Committee members:

Dr. Zhong Lin Wang (MSE, advisor)

Dr. Meilin Liu (MSE)

Dr. Russell D. Dupuis (ECE/MSE)

Dr. John D. Cressler (ECE)

Dr. Farrokh Ayazi (ECE)

Title: Theory of triboelectric nanogenerators for self-powered systems

Abstract:

Energy science is becoming an increasingly important multi-disciplinary area, for not only addressing the worldwide energy crisis, but also realizing desired power sources with advanced features for portable electronic devices and sensor networks. As for energy generation from environment, mechanical energy is one of the most important forms, which has a wide range of existence and can potentially be the energy supply for the independent and portable operation of electronic devices at anywhere. Very recently, based on triboelectric effect and electrostatic induction, a fundamentally new technology, triboelectric nanogenerator (TENG), has been demonstrated which shows unique merits including large output power, high efficiency, cost effective materials, and simple fabrication. But so far, the main limitation for continuing optimizing their output performance is a lack of fundamental understanding of their core working mechanism. Although some experimental work has been demonstrated, there is neither any theoretical research nor any existing theoretical method to deal with systems like TENGs that includes the complex coupling of both electrostatic and circuit simulation. Thus, the aim of this research has three folds:  (1) to develop a new simulation method to solve this kind of systems; (2) to unveil the fundamental working mechanism of TENGs by utilizing this new method, so the unique TENG output characteristics can be theoretically explained and optimization strategy for the whole TENG systems can be proposed; (3) to develop the first rational designed TENG-based self-powered system to produce mW-level DC electricity from widely-accessible human biomechanical energy, which can put this technology into practical applications.

In this thesis research, we first unveil the inherent capacitor behavior of TENG from basic electrodynamics. Then we derive the first governing equation for triboelectric nanogenerators, which are their V-Q-x relationship. With the V-Q-x relationship, we propose the first lump-parameter triboelectric nanogenerator equivalent circuit model and build the first generalized simulation tool for triboelectric nanogenerators. With this powerful simulation tool, we study the intrinsic output characteristics and load characteristics for different fundamental modes. From this analysis, the TENG optimization technique and the first TENG standard and figure-of-merit for quantifying the TENG performance are first-time brought out.

Besides the theoretical research, we also apply the developed theory to TENG-based self-powered system design. We have developed the first genuine self-powered system to meet mW requirement of personal electronics. The system includes a multilayered TENG, a power management circuit with 60% total efficiency, and a low leakage energy storage device. Our power management circuit provides the total efficiency that is about two magnitudes higher than the traditional direct charging. And the total system performance is 330 times higher than the state-of-art designs. Driven by palm tapping, this power unit can provide a continuous DC electricity of

1.044 mW on average power in a regulated and managed manner that can be universally applied as a standard power source for continuously driving numerous conventional electronics, such as a thermometer, a heart rate monitor (electrocardiograph/ECG system), a pedometer, a wearable electronic watch, a scientific calculator, and a wireless radio-frequency communication system. Our study demonstrates the first power unit that utilizes widely accessible biomechanical energy source to sustainably drive a broad range of commercial mobile and wearable electronic devices. This self-charging unit is a paradigm shift towards infinite-lifetime energy sources that can never be achieved solely by batteries.