Design Of Data Acquisition System For Microwave Tomography

Because of the unavoidable problems in traditional biomedical imaging methods,microwave imaging technology has been on the rise,and the research of microwave tomography technology has been attracting more and more attention.In order to perform microwave tomography experiment,we have designed a set of microwave tomographic data acquisition system with a central frequency of 2.45 GHz and capable of imaging objects in water.Above all,this paper briefly introduces the development history and the research status at home and abroad of microwave imaging,especially the microwave tomography technology.The necessity of designing the appropriate data acquisition system is also discussed.Then the design plan of the system is introduced,which is innovative.In the past,the imaging system placed the object to be measured in the solution whose dielectric constant close to the object.Antennas were placed outside the container.The experiment designed in this paper needs to immerse antennas in the water.In this way,the reflect at the wall of the container can be reduced,and the imaging accuracy effectively can be improved.The main work of this paper are as follows:1.The principle of the transmission line is introduced first and the working principle of the micro-strip line in the transmission line is analyzed which lays a theoretical foundation for the later design work.2.The working principle of PIN diode microwave switch is expounded,and the switch is designed on the basis of micro-strip circuit through ADS software.The designed SPDT switch,at the center frequency 2.45 GHz,has the smallest reflection.S11 is less than-30 d B,and the insertion loss is less than 1.2d B.SPDT switch is also designed in this paper.When the working frequency is2.45 GHz,S11 is less than-20 d B with a 400 MHz bandwidth,and the insertion loss is less than 4d B in 2.0~2.92 GHz.Besides the third branch,the isolation between the other branches and the second branch is far greater than 40 d B.The simulation results basically meet the design requirements.3.We designed a microwave rectifying circuit,including low pass filter and rectifying circuit next.The microwave rectifier circuit has the highest rectification efficiency of 72%.When the input power range from 11.690 m W to 72.460 m W,the rectification efficiency is higher than 60% at 2.45 GHz.4.The finished switching circuit and the microwave rectifier circuit were tested respectively.The test results of the switching circuit and the microwave rectifying circuit are basically consistent with the simulation results and the requirements of the design index are reached.5.The simulation and optimization of the underwater horn antenna involved in the design are carried out and the antenna is tested.The test results of the horn antenna in water show that the antenna signal can be transmitted and received in water,which proves the correctness of the design principle.