High-$T_{\rm c}$ DC SQUIDs for Magnetoencephalography

Abstract

We have investigated the microstructural and electron transport properties of 45° step-edge Josephson junctions grown on MgO substrates and used them for the preparation of superconducting quantum interference device (SQUID) magnetometers intended for magnetoencephalography (MEG) measurement systems. The high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> SQUID magnetometers also incorporate 16 mm multilayer superconducting flux transformers on the MgO substrates and demonstrate a magnetic field resolution of ~ 4 fT/√Hz at 77 K. Results are illustrated for the detection of auditory evoked magnetic responses of the human cortex and compared between high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> SQUIDs and a commercial low- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> MEG system. Our results demonstrate that MEG systems can be upgraded using high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> SQUIDs to make them independent of helium and more user-friendly, saving operating costs and leading to the widespread utilization of MEG systems in clinical practice and at universities.