Ahn Dukju, Ghovanloo Maysam
IEEE Trans Biomed Circuits Syst. 2016 Feb;10(1):125-37. doi: 10.1109/TBCAS.2014.2370794. Epub 2015 Jan 20.
This paper presents a design methodology for RF power transmission to millimeter-sized implantable biomedical devices. The optimal operating frequency and coil geometries are found such that power transfer efficiency (PTE) and tissue-loss-constrained allowed power are maximized. We define receiver power reception susceptibility (Rx-PRS) and transmitter figure of merit (Tx-FoM) such that their multiplication yields the PTE. Rx-PRS and Tx-FoM define the roles of the Rx and Tx in the PTE, respectively. First, the optimal Rx coil geometry and operating frequency range are identified such that the Rx-PRS is maximized for given implant constraints. Since the Rx is very small and has lesser design freedom than the Tx, the overall operating frequency is restricted mainly by the Rx. Rx-PRS identifies such operating frequency constraint imposed by the Rx. Secondly, the Tx coil geometry is selected such that the Tx-FoM is maximized under the frequency constraint at which the Rx-PRS was saturated. This aligns the target frequency range of Tx optimization with the frequency range at which Rx performance is high, resulting in the maximum PTE. Finally, we have found that even in the frequency range at which the PTE is relatively flat, the tissue loss per unit delivered power can be significantly different for each frequency. The Rx-PRS can predict the frequency range at which the tissue loss per unit delivered power is minimized while PTE is maintained high. In this way, frequency adjustment for the PTE and tissue-loss-constrained allowed power is realized by characterizing the Rx-PRS. The design procedure was verified through full-wave electromagnetic field simulations and measurements using de-embedding method. A prototype implant, 1 mm in diameter, achieved PTE of 0.56% ( -22.5 dB) and power delivered to load (PDL) was 224 μW at 200 MHz with 12 mm Tx-to-Rx separation in the tissue environment.
本文提出了一种用于向毫米级可植入生物医学设备进行射频功率传输的设计方法。通过该方法找到最佳工作频率和线圈几何形状，以使功率传输效率（PTE）和组织损耗受限允许功率最大化。我们定义了接收器功率接收敏感度（Rx-PRS）和发射器品质因数（Tx-FoM），使得它们的乘积得出PTE。Rx-PRS和Tx-FoM分别定义了接收器和发射器在PTE中的作用。首先，确定最佳的接收器线圈几何形状和工作频率范围，以便在给定的植入约束条件下使Rx-PRS最大化。由于接收器非常小且设计自由度比发射器小，整体工作频率主要受接收器限制。Rx-PRS确定了由接收器施加的此类工作频率约束。其次，选择发射器线圈几何形状，以便在Rx-PRS饱和的频率约束下使Tx-FoM最大化。这使发射器优化的目标频率范围与接收器性能较高的频率范围对齐，从而实现最大的PTE。最后，我们发现即使在PTE相对平坦的频率范围内，每个频率下每单位传输功率的组织损耗也可能有显著差异。Rx-PRS可以预测在保持高PTE的同时每单位传输功率的组织损耗最小化的频率范围。通过表征Rx-PRS，实现了对PTE和组织损耗受限允许功率的频率调整。通过全波电磁场模拟和使用去嵌入方法的测量对设计过程进行了验证。在组织环境中，一个直径为1毫米的植入式原型在200兆赫兹、发射器与接收器间距为12毫米时，实现了0.56%（-22.5分贝）的PTE，传输到负载的功率（PDL）为224微瓦。
