| The development and application of implantable electronic devices provide more possibilities for medical diagnosis and treatment.They can monitor the health of patients remotely,and can even replace the damaged organs to continue to work,and gradually become an important medical means.After an implantable electronic device is implanted into the human body,it not only needs to work normally in the body,but also does not affect the health of the body,which requires the use of medical imaging technology to ensure that it is in a suitable position and work steadily.At present,medical imaging technology is becoming more and more mature,different methods have their application scenarios.Microwave imaging technology has the characteristics of low cost,security and so on,which has been concerned by researchers.According to the difference of electromagnetic waves in far-field and near-field,microwave imaging can be divided into near-field microwave imaging and far-field microwave imaging.The near-field microwave imaging has strong penetrability,but the transmission distance is limited and the cost is high.The far-field microwave imaging method used in this thesis uses the mechanism of single transmit antenna and single receive antenna to collect signals and obtain information of the target.Considering that the use of microwaves in the safe range will hardly harm the human body,a far-field microwave imaging system is built in this thesis and conducts research on imaging methods of metal implants in biological tissue phantom in S-band.The main contributions of this thesis are summarized as follows:(1)Based on the electromagnetic theory,a far-field microwave imaging system is built.In order to eliminate the interference of the surrounding electromagnetic wave,an experimental darkroom is designed,and the method of collecting data is proposed,that is,fixing the position of the transmitting antenna and moving the receiving antenna in the scanning area.The imaging principle is described.(2)Based on the designed far-field microwave imaging system,the influence of different experimental conditions on the imaging quality is explored.Through the data processing and analysis,the relationship between the imaging quality and the experimental variables in the system is obtained,then the experimental parameters are determined,and the experimental platform is continuously improved.The influence of different transmitting antennas on the imaging quality is also explored.According to the experimental results,an antenna is selected as the transmitting antenna of the system under the existing experimental conditions.(3)There is a diffraction limit in far-field microwave imaging.When the microwave frequency is 3.5GHz,the theoretical ultimate resolution diameter is 4.3cm.In this thesis,under the condition of microwave frequency of 3.5GHz and sensitivity of-85 d Bm,we image the diamond-shaped metal with the side length of 2cm and the metal ring with the diameter of 2.5cm respectively.Because of the scattering of the radiation source in the real system,even if the size of the metal target is smaller than the ultimate resolution diameter,the result is also observed.The experimental results show that the far-field scanning method can obtain the position and shape information of the object without involving complex algorithms.(4)We use agar to prepare biological tissue phantom,and carry out scanning experiments on the agar culture dish with square metal objects(side length of 2cm).After processing the collected data,the position information of metal target is obtained.The experimental results preliminarily verify the feasibility of the imaging system for detecting metal implants in biological tissue phantom.In summary,the experimental system in this thesis can effectively obtain the state information of metal objects and the research of this thesis can provide an idea for the detection of the implantable electronic device. |
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