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a The schematic illustration of the SPST-cotton tapping. b The electricity generation mechanism with SPST-cotton tapping. c The open-circuit voltages and d short-circuit currents with SPST-cotton tapping at different tapping frequencies. e Measured voltage curves of various capacitors at frequency of 3 Hz and force of 100 N. f The LEDs and electric watch were driven by the SPST-cotton device
