填空题
Watching Microcurrents Flow
We can now watch electricity as it flows through even the tiniest
circuits. By scanning (扫描) the magnetic field (磁场) generated as electric
currents flow through objects (物体), physicists have managed {{U}} {{U}}
1 {{/U}} {{/U}}. 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 (细微的) changes in the magnetic field of an object and {{U}} {{U}}
2 {{/U}} {{/U}}.
Their sensor is adapted from an
existing piece (现有配件) of technology that is used to measure large magnetic
fields in computer hard drives. "We redesigned the magnetic sensor to make it
capable of measuring (测量) very weak changes in magnetic fields," says
Xiao.
The resulting device is capable of detecting (测定) a
current as weak as 10 microamperes, even when the wire is buried deep within a
chip, and it shows up features (图案) as small as 40 nanometers across.
At present, engineers looking for defects (缺陷) in a chip have to peel off
(剥开) the layers and examine the circuits visually; this is one of the obstacles
{{U}} {{U}} 3 {{/U}} {{/U}}. 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 (电迁徙)—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. For example, it could look directly at microscopic
cracks in an airplane's fuselage, {{U}} {{U}} 4 {{/U}} {{/U}}.
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 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 {{U}}
{{U}} 5 {{/U}} {{/U}}.
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