Digital SQUID Magnetometers for Read-out of Detectors and Magnetic Particles

Detectors utilized in high energy and nuclear physics research have, historically, been instrumented with FET amplifiers operated in the cryogenic environment. These amplifiers require heated operation, suffer from large 1/f noise, are very sensitive to microphonic pickup, and dissipate high power. More recently, analog SQUIDs (Superconducting QUantum Interference Devices) have replaced FETs and have solved all of the problems associated with FETs. However, analog SQUIDs are extremely sensitive to magnetic fields, require sophisticated read-out electronics, and in their present configuration are not suitable when large fields are present. In addition, the complexity of peripheral electronics has prevented widespread use of analog SQUIDs in imaging applications that require hundreds of channels. The proposed digital SQUID integrates an analog SQUID with a superconducting pickup coil and an on-chip digital processing circuit. The front-end analog SQUID provides the best energy resolution whose output is digitized on-chip for further processing by room temperature electronics. The analog SQUID is coupled to two highly balanced pickup loops for rejecting large uniform fields. One of the loops is utilized to couple to detectors, magnetically polarized beams, or to other magnetic signals of interest. The second loop is utilized to measure and cancel large background fields. Digital outputs are instrumented with simple peripheral electronics facilitating data acquisition for multi-channel systems. Under the Phase I SBIR project, a novel approach for implementing a digital SQUID for high performance multi-channel applications was developed and demonstrated. This approach can be utilized for multiplexed systems operating at 40 GHz. Such a high frequency operation allows this multiplexed digital SQUID array to be easily implemented with high density detector arrays. The digital SQUID chip was designed, simulated, fabricated, and allits components were successfully demonstrated. The objective of this Phase II SBIR program is to develop a complete multiplexed ultra-low noise digital SQUID magnetometer/amplifier system. The system will be designed for read-out of detectors in unshielded environments and detection of magnetization of polarized nuclei in a magnetic field, and to act as a receiver for Magnetic Resonance Imagining systems. As the first prototype, the system will consist of a 4-channel digital SQUID --each coupled to its own pickup loops--and a single set of peripheral electronics for simultaneous data acquisition of all four channels. The system will be designed and implemented cost-effectively in a modular form so it can be easily extended to a higher number of channels. Commercial Applications and Other Benefits: The availability of low-cost, multi-channel SQUID systems would result in their wide-spread use in high-resolution X-ray spectroscopy, detector array imaging, particle identification systems, electron microscope systems (for material surface characterization studies), medical imaging, and non-destructive evaluations.