Boost the Performance of Triboelectric Nanogenerators through Circuit Oscillation

Abstract

DOI: 10.1002/aenm.201900772 and sustainable energy. Triboelectric nanogenerator (TENG), as a novel mechanical energy harvesting technique invented by Wang et al., has proven to be an effective power alternative for small electronics and attracted plenty of interests in recent years.[4–11] To make TENG more practical and compatible to the commercial electronics, it is always desirable to improve the output performance. One way is from the device perspective, for example, choosing appropriate materials, designing the device structure, etc.,[12–21] which is effective but needs specific optimization. The other one is from the power management perspective,[22–31] which is more general. Over the past few years, extensive efforts have been put into the power management of TENG for enhancing its output performance.[22–32] Zi et al. first proposed the concepts of “figure of merits” and “cycles for maximum energy output (CMEO),”[28] which provide the guideline for the maximum energy output per cycle of a TENG device. Afterward, Xi et al.[29] and Cheng et al.[30] have separately demonstrated the power management circuits which assist the TENG to achieve the 72% and 80% of the CMEO. However, the further approaching or even beyond the CMEO is more than difficult. Moreover, the maximum energy output can only be achieved when the load matches the impedance of TENG. Considering the low intrinsic capacitance of TENG and low frequency characteristics of the ambient vibration, the matching impedance is always beyond magnitude of tens or hundreds of megaohms.[15,33,34] Although several existing power management strategies can help reduce the matched impedance to several megaohms,[28,30] it is still much larger than the input resistance of common electronics, which are typically around hundreds of ohms. Recently, Qin et al. reported an interesting TENG system which can eliminate the requirement of impedance matching,[31] however, their system is only applicable for elaborate devices. Herein, in both theory and experimental verification, we report a novel power management strategy named oscillation assisting TENG (OA-TENG), which can exceed the CMEO limit of individual TENG under arbitrary load resistance. Unlike the previous power management strategies, the farther the load resistance from the matching impedance, the higher energy output per cycle can be provided from the OA-TENG, which means this strategy is especially suitable for the common electronics of low resistance. This OA-TENG is achieved by Triboelectric nanogenerator (TENG) which harvests ubiquitous ambient mechanical energy is a promising power source that can meet the distributed energy demand in the internet of things, wearable electronics, etc. However, the available output of TENG is severely limited by the saturated polarized charge density, small intrinsic capacitance, and large matching impedance. Herein, an effective power management strategy is proposed that flips the free charges on the conductive layer through a controlled LC oscillating circuit composed of the diode, switch, inductor, and the intrinsic capacitor of TENG. In this way, the equivalent charge density reaches a level higher than the saturated polarized charge density. The simulation and experiments show that the limit of energy output can be exceeded under arbitrary load resistance, especially for the low-impedance common electronics. It is believed that such a general, low-cost, and highly effective strategy can further broaden the applications of TENG devices across the fields and probably be a new performance evaluation standard for TENG.