PORTLAND, Ore. A mini-magnetometer 1,000 times more sensitive than current chip-based magnetometers has been developed by the National Institute of Standards and Technology (NIST).
The small, inexpensive mini-magnetometer achieves the femtotesla accuracy that used to be the exclusive domain of bulky, expensive superconducting quantum interference devices called SQUIDs.
By passing a semiconductor laser through a rice-grain-sized vial of rubidium vapors, NIST researchers achieved 70 femtotesla accuracy in a millimeter-sized package. The team has already demonstrated using the mini-magnetometer to record the heartbeat of a rat, and they expect the magnetometer to also enable applications in magnetoencephalography (MEG), the sensing of brain waves.
For example, a MEG helmet could perform real-time brain scans and low-cost MRIs as well as enable ultra-sensitive airport detectors for explosives and toxins.
SQUIDs can achieve only slightly better resolution, but require expense cooling to cryogenic temperatures, making them expensive and bulky. NIST's new mini-magnetometer is small and operates at room temperature.
The key to its small size and room-temperature operation is a transparent rubidium vapor vial measuring 3-by-2-by-1 millimeters. The vial holds about 100 billion atoms of rubidium gas. NIST's technque uses an inexpensive infrared semiconductor laser beam passed through the vial. The IR semiconductor detector measures the amount of transmitted light. In the presence of a magnetic field, the light will be dimmed--the stronger the field, the more light that is absorbed by the rubidium vapors.
The mechanism for dimming the light in the presence of a magnetic field is spinning rubidium atoms that naturally align themselves with the polarity of the laser beam. This allows light to pass through undiminished. But in the presence of a perpendicular magnetic field, the spins of the rubidium atoms turn against the grain of the laser beam, dimming its light.
NIST researchers are currently working on a nuclear quadrupole resonance device that uses the mini-magnetometer. The scheme will be able to perform spectral scans for detecting, for instance, the nitrogen compounds in explosives.