Non-destructive flaw detection and profiling in paramagnetic materials using QWHE sensors

This project aims to develop new methods of electromagnetic Non-Destructive Testing (NDT) using advanced Quantum Well Hall Effect (QWHE) sensors. The focus of this PhD is on developing systems for the imaging of paramagnetic materials using multifrequency field applications, allowing multilayer images of the samples. The underpinning knowledge developed over the course of this PhD will be applicable to real industrial applications such as oil and gas pipe monitoring, and aerospace production.

The project currently consists of development of handheld systems for Eddy Current Testing (ECT), both at high frequencies (>100kHz) and low frequencies (<1kHz), along with image processing techniques for multifrequency scan combination. As the project continues, multifrequency field application techniques will also be developed.

This will be achieved through a process of electromagnetic modelling, circuit design, electromagnet profiling, and signal/image processing. These general steps apply to any systems to be developed over the course of this PhD. As systems are developed the PhD will also include collection of data in order to characterise the optimal parameters for paramagnetic metal imaging.

While standard ECT systems are used in industry, they all use mostly coil based detection, limiting them to the physical size restrictions of their sensors. As coils have a non-linear response to magnetic field, the images produced by coil based ECT systems are often difficult to interpret. In contrast, the high linearity, wide dynamic range, and sensitivity of the QWHE sensors leads them to be excellent for high resolution magnetic imaging and at high frequencies ( > 100kHz) there is the opportunity to integrate the actual coils itself within the semiconductor die leading to extremely compact illumination-sensor probes ( < 0.5x0.5 mm2). The frequency linear response of the sensors also opens the possibility for ECT performed at very low frequencies, allowing for magnetic penetration depths not possible to scan with current methods.

Finally, while coils detect magnetic flux confined within their area, their sensitivity is limited by size. In contrast, QWHEs detect magnetic flux density, and as such, they are confined to 3x2mm packages, with the actual sensing area is around 20x20 to 5x5microns in size. This opens possibilities for creating QWHE arrays, potentially leading to real time electromagnetic NDT.

The novelty of this is in the potentials for discovering and monitoring flaws and defects that are currently not visible through NDT methods, allowing for a deeper understanding of how metals in industrial use develop flaws over their lifetimes.