Structural engineering of triboelectric energy harvester

Abstract

With recent advances of electronics, size and operating power of a wearable as well as portable device, an implantable device, and a wireless sensor networks (WSN) has been intensively scaled down. These small-scale wireless systems are usually powered by a battery, but an inevitable recharging process and limited lifetime of the battery demand an alternative powering method. Small-scale energy harvesting from the wasted ambient energy becomes an attractive solution for implementing a sustainable, reliable, and cost-effective system. In particular, the triboelectric energy harvester (TEH) attracts special interests based on distinguished advantages such as high power, design flexibility, wide material spectrum, wide energy sources available, low temperature fabrication, and wide application area. From the four parts of this paper, progresses on structural engineering of TEH are discussed. In the first part, TEH with nature-replicated surfaces are introduced. Output electrical energy is en-hanced due to the enlarged contact area stemmed from the micro and nanostructures in nature. In addition, improvement of humidity resistance property is firstly observed after the interfacial structural formation. In the second part, the interfacial structure of TEH is discussed in analytical viewpoints. In particular, deformation behavior of interfacial structures with applied force is determined. A force-voltage relationship stemmed from the deformation of interfacial structures is discussed in detail. Based on the analysis, design guideline of interfacial structures of TEH is suggested. In the third part, a TEH with new structure platform is suggested. External mechanical vibration re-peats an oscillating motion of a polymer-coated metal oscillator floating inside a surrounding tube. Continu-ous sidewall friction at the contact interface of the oscillator induces current between the inner oscillator elec-trode and the outer tube electrode to convert mechanical vibrations into electrical energy. The floating oscilla-tor embedded TEH is versatile for almost any kinds of external vibration form. In the last part, a TEH with hybrid mechanism of triboelectricity and induced electricity is introduced. The triboelectric generator (TEG) part and the electromagnetic generator (EMG) part are independently but simultaneously yielding power by sharing the floating oscillator. There is clear energy benefit not only in the equal-displacement condition but also in the equal-energy condition with consideration of increased mass. Based on the collected electrical energy, actual charging of the smart phone and real-time operating the wire-less illuminance sensor as well as turning on the LED lamp and driving the portable fan are successfully demonstrated.