2D Magnetic Field Sensing around Defects in Ferromagnetic and Non-Ferromagnetic Materials Using 2DEG Quantum Well Hall Effect Sensor Arrays

摘要

Multidimensional sensing of the magnetic field distribution around a defect is a key measurement in Non-Destructive Testing (NDT). Measurements of the component normal to the test surface, B_Z, and parallel to the direction of the magnetic flux in a test piece, B_X, are well established for Magnetic Flux Leakage (MFL). However, MFL is only effective in ferromagnetic materials and the concept of mapping at least two of these components from defects in both ferromagnetic and non-ferromagnetic materials is a further opportunity to study the behaviour of field distributions around defects in materials with varying magnetic permeabilities. The development of 2D Electron Gas (2DEG) Quantum Well Hall Effect (QWHE) [1] sensors has made it possible to detect stray magnetic fields down to the nano-tesla range with unprecedented sensitivity. The prototype device used in this experiment uses 16 QWHE sensors arranged in a 1 by 16 linear array. The sensors are positioned such that a B_X sensor is placed orthogonally after a B_Z sensor and this pattern is repeated throughout the 16 sensors. The device is equipped with an on-board AC electromagnet that illuminates the test piece with the required magnetic field. Both Finite Element Analysis (FEA) and experimental data show that the device is promising in terms of locating defects in both ferromagnetic and non-ferromagnetic materials. The experiments conducted suggest that with improved circuitry and inclusion of a third-dimension, B_Y, sensor array, perpendicular to the direction of flux in the test piece, the device can be used to successfully characterise defects in terms of shape, size and orientation in both ferromagnetic and non-ferromagnetic materials.