Ultra-High Resolution Magnetometers Based on APF SQUIDs

DESCRIPTION (provided by applicant): The objective of the proposed research is to develop Ultra-High Resolution, thin film low-temperature superconductivity (LTS) SQUID Magnetometers (UHRSM) with integrated pickup-loops and Additional Positive Feedback (APF). The UHRSM will be optimized for imaging of the magnetic fields produced by action currents, injury and developmental currents, remanent magnetization, and magnetic susceptibility in isolated living tissue and small experimental animal preparations. As a collaborative effort between HYPRES and several research institutions, including Living State Physics of Vanderbilt University, we are building analog SQUID magnetometers for imaging action currents in isolated living tissue. In order to utilize SQUIDs for these applications, their voltages are amplified by a step-up transformer so it could be instrumented with room temperature electronics. In addition, SQUID's transfer characteristics should be linearized. The use of a step-up transformer requires extensive peripheral electronics for linearization, thus limiting the number of SQUID magnetometer channels in a practical system. We are proposing to develop a novel SQUID with Additional Positive Feedback (APF) that eliminates the need for the transformer, and as a result simplifies the peripheral electronics significantly. The proposed APF SQUID integrates an on-chip feedback coil with the SQUID. This can increase the gain of the device substantially, and as a result no step-up transformer is required for read out. The APF SQUID system is compact and cost effective, and requires minimal support electronics. The proposed research involves the staged development and implementation of a SQUID design to enhance the spatial resolution and maximize the field sensitivity for specific applications. The existing expertise will be exploited further to develop and improve SQUID sensors for general and custom biomagnetic applications which require higher-sensitivity SQUID magnetometers and gradiometers but lower spatial resolution. An aggressive program of biophysical measurements at Vanderbilt coupled with the technical expertise at HYPRES will lead to both a commercially attractive UHRSM instrument and a valuable national capability for fabrication of new designs for SQUID sensors.