Watching Microcurrents Flow

　　We can now watch electricity as it flows through even the tiniest circuits. By scanning the magnetic field generated as electric currents flow through objects, physicists have managed ____1____. The technology will allow manufacturers to scan microchips for faults, as well as revealing microscopic defects in anything from aircraft to banknotes.

　　Gang Xiao and Ben Schrag at Brown University in Providence, Rhode Island, visualize the current by measuring subtle changes in the magnetic field of an object and ____2____.

　　Their sensor is adapted1 from an existing piece of technology that is used to measure large magnetic fields in computer hard drives.2”We redesigned the magnetic sensor to make it capable of measuring very weak changes in magnetic fields,” says Xiao.

　　The resulting device is capable of detecting a current as weak as 10 microamperes, even when the wire is buried deep within a chip, and it shows up features as small as 40 nanometers across.

　　At present, engineers looking for defects in a chip have to peel off the layers and examine the circuits visually; this is one of the obstacles ____3____. But the new magnetic microscope is sensitive enough to look inside chips and reveal faults such as short circuits , nicks in the wires or electro migration — where a dense area of current picks up surrounding atoms and moves them along. “It is like watching a river flow,” explains Xiao.

　　As well as scanning tiny circuits, the microscope can be used to reveal the internal structure of any object capable of conducting electricity.3 Fpr example, it could look directly at microscopic cracks in an aeroplane’s fuselage, ____4____. The technique cannot yet pick up electrical activity in the human brain because the current there is too small, but Xiao doesn’t rule it out4 in the future. “I can never say never,” he says.

　　Although the researchers have only just made the technical details of the microscope public, it is already on sale,5 from electronics company Micro Magnetics in Fall River, Massachusetts. It is currently the size of a refrigerator and takes several minutes to scan a circuit, but Xiao and Schrag are working ____5____.

　　词汇：

　　circuit 电路 scan 扫描;细看

　　magnetic 磁铁的;磁石的 subtle 精巧的;细微的

　　visualize 使……形象化;使……具体化 dense 密集的;稠密的

　　sensor 感应器