Comparative electrothermal analysis of single and small-electrode grid configurations for HD-inspired peripheral transcutaneous neurostimulation.

Background: High-density (HD)-inspired peripheral transcutaneous neurostimulation systems employing clusters of small-area electrode arrays may improve spatial controllability during electrical stimulation of superficial limb tissues, as used in TENS/NMES/FES-like wearable applications. However, the electrothermal consequences of small electrodes can affect usability due to complexities in safety considerations. Therefore it is of critical interest to understand the effects of these systems, and to determine how subdivision topology shapes localized current concentration and thermal accumulation under fixed electrode geometry conditions. Objective: This study investigates how high-density clusters of small-area electrodes influences current-density distribution and electrothermal behavior. This project is part of a larger study to design and optimize these high-density neurostimulation arrays to improve spatial scaling. Methods: A coupled electrical-thermal finite-element model was developed in COMSOL Multiphysics 6.3 to compare conventional single-electrode configurations with a systematic series of HD-inspired small-electrode grid configurations ranging from 1 to 16 electrodes (grid1 through grid16). The individual electrode radius and inter-electrode spacing were held constant while the number of active electrodes was varied. Current-density distribution, temperature change, and thermal transient effects were evaluated using current-controlled pulsed stimulation with varying current amplitudes, pulse widths, and frequencies. Results: Electrothermal effects did not increase linearly with the number of active electrodes. Three distinct electrothermal regimes were identified based on stimulation-side behavior: an extreme concentration regime ( Conclusion: Under the idealized modeling conditions investigated here, electrothermal behavior was jointly determined by electrode count and total active electrode area. These two variables are intrinsically coupled in the fixed-radius grid1-grid16 design where both contribute to a reduction in stimulation-side electrothermal load. These findings represent comparative, geometry-specific modeling trends rather than validated thermal safety predictions. The present study provides a comparative computational framework for evaluating HD-inspired electrode subdivision strategies in compact peripheral transcutaneous neurostimulation design, where electrode count and total active area jointly determine the resulting current-distribution topology and associated localized thermal accumulation.