IEEE Trans Biomed Circuits Syst. 2016 Dec;10(6):1100-1111. doi: 10.1109/TBCAS.2016.2515541.
Power transmission efficiency (PTE) has been the key parameter for wireless power transmission (WPT) to biomedical implants with millimeter (mm) dimensions. It has been suggested that for mm-sized implants increasing the power carrier frequency (f) of the WPT link to hundreds of MHz improves PTE. However, increasing f significantly reduces the maximum allowable power that can be transmitted under the specific absorption rate (SAR) constraints. This paper presents a new figure-of-merit (FoM) and a design methodology for optimal WPT to mm-sized implants via inductive coupling by striking a balance between PTE and maximum delivered power under SAR constraints (P). First, the optimal mm-sized receiver (Rx) coil geometry is identified for a wide range of f to maximize the Rx coil quality factor (Q). Secondly, the optimal transmitter (Tx) coil geometry and f are found to maximize the proposed FoM under a low-loss Rx matched-load condition. Finally, proper Tx coil and tissue spacing is identified based on FoM at the optimal f. We demonstrate that f in order of tens of MHz still offer higher P and FoM, which is key in applications that demand high power such as optogenetics. An inductive link to power a 1 mm implant was designed based on our FoM and verified through full-wave electromagnetic field simulations and measurements using de-embedding method. In our measurements, an Rx coil with 1 mm diameter, located 10 mm inside the tissue, achieved PTE and P of 1.4% and 2.2 mW at f of 20 MHz, respectively.
功率传输效率 (PTE) 一直是医学植入物无线电能传输 (WPT) 的关键参数，其尺寸为毫米 (mm)。有研究表明，对于 mm 尺寸的植入物，将 WPT 链路的功率载波频率 (f) 提高到数百 MHz 可以提高 PTE。然而，f 的增加会显著降低在特定吸收率 (SAR) 限制下可传输的最大功率。本文提出了一种新的质量因数 (FoM) 和设计方法，通过感应耦合优化对 mm 尺寸植入物的 WPT，在 SAR 限制下的 PTE 和最大传输功率 (P) 之间取得平衡。首先，确定了宽频率范围内的最佳 mm 尺寸接收器 (Rx) 线圈几何形状，以最大化 Rx 线圈品质因数 (Q)。其次，找到了最佳的 Tx 线圈几何形状和 f，以在低损耗 Rx 匹配负载条件下最大化所提出的 FoM。最后，根据 FoM 在最佳 f 下确定适当的 Tx 线圈和组织间距。我们证明了几十兆赫兹的 f 仍然具有更高的 P 和 FoM，这对于需要高功率的应用（如光遗传学）至关重要。根据我们的 FoM 设计了一个感应式链路，以对 1mm 的植入物供电，并通过全波电磁场仿真和使用去嵌入方法的测量进行了验证。在我们的测量中，位于组织内 10mm 处的直径为 1mm 的 Rx 线圈在 f 为 20MHz 时实现了 1.4%的 PTE 和 2.2mW 的 P。
