“For every device running at a specific
frequency, you need a timing source,”
says Argonne nanoscientist Dave
Czaplewski. “Multiple devices running at
multiple frequencies makes the network
much more complex.”
A common solution to this problem
involves the use of several resonators,
several signals, or both. In this case, the
researchers created a single, small reso-
nator that generates several frequencies
from one signal. This set of frequencies is
called a frequency comb, named for the
way frequencies appear evenly spaced,
like teeth, when plotted on a graph. So
with this you could fabricate a single oscil-
lator that generates a signal at all the dif-
ferent frequencies needed instead of mak-
ing a specific oscillator for each device.
The silicon device is no bigger than a
few grains of salt laid end to end. It con-
sists of three beams anchored together
that move together in two vibrations: a
side-to-side swaying motion and a twist-
ing motion.
“We used the interplay between those
two vibrations to obtain this frequency
response that ends up looking like a fre-
quency comb,” Czaplewski said.
Frequency combs are more commonly
used in optics, where they consist of laser
light pulses and are used to accuratelymeasure time. This new mechanical comb
could find use in the studying a dynamic
known as a SNIC bifurcation (saddle node
on an invariant circle) in mechanical, opti-
cal, and biological systems.
“In a biological setting, for example, un-
derstanding this behavior could help sci-
entists design MEMs elements that mimic
the way neurons respond to stimuli,” he
added.
The next step in the research, Lopez
said, will be to reproduce the frequency
comb phenomenon in higher-frequency
resonators and extend the number of
“teeth”—or frequencies—that can be
generated. NewsThis scanning electron micrograph shows a microelectromechanical resonator. The resona-
tor three silicon beams are clamped at both ends. The center of the beams are connected
to two comb drives for actuation and motion transduction. The fundamental vibration of the
beam is in the plane of the comb drives. However, at higher frequencies, the resonator can
move with a twisting motion around the center beams. When these two vibrational motions
interact, a periodic motion can be induced with a spectrum consisting of many equally-
spaced frequencies. (Credit: Argonne National Laboratory.)16
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