Since the current and voltage output on the resistor is the differential of and by the QA QB t, calculated current and voltage output will be independent of the choice of charge reference state. Similarly, if the periodic boundary condition is utilized to solve the equation, the calculated current and voltage output will also be independent of the choice of charge reference state. 1.4 Minimum Achievable Charge Reference State (MACRS) The most commonly utilized charge reference state is called minimum achievable charge reference state, which utilizes the amount of charge on metal 2 under SC condition when = 0 x as (which is also the minimum achievable amount of charges on metal 2 under real Q0 operation). The main advantage to utilize the minimum achievable charge reference state is to set both and to 0 and this time stands for the total transferred QSC(x=0) VOC(x=0) QSC charges amount from one electrode to another under SC condition. FEM results from other charge reference states can be easily converted to the MACRS. From the above derivation, we can easily get the below conversion equation. 1.5 Symmetric charge reference state in FTENGs The minimum achievable charge reference state is the most commonly utilized charge reference state, but in FTENGs, utilizing this charge reference state will cause the calculated nonsymmetrical. However, an inherent symmetry can be easily observed in the structure VOC for both contact-mode FTENGs and sliding-mode FTENGs. The reason that the calculated are nonsymmetrical under MACRS mainly because the amount of charges assigned on VOC metal 1 and metal 2 are different. To maintain the symmetry, we can assign both metal 1 and metal 2 have the same amount of charges (σwl/2). Then the calculated will be fully VOC symmetric. Figure S1 shows the FEM calculation result of under symmetric charge VOC
Since the current and voltage output on the resistor is the differential of QA and QB by t, the calculated current and voltage output will be independent of the choice of charge reference state. Similarly, if the periodic boundary condition is utilized to solve the equation, the calculated current and voltage output will also be independent of the choice of charge reference state. 1.4 Minimum Achievable Charge Reference State (MACRS) The most commonly utilized charge reference state is called minimum achievable charge reference state, which utilizes the amount of charge on metal 2 under SC condition when x = 0 as Q0 (which is also the minimum achievable amount of charges on metal 2 under real operation). The main advantage to utilize the minimum achievable charge reference state is to set both QSC(x=0) and VOC(x=0) to 0 and this time QSC stands for the total transferred charges amount from one electrode to another under SC condition. FEM results from other charge reference states can be easily converted to the MACRS. From the above derivation, we can easily get the below conversion equation. 1.5 Symmetric charge reference state in FTENGs The minimum achievable charge reference state is the most commonly utilized charge reference state, but in FTENGs, utilizing this charge reference state will cause the calculated VOC nonsymmetrical. However, an inherent symmetry can be easily observed in the structure for both contact-mode FTENGs and sliding-mode FTENGs. The reason that the calculated VOC are nonsymmetrical under MACRS mainly because the amount of charges assigned on metal 1 and metal 2 are different. To maintain the symmetry, we can assign both metal 1 and metal 2 have the same amount of charges (σwl/2). Then the calculated VOC will be fully symmetric. Figure S1 shows the FEM calculation result of VOC under symmetric charge
1-s2.0-S2211285515000142-mmc1.docx