| Compared with MRI, CT and other conventional detection techniques, wearable stroke detection system which relays on microwave imaging technology, has some advantages, such as low cost, portable and so on. In the microwave imaging system, antenna as front-end component which sends and receives RF signal, is a key element. Its performance is critical for the imaging results. For clearer imaging results and more portable imaging systems, microwave stroke detection system put forward demands to antenna: ultra-wideband, compact, low profile, low frequency and vertical radiation or directional radiation. However, the current systems mostly use side radiation antenna and radiation gain of the antenna is generally relatively high, such as vivaldi antenna. But it’s not suitable to wearable system and there is a certain degree of difficulty when applying to wearable systems. The wearable stroke detection system requires highly wearable feature and the antenna should also be able to achieve a good combination with brain. In order to more easily embed into wearable system, it is necessary to design a flexible antenna with directional radiation or vertical radiation so that the antenna has good bending feature.Work content of the paper is divided into six parts, the first describes the background and significance of stroke microwave detection system, research status of expanding bandwidth of antenna and the antenna used in detection system, the main work of this article.Secondly, the micro-strip antenna basic theoretical concepts, such as the concept of micro-strip antenna, the radiation mechanism, type, feeding mode, the main electrical parameters of the antenna and so on; Simulation software platform used in this project is the three-dimensional electromagnetic simulation software platform HFSS developed by the American company Ansoft. The software bases on the finite element method and the results highly accurate. So it is recognized as the industry standard of three-dimensional electromagnetic design and analysis; Human microwave detection involve some key issues, such as security as the primary issue, the thermal effect of the terminal radiation often used to be measured by SAR values. SAR value indicates the impact of electromagnetic radiation on human health. In antenna design, the influence of electromagnetic radiation energy to the brain should be given high priority.Next, micro-strip antenna is chosen as the study object. Base on the semi-circular micro-strip antenna, this paper proposes a small ultra-wideband micro-strip antenna, which uses a dipole form. The bandwidth of micro-strip antenna is expanded by optimizing the shape and size of antenna radiation arm and opening rectangular groove as well as loading coupled patch. The maximum radiation direction is perpendicular to the front of the antenna. It is beneficial to come true wearable system.Then, under the guidance of pre-designed experimental program, a simple head model was created by plastic barrel filled with cooking oil and water pipe and simulation experiment was built by a vector network analyzer, coaxial cable, antenna entity, PC and head model. Meanwhile, valid experimental data was collected. The data is processed by confocal imaging algorithm which is implemented by MATLAB program to obtain permittivity distribution of head model and it could verify the feasibility of the antenna for detection system.The bendability of antenna is also research emphasis in this article. Due to the thickness of the current restrictions on domestic bendable material, so it is necessary to adjust the antenna to improve the model in order to study the bending effect on the antenna performance; Polyimide is great organic polymer material on the consolidated performance. So it’s chosen as substrate material of flexible antenna. On HFSS platform, building bending simulation model analyzes the influence of bending on antenna; it also made some exploration and research on slim directional antenna. |
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