Watching Microcurrents Flow

　　We can now watch electricity as it'flows through even the tiniest circuits. By scanning(掃描) the magnetic field(磁場(chǎng)) generated as electric currents flow through objects(物體), 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 thecurrent by measuring subtle(細(xì)微的) changes in the magnetic field of an object and __(2)__.

　　Their sensor is adapted~ from an existing piece(現(xiàn)有配件) 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 (測(cè)量)very weak changes in magnetic fields," says Xiao.

　　The resulting device is capable of detecting(測(cè)定) a current as weak as 10 microamperes, even when the wire is buried deep within a chip, and it shows up features (圖案)as small as 40 nanometres across.

　　At present, engineers looking for defects(缺陷) in a chip have to peel off(剝開) the layers and examine the circuits visually; this is one of the obstacles _(3). But the new magneticmicroscope is sensitive enough to look inside chips and reveal faults such as short circuits, nicksin the wires or electromigration(電遷移) -- 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 For example, it could look directly atmicroscopic cracks in an aeroplane's fuselage, ___(4) ___. The technique cannot yet pick upelectrical activity in the human brain because the current there is too small, but Xiao doesn't rule it out(排除。。。的可能性) 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,(上市)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) ___.

　　練習(xí)：

　　A to shrink it to the size of a desktop computer and cut the scanning time to 30 seconds

　　B to making chips any smaller

　　C to take tiny chips we require

　　D to picture the progress of the currents

　　E converting the information into a color picture showing the density of current at each point

　　F faults in the metal strip of a forged banknote or bacteria in a water sample

　　練習(xí)答案

　　1D 2E 3B 4F 5A

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