Friday, October 28, 2016

A New Style of Power Generation

Fashion has a way of circling back to earlier times, although often with a twist. From bellbottoms to bootcut and stretch pants to leggings, styles often seem to move forward and backward simultaneously. In one aspect, however, we are always moving forward. With smartwatches that can alert you to an incoming call, dresses adorned with LEDs, and bracelet fitness trackers, the market for wearable technology seems to be expanding right along with our capabilities.

Smart clothes and wearable monitors have the potential to do more than “wow” users and their friends; they can monitor health, increase safety, and even turn your pants into a keyboard. Data gathered from health monitors can potentially be pooled and studied, offering new insight into our lifestyles, biology, and health conditions. Through wearable technology we may even find ways to interact with social media that support our face-to-face interactions instead of distract us from them. The possibilities are exciting, but there are technological hurdles that scientists and engineers are busy working to overcome. A big one is limited battery life.

In order to make wearable electronics practical for more applications by eliminating their reliance on batteries, an international team of scientists led by Zhong Lin Wang from the Georgia Institute of Technology designed a lightweight, easy to make, wearable fabric that can power electronics. The scientists describe their work this week in the AAAS journal Science Advances.

The prototype fabric captures energy from the Sun and the motion of the person wearing the fabric, converts it into electricity, and then stores the energy—acting kind of like a charger and a battery all in one. Imagine if you could power your hearing aid, cell phone, fitness tracker, or twinkling dress just by taking a walk. That definitely beats a bulky battery pack that needs frequent charging.

In this work, the team combined recent developments in solar cells that harvest energy from sunlight, nanogenerators that harvest energy from the motion of their environment, and supercapacitors that store energy. The key lies in using fiber-shaped solar cells and supercapacitors that are connected in such a way that they form a nanogenerator, a device that turns mechanical energy into electricity.
As illustrated below, the fabric consists of two layers. The top layer is composed of a specific kind of fiber-shaped solar cell, noted as F-DSSC. The bottom layer is made of fiber-shaped supercapacitors (F-SC). These two devices are woven together and then paired to form a specific kind of nanogenerator called a triboelectric nanogenerator (F-TENG), that harvests energy when the wearer moves.

Schematic of the self-charging power textile.
Image Credit: From Science Advances 26 Oct. 2016: Vol. 2, no. 10, e1600097
This work is licensed under CC BY-NC.
One of the most promising features of this design is that it harvests energy from sunlight AND from motion. Past research has demonstrated that you can self-power LEDs by integrating solar cells into fabric, but this only works if you have enough light. Anyone that has planned an outdoor wedding knows that relying on the weather to act in your favor without a backup plan is risky. The nanogenerator is like the tent of outdoor weddings. Together, these devices create a much more reliable power source.

Members of the research team have been working on this kind of hybrid energy harvester for several years, and with this paper they go as far as testing a prototype. After characterizing each of the three devices separately, the team weaved them into net-like patches. They attached the patches to a t-shirt. Tests of the power generated by someone wearing the t-shirt while participating in regular indoor and outdoor activities showed promising results.

While this isn’t mall-ready technology yet, activity in the field of wearable technology indicates that self-powered clothing may not be too far away. Don’t be surprised if future fashion trends center on how best to wear your power.

Kendra Redmond

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