| In recent years,cerebrovascular diseases such as cerebral hemorrhage and cerebral tumor have attracted wide attention from scientists at home and abroad.At present,the main medical methods used in the detection of brain diseases include computed tomography,Magnetic resonance imaging scan,scanning positron radiation tomography and ultrasonic sensors.Microwave imaging technology has been widely concerned because of its advantages of low processing cost and high image quality.This chapter mainly studies the antenna and confocal imaging methods and simulation experiments of the test equipment.The main contents include:1.An ultra wideband Vivaldi antenna with the size of 0.51 λc × 0.29λc × 0.005 λc load guide is designed.Based on the traditional Vivaldi antenna structure,the antenna is loaded with a guide to improve the characteristics of the antenna over the whole spectrum.The S11 of the antenna in the working band of 1～4 GHz is less than-10 dB,the relative bandwidth is 114%,and the peak gain of 4 GHz can reach 9.2 dBi.Secondly,in order to reduce the antenna size to achieve antenna miniaturization,a Uwideband extension Vivaldi antenna with size 0.25λc × 0.2λc × 0.003 λc loaded with sidelobal suppressor is designed.The traditional extension Vivaldi antenna is used as the basic structure,and the sidelobe suppressor is loaded to enhance the directional radiation performance of the antenna.The extension Vivaldi antenna loaded with sidelobber suppressor operates at 0.6～3.6 GHz,with a relative bandwidth of 143%and a peak gain of 9.2 dBi in the working band.Meanwhile,the antenna gain of the antenna loaded with sidelobber suppressor has a better overall consistency.The processing and measurement of the extension Vivaldi antenna are carried out,and the measured results are in good agreement with the simulation results.Both antennas can operate normally in ultra-wideband and meet the safety requirements of electromagnetic radiation with SAR value.2.In order to achieve better imaging results,the 6-element array and the 12-element array composed of the loaded navigator Vivaldi antenna and the loaded sidelobe suppressor Vivaldi antenna were placed in different positions of the electromagnetic simulation software DUKE head model for ring array,and microwave detection simulation was carried out in different situations.Then the imaging results of different array elements,different bleeding positions and different bleeding amounts are detected.By comparing the imaging results under different conditions,it can be seen that the scattered signals obtained by the two antennas can invert the bleeding position well.However,compared with the director-loaded Vivaldi antenna,the extension Vivaldi antenna loaded with sidelobal suppressor has better imaging effect,fewer artifacts and higher image resolution.The imaging effect of the two antennas is studied and analyzed through the electric field distribution.Finally,the imaging effect is judged by the fuzzy comprehensive judgment method.3.The bionic head model(which is filled with different substitute substances),turntable,Uwiband extension Vivaldi antenna loaded with sidelobal suppressor and vector network analyzer were used to build the experimental detection platform to simulate cerebral hemorrhage.The bleeding position of the bionic head model was tested by using 6-element and 12-element antenna arrays respectively.The antenna array collected time domain signals at different bleeding locations(near forehead,near left ear,near right ear)and different bleeding amounts(3ml,14ml).By comparing the imaging results after algorithm inversion,it is found that the 12-element antenna array imaging results are better than the 6-element antenna imaging results.Specifically,the bleeding location is more accurate,fewer artifacts,and higher image resolution.The accuracy of simulation data and feasibility of microwave detection system are further verified. |
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