Researchers at the National Institute of Standards and Technology have developed a sensor that detects magnetic fields as weak as one picotesla (one-trillionth of a tesla). For comparison, the Earth’s magnetic field is 50 million times stronger than a picotesla. The sensor, about the size of a sugar cube, contains about 100 billion rubidium atoms heated and vaporized into a gas. A low-powered IR laser is fired into the atoms and a fiber-optic sensor detects how much of the laser makes it through the rubidium. Rubidium atoms absorb more light as the magnetic field around them increases, the quality that let the researchers actually measure magnetic fields.
The new device is slightly less sensitive to magnetic fields than a squid (superconducting quantum interference device), which is considered the gold standard of magnetic sensors and is the preferred sensor in magnetoencephalography (MEG) machines.
MEG is a noninvasive procedure for imaging magnetic fields generated by electrical brain activity. It is used to explore the perceptual and cognitive process in healthy humans and to test the vision of newborns and map brain activity prior to brain surgery for removing tumors or treating epilepsy.
The downside of squids: they must be kept at –269°C to get good results, which requires they have cryogenic cooling. The new sensor, however, operates at room temperature and is small and lightweight. It can also be mass produced, while squids are difficult to fabricate and assemble.
Researchers hope to get the cost of MEG machines down to where every hospital can afford one to test for traumatic brain injuries. They even foresee the day football teams have their own MEG machines. The research team is currently trying to boost the amount of light that gets detected and measured after making it through the rubidium. This would make the new sensor as sensitive as squids.