Implant depth analysis from the literature.

Two two-element slotted patch multiple-input multiple-output (MIMO) antenna with coplanar waveguide (CPW) feed is proposed for deployment in implantable medical devices. Implantable devices are compact and demand high-gain antennae with unidirectional radiation patterns. Regarding compactness, the antenna has a size of 16 × 6×0.25 mm3 for the operating frequency of 2.45 GHz ISM band. Miniaturized antenna geometry is attained using the slots in the radiator and with the coplanar waveguide feed. An element MIMO configuration is used for establishing a reliable communication link. The two radiators maintain a connected ground topology with a minimum edge-to-edge spacing of 7.7 mm. Mutual coupling of -29 dB and operating frequency spectrum of 1300 MHz is attained at the center cut off frequency. Unidirectional power pattern and high gain of 2.3 dB is achieved. The proposed MIMO structure is suitable for mitigating multipath fading effect and realizing higher spectral efficiency in short range communication. The in-tissue measurement results for the scattering parameters and radiation characteristics are done by placing the antenna in a pork loin. Specific absorption rate (SAR) analysis is performed to confirm the user’s safety from nearfield EM waves. Antenna has safe SAR value of 0.798 W/kg for 1-g of average tissue for the power of 1-mW. The low envelope correlation coefficient of 0.035 depicts the excellent diversity performance for MIMO operation.本文提出一款采用共面波导（coplanar waveguide, CPW）馈电的双元缝隙贴片式多输入多输出（multiple-input multiple-output, MIMO）天线，可应用于植入式医疗设备。植入式医疗设备通常尺寸紧凑，且需要配备具备单向辐射方向图的高增益天线。针对紧凑性设计需求，该天线在2.45 GHz工业科学医疗（ISM）频段下的尺寸仅为16×6×0.25 mm³。通过在辐射单元上开设缝隙并采用共面波导馈电的方案，实现了天线的小型化几何结构。采用二元MIMO配置以构建可靠的通信链路。两个辐射单元采用共地拓扑结构，单元间最小边间距为7.7 mm。在中心截止频率处，该天线可实现-29 dB的互耦合以及1300 MHz的工作频谱带宽。该天线可获得2.3 dB的高增益与单向辐射方向图。所提出的MIMO结构可有效缓解多径衰落效应，并在短距离通信中实现更高的频谱效率。通过将天线置于猪里脊肉中，完成了其散射参数与辐射特性的组织内测量。开展比吸收率（specific absorption rate, SAR）分析以验证用户免受近场电磁波的辐射危害。在1 mW的输入功率下，针对1 g平均组织的比吸收率安全值为0.798 W/kg。极低的包络相关系数（envelope correlation coefficient, ECC）为0.035，表明该天线在MIMO工作模式下具备优异的分集性能。