Mini-Sensor for Biomedical and Security Applications

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 non-invasive bio magnetic measurements such as fetal heart monitoring. The device also may have applications such as homeland security screening for explosives.

The prototype device is almost 1000 times more sensitive than NIST's original chip-scale 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, so-called 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 NIST prototype consists of a single low-power (milliwatt) infrared laser and a rice-grain-sized container with dimensions of 3 by 2 by 1 millimetres. The container holds about 100 billion rubidium atoms in gas form. As the laser beam passes through the atomic vapour, 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 small size and high performance of this sensor will open doors to applications that we could previously only dream about", project leader John Kitching says.

The new NIST mini-sensor could reduce the equipment size and costs associated with some non-invasive biomedical tests.; Quelle: National Institute of Standards and Technology (NIST)