposes. The rationale behind this is in the availability of high strength permanent magnets and the ability to easily create stronger electromagnets at low frequency (using 50 Hz mains). As such, most MFL-based methods typically use frequencies which are practical to achieve the high field strengths required for near sample saturation or due to magnetic field sensor and detection media insensitivity to weaker field strengths. Over the past five years, The University of Manchester has developed pioneering magnetic field imaging scanners and techniques using Quantum Well Hall Effect (QWHE) sensors [2], exploiting their unique combination of sensitivity and linearity over the large dynamic range (20 nT to 2 T ? 160 dB) with a compact size (200 ?m). Previous research has shown that this sensitivity enables the detection of surface-breaking cracks and other flaws down to 1 mm in length in mild steel welds [3] using comparatively low strength applied magnetic fields (5 to 100 mT) by mapping the MFL response across samples under test. Because of these relatively low-strength applied magnetic fields required, QWHE sensors have the potential to be used as key components in low-power (i.e. portable) magnetic field scanners, using magnetic field frequencies which are better suited to the frequency response of the material of the sample under test. As such, this research focuses on the optimization of applied magnetic field frequencies within the range of DC to 1 kHz for MFL detection of surface-breaking flaws in mild steel welds via magnetic field mapping using QWHE sensors.

How to Cite:

Watson, J. M., Liang, C. ., Sexton, J. . & Missous, M. ., (2019) “Magnetic field frequency optimisation for MFL imaging using QWHE sensors”, Review of Progress in Quantitative Nondestructive Evaluation .