NIST researchers have built and demonstrated a magnetometer about the size of a rice grain and capable of detecting magnetic field changes down to 50 pT. When packaged with its associated electronics, the sensor, which can run off a battery, is expected to measure ~1 cc. It can be fabricated and assembled on semiconductor wafers using existing techniques for making microelectronics and microelectromechanical systems.
The secret ingredient is rubidium vapor, formed by heating a minute portion of the element inside a sealed, transparent cell. Semiconductor laser light is transmitted through the vapor. The amount of light energy absorbed by the rubidium atoms is affected by the presence of a magnetic field, and these changes are detected by a photocell. Stronger fields produce proportionally higher energy levels and thus greater changes in the amount of energy absorbed.
According to researcher Peter Schwindt, the sensor's primary advantages are its accuracy, its ability to detect total field strength and, of course, its extremely small size. These features give it an edge over fluxgate magnetometers, SQUIDs, and magnetoresistive devices. The atomic model could find applications in precision navigation, geophysical mapping to locate minerals or oil, medical instruments, and handheld devices for sensing unexploded ordnance.
In addition to Schwindt, the research team consists of S. Knappe, V. Shah, L. Hollberg, J. Kitching, L. Liew, and J. Moreland. The work was funded by DARPA-MTO.