Breakthrough Magnetic Field Sensor Developed
National Institute of Standards and Technology scientists have demonstrated a tiny sensor that can detect magnetic field changes as small as 70 femtoteslas (a level that is equivalent to the brain waves of a person who is daydreaming). NIST calls this a breakthrough with applications including explosives screening and medicine. The sensor could be battery operated and could reduce the costs of non-invasive biomagnetic measurements, such as fetal heart monitoring.
The prototype device will be described in the November issue of Nature Photonics. It is almost 1,000 times more sensitive than NIST's original chip-scale magnetometer demonstrated in 2004 and is based on a different operating principle. Its performance is close to the current "gold standard" for magnetic sensors, superconducting quantum interference devices (SQUIDs), which require cooling to cryogenic temperatures and thus are expensive.
The prototype consists of low-power infrared laser and a rice-grain-sized container holding gaseous rubidium atoms. As the laser beam passes through the atomic vapor, scientists measure the transmitted optical power while varying the strength of a magnetic field applied perpendicular to the beam. The amount of laser light absorbed by the atoms varies predictably with the magnetic field, providing a reference scale for measuring the field. The stronger the magnetic field, the more light is absorbed. The NIST group and collaborators have used a modified version of the sensor to detect magnetic signals from a mouse's heart.
"The small size and high performance of this sensor will open doors to applications that we could previously only dream about," project leader John Kitching said.