A Systematic Method for Efficient Wireless Powering to Implantable Biomedical Devices

Wireless power transfer (WPT) technology has played a vital role in the rapid development of biomedical devices. While several single methods to improve WPT efficiency have been reported, the lack of integrality in these single methods limits the effect of the improvements. In this investigation, we analyze the physical process of a typical WPT scenario and find that the high propagation loss consisting of in-tissue attenuation and interface reflection degrades the WPT performance. A systematic method to comprehensively improve WPT efficiency is then proposed. Specifically, a Fresnel zone plate (FZP) is applied against the attenuation of inner biological tissue, and a practical air layer-artificial matching layer (AL-AML) is applied to decrease the reflection on the surface of biological tissue. According to a simulation of possible analytical models, the efficiency is significantly improved when using the proposed method. In an experiment with an implant depth of 20 mm, the proposed systematic method is found to enhance maximum relative received power by 12 dB, with an almost 15-fold increase in efficiency over the conventional system with just a transmitter (Tx) and a receiver (Rx). It is also verified that the improvement in efficiency is greater in the systematic method than in single methods. Also, various misalignment tolerances between the proposed structures and the Rx are determined from the coupling strength of the proposed WPT system. The results of this investigation show the potential of the proposed systematic method for further improvements in WPT efficiency.