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Generating Electricity from Simple Motion – Even Underwater

This is a modified version of an article written by Matt Shipman, Research Lead in University Communications.

Professor Michael Dickey and his colleagues have created a soft and stretchable device that converts movement into electricity and can work in wet environments.

“Mechanical energy – such as the kinetic energy of wind, waves, body movement and vibrations from motors – is abundant,” says Prof. Dickey, corresponding author of a paper on the work. “We have created a device that can turn this type of mechanical motion into electricity. And one of its remarkable attributes is that it works perfectly 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 energy harvester
The Energy Harvester

The water in the hydrogel contains dissolved salts called ions. The ions assemble at the surface of the metal, which can induce electric charge in the metal if it’s deformed. Increasing and decreasing the area of the metal changes the amount of surface area that attracts charge. This generates electricity, which is captured by a wire attached to the device. Video of the technology can be found at https://www.youtube.com/watch?v=VB3jGaPWQGE.

“Since the device is soft, any mechanical motion can cause it to deform, including squishing, stretching and twisting,” Dickey says. “This makes it versatile for harvesting mechanical energy. For example, the hydrogel is elastic enough to be stretched to five times its original length.”

“However, other technologies don’t work well, if at all, in wet environments,” Dickey says. “This unique feature may enable applications from biomedical settings to athletic wear to marine environments. Plus, the device is simple to make.”

In experiments, researchers found that deforming the device by only a few millimeters generates a power density of approximately 0.5 mW m-2. This amount of electricity is comparable to several popular classes of energy harvesting technologies.

“There is a path to increase the power, so we consider the work we described here a proof-of-concept demonstration.”

The researchers already have two related projects under way.

One project 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.

The paper, “A Soft Variable-Area Electrical-Double-Layer Energy Harvester,” is published in the journal Advanced Materials. First author of the paper is Veenasri Vallem, a Ph.D. student in Prof. Dickey’s research group. Co-authors include Erin Roosa and Tyler Ledinh, who were CBE undergrads when the work was done; Sahar Rashid-Nadimi and Abolfazl Kiani, who were visiting scholars with Prof. Dickey’s group and are now at California State University, Bakersfield; and Woojin Jung and Tae-il Kim of Sungkyunkwan University in South Korea, who worked on the project while working with Prof. Dickey’s group.

The work was done with support from NC State’s ASSIST Center, which is funded by the National Science Foundation under grant EEC-1160483. Additional support came from the Coastal Studies Institute of North Carolina and the Fostering Global Talents for Innovative Growth Program supervised by the Korea Institute for Advancement of Technology.