Soft Electronics

A completely soft, stretchable energy harvesting device from liquid metal and hydrogels

Motivation: "Using liquid metal and hydrogels we can create a soft, stretchable power harvester to operate round-the-clock health monitoring devices."

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NC State University, ASSIST Center – Raleigh NC

What if you could charge your phone, headset, or fitbit by simply stretching or walking?

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From September 2015 to May 2018, I worked with the Advanced Self-Powered Systems of Integrated Sensors and Technology (ASSIST). Under the supervision of Dr. Michael Dickey, I used soft materials like hydrogel and liquid gallium alloy to create a device that generates electricity by stretching and squishing. It works using a phenomenon called electric double layer capacitance (EDLC) which is essentially layers of electric charges that form at an interface. In our case, we created an electric double layer between liquid metal and hydrogel. By stretching the device, which can be small enough to fit onto your portable electronic, we can create an electric current. And voila, your everyday motion becomes your source of electricity.

Presenting at “Posters on the Hill” April 2017 and meeting Senators Tom Tillis (left) and Richard Burr (right) on Capitol Hill.

Presenting at “Posters on the Hill” April 2017 and meeting Senators Tom Tillis (left) and Richard Burr (right) on Capitol Hill.

I fabricated my devices using polymeric hydrogels and liquid eutectic indium-gallium alloys by combining principles of microfluidics and 3D printing technology. I tested for IV-curves, energy density, and mechanical strength. The result of my research was to find that the largest energy density corresponded to the largest surface area. Capacitance, or the amount of electric charge per surface area, is directly proportional to surface area. The trick with this device is to maximize the area of the EDLC so we can extract the highest energy out of the system. The result is scavenging micro-watts of "free" energy that would otherwise be wasted, but now can now be used to power small electronics.

 I have submitted an invention disclosure to the university and have presented my work at five different conferences, most notably Washington D.C. "Posters on the Hill" and the Africa Materials Research Society (A-MRS) in Gaborone, Botswana.

 Appalachian State Energy Summit

 In summer 2016 I was invited as a student highlight speaker to present my research and motivation for self-powered electronics. I was chosen as the first recipient of the annual IMPACT Award for my research, and won first place in the undergraduate poster symposium.

Skills

Over the course of this project, I've learned what "iterative design process" really means. I've gained skills in prototyping, circuit building, and composite materials engineering.

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Microfluidics & Surface Science

I maximized change in surface area by altering the surface chemistry of my device. I used perfluorocarbons and silanes to increase hydrophobicity and O2 plasma treatment for the opposite effect.

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Prototyping & Circuit Building

I've built dozens of model systems for my energy harvester, always starting from schematics. Using SolidWorks, I've designed and 3D printed hydrogel molds to cure my polymer into various shapes and sizes. I've learned how to decrease series resistance in order to maximize energy output.

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Electrical Characterization

I used a standard electrometer to study the effects of stretching and squishing on current output. I was able to correlate a change in surface area to an increase in current output using a goniometer and high-speed camera.

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Electrochemistry

Before working with hydrogels, I performed studies on various ionic liquids and their effectiveness as charge carriers. I looked at parameters including concentration, solubility, and ionic radius and their effect on charge density.