Dielectric loss occurring in tissues in close proximity to UHF-implanted antennas is an important factor in the performance of medical implant communication systems. Common practice in numerical analysis and testing is to utilize radiation efficiency (RE) measures external to the tissue phantom employed. This approach means that RE is also dependent on the phantom used and antenna positioning, making it difficult to understand antenna performance and minimize near-field tissue losses. Therefore, an alternative methodology for determining the intrinsic radiation performance of implanted antennas that focuses on assessing structural and near-field tissue losses is presented. The new method is independent of the tissue phantom employed and can be used for quantitative comparison of designs across different studies. The intrinsic RE of an implant antenna is determined by assessing the power flow within the tissue phantom at a distance of at least $\lambda _{g}/2$ from the radiating structure. The simulated results are presented for canonical antennas at 403 and 2400 MHz in homogeneous muscle and fat phantoms. These illustrate the dominance of propagating path losses in high-water content tissues such as muscle, whereas near-field dielectric losses may be more important in low-water tissues such as fat due to the extended reactive near-field.

中文翻译：

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评估组织植入式 UHF 天线的固有辐射效率

靠近 UHF 植入天线的组织中发生的介电损耗是影响医疗植入通信系统性能的一个重要因素。数值分析和测试中的常见做法是利用所采用的组织体模外部的辐射效率 (RE) 措施。这种方法意味着 RE 还依赖于所使用的体模和天线定位，因此很难了解天线性能并最大限度地减少近场组织损失。因此，提出了一种用于确定植入天线的固有辐射性能的替代方法，该方法侧重于评估结构和近场组织损失。新方法独立于所采用的组织体模，可用于不同研究之间设计的定量比较。植入天线的固有 RE 是通过评估距辐射结构至少 $\lambda_{g}/2$ 距离处的组织体模内的功率流来确定的。模拟结果显示在 403 和 2400 MHz 的同质肌肉和脂肪体模中的标准天线。这些说明了在肌肉等高含水量组织中传播路径损耗的主导地位，而由于扩展的反应近场，近场介电损耗在脂肪等低水分组织中可能更为重要。