Doctoral thesis defense with Minshu Xue, Quantum Device Physics Laboratory

Doctoral thesis defense with Minshu Xue, Quantum Device Physics Laboratory

När: 10/11/2017 , 10:00 - 13:00
Plats: Kollektorn
Adress: MC2-huset, Campus Johanneberg, Chalmers, Göteborg


On 10 November, Minshu Xue, Quantum Device Physics Laboratory, will be defending his doctoral thesis with the title “Development of high-Tc SQUID magnetometers for on-scalp MEG” at MC2 at Chalmers University of Technology. Faculty opponent is Associate Professor Lauri Parkkonen, from Department of Neuroscience and Biomedical Engineering at Aalto University.

When? 10:00-13:00 on 10 November, 2017
Where? Kollektorn, lecture room, MC2-huset, Campus Johanneberg, Chalmers

Abstract
Magnetoencephalography (MEG) is a method of mapping neural dynamics in the human brain by recording the magnetic fields produced by neural currents. Its passive and non-contact nature allows doctors and neuroscientists to safely and effectively carry out clinical diagnoses and scientific research on the human brain. In order to measure the extremely tiny biomagnetic fields (~100 fT) from the brain, SQUID sensors are utilized. State-of-the-art MEG systems are based on low-Tc SQUID sensors with sensitivities of 1-5 fT/√Hz at 10 Hz. However, low-Tc SQUIDs require liquid helium cooling to reach their operating temperature (< 10 K). The complicated cryogenics limit the sensor-to-subject distance to 20 mm at best. In addition, liquid helium is a scarce and expensive resource and its price is expected to increase further. On-scalp MEG, in which sensors are placed with close proximity (few millimeters) to the subject’s scalp, is a new approach for overcoming the limitations of today’s technology. We utilize high-Tc SQUID sensors that can operate with liquid nitrogen cooling (77 K) and enable on-scalp MEG with a reduction of the sensor-to-subject distance to ~1 mm. We benchmark a single-channel bicrystal high-Tc SQUID-based MEG system with low-Tc SQUIDs in a state-of-the-art MEG system (Elekta Neuromag® TRIUX, courtesy of NatMEG) based on recordings on a head phantom. We establish a systematic benchmarking procedure that is objective, fast, and feasible for application to various on-scalp MEG sensing technologies and prove the functionality with MEG recordings of auditory and somatosensory evoked fields on one human subject. In addition, we investigate high-Tc SQUIDs based on nanowires as a promising sensor technology for multi-channel on-scalp MEG systems. We study different designs and coupling approaches to improve the sensitivity of these sensors.