Powering electronic implants by high frequency volume conduction: in human validation

Abstract

Objective: Wireless power transfer (WPT) is used as an alternative to batteries to accomplish miniaturization in electronic medical implants. However, established WPT methods require bulky parts within the implant or cumbersome external systems, hindering minimally invasive deployments and the development of networks of implants. As an alternative, we propose a WPT approach based on volume conduction of high frequency (HF) current bursts. These currents are applied through external electrodes and are collected by the implants through two electrodes at their opposite ends. This approach avoids bulky components, enabling the development of flexible threadlike implants. Methods: We study in humans if HF (6.78 MHz) current bursts complying with safety standards and applied through two textile electrodes strapped around a limb can provide substantial powers from pairs of implanted electrodes. Results: Time averaged electric powers obtained from needle electrodes (diameter = 0.4 mm, length = 3 mm, separation = 30 mm) inserted into arms and lower legs of five healthy participants were 5.9 ± 0.7 mW and 2.4 ± 0.3 mW respectively. We also characterize the coupling between the external system and the implants using personalized two-port impedance models generated from medical images. Conclusions: The results demonstrate that innocuous and imperceptible HF current bursts that flow through the tissues by volume conduction can be used to wirelessly power threadlike implants. Significance: This is the first time that WPT based on volume conduction is demonstrated in humans. This method overcomes the limitations of existing WPT methods in terms of minimal invasiveness and usability.