Just last week, a research team in South Korea devised a way to improve the electrical output of the triboelectric nanogenerators (TENGs) developed by researchers at the Georgia Institute of Technology.
Not to be outdone, a team of scientists at Georgia Tech, led by Zhong Lin (Z.L.) Wang, have improved the capabilities of their TENGs technology by making them far more flexible. In the process, the team has given the devices a new name: skin-like triboelectric nanogenerators, or STENGs. These stretchy generators should provide another flexible power source for the increasing number of flexible electronics.
In research described in the journal Science Advances, the Georgia Tech researchers combined a hybrid material made up of an elastomer and an ionic hydrogel that can harvest energy from movement and provide tactile sensing. The flexibility and tactile sensing suggests that the material could be used to make self-powered electronic skin or self-powered soft robots.
Like TENGs, STENGs harvest static electricity from friction. A typical TENG device consists of two different materials that are rubbed together. The trick is to use one material that tends to give off electrons, such as glass or nylon, so that it will donate them to materials that tend to absorb them, such as silicon or teflon. By converting this mechanical energy to electricity, the TENGs can power small electronic devices.
The major difference between STENGs and TENGs is the use of electrical conductors as the electrode. The elastomer serves as the electrification layer, and the ionic hydrogel acts as the electrode. The main benefit: The researchers report that using these new materials gave the STENGs stretch ratios of over 1000 percent. In an e-mail interview with IEEE Spectrum, Wang noted that the flexible TENG his team developed last year—dubbed the shape-adaptive TENG—could be stretched to just 300 percent of its original length.
In addition to flexibility, the new stretchable material is highly transparent. It allows 96.2 percent of visible light to pass through it, which should help in transmitting optical data. The material is also able to cope with fairly high temperatures of 30 degrees Celsius, and with humidity as high as 30 percent. That may not offer much benefit if you’re in a tropical jungle, but it would make the STENGs suited to a lot of other climates.
Wang also points out that the material, which is biocompatible, is relatively low cost thanks to the use of fairly conventional materials that still provide high performance.
The research out of the Ulsan National Institute of Science and Technology (UNIST) in South Korea reported last week yielded a new polymer that serves as a dielectric material (or insulator) for TENG devices, and provides a 200-fold increase in the power output over traditional TENG devices.
But the new STENG devices achieved areal power densities approaching 35 milliwatts per square meter—far better than traditional TENGs—without the new polymer insulator. Wang said that the UNIST polymer could be adapted into the latest STENG devices, promising not only greater flexibility but also increased power output.