Energy Transfer Efficiency in Volume Induction through Soft Tissue

Abstract

Understanding how alternating current (AC) signals propagate through soft tissue is essential for optimizing implantable neurostimulation systems. This study quantifies frequency- and depth-dependent attenuation of AC signals transmitted through ex vivo porcine skin using inductive volume coupling and an implanted Schottky diode circuit. Signals at 50 kHz, 500 kHz, and 1 MHz were delivered through surface electrodes while output voltages were recorded from implanted dipoles of 13 mm and 24 mm length placed at depths of 3-, 6-, 10-, and 15-mm. Attenuatioan values ranged from ~17–26 dB across all conditions. Higher frequencies and deeper implant locations consistently exhibited greater attenuation, reflecting the expected transition from conduction-dominated to dielectric-dominated tissue behavior. Dipole geometry significantly influenced transmission efficiency, with 24 mm dipoles producing higher output amplitudes and reduced attenuation compared to the 13 mm configuration. A three-way ANOVA confirmed that frequency, depth, and dipole length each exert significant main effects on attenuation, with strong interaction effects indicating that signal propagation depends on the combined influence of tissue thickness, operating frequency, and electrode geometry. These findings provide quantitative insight into the biophysical limits of AC energy transfer in soft tissue and offer design guidance for improving coupling efficiency, reducing power requirements, and optimizing electrode architecture in implantable neurostimulation devices.

Video