Science News for Students - Spring 2021

Self-powered surface may evaluate table- tennis play Engineers have used wood to create self-powered sensors that track the ball

Can a smart surface up your table-tennis per- formance? Engineers at Georgia Tech have built a self-powered one that tracks your plays—no batteries or power cord required.

By Stephen Ornes

JONATHAN STOREY/GETTY IMAGES PLUS; ANGELO D’AMICO/ISTOCK/GETTY IMAGES PLUS Wang’s team published its findings on the in- novative sensors November 26, 2019, in Nature Communications . × Zhong LinWang started playing table tennis only five years ago. But two years ago he and other researchers came up with a clever way to up their game: Build a smart table. Their new prototype can measure where a ball lands, how fast the ball’s going and where it’s headed. It can do this because its surface forms the top layer of a novel self-powered sensor. The data it acquires could guide players to perform better. Wang is a materials scientist at the Georgia Institute of Technology, in Atlanta. He’s an expert at inventing devices that provide their own power. In 2012, he invented a triboelectric nano generator . He calls it TENG, for short. You know “triboelectricity” by its more common name—static electricity. Over the years, Wang has worked with research- ers to build many devices using TENGs. What makes the new game table truly unique is its use of wood as the source of one of the TENG’s layers. Lignin is the stuff that makes wood and other plants rigid and hard. But after boiling in chemicals, this lignin now flexes and bends eas- ily. Squares of it become the top layer of a TENG. Beneath it, Wang’s team added a layer of copper to conduct electricity. They attached that layer to a copper wire. As a ball strikes the table’s TENG surface, the top layer pushes against the copper layer. Electrons accumulate. When the surface bends back to its original position, a small amount of electric current travels through the wire. In lab tests, the engineers showed that a grid made of wood TENGs could be used to measure where the ball hit, how fast it was going and the angle it was traveling. Table-tennis players can use such data to learn more about their game and how to play better, saysWang. (Fact: He’s been using it to improve his own technique.) Im- portantly, the new smart table won’t need a battery to detect the ball.

Explainer What are polymers?

Polymers are everywhere. Just look around. Your plastic water bottle. The silicone rubber tips on your phone’s earbuds. The nylon and polyester in your jacket or sneakers. The rubber in the tires on the family car. Now take a look in the mirror. Many proteins in your body are poly- mers, too. Consider keratin, the stuff your hair and nails are made from. Even the DNA in your cells is a polymer. By definition, polymers are large molecules made by bonding (chemically linking) a series of building blocks. The word polymer comes from the Greek words for “many parts.” Each of those parts is what scientists call a monomer (which in Greek means “one part”). Think of a polymer as a chain, with each of its links a monomer. Those monomers can be simple — just an atom or two or three — or they might be complicated ring-shaped structures containing a dozen or more atoms. In an artificial polymer, each of the chain’s links will often be identical to its neighbors. But in proteins, DNA and other natural polymers, links in the chain often differ from their neighbors. —Sid Perkins

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