Figure 4. V signals of the KLP, HILP, and HOLP-TENGs with (a, b) varying F from 3 to 9 N with a fixed f of 9 Hz and (c, d) varying f from 3 to 9 Hz with a fixed F of 9 N. (e) Cyclic tapping tests of the KLP-, HILP-, and HOLP-TENGs for 100,000 cycles. (f) η vs . S for the previously-reported tribopositive biopolymer-based TENGs.