High Scan Speed High Spatial Resolution Quantum Well Hall Effect Magnetovision System with programmable AC coils illumination

摘要

A new class of highly sensitive Quantum Well Hall Effect (QWHE) sensors have been developed in this research and a prototype hand held magnetovision system has been developed (270mm × 135mm) using 8×8 arrays of these sensors. In this prototype, DC magnetic fields can be measured with magnetic and spatial resolutions of 3μT and 10mm, respectively. Measured results are displayed as a 2-dimension (2D) figure on a LCD display unit, with blue and red colours representing south and north poles, respectively. In order to achieve further improvement in the sensitivities and to introduce additional functionalities, such as AC magnetic field measurement, a second generation prototype is under development. This 2nd generation prototype not only has improved magnetic field and spatial resolutions of 50nT and 5mm, respectively, but also can be used to detect both DC and AC magnetic fields ranging from DC to 20 kHz. This new design utilizes a superheterodyne technique to improve both pick-up and noise problems. With the assistance of simulation to understand how AC magnet field can be used in Magnetic Flux Leakage (MFL) techniques, an AC electromagnet has also been designed. Using this specially designed AC electromagnet, the improved magnetovision system can be used to detected defects and flaws in both magnetic and nonmagnetic materials, such as stainless steel and aluminum. With a powerful microcontroller and high-resolution AC/DC, this magnetovision system has the ability to increase theDC magnet field scanning frame rate and to reconstruct images by measuring AC magnetic field at different frequencies.