Tiny sensor offers new medical, security uses

U.S. researchers have developed a magnetic sensor smaller than a grain of rice and sensitive enough to detect a fetal heart beat, offering the potential for a host of new medical and security uses.

The sensor, described in the journal Nature Photonics, provides a low-cost and portable way to detect changes in a magnetic field, they said.

"What we've done is demonstrate a very good sensitivity with a very small cell," said John Kitching of the U.S. Department of Commerce's National Institute of Standards and Technology, who led the project.

The device is 1,000 times more sensitive than NIST's last microchip-sized mini-sensor. Kitching said the device could be used in a range of applications, from fetal heart monitoring to screening for explosives.

Electric currents, such as those from power lines, emit a magnetic field, as do the electrical impulses that make the heart contract or brain cells fire.

The most sensitive magnetic sensors -- superconducting quantum interference devices, or SQUIDS -- can detect very weak changes in magnetic fields but must be kept very cold, making them much bigger and far more power-hungry.

While the NIST device sacrifices a bit of that sensitivity, it makes up for it in portability.

Kitching said the device is highly adaptable. It could be used to measure electrical activity in the brain, helping to spot tumors or monitor brain function. Or it could be used in war zones to detect bombs that may not have exploded.