Low-power 3-axis magnetometers using spin dependent tunneling for UGS and security applications

Spin Dependent Tunneling (SDT) magnetic field sensors are under development as high performance magnetometers for Unattended Ground Sensing applications. These sensors have been successfully incorporated into a 3-axis magnetometer circuit for prototype level demonstrations with noise floors on the order of 1 nT / root Hz. at 1 Hz. Future versions of these magnetometers will require lower power and lower noise floor than the existing prototype. This paper examines near term developments in the SDT magnetometer power requirements, considering the transducer + amplifier combination as the basic unit. An emphasis is placed on discussing the trade-offs between low power and high sensitivity. The impact of both SDT transducer impedance and amplifier power and noise are considered. Projections show that a 1 pT / root Hz at 1 Hz noise floor is achievable in a transducer + amplifier unit consuming 1 to 10 mW. SDT sensors are being made in an effort to reach these goals. Special emphasis in this paper is on efforts to make an intrinsically low power transducer. Further discussion will explain some fundamentals of SDT sensor operation and how they impact ultimate expected magnetometer performance.