By BBC News Online Science Editor Dr David Whitehouse
April 4, 1999
First they brought you the world's smallest guitar,
bring you world's smallest musical instrument - the
The microscopic guitar made by Cornell University
researchers two years ago was just a whimsical demonstration
of new nanofabrication technology.
But the nanoharp is a true stringed instrument that
real music, if only we could hear it. It plays a tune too
high for even a dog to hear.
The nanoharp's strings vibrate at frequencies as high
MHz and are probably the fastest human-made moving object.
The human ear cannot hear frequencies above 22 kHz.
"This is another use for our new ability to make
mechanical systems," said Harold Craighead, Cornell's
professor of applied and engineering physics, who supervised
"By making things very small you bring out properties
aren't evident in larger materials. We can combine this
information with other types of measurements made by
researchers in materials science to help understand how
The new device is carved out of a single crystal of
The strings are actually silicon rods 50 nanometres (nm) in
diameter, ranging from about 1,000 to 8,000nm long. A
nanometre is one billionth of a meter, making each string
about 150 atoms thick.
The entire device is about the size of a red blood cell.
Cornell University scientists hope to use it to study
properties of very small vibrating systems - ones that some
day could be used to make extremely sensitive chemical
sensors, for example.
The researchers are studying resonance effects in these
They make the silicon rods vibrate by applying a radio
frequency voltage signal through the silicon base.
Then they measure the resulting vibrations by bouncing
light off the strings and observing the reflected light with
a sensitive interferometer.
The researchers have measured the highest frequency
vibrating strings, and the smallest vibrating strings,
smaller by a factor of four than anyone else has measured.
Many aspects of the nanoharp's behaviour have yet to be
As with a full-sized harp, the resonant frequency at
one of these tiny strings vibrates depends on the length and
However, scientists say that the microscopic strings
under tension like those in a musical instrument, and the
resonant frequency of the nanoharp's strings follows a
different rule, varying as the square of the length, like a
metal bar struck by a hammer.
"It's really more like a xylophone than a harp," they say.
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