Wearable And Self-Powered Electronic Devices Based On Flexible Electret Generators

Owning to the advantages of intelligent management and portability, flexible and wearable electronics have been widely applied in wireless communication, personal mobile health, etc. However, the batteries used in the wearable electronics will bring some problems, such as inconvenient recharging. Notably, converting 1-5% mechanical energy from human body into electricity can power various wearable electronics. In this thesis, flexible electret generators are fabricated to harvest mechanical energy generated by human body, and some typical applications in wearable electronics for these generators have been demonstrated as wel. The main results are listed below:1. The ideal model and fundamental working mechanism of the flexible electret generators are demonstrated, which are a parallel-plate capacitor with constant charges and electrostatic induction, respectively. Finite element simulation and numerical calculation method are used to theoretically analyze the working mechanism and processes of flexible electret generators. The influences of key physical parameters on the outputs of the flexible electret generators are also studied. Additionally, it's demonstrated that energy conversion efficiency of an arch-shape flexible electret generator is-0.32%.2. An arch-shaped flexible electret generator with simple structure is fabricated based on polytetrafluoroethylene (PTFE) electret film. Finger pressing the generator can light up 50 blue LEDs connected in series. By connecting a transformer for enhancing the output current, the generator can power a commercial infrared transmitter with an output current of-6 mA. Besides, generators are assembled with textile and a shoe to form the "Power textile" and "Power shoe" for harvesting the mechanical energy generated by human body, indicating the potentiality as wearable power source.3. A fiber-based generator (FBG) is fabricated by using cotton threads, polytetrafluoroethylene aqueous suspension and carbon nanotubes as raw materials. The FBGs based on electricity electrostatic effect can convert biomechanical motions/vibration energy into electricity with an average output power density of-0.1?W/cm2. Moreover, FBGs have been identified as an effective building element for a power textile that could trigger a wireless homemade body temperature sensor system, indicating the potential applications in personal mobile health.4. An active fiber-based strain sensor (AFSS) is fabricated by coiling a fiber-based generator around a stretchable silicone fiber. By virtue of the helix device structure and highly stretchable silicone fiber, AFSS shows high sensitivity and stable output performances and can detect the strain up to 25%. Furthermore, AFSS was demonstrated to detect finger motions, indicating the potential applications in future self-powered sensor system.5. Cellular composite electret film is fabricated with the ethyleno vinyl acetale copolymer (EVA) and biaxially oriented polypropylene (BOPP) via hot-pressing process. By virtue of the electric dipoles inside the air bubbles generated via corona charging process, the surface charges on both EVA and BOPP side could self-recover, even after the film being soaked in water and then naturally dried. Hence, sandwich-structured flexible generator based on EVA/BOPP composite film can effectively harvest energy from walking motion to power a wireless emitter and shows great ability to operate in extreme moisture conditions. This study potentially opens up new perspective for low-cost and robust wearable energy conversion.