Magnetometers and Navigation

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Magnets and magnetic compasses had been used since centuries ago to help navigators cross oceans. Such devices did help the early explorers; however, magnets usually do not tell you where you are but only the direction you are going. However, a new form of magnet, a magnetometer being developed by the Air Force Research Laboratory (AFRL) in collaboration with the Massachusetts Institute of Technology’s Lincoln Laboratory, is aiming to make magnetometers not only tell you about direction of travel but also provide precise location information.

The new magnet being developed by AFRL contains small diamonds that contain nitrogen-vacancy defects. The lattice contains carbon, which is what diamonds are made from, and nitrogen replacing a carbon atom with the lattice having an adjacent carbon missing. In addition to the magnetic poles, there is a fainter terrestrial (or crustal) magnetic field that are more distinctive and specific to the place you are on. Unlike the magnetic field produced by the Earth’s core, this magnetic field is static, meaning it can be used for location information since it does not move like the magnetic poles. The goal for the US Air Force has been is to develop a compass-like device that can also use the location-specific magnetic field that can then translate that signature to a location unique to where someone is. In this new developing device, a fluorescence forms when exposing the carbon-nitrogen lattice to green laser light with that fluorescence giving a signature on the strength and alignment of the magnetic field at a given point. Such information would provide location information based on a detailed map of the location and known magnetic signature. The interactions that make this information possible also happens at a sub-atomic or quantum level, where interactions at the lattice means that the device needed for this to work could be very small.[1]

It is clear that from such an application one does not have to depend on satellite-based GPS data. The reason why a terrestrial-base GPS is needed is that if the United States goes to war against a major adversary then satellites could be lost and GPS would not be possible to use. Once created, a terrestrial-based magnetometer is not only compact, but that would allowing them to be easily used in the field or integrated within larger systems. While the theory and capabilities are now known ad well uderstood, the devices themselves still require cooling, limiting their current application in different temperatures. However, the application of allowing these quantum interactions to operate at room temperature or other temperature extremes is a key goal that scientist soon hope to fully solve. The benefit of such magnetometers is they can revolutionize a variety of field including navigation, with fields such as medical imagery and geosciences potentially benefiting from these new magnetometers.[2] Current devices do now exist that allow the use of magnetometers to detect the crust’s magnetic field, but most tools have been cumbersome and do not operable in normal conditions. 

The crustal field, shown here, is weaker than the core field, but is fixed and has features that are useful in non-GPS navigation. The intensity of the fields are measured in nano teslas (nT), shown increasing in strength from blue to red. (Graphic courtesy of NOAA)
The crustal field, shown here, is weaker than the core field, but is fixed and has features that are useful in non-GPS navigation. The intensity of the fields are measured in nano teslas (nT), shown increasing in strength from blue to red. (Graphic courtesy of NOAA via Air Force Research Laboratory)

For navigation, the sensitivity of magnetometers should also make them more accurate than most GPS devices. This then has great utility beyond military applications and many civilian uses will likely benefit from these systems. However, for the systems also to be operational, detailed maps of the Earth’s surface will be needed so one can locate the magnetic field to a given area at high resolution. This can be done using both aerial and satellite imagery, although even remote regions need to be covered to allow full global navigation. Beyond GPS signals potentially being jammed, the dependence on a terrestrial-based location system will be of great benefit if other unforeseen events make satellite systems inoperable. Magnetometer-based navigation should be accurate to within 13-meters in places and likely more accurate in some other regions.[3]

It is clear that magnetometers that can operate using sub-atomic interactions and are sensitive to the more subtle terrestrial magnetic field could create a revolution in navigation, among other fields. There is still a lot of work to do to make devices that can be sensitive and easy to create and operate; however, the basic physics has been solved and the key theoretical limitations are understood. We might expect that magnetometers usable for navigation could be on the horizon in the next few years. Another obstacle could be costs, but it is hoped such devices will only have a small amount of diamonds needed to operate. 

References

[1]    For more on the new magnetometers being developed for location information and how they may replace GPS devices, see: Air Force investigates using quantum materials in new navigation tool – https://www.wpafb.af.mil/News/Article-Display/Article/2172915/air-force-investigates-using-quantum-materials-in-new-navigation-tool/

[2]    For more on how magnetometers can potentially benefit many domains, see:  Fescenko, I., Jarmola, A., Savukov, I., Kehayias, P., Smits, J., Damron, J., et al. (2020). Diamond magnetometer enhanced by ferrite flux concentrators. Physical Review Research2(2), 023394. https://doi.org/10.1103/PhysRevResearch.2.023394


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[3]    For more on possible navigation benefits, see: https://www.economist.com/science-and-technology/2020/07/18/magnetometers-based-on-diamonds-will-make-navigation-easier.


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