Bob Grimm - SDT Magnetometer

Spin-Dependent Tunneling (SDT) Wideband Magnetometer

Magnetoresistance (MR) - a change in the resistance of a material in response to an applied magnetic field - is now widely used for computer disk read/write heads and wherever compact sensors are required, as in motor vehicle brakes. This sensor was sponsored by NASA PIDDP (R. Grimm, PI) and uses a quantum-mechanical form of MR (SDT, also called tunneling magnetoresistance or TMR). It was built by Mark Tondra, Cathy Nordman, and colleagues at Nonvolatile Electronics, Inc, achieving TRL 4. While MR sensors have much greater bandwidth (~MHz) and much smaller size (10s g) than any other sensor, they still could not outperform other sensors designed for particular niche bands. Basic research performed by Jagadeesh Moodera (MIT) under this grant showed that 1/f noise is fundamentally related to the quantum-mechanical behavior and not to materials. For spaceflight applications that allow sensor masses of hundreds of grams and require low-field (pT-nT @ 1 Hz) measurements, conventional sensors (fluxgates, induction coils) are still preferred.

Integrated single-axis SDT sensor package is rightmost, single chip. Other electronics include analog pre-amp, A/D signal converter, D/A converter for feedback, and microcontroller module.