Electret-based rotational energy harvesting (EBREH) technology is promising to overcome the electrostatically converted power limitation of velocity-damped resonance generators. Its structural parameter-dominated capacitance variation and parasitic capacitance should be correctly evaluated for the optimal design of EBREH devices regarding the high power output implement. Basically, finite-element analysis (FEA) seems the only access to predict capacitances across the complicated interdigitated electrodes in 3-D space because of partially or completely neglected fringing effects in currently available theoretical models. In this paper, we proposed a more efficient model for the capacitance of EBREH devices based on four-positioned capacitors, i.e., coplanar, parallel-plate, flat-plate nonparallel, and sector coplanar capacitors. Distinctively differing from other models, our model takes 3-D fringing effects associated with fringing fields into account properly in each type of the capacitor. In addition, the accuracy of the proposed model was much improved by combining parallel-wire capacitance theory and Schwarz-Christoffel mapping. Our model was verified through both the FEA and practical measurements with a fabricated EBREH structure. The measurement indicated that this novel capacitance model can be readily applicable to rotary and linear motion-driven EBREH devices and electrostatic sensors for further design optimizations with device parameters.

Charge trap in amorphous perfluoro-polymer electret is studied, focusing on electron trap site and trap energy. Low-energy inverse photoelectron spectroscopy is adopted to measure solid-state electron affinity (EA) of cyclic transparent optical polymer (CYTOP). EA of CYTOP CTL-S is discovered by compensating the unwanted charge-up effect. Negatively-charged electret materials (polyethylene, ethylene-tetra-fluoro-ethylene, poly-tetra-fluoro-ethylene, and CYTOP) are analyzed by quantum mechanical calculation. Density functional theory with long-range correction is adopted to analyze orbital energies of single molecular systems. Intramolecular distribution of trapped electron and EA are investigated. Calculated electron affinities of CYTOP polymers with different end group are qualitatively in accordance with trapped charge stability measured with thermal stimulated discharge, signifying that electron affinities obtained with the present simulation can be used as an index of amorphous polymer electret.

We designed a high-performance polymer electret material using a deep-learning-based de novo molecule generator. By statistically analyzing the enrichment of the functional groups of the generated molecules, the hydroxyl group was determined to be crucial for enhancing the electron gain energy. Incorporating such acquired knowledge, we designed a molecule using cyclic transparent optical polymer (CYTOP; perfluoro-3-butenyl-vinyl ether). The molecule was synthesized, and its surface potential for a 15-μm-thick film is kept at −3 kV for more than 800 h. Its performance was significantly better than all commercialized CYTOP polymer electrets, indicating great potential for its application in vibration-based energy harvesting. Our results demonstrate the application of machine learning in polymer electret design and confirm the combination of molecule generation and functional group enrichment analysis to be a promising chemical discovery method achieved via human–artificial intelligence collaboration.