A two-stage power management and storage system from Georgia Institute of Technology improves the efficiency of triboelectric generators to harvest energy from irregular human motion, such as walking, running or finger tapping. The storage device supplies DC current at voltages appropriate for powering wearable and mobile devices such as watches, heart monitors, and thermometers.

Triboelectric nanogenerators generate small amounts of electrical power from mechanical motions.
(Credit: Zhong Lin Wang Laboratory)

The system uses a small capacitor to capture alternating current generated by the biomechanical activity. When the first capacitor fills, a power management circuit then feeds the electricity into a battery or larger capacitor.

By matching the impedance of the storage device to that of the triboelectric generators, the new system can boost energy efficiency from just one percent to as much as 60 percent. The power management system power converts fluctuating power amplitudes and variable frequencies to a continuous direct current.

The power management system can work with any triboelectric generator that produces a minimum of 100 microwatts.

The system requires some power to operate. With finger tapping as the only energy source, the power unit provides continuous direct current of 1.044 milliwatts. The unit can work continuously with the motion, allowing devices to be operated even as the device charges the battery or capacitor.

Beyond portable electronics, the researchers believe that the system could be useful in powering networks of sensors, allowing long-term operation without the need for replacing batteries.