N13A-T019 TITLE: Low Frequency / High Sensitivity Tri-Axial Magnetometer

TECHNOLOGY AREAS: Air Platform, Sensors, Battlespace

ACQUISITION PROGRAM: Distributed Netted Systems (DNS)

OBJECTIVE: Create a compact low cost tri-axial magnetometer with low noise at low frequencies that can be used for airborne and undersea applications.

DESCRIPTION: Significant progress has been made recently in developing room temperature magnetometers with sensitivities approaching that of Superconducting Quantum Interference Devices (SQUIDs).[1] The Defense Advanced Research Project Agency (DARPA) has pushed the limit in sensitivity with advances in multiferroic materials and atomic magnetometers pursuing a sensitivity goal of 0.1 femtotesla (fT)/rtHz in the frequency band between 1�100 Hz, which is an order of magnitude better than the best SQUIDs.[2] Other work has focused on designing tri-axial magnetometers based on vapor cell technology.[3] Extracting the vector components of the magnetic field eliminates sensor dead-zones and allows for better signal characterization compared to only collecting a total-field value.

Lower frequency tri-axial operation presents the additional challenge of sensor stability in achieving low noise, both stability of electronic components and stability of sensor orientation in Earth�s magnetic field. A current Navy SBIR should achieve a total-field noise level of 10 picotesla(pT)/rtHz in the 0.01 � 100 Hz frequency band using less than 10 Watts of power for airborne applications,[4] but additional noise reduction at still lower frequencies and power levels is needed for surveillance applications. This solicitation seeks to take the next step in magnetometer designs by combining recent developments in high sensitivity with a tri-axial design to create a compact low-cost/low power device that is operational in Earth�s background magnetic field.

PHASE I: Define the concept for a tri-axial magnetometer having a noise level of 1 pT/rtHz in the frequency band between 0.001 � 10 Hz along each axis and having less than 30 pT of variation in the scalar field value over all orientations. The magnetometer should consume less than one watt of power on average, be a compact design (<100 cm3 for the sensor head and <1000 cm3 for the electronics), and be cost competitive with flux gate magnetometers in quantities of 1000. Explicitly show how the magnetometer can achieve these goals in Earth�s field and identify key sensor components. While not required, designs that can measure the vector field components in a stable frame of reference during physical rotation of the sensor will be highly favored.

PHASE II: Demonstrate the design meets the Phase I requirements in a laboratory bench top test. Then construct two compact prototype magnetometers for verification of performance in Earth�s background field. Provide an assessment of manufacturing yield and product reliability of the final design.

PHASE III: This sensor would be expected to transition to commercial low cost production for PMS 485 in support of the DNS Shallow Water Surveillance System.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The developed technology could improve attitude control on commercial satellites and provide an error correction signal for Global Positioning System (GPS) receivers. The National Aeronautics and Space Administration (NASA) would be interested in the technology for geologic surveys with an absolute accuracy of �1 nT in the calibrated vector components and an absolute scalar accuracy of �200 pT.

REFERENCES:
1. Dmitry Budker & Michael Romalis, "Optical Magnetometry," Nature Physics 3, 227-234 (2007).

2. Bill Coblenz, "DARPA HUMS Program," http://www.darpa.mil/Our_Work/DSO/Programs /Hetersostructural_Uncooled_Magnetic_Sensors_(HUMS).aspx, 2011.

3. S. J. Seltzera and M. V. Romalis, "Unshielded three-axis vector operation of a spin-exchange-relaxation-free atomic magnetometer," Applied Physics Letters Vol. 85, No. 20, 15 November 2004.

4. Smullin, S.J., Savukov, I., Vasilakis, G., Ghosh, R.K., and Romalis, M.V., "A Low-Noise High-Density Alkali Metal Scalar Magnetometer." arXiv:physics/0611085, 24 Jul. 2009. Web. 11 Nov. 2009.