Design Of Microstrip Circularly Polarized Implantable Antenna

With the advancement of technology and the improvement of living standards,the personal medical care technology has been developed continuously.For example,patients can receive treatments without going out with the research of wireless medical equipment,bringing great convenience to people's lives.In the wireless medical system,the implanted antenna is an important part of it.It is used as an information transmission tool to transmit signals to external receiving devices,and doctors can analyze the patient's physical function based on these informations.Therefore,it is important to study implantable antennas with good performance.There are many types of implantable antennas,in which circularly polarized antennas have obvious anti-multipath effects in medical environments.The dual-frequency implantable antenna can switch between two working modes,one working at the sleeping mode with less energy consumption and the other working at the awake mode.Dual-frequency implantable antennas can save energy and extend the life of implantable devices.When designing an implanted antenna,the following factors need to be considered: size,bandwidth,SAR coefficients,gain and so on.The implementation mechanism and the design methods of various single band and dual-band circularly polarized implantable antennas are studied in this thesis.The main contents include:1)Single-frequency circularly polarized implantable antenna operating at 2.4 GHz.The circular polarization performance and miniaturization are achieved by introducing a slotting technique on the patch and simultaneously loading shorting pins.The size of the antenna is 9.8 mm?9.8 mm?1.27 mm,and the simulated impedance bandwidth and axial ratio bandwidth are 21.5% and 15.8%,respectively.Compared with the existing 2.4 GHz circularly polarized implantable antenna,the AR bandwidth has a big advantage.Firstly,the antenna structure is optimized and simulated in a single-layer human skin model.To test the robustness of the antenna,other human models are used to analyze the performances,which include the muscle model,the scalp model,and the three-layer human body model.Then,the antenna is bent at different degrees of curvature to discuss the conformability of the proposed antenna.Subsequently,the antenna performances with different implantation depths are also discussed.Finally,the SAR value and the communication link margin are considered.2)Dual-band and dual-circularly polarized implantable antenna working at 1.4 GHz and 2.45 GHzCapacitive loading is used to design a small size antenna,which obtains performance of dual-frequency dual-circular polarization.The proposed antenna has a low profile,whose volume is only 7.1 mm?7.2 mm?0.835 mm.The 3-dB spatial axis ratio of the antenna at 2.45 GHz covers from-73° to 75°;while at 1.4 GHz,the 3dB spatial axis ratio is from-63° to 20° in xoz plane and ranges from-16° to 98° in yoz plane.The SAR value and effect of different implant depths on the antenna performance are also discussed.