Patterned thin-film triboelectric generator for harvesting micro-meso scale ambient energy for kinematic sensing
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Harnessing random micro-meso scale ambient energy (M2SAE), which is widely available in human motions, wind driven vibrations, water surface fluctuations, etc., is not only clean and sustainable, but it also enables self-powered sensors and devices to be realized. In my research, I have fabricated a case-encapsulated triboelectric generator (cTENG) based on the principles of sliding electrification for harvesting M2SAE from reciprocating motions. Patterned with multiple sets of grating electrodes and lubricated with polytetrafluoroethylene (PTFE) nanoparticles, cTENG generated an average effective output power of 12.2 mW over a 140 kΩ external load and a power density of 1.36 W/m2 at a sliding speed of 1 m/s. The cTENG can also be triggered by direct-applied forces, as well as, inertia forces to effectively capture ambient energy from vibrations of large amplitudes and low frequencies such as those arising in human motions and water surface fluctuations. Based on the success of the patterned cTENG, I have built a self-powered velocity sensor for either rectified linear or rotary motion by sourcing the energy from the triboelectric generator. Employing alternating Kapton-copper strips arranged in a spiral configuration wrapped on the inner and outer surfaces of two concentric cylinders, voltage assays for linear and rotary motions can be measured without the need for an external power source. The triboelectric generated output signals when integrated with a digital circuit and a microcontroller unit can be directly processed into remarkably stable, macro-scale output signals for measurements of (0.1-0.6) ms-1 +_ 0.5% for linear velocities and (300-700) rpm +_ 0.9% for rotary velocities. I have also fabricated a self-powered, thin-film motion direction sensor by harvesting the operational energy from a close-proximity triboelectrification of two surfaces in relative reciprocation. The mover made by coating a thin polytetrafluoroethylene film with a 2-column, specially arranged array of copper electrodes and the stator is made by coating the top and bottom surfaces of a thin polyimide film with a 2-column aligned array of copper electrodes placed in an alternating pattern. As the mover traverses over the stator, the electrodes in the mover actively generate electric signals of ±5 V to attain a peak power density of ≥ 65 mW/m2 at speeds of 0.3 ms-1. The prototype can be extend for 2-D motion direction sensing. The highly pliable sensor can be easily bent to spread over curved and uneven surfaces. Finally, I have demonstrated a quasi-static angular positioning sensor based on 4-channel encoded pattern on the electrification surface. The sensor consists of a rotator designed with 4-channel coding Cu foil material and a stator including electrodes covered with FEP (fluorinated ethylene propylene) ﬁlm. Due to coupling effect of triboelectriﬁcation and electrostatic induction, the sensor generates electric output signals in response to mechanical rotating motion of an object mounted with the sensor. The sensor can read and remember the absolute angular position regardless being continuously monitored or segmented monitored. Velocity and acceleration can be calculated as well. Under a rotation speed of 100 rad min-1, the output voltage of the sensor reaches as high as 60 V. Angular resolution of 22.5° is achieved and can be further improved by increasing the number of channels. Triggered by the output voltage signal, the rotating characteristics of the steering wheel can be real-time monitored and mapped by being mounted to the sensor. My work represents the first successful attempt in harvesting M2SAE using a patterned triboelectric generator and then, using the harvested ambient energy to drive a kinematic sensor that is integrated with a commercial digital circuit for a dual-mode speed and direction sensing. I believe my pioneering demonstration of the applied triboelectric technology will have a huge impact in the industrial commercialization of self-powered devices and sensors.