A tiny sensor that can detect magnetic field changes as small as 70 femtoteslas—equivalent to the brain waves of a person daydreaming—has been demonstrated at the National Institute of Standards and Technology (NIST). The sensor could be battery-operated and could reduce the costs of noninvasive biomagnetic measurements such as fetal heart monitoring. The device also may have applications in Department of Homeland Security screening for explosives.
Described in the November issue of Nature Photonics, the prototype device is almost 1,000 times more sensitive than NIST's original chipscale magnetometer demonstrated in 2004 and is based on a different operating principle.
Its performance puts it within reach of matching the current gold standard for magnetic sensors, socalled superconducting quantum interference devices, or SQUIDs.
These devices can sense changes in the 3- to 40-femtotesla range, but must be cooled to very low (cryogenic) temperatures, making them much larger, power-hungry, and more expensive.
"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.
The new NIST mini-sensor could reduce the equipment size and costs associated with some noninvasive biomedical tests. The NIST group and collaborators have used a modified version of the original sensor to detect magnetic signals from a mouse heart. The new sensor is already powerful enough for fetal heart monitoring.
More info: www.nist.gov/public_affairs/releases/magnetometer.html
In NIST's new minimagnetometer, light from a laser (small gray cylinder at left) passes through a small container (green cube) containing atoms in a gas. The cell and any sample being tested are placed inside a magnetic shield (large grey cylinder). When no sample is present the atoms' "spins" align themselves with the laser beam, and virtually all the light is transmitted through the cell to the detector (blue cube). In the presence of a sample emitting a magnetic field, such as a bomb or a mouse, the atoms become more disoriented as the field gets stronger, and less light arrives at the detector. By monitoring the signal at the detector, scientists can determine the strength of the magnetic field. Photo by Loel Barr. (Click image to enlarge)
