micromachines Article Technique for Measuring Power across High Resistive Load of Triboelectric Energy Harvester Subhawat Jayasvasti, Panu Thainiramit , Phonexai Yingyong and Don Isarakorn *   Citation: Jayasvasti, S.; Thainiramit, P.; Yingyong, P.; Isarakorn, D. Technique for Measuring Power across High Resistive Load of Triboelectric Energy Harvester. Micromachines 2021, 12, 766. https://doi.org/10.3390/mi12070766 Academic Editor: Nam-Trung Nguyen Received: 26 April 2021 Accepted: 26 June 2021 Published: 29 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Instrumentation and Control Engineering, School of Engineering, King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok 10520, Thailand; 60601162@kmitl.ac.th (S.J.); panu.th@kmitl.ac.th (P.T.); 62601019@kmitl.ac.th (P.Y.) * Correspondence: don.is@kmitl.ac.th Abstract: This paper proposed a more-accurate-than-conventional measurement technique for de- termining electrical power across exceptionally high-impedance of triboelectric energy harvester (TEH). The key idea of this proposed technique was to measure the voltage across an introduced, parallelly-connected resistor divider to the oscilloscope instead of the voltage across the harvester. An experiment was set up to verify the measurement accuracy performance of this technique against the ideal theoretical values. The maximum percentage error found was only 2.30%, while the conven- tional measurement technique could not be used to measure voltage across high impedance TEH at all because the readings were not accurate, i.e., the measurement error would be at least over 10%. Therefore, we concluded that this proposed technique should always be used instead of the conventional measurement technique for power measurement of any TEH. A suggestion that we would like to offer to researchers investigating or developing a TEH is that, in using our measurement technique, a good starting point for a load to probe resistance ratio is 1:10, a ratio that worked well for our TEH test bench that we developed. Keywords: internal resistance; electrical measurement; power measurement; triboelectric energy har- vester 1. Introduction Power generation by harvesting waste energy has been investigated intensively in the last decade. Specifically, an energy harvester is required for uses of internet of things (IoTs) applications, including autonomous wireless devices [1,2]. It can reduce the use of conventional battery, whose disposal can create an environmental problem. Its proper recycling process is also expensive. Many kinds of external energy are produced all the time and everywhere (e.g., wind flow, sun light, gradient thermal, and mechanical vibration). Mechanical vibration energy can be captured and converted into electrical power. Research has reported on the mechanical energy harvesting in different transduction principles, e.g., electrostatics, electro-mechanism, and piezoelectricity. Recently, the triboelectric effect has been given much attention because of its potential and advantages as an energy harvester. The working principle of triboelectricity is simply the generation of a static electrical charge by friction or temporary contact based on charge transfer between two materials. However, measuring the electrical power across triboelectric energy harvester (TEH) could be problematic due to its high resistivity. To be able to determine the maximum electrical power produced by triboelectric energy harvester (TEH), as a power generator, its internal resistance R int must be known first because the internal resistance R int dictates the value of a proper resistive output load (i.e., the optimal resistance) to which the generator can deliver. At a proper value of load resistance R L , an electrical power generator can provide the maximum power. In other words, the maximum power transfer occurs when the load resistance R L is optimal for the generator. Micromachines 2021, 12, 766. https://doi.org/10.3390/mi12070766 https://www.mdpi.com/journal/micromachines