Powering electronic implants by high frequency volume conduction: in human validation
Wireless power transfer (WPT) is frequently used as an alternative to batteries to accomplish miniaturization in electronic medical implants (eMIs). However, established WPT methods require bulky parts within the implant or cumbersome external systems, hindering minimally invasive deployments and the development of networks of eMIs. As an alternative, we propose a WPT approach based on volume conduction of high frequency (HF) current bursts. These currents are applied through external textile electrodes and are collected by the eMIs through two electrodes at their opposite ends. This approach avoids bulky components to obtain power, making it possible to develop implants with a flexible threadlike conformation. In here 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. 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 report a procedure to characterize the coupling between the external system and the implants using two-port impedance models generated from medical images. The results demonstrate for the first time in humans that innocuous and imperceptible HF current bursts that flow through the tissues by volume conduction can be used to wirelessly power threadlike eMIs, overcoming the limitations of existing WPT methods in terms of minimal invasiveness and usability.