A novel MEMS triboelectric energy harvester and sensor with a high vibrational operating frequency and wide bandwidth fabricated using UV-LIGA technique

A novel triboelectric energy harvesting (TEH) and sensing system scaled down to microelectromechanical systems (MEMS) size is presented. The design is structurally optimized for harvesting the highest average power and power density while ensuring the structural robustness. Unlike traditional triboelectric energy harvesters, this design results in a high operating frequency with a wide bandwidth. Adoption of MEMS fabrication techniques including the use of spin-coated Teflon AF rather than a Teflon sheet, adaptation of UV-LIGA (Ultra-Violet Lithographie, Galvanoformung, Abformung) with modifications and implementation of a thick polyimide sacrificial layer make the fabrication process unique. If excited by +/- 9.33 g external vibration with a frequency of 1.15 kHz, the TEH can generate 0.179 mu W average power and 0.597 mu W peak power at an optimum resistive load of 256 k Omega. The peak surface power density, volumetric power density and acceleration-normalized volumetric power density reach 3.98 mu Wcm(-2), 2.64 mWcm(-3) and 30.3 mu Wcm(-3)/g(2), respectively. While the surface power density of the presented TEH is moderate, the volumetric power density and acceleration-normalized volumetric power density are quite competitive among the state-of-the-art designs. The TEH also demonstrates a wide operating frequency bandwidth of 920 Hz. If operated as an accelerometer, the device shows a linear sensitivity of 43 mV/g. Although the simulation predicts the optimum operating frequency and load resistance of the system to be at 800 Hz and 10 M Omega, respectively, the experimental results demonstrate these values to be at 1150 Hz and 256 K Omega. A few fabrication anomalies, most notably the notching in the Teflon layer and bowing of the proof-mass, are responsible for this deviation. In addition, a distortion is observed in the simulated output voltage profile which is not present in the experimental output voltage profile due to the presence of the parasitic capacitance in the experimental circuit. The aforementioned triboelectric energy harvester can have specific applications in the sensor and actuator systems in the aircraft industry as well as in the automobile industry, micro-robotic systems, prosthetic systems, and sensor nodes in the internet of things (IoT) due to its operating frequency and bandwidth range. (C) 2020 Elsevier B.V. All rights reserved.