Pulsewidth optimisation for transformer-coupled transcutaneous current pulse generation

A general theoretical approach for the determination of the optimum pulsewidth used for TENS/EMS/FES is presented. Analysis based on the interaction between a step-up transformer-coupled nerve stimulator and an electrode-tissue load modelled as a simple lossy capacitive load results in excellent agreement between the predicted and measured performance. The analysis shows that, by adjusting the pulsewidth (PW) of a push-pull symmetric square waveform such that PW=4.5 tau, the total charge delivered to the tissue load can be minimised without impacting the efficiency of the nerve stimulation. Additionally, by minimising the charge exchange supported portion of the current pulse, which is primarily responsible for the pH shift and subsequent tissue burning with long-term use, the latter can be reduced to an acceptable level.