A Selectivity Measure for Transcutaneous Electrodes

Transcutaneous electrical stimulation (TES) enables functional movements of human limbs by applying electrically generated pulses to pairs of electrodes placed on the skin surface. New TES technology uses multi-channel configurable electrodes that can dynamically distribute the stimulation current across the skin surface. Such systems require a quantitative understanding of the spatial and temporal activations of underlying neural structures. We have developed a versatile TES simulation framework that calculates nerve activation using a transient finite element model combined with a nerve model. Recruitment volumes (RVs) are used to describe regions where nerves are activated. Using RVs we introduce measures for the recruitment depth and for the selectivity. This allowed us to find optimized electrode sizes for different fat thicknesses. The optimized electrode size for square electrodes was 1cm for a thin fat layer (0.25cm) and 2cm for a thicker fat layer (2cm).