"Energy-Efficient Pulse Parameter Optimization in Dual Coil Peripheral Magnetic Stimulation with a Monopolar-Like Axial Field "

"Peripheral magnetic stimulation (PMS) is attractive as a contact-free neuromodulation approach, but its clinical translation is limited by high energy demand and coil heating. Here, we experimentally characterize how rectangular current-pulse parameters shape peripheral nerve responses and energy efficiency using a gradient-enhanced dual coil interface. The dual-coil geometry was implemented using commercially available inductors and selected via COMSOL simulations to increase the induced axial electric-field gradient along the nerve. In vivo experiments were performed in Sprague\u2013Dawley rats with the device positioned near the common peroneal nerve, and evoked muscle activity was recorded from the tibialis anterior. We systematically varied the durations of the rising phase (RP), maintaining phase (MP), and falling phase (FP), and quantified response magnitude and latency together with per-pulse energy loss. EMG amplitude increased with MP but exhibited diminishing returns at longer MP values. In contrast, the energy-normalized response peaked at intermediate MP values, supporting a practical operating range of approximately 100\u2013150 \u00b5s under our conditions. RP\/FP sweeps and latency analysis further supported RP-dominant initiation, with EMG latency tracking the timing of the first artifact component. Moreover, shorter MP and FP reduced EMG amplitude, consistent with stronger interaction between the two induced components. Finite-element field comparisons further showed that the dual coil exhibits a monopolar-like profile with respect to the nerve-axis electric-field component. These results provide experimentally grounded guidance for pulse design in dual coil PMS and clarify how coil-induced field structure shapes parameter sensitivity."