A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head and a closed retainer ring. The gate electrode so produced serves as a floating gate electrode and includes a recessed central portion flanked by a pair of opposed upwardly extending fins which may terminate upwardly at an apex. The pixel electrode has at least one vertical portion and a plurality of horizontal portions, and the common electrode has at least two horizontal portions and a plurality of horizontal portions. The pulse sequence includes multiple radio frequency pulses and multiple recovery times between the rf pulses.