A New Design and Analysis for Metasurface-Based Near-Field Magnetic Wireless Power Transfer for Deep Implants

Wireless power transfer (WPT) is a crucial enabler for the long-term powering of existing implantable medical devices (IMDs). This article proposes a new design and analysis methodology for a tunable metasurface (MTS) based near-field magnetic WPT system. A near-field magnetic WPT system using a multi-coil topology creates stable power with a low specific absorption rate. However, maintaining the optimal performance of a system under misalignment conditions continues to be a challenging issue. To address this issue, the proposed design method enables the optimal coupling of the WPT system by tuning the system capacitances at a fixed frequency. Moreover, it is undefined to accurately determine the effective permeability of the MTS in the near-field range. Therefore, based on optimized results, a method is proposed to retrieve effective permeability in near-field scenarios. The effective permeability results are distinct from the typical response of the Lorentz oscillator. As a result, the specific connection between the optimization method and retrieval of effective permeability has been established. The methodology is applied to an exemplified system, where the maximal simulated and measured power transfer efficiencies at an implant depth of 8 cm are 2.32% and 2.60%, respectively. In addition, the planar MTS exhibits a high lateral misalignment tolerance, thereby enabling the development of a reliable WPT system for continuous power supply to IMDs.

I. Introduction

Wireless power transfer (WPT) is a crucial enabler for sustainable powering in unique environments, especially for implantable medical devices (IMDs) [1]. The WPT system advantageously ensures an efficient, safe, and reliable track for transmitting energy without physical contact. It has drawn extensive attention in the field of noninvasive powering and monitoring. The WPT is an available option to promote the development of miniaturized biomedical implants [2]. However, active IMDs utilized in a clinical setting are battery-powered to provide a reliable energy supply. The batteries occupy a significant device footprint (up to 90% of the volume and 60% of the weight [1]). Such bulky volume leads to difficult miniaturization. Moreover, a life-limited battery must be replaced after IMD experiences long-term performance, and complications and risks are prone to arise. To mitigate these issues, adopting the wireless delivery of power strategies would enable IMDs to extend the battery lifespan and even operate battery-free solutions [3].