Quantum Sensors for Electromagnetic Induction Imaging : from Atomic Vapours to Bose-Einstein Condensates

• Main Author: Maddox, Benjamin Paul
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022
• Subjects: Matter & antimatter; Sensors

In this thesis, two sensors for electromagnetic induction imaging (EMI) are presented based on radio-frequency atomic magnetometry (RF-AM) in alkali atoms. The first sensor addresses portability and real-world use of EMI with AMs, by housing the major components of the RF-AM within a lightweight, minaturised system that can be mechanically translated. The atomic source was provided by a thermal vapour of 87Rb and was pumped/probed on the D1 line. The performance of the sensor is detailed and an RF sensitivity of dBAC = 19pT/√Hz was achieved. Stability of the device was investigated and potential improvements to the design are discussed. EMI with the sensor is then tested by application to two real-world industrial problems. Through-skin pilot-hole detection in Al strut-skin arrangements and corrosion detection under thermal/electrical insulation. The mechanically translatable RF-AM was able to detect and localise pilot-holes of diameter 16 mm concealed by an Al skin of thickness 0.41 mm with sub-mm precision. For corrosion detection, localisation and depth detection of recesses in an Al plate was achieved when concealed with a 1.5 mm thick piece of rubber acting as an electrical/thermal insulator. The sensor demonstrates key advantages over existing solutions to these challenges in a package that is within the reach of real-world deployment. The second sensor addresses the spatial resolution limitations of thermal vapours, by instead utilising ultra-cold atoms trapped in a tight optical potential, as the atomic source for the RF-AM. Initially an existing 87Rb BEC setup is optimised and characterised. A BEC of 65k atoms is produced via optical evaporation with a final volume of 3.2×10^−8 cm^−3. The BEC RF sensitivity is measured to be 268pT/√Hz with a volumetric sensitivity of 50.2fT/(cm3/Hz). The BEC RF-AM is found not to be limited by the atomic projection noise and a strategy for further improvements is discussed.