Engineers have been converting mechanical stress into electricity using piezoelectric devices for more than a hundred years, but the goal of powering an iPod by pounding the pavement has remained elusive. Current piezoelectric materials are difficult to manufacture and typically contain toxic metals, such as nickel and lead. Researchers at Lawrence Berkeley National Laboratory have solved both problems by using a genetically engineered virus that self-assembles into a film. When pressure is applied, helical proteins on the viruses’ shells twist and turn, generating a charge. Tapping a postage-stamp-size swatch produces 400 millivolts of electricity, or enough to briefly power an LCD screen. Within 5 to 10 years, says bioengineer Seung-Wuk Lee, the film could be used to harness power from building vibrations, heartbeats, and other types of movement, too.
Like sunflowers bending toward light, solar panels can increase their energy output by rotating as the sun moves. But swiveling requires energy too. “Not many materials can respond to sunlight and also have a mechanical response,” says Hongrui Jiang, an engineer at the University of Wisconsin at Madison. Jiang developed a material that could passively shift the base of a solar array. He combined carbon nanotubes, which absorb sunlight, with
a liquid-crystalline elastomer (LCE) that contracts when it heats up. As solar energy warms one side of the base, the LCE shrinks, causing the solar panel to tilt toward the sun; once that side falls into shadow, the LCE cools and returns to its original height. Field tests show the system increases the efficiency of solar panels by an average of 10 percent.
Bacterial infections caught at U.S. hospitals kill about 100,000 patients annually; staff must continually sterilize surfaces to halt their spread. A material pioneered by a Harvard lab could prevent organisms from growing on medical equipment like catheters in the first place—it’s so slippery not even bacteria can stick to it. Based on SLIPS (slippery liquid-infused porous surfaces) technology, it leverages the same mechanism that causes insects to slide into a pitcher plant. Nanopores texturing a solid base, such as Teflon or metal, wick an ultrasmooth lubricant to it; everything else, including germs, simply slides off the liquid coating. Harvard materials scientist Tak-Sing Wong says SLIPS have the same effect on dust, ice, and graffiti, making them potentially useful to many more industries.
—Laura Geggelsingle page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.