Tech Briefs Magazine - October 2021 - MD-20

Liquid Metal Turns Motion into Electricity, Even
Underwater
The soft and stretchable device converts movement into electricity and can work in wet
environments.
North Carolina State University, Raleigh
Mechanical energy - such as the
kinetic energy of wind, waves, body
movement, and vibrations from motors
- is abundant. Researchers have created
a device that can turn this type of
mechanical motion into electricity. One
of the device's attributes is that it works
well underwater.
The heart of the energy harvester is a
liquid metal alloy of gallium and indium.
The alloy is encased in a hydrogel
- a soft, elastic polymer swollen with
water. The water in the hydrogel contains
dissolved salts called ions. The ions
assemble at the surface of the metal,
inducing charge in the metal. In -
creasing the area of the metal provides
more surface to attract charge. This
generates electricity, which is captured
by a wire attached to the device.
Since the device is soft, any mechanical
motion can cause it to deform
including squishing, stretching, and
twisting. This makes the device versatile
for harvesting mechanical energy. The
hydrogel is elastic enough to be
stretched to five times its original length.
In experiments, researchers found
that deforming the device by only a few
Any mechanical motion can cause the device to deform including squishing, stretching, and twisting. (Photo:
Veenasri Vallem)
millimeters generates a power density of
about 0.5 mW m-2. This amount of electricity
is comparable to several popular
classes of energy harvesting technologies.
Other technologies, however, do
not work well, or at all, in wet environments.
This feature may enable applications
from biomedical settings to athletic
wear to marine environments.
The researchers already have two re -
lated projects underway. One is aimed at
using the technology to power wearable
devices by increasing the harvester's
power output. The second project evaluates
how this technology could be used
to harvest wave power from the ocean.
For more information, contact Matt Shipman
at matt_shipman@ncsu.edu; 919-515-6386.
Built-In Vibration Control to Soundproof Spaces
Vibration-absorbing resonators could better soundproof walls and make vehicles more streamlined.
The Ohio State University, Columbus
Researchers have determined how
built-in resonators handle vibrations
under a variety of scenarios.
Resonators are devices that help manage
vibrations - some vehicles have
them to limit the sound emitted from
a car's muffler and some bridges and
buildings use them to limit noise and
movement from those structures.
Resonators use spring-like oscillation
to control and change vibrations -
some absorb and neutralize them
20
Cov
ToC
while others amplify and direct them
to specific places.
Resonators cut directly into materials can control vibrations.
Prior studies examined how to use
resonators to control sound that is
passed through walls or to reduce the
vibrations of moving vehicles. Those
studies focused on adding a resonator
to an existing structure or vehicle
part. The new study found that cutting
resonators directly into the wall
or vehicle material suppressed the
vibrations that could spread.
Motion Design, October 2021

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Tech Briefs Magazine - October 2021

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