Design of a graphene-based wide-band circular polarized antenna for capsule endoscopes
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摘要: 为了提高胶囊内窥镜天线的工作性能，提高天线抗干扰能力和兼容性，进一步缩小尺寸，设计了一种基于石墨烯的用于胶囊内窥镜的宽频圆极化天线。该天线由3层辐射单元和地板构成，利用石墨烯薄膜优良的导电性能，制作天线的各层辐射单元和地板以有效增强胶囊天线的工作带宽与增益，提高传输效率并降低损耗。通过4个短路探针使第1层与第2层辐射单元相连接，构成复合螺旋天线，进而产生圆极化特性，既能减少误码率又能抑制多径干扰，并且能够更加高效地耦合电磁能量，有效改善阻抗匹配并调节圆极化纯度。详细分析了第1层、第2层和第3层辐射单元开口圆环尺寸、石墨烯薄膜厚度、天线摄入环境（胃、小肠、结肠等）对天线性能的影响。测试结果表明，设计的体积仅为π×4.52×1.905 mm3，阻抗带宽为2.2~2.78 GHz，轴比带宽为2.26~2.66 GHz，增益为−22.9 dBi，实际测量与仿真结果吻合良好，工作频段内辐射特性稳定，与现有技术相比，本文设计天线外形兼容性强，功能带宽更宽，具有宽频带、圆极化、抗干扰、电磁兼容性好、体积小等特点。该天线适用于ISM 2.4 GHz频段，能满足胶囊内窥镜摄入不同消化器官的工作要求。Abstract: In order to improve the performance of the capsule endoscope antenna and its anti-interference ability and compatibility, and further reduce its size, a graphene-based and wide-band circular polarized antenna for capsule endoscopes is designed. The antenna is composed of three layers of radiation units and a floor. By making use of the excellent electrical conductivity of multi-layer graphene film, the radiation units and the floor of each layer of the antenna can enhance the working bandwidth and gain of a capsule antenna, improve the transmission efficiency and effectively reduce the loss. Four short-circuit probes are used to connect the radiation units of first layer and second layer to form a composite spiral antenna, thus generating circular polarization characteristics, which can not only reduce bit error rate but also inhibit multipath interference. In addition, it can couple electromagnetic energy, improve impedance matching and adjust the purity of circular polarization. The effects of the size of the radiation units of first, second and third layers on the performance of the antenna, such as the size of the opening ring, the thickness of the multilayer graphene film, and the antenna intake environment of the stomach, small intestine and colon are analyzed in detail. The test results show that the antenna volume is only π×4.52×1.905 mm3, the impedance bandwidth is 2.2~2.78 GHz, the axial ratio bandwidth is 2.26~2.66 GHz, and the gain is −22.9 dBi. The actual measurement results agree well with the simulation results, and the radiation characteristics in the working frequency band are stable. Compared with the existing technology, this antenna is more compatible and its functional bandwidth is wider. The antenna has a wide band, circular polarization, good anti-interference, good electromagnetic compatibility and a small volume. The antenna is suitable for the ISM 2.4 GHz band, which can meet the working requirements of a capsule endoscope intake for different digestive organs.
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Key words:
- capsule endoscope /
- wide band /
- circular polarization /
- graphene
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图 1 天线结构示意图。（a）三维结构;（b）第1层、（c）第2层、（d）第3层辐射贴片结构参数
Figure 1. Schematic diagram of the antenna structure. (a) Three-dimensional structure; structure parameters of (b) the first, (c) the second, and (d) the third radiation patchs
图 3 第1层和第2层辐射单元开口圆环的外径R3、内径R4对天线阻抗带宽和轴比带宽的影响
Figure 3. Influence of theinner diameter R4 and outer diameter R3 of open rings in the first and second lagers radiation units on the impedance bandwidth and axial ratio bandwidth
图 4 第3层辐射单元4个开口圆环内径R9、外径R10对天线阻抗带宽和轴比带宽的影响
Figure 4. Influence of the inner diameter R9 and outer diameter R10 of four open rings in the third layer radiation unit on the antenna’s impedance bandwidth and axial ratio bandwidth
图 5 石墨烯薄膜厚度T对天线阻抗带宽和轴比带宽的影响
Figure 5. Effect of graphene coating thickness T on the antenna’s impedance bandwidth and axial ratio bandwidth
图 6 天线摄入不同消化器官位置示意图
Figure 6. Schematic diagram of the locations for antenna intaked in different digestive organs
图 7 天线摄入人体不同消化环境对阻抗带宽和轴比带宽的影响
Figure 7. Influence of different digesting environments on the impedance bandwidth and axial ratio bandwidth
图 8 天线摄入不同消化器官的辐射特性。（a）胃；（b）小肠；（c）结肠
Figure 8. Radiation characteristics of antenna intaked to different digestive organs. (a) Stomach; (b) small intestine; (c) colon
图 10 仿真与实测阻抗带宽和轴比带宽曲线
Figure 10. Simulated and measured impedance bandwidth and axial ratio bandwidth curves
表 1 天线的初始结构尺寸
Table 1. Initial structural parameters of the proposed antenna
参数 尺寸/mm 参数 尺寸/mm R1 4.5 R9 1.05 R2 0.8 R10 1.4 R3 2.25 R11 0.8 R4 1.9 L1 2.3 R5 2.08 L2 0.85 R6 0.3 L3 0.5 R7 0.3 W1 0.55 R8 0.2 
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表 2 与其他典型天线的性能比较
Table 2. Performance comparison of proposed antanna and other typical antennas
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