The team, led by Nelson Sepulveda, an associate professor in the Electrical and Computer Engineering Department at Michigan State University and lead investigator of the project, has created three devices: an LCD screen which “harvests energy from a user’s touch;” an array of LEDs which lights up when somebody squeezes its pressure pad; and a keyboard which is powered only by tapping its keys. The ground-breaking findings, published in the journal Nano Energy, suggest “we’re on the path toward wearable devices powered by human motion,” said Sepulveda. “What I foresee, relatively soon, is the capability of not having to charge your cell phone for an entire week, for example, because that energy will be produced by your movement,” added Sepulveda, whose research is funded by the National Science Foundation. The device is made of a thin, film-like material that functions on a principle similar to the piezoelectric effect. The piezoelectric effect is a property of some materials to produce an electric charge in response to stress. However, piezoelectric materials are solid and inflexible, like glass. The technology uses a nanogenerator, called a biocompatible ferroelectret nanogenerator, or FENG that can be bent and folded. The thin film that the researchers have created with a charge on both sides, the energy in it is produced by a small-scale physical change, such as the tap or swipe of a finger. When the film is squeezed, the relative charge between the sides changes, and electricity flows.
To manufacture the nanogenerator, a silicon wafer is created with a few thin layers of substances that include environment friendly substances such as silver, polyimide and polypropylene ferroelectric (all natural well-disposed materials), in addition to particles or charged particles. When the device is compressed by human motion, or mechanical energy, it creates electrical energy. The researchers also discovered that the device becomes more powerful when folded. By folding the material over and over, the electricity output can be upped to levels that power gadgets. Actually, it produced enough power to light 20 LEDs.
“Each time you fold it you are increasing exponentially the amount of voltage you are creating,” Sepulveda said. “You can start with a large device, but when you fold it once, and again, and again, it’s now much smaller and has more energy. Now it may be small enough to put in a specially made heel of your shoe so it creates power each time your heel strikes the ground.” Whether the device would be commercially available, Sepulvida says it will need more development before it can be commercialized. Currently, he does not have any agreement with a company to produce a FENG for the market at this time. “At this point we’re still trying to understand all the details on how the device operates and works so that we could optimize the power that we could extract from the device and make it more efficient,” says Sepulvida. While the researchers are not sure how much energy the device might be able to produce, they say that based on energies known to be produced by human movement; it is possible to make some back-of-the-envelope estimates. Sepulvida says, “If we are able to completely harvest the energy that is dissipated from the human heel strike, you should be looking at charging your smart phone completely by just regular walking during a day.” Source: Sciencealert
