Analysis Of Radiation Properties Of A402MHz Antenna Implanted In Human Body

With the development of remote medical biotelemetry, the implantable antenna hasbecome a research topic of increasing importance. In the remote medical biotelemetry,the implantable antenna working in the band of402MHz~405MHz is used to transportinformation from the human tissue. The performance quality of the antenna determinesthe reliability and security of the entire system. This thesis analyzes the performance ofthe implantable antenna by using the finite-difference time-domain (FDTD) algorithm.In the study, we use a three-dimensional data array of the human body to build theelectromagnetic human head model with1mm resolution, by meshing the data arraywith a developed C program. The model includes twenty kinds of tissues whichcorrectly reflect the true anatomical structure of the human head. After the analysis ofthe specific working environment of the implantable antenna, we choose a planarinverted F antenna (PIFA) for the application. This thesis designs a meander PIFAgeometry and analysis the performance of the antenna in a tissue block. In view of the402MHz~405MHz band, the resonant frequency of the originally designed antenna inthe tissue block is390MHz. Therefore, we optimize the antenna by adjusting theresonant frequency back to402MHz, while maintaining the shape of the meander piece.The reflection coefficient of the optimized antenna is less than-20dB. The thesis alsoanalyzes the influence of the feed point location on the antenna performance. Theconclusion is that the input impedance of the antenna increases with the distancebetween the feed point and the shorting pin.The optimized antenna is planted into the top of the human head model andcompared to the antenna in the tissue block on performance, with the emphasis on theradiation characteristics of the antenna in the human head model and the specificabsorption rate (SAR) in tissues. The input power of the antenna is calibrated accordingto the secure SAR standard. This thesis advances the research by using unbalancedradiator patches to change the original geometry of the meander antenna and introducestwo new designs. The new antennas are placed in tissue blocks and compared to theoriginal meander antenna. The resonant frequencies of the new antennas fulfill the bandrequirement. The electric field strength around the tissue block with either new antennais less than that with the original meander antenna. The tissue SAR is also relativelysmaller and the radiation power is larger.