Electric circuit of pulse generator and field diagram. a) Electric circuit diagram for generating positive (+E) and negative (-E) square-wave electric fields during field inversion experiments. Direct current (DC) supply is from an external source. NC, normally closed switch; AC relay, alternate current relay; Com, common outlet. Inset b) shows a profile of the electric field during a typical FIGE experiment where + E = - E and t a (forward field time) is longer than t r (reverse field time).