Non-Destructive Testing and Evaluation Applications of Quantum Well Hall Effect Sensors

  • James Martin Watson

Student thesis: Phd


Over the past 4 years of this ICASE PhD, there has been significant developments in the application of using QWHE sensors for NDT&E applications. This thesis outlines the journey of this development, including the success, failure and technical achievements made in developing the Technology Readiness Level of QWHE sensors and QWHE sensor technology for NDT&E applications. This includes the process and outcomes of a study regarding analysing the feasibility of using QWHE sensors for NDT&E applications; using a real NDT&E weld validation sample with electromagnet and QWHE sensor magnetometer for the mapping of Magnetic Flux Leakage that occurs due to the presence of a surface-breaking flaw. This successful study showed that QWHE sensors can be used for NDT&E, with their inherent advantages over other magnetic sensors (increased sensitivity and linearity over a wide operating range) of genuine benefit to NDT&E applications. The iterative development of the XYZ scanner for magnetic imaging using QWHE sensors is also outlined, detailing the relevant systems, methods and performance relevant to NDT&E. This includes: the electromagnet design and subsequent applied magnetic field footprint and behaviour; control and calibration of the applied magnetic field strength; scanning methods and the relevant data acquisition and processing; repeatability and error analysis; as well as autonomous lift-off control for higher quality images and repeatability. Using an early version of this XYZ scanner (limited operational range of applied magnetic field and frequencies and no autonomous lift-off control), a comparative study was conducted to serve as an initial baseline into comparing and quantitatively evaluating the performance and capabilities of the main electromagnetic NDT&E techniques commercially available at the time to the QWHE sensor Magnetic Flux Leakage technique(s). This study involved a collaboration with leading UK companies within RCNDE and the NDT&E community and found that the inherent advantages of QWHE sensors have benefit to NDT&E, with future systems potentially as sensitive as conventional Eddy Current Testing probes, considered the benchmark in sensitivity at the time. With continued development of the XYZ scanner, the capabilities and performance of the technology developed, including the imaging of various NDT&E samples. The magnetic images from these have been qualitatively and quantitatively examined, including using the data to explore various image processing techniques for the enhancement of flaw detectability. This also included the iterative development of inspection parameters to enhance flaw detectability and other relevant NDT&E factors. This included the development in procedures used for the quantitative analysis of investigating the effects of different applied magnetic field strengths and frequencies, not commonly used in NDT&E due to the inherent limitations (i.e. low sensitivity and/or narrow operating range) of other magnetic sensors used in NDT&E, such as silicon Hall sensors, GMRs and coils. This found that there was no particular “optimumâ€� frequency within the operational range of the XYZ scanner (DC – 1 kHz, 5 mT – 100 mT rms) based on the material properties (i.e. magnetic permeability, electrical conductivity, surface condition, etc.) or contributing electromagnetic phenomena such as electromagnetic skin effect. However, in doing so, this work was able to shed more light on the underlying mechanisms and behaviour of AC MFL, developing procedures for future analysis and investigation to understand more about this phenomenon and therefore add benefit to the NDT&E community.
Date of Award1 Aug 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorMohamed Missous (Supervisor) & Massimiliano Migliorato (Supervisor)


  • QWHE sensor
  • Weld inspection
  • Hall sensor
  • Non-destructive testing

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