Optimal Pulse Widths for Effective Use of the Electrode Surface Area

The strength-duration curve defines the relation between pulse amplitude and pulse width for threshold pulses in neural stimulation. Both Blair´s and Lapicque´s equations predict the minimum charge to occur at the shortest pulse widths. On the other hand, the maximum injectable charge through a practical neural electrode increases with the pulse width, as suggested by some reports. Therefore, it is conceivable that there may be an optimum pulse width where the goal function of charge injection capacity of the electrode/the activation threshold for neural stimulation is maximized. In this paper, the strength-duration relation for mammalian nerves was simulated using a local nerve model and the charge injection capacity of titanium nitride electrodes was measured experimentally. The goal function was maximum for the smallest pulse width tested with the rectangular pulses. However, the optimal point occurred at larger pulse widths for the linearly decreasing pulse waveforms. These optimized pulse parameters may be preferable in applications where current requirements are demanding in order to keep the electrode contact areas small.