SAN JOSE, Calif. The National Institute of Standards and Technology (NIST) claims to have demonstrated a tiny, magnetic sensor that can detect magnetic field changes as small as 50 picoteslas a million times weaker than the Earth's magnetic field.
The device, which is about the size of a grain of rice, can be powered with batteries and is about 100 times smaller than current atom-based sensors with similar sensitivities, according to NIST.
The research was funded by the U.S. Defense Advanced Research Projects Agency (DARPA). The device is described in the Dec. 27 issue of Applied Physics Letters.
Applications include hand-held devices for sensing unexploded ordnance, precision navigation, geophysical mapping to locate minerals or oil, and medical instruments.
The new magnetic sensor can be fabricated and assembled on semiconductor wafers using existing techniques for making microelectronics and microelectromechanical systems (MEMS).
"Magnetic fields are produced by the motion of electrons either in the form of an electrical current or in certain metals such as iron, cobalt and nickel," according to NIST. "The NIST miniature magnetometer is sensitive enough to detect a concealed rifle about 12 meters (40 feet) away or a six-inch-diameter steel pipeline up to 35 meters (120 feet) underground.
"The sensor works by detecting minute changes in the energy levels of electrons in the presence of a magnetic field. A tiny sample of the element rubidium is heated within a sealed, transparent cell to form a rubidium vapor," according to NIST.
"Light from a semiconductor laser is transmitted through the atomic vapor. In the presence of a magnetic field, the amount of laser light that is absorbed by the atoms changes and this is detected by a photocell. Larger magnetic fields produce proportionally bigger changes in the atomic energy levels and change the absorption by the atom," according to NIST.