By Aalyia Shaukat, contributing writer
A team of scientists and student researchers at Clemson’s Nanomaterials Institute (CNI) have recently developed a wireless charging technology that converts mechanical energy into an electric field that can charge local batteries or capacitors up to 3 meters away. An article recently published in Advanced Energy Materials reveals that the device harnesses the triboelectric effect — a phenomenon that occurs as a material becomes electrically charged when contacting a different material through friction. When actuated by constant mechanical motions such as hand-tapping, the wireless triboelectric nanogenerator (W-TENG) can yield output voltages up to 2,000 V and peak powers of 70 mW — enough to power most wireless sensor nodes for modern IoT applications.
The evolution of triboelectric nanogenerators (TENGs)
The occurrence of triboelectricity is nothing new — we’ve all experienced some form of triboelectricity in our daily lives through the static electricity produced when running a comb through our hair, rubbing our shoes over a carpet, or even rubbing a balloon on our heads. The effect was originally documented as far back as the 18th century, when Swedish physicist Johan Carl Wilcke published the first paper on triboelectric in 1757. More recently, though, there has been heavy research in leveraging TENGs for energy harvesting in wireless sensor networks (WSNs).
This technology can potentially take the free energy expended from the environment — such as vibrations from humans walking, hands pressing, and vibrations from machinery — and convert it into a sustainable micro-scale power source for the millions of sensor nodes coming into existence. Power consumption and battery life are a major tipping point for wireless sensor nodes. It’s the reason why LPWAN technology has become so popular for its 10-year battery life and ability to transmit data for vast distances. But to be able to constantly keep a battery charged over its lifetime is a pretty desirable alternative considering that it cuts down on the major cost of battery charging and replacement. Energy harvesting is particularly helpful in scenarios in which it is critical for the sensing and transmitting equipment not to go offline, such as in medical body area network (MBAN) applications for wireless cardiac monitoring of a patient in the cardiac care unit (CCU).
Wireless triboelectric nanogenerator (W-TENG)
The W-TENG may have broader implications with the ability to wirelessly charge local energy storage devices or even directly power simple transmissions. A video released by the university showed a student researcher remotely powering a smart mirror by tapping the W-TENG device.
“It not only gives you energy, but you can use the electric field also as an actuated remote,” said Sai Sunil Mallineni, a Ph.D. student working on the project. “For example, you can tap the W-TENG and use its electric field as a ‘button’ to open your garage door, or you could activate a security system — all without a battery, passively and wirelessly.”
The W-TENG is based upon CNI’s ultra-simple triboelectric nanogenerator (U-TENG) that is constructed of commercially available indium-tin oxide coated polyethylene terephthalate and Kapton electrodes. Instead of plastic, the W-TENG’s bottom electrode is constructed from a carbon composite composed of graphene and polylactic acid (PLA) — a biodegradable polymer that can be found in cornstarch and sugarcane. A sheet of Teflon is placed over the 3D-printed electrode to generate the triboelectric effect.
“We use Teflon because it has a lot of fluorine groups that are highly electronegative, whereas the graphene-PLA is highly electropositive,” says Podila. “That’s a good way to juxtapose and create high voltages.” Electric charges build up on the connected copper ribbon to a large-enough degree that a strong electric field is induced.
TENGs exhibit one distinct setback: The large output voltage is accompanied by a low output current for nominal power? This can potentially be resolved by shrinking the device and placing a number of them in a package to lessen voltage and increase current at the output. Naturally, power management circuitry is necessary to charge a battery or capacitor. Still, this technology is a strong addition to the arsenal of energy-harvesting techniques (e.g., thermoelectric generators (TEGs), piezoelectric materials, and photovoltaic cells) for WSNs.
Advertisement
