Electrical pulses used for electroporation. Exponential decay pulse: When a capacitor charged to a voltage V₀ is discharged into cells, the voltage applied to the cells reduces exponentially with time. The time required for V₀ to drop to V₀/e is the time constant T, which denotes the pulse length. Square wave pulse: When the pulse from a capacitor is abruptly stopped after discharge, a square wave pulse is generated. The pulse length is the time for which the cells are subjected to the discharge. A slight drop in voltage occurs during the pulse length in all instruments. This is called the “pulse droop” and is measured as a percentage of V₀.