(color online) The variation of w when the input voltage is 6 pulses with different duration, interval, and amplitude: (a) duration = 0.01 s, interval = 0.2 s, amplitude = 0.9 V; (b) duration = 0.01 s, interval = 0.2 s, amplitude = 0.6 V; (c) duration = 0.005 s, interval = 0.2 s, amplitude = 0.9 V; (d) duration = 0.01 s, interval = 20 s, amplitude = 0.9 V. T is the period of the applied pulse signal, T = duration+interval.