Spatially Integrating Magnetometer
Navy SBIR 2019.2 - Topic N192-122
NAVSEA - Mr. Dean Putnam - firstname.lastname@example.org
Opens: May 31, 2019 - Closes: July 1, 2019 (8:00 PM ET)
TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors
ACQUISITION PROGRAM: PMS 450, Virginia Class Submarine Program Office
OBJECTIVE: Develop a magnetic field sensor that measures the magnetic field over a long, thin volume, and produces a triaxial vector result that quantifies the integral of the magnetic field vector over the volume.
DESCRIPTION: The Closed Loop Degaussing (CLDG) System (also called Circuit-D) presently used on Virginia- class submarines requires permanently installed triaxial magnetic field sensors at locations throughout the ship.
These sensors are subject to interference caused by nearby magnetic materials, adversely affecting system performance and requiring additional sensors for mitigation. Cabling/mounting space and magnetic interference considerations were an issue during ship design due to the large number of sensors required (40-60), and improvements in these areas provide a cost reduction opportunity for future hulls. Reducing the number of sensors and/or reducing the impact of nearby magnetic interference would significantly reduce the cost and complexity of the CLDG system, and simultaneously improve the performance of the system by eliminating a source of magnetic interference.
CLDG is an enhanced version of an ordinary shipboard degaussing system, designed to address the problem of long- term ship hull magnetization changes. A CLDG system measures the magnetic fields inside the ship and calculates the corresponding off-board fields using the onboard measurements. The CLDG system will automatically monitor and maintain a ship's ferromagnetic signature at a low level for all operational maneuvers and geographic locations, automatically detecting and compensating for changes in hull magnetization caused by ambient geomagnetic fields, stress, and temperature.
The magnetic sensors used for CLDG require high stability (both physical and electronic), low sensor noise, and high measurement accuracy over the range of temperatures and magnetic fields encountered in shipboard engineering spaces. Incorrect magnetic field measurements will produce incorrect degaussing controller behavior, and a corresponding increase in the ship’s electromagnetic signature.
There are large spatial magnetic field gradients close to a surface ship or submarine hull which are produced by local hull in-homogeneities (e.g., welds, bulkheads, support beams) and material characteristic changes induced by pressure. Present "point" triaxial fluxgate magnetometers measure the hull fields using small transducers that vary in size from one to three cm in diameter. Large spatial gradients caused by local hull anomalies may influence the measured field amplitude, causing the resulting measurement to indicate erroneous large-scale hull effects. The difference between the "point" field measurement and the large-scale aggregate field must be minimized for accurate control of the shipboard degaussing system. An integrating magnetometer would still include the local anomaly fields, but the local anomaly effects would be "averaged" over the length of the transducer, reducing their effect.
This is a very specialized application and there are currently no commercially available devices that measure magnetic fields in this manner. Arrays of many individual magnetometers could possibly be configured to produce a similar response, but would be costly due to the high sensor and wiring count. Navy R&D efforts to date demonstrated the feasibility of a fluxgate-based integrating magnetometer. Some integrating sensors using other sensing modalities such as magnetoimpedance have been reported in academic literature, but stability and accuracy in a harsh, high field shipboard environment (i.e. MIL-STD-2036 internal or external to a submarine pressure hull) is challenging. Fluxgate sensor technology with sufficient high field, temperature, and dimensional tolerance/control/correction would be the logical extension of past research and development (R&D) efforts, but
more recent magnetic sensing techniques such as doped fiber optics, high temperature superconductors, diamond nitrogen vacancy sensors, or miniature quantum magnetometers could also be applied to this problem as a completely new R&D approach.
The final sensor should be easy to integrate into a ship or submarine hull (i.e., able to be embedded into internal or external hull coatings, able to be integrated into or included with existing cable runs). It should be able to integrate over curved paths up to 100 meters long, and it needs to have high reliability and tolerance for harsh shipboard conditions. A capability for in-situ calibration would also be an advantage.
The sensor must meet the following minimum performance requirements: (1) Dynamic Range of +/- 200,000 nT or more; (2) Operating Temperature Range of 0°C (or lower) to 50°C (or higher); (3) Measure integrated triaxial (normal and 2 tangential) magnetic field components along a defined linear path in close proximity to a magnetic hull steel surface. The integration path shall be at least 2 meters in length, and no more than 10 cm from an HY80 steel surface; (4) Accuracy of vector components (deviation from actual field value) less than 10 nT over the entire dynamic and temperature range; (5) Noise less than 0.1 nT per root Hz at 0.1 Hz (same as a typical fluxgate) over the entire dynamic and temperature range; (6) DC bandwidth to no less than 10 Hz; (7) Deviation from exact linearity (field applied vs field measured) less than or equal to 0.005% of full scale over the entire dynamic and temperature range; and (8) Variation of field reading with temperature less than 0.1 nT/degree Celsius over the entire dynamic range.
PHASE I: Provide a concept for a magnetic sensor design to address the stated minimum requirements and desired characteristics in the Description. Demonstrate the feasibility of the sensor design by performance predictions based on peer-reviewed literature, physics-based modeling and simulation, and/or data obtained from laboratory testing of sensor components. Show that the proposed sensor design meets at least all of the requirements in the Description, and that the proposed sensing technology has no inherent limitations that would prevent the final product from achieving any of the remaining requirements. Develop a Phase II plan. The Phase I Option, if exercised, will include the initial layout and capabilities description to build the unit in Phase II.
PHASE II: Develop and deliver a prototype magnetic sensor that demonstrates the performance of the chosen technology for this application and meets all stated minimum requirements. Mount the prototype on a sheet of HY80 or similar magnetic steel, and test it in a magnetically controlled environment. Use separate tests and test equipment configurations as necessary to evaluate the prototype against individual requirements.
PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the magnetic sensor to Navy use. The sensor is expected to be integrated into Virginia class submarines and eventually the Columbia class. The sensor will require validation testing and combat system certification.
The sensor to be developed would have no obvious commercial applications. Military applications are in the general area of ship susceptibility to magnetic influence mines. The Navy need is focused on Virginia class submarines, but the technology is applicable to present and future degaussing systems on any naval platform.
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2. Scarzello, John F., Holmes, John J., and O'keefe, Edward C. "Spatially integrating fluxgate manetometer having a flexible magnetic core." U.S. Patent No. 6,417,665, 9 July 2002. https://www.google.com/patents/US6417665
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5. Ripka, P. “Sensors based on bulk soft magnetic materials: Advances and challenges.” Journal of Magnetism and Magnetic Materials, 320(20), 2008, pp.2466-2473. https://www.sciencedirect.com/science/article/abs/pii/S0304885308003867
KEYWORDS: Electromagnetic Sensor; Fluxgate; Integrating Magnetometer; Integrating Magnetic Sensor; Integrating Racetrack Fluxgate Electromagnetic; Diamond Nitrogen Vacancy Sensors