Portland, Ore. - The National Institute of Standards and Technology has developed a chip-scale atomic magnetometer, the size of a grain of rice, that can sense magnetic fields as weak as 50 picoteslas, or a million times weaker than Earth's magnetic field. Said to be far more sensitive and accurate for its size than existing designs, the tiny instrument could find use in handhelds that would sense unexploded ordnance, perform precise navigation or create geophysical maps (for locating minerals or oil). It could also enable medical instruments to be downsized.
NIST's Peter Schwindt, architect of the mini magnetometer, called it "sensitive enough to detect a concealed rifle at 12 meters or a 6-inch-diameter steel pipeline as much as 35 meters underground."
State-of-the-art flux gate magnetometers, such as the one used in the Mars rover, weigh as much as 6 pounds and are 100 times larger than Schwindt's battery-powered device. NIST estimates that when the sensor is integrated into a handheld system with all necessary supporting electronics, the system will measure only about 1 cm3, the size of a sugar cube.
Flux gate magnetometers can achieve equivalent sensitivity to the NIST device, but NIST says its design is more accurate. Further, a flux gate magnetometer measures only those magnetic fields that are parallel to its axis, whereas the NIST design simultaneously measures fields from all directions.
The only devices that rival the NIST magnetometer in accuracy and sensitivity are superconducting quantum interference devices-squids for short-but those devices must be cryogenically cooled, making them bulky, power-hungry and expensive, NIST said.
The atomic magnetometer contains a transparent chamber that holds rubidium vapor (made on-chip via a small heater). Semiconductor laser light is shone through the vapor to enable measurement of the energy levels of the electrons orbiting the rubidium atoms. Because a magnetic field changes the amount of energy that can be absorbed by the electrons, a simple photocell can read out the magnetism detected by measuring the amount of light passing through the chamber.
NIST thinks standard fabrication techniques will enable devices integrating the magnetometer.