| Wireless Capsule Endoscopy(WCE) system can capture the images of the human gastrointestinal(GI) tract,which allows clinicians to observe the lesions and diagnose the GI tract diseases. Compared to traditional endoscopic detection technology, WCE is convenient, noninvasive, and painless, and could detect the entire GI tract without a dead zone. The WCE has become popular in the medical device industry at home and abroad. As a novel technology, the existing WCE systems have the disadvantages of limited working time, low frame rate and low quality image. The reason which causes these disadvantages is that WCE adopts two button batteries as the power source. With the wide application of wireless power transmission(WPT) technology to implantable medical devices, the researchers regard this power supply technology as the feasible way to solve the bottleneck of WCE. Support by many scientific research projects at the national and provincial level, this project researches the video capsule endoscopy based on WPT technology.Aimed at the working environment and the related electromagnetic technology, the research on the interaction of human body and electromagnetic field has been launched. After elaborating the coupling mechanism of human body and electromagnetic field, the electromagnetic parameters has been proposed and calculated by fit method. A high-precision electromagnetic calculation human body model has been established based on the data sets of VHP(Visible Human Project). Two problems of the interaction between human body and electromagnetic field have been considered. One is the power loss of the electromagnetic signal that transmitted from the GI tract to external receiving device. The other one is the tissue safety when human body exposed in the electromagnetic field that induced by the WPT system. Based on the human body electromagnetic calculation model, a model of power loss when the electromagnetic wave transmitted in the human body has been established to calculate the power loss that respectively caused by antenna gain, radiation, attenuation and reflection. After analyzing and comparing the international electromagnetic safety standards, the distribution of current density and SAR value in the human body has been simulated and the upper limitation of the two parameters at different frequencies has been concluded.Based on the physiological features of the GI tract, the problems and the probable solutions of designing the capsule endoscopy have been proposed. After determined the system framework, each functional module of capsule endoscopy have been studied and designed. As the core part of the capsule endoscopy, the selection of the image sensor is important. Compared the production process of CMOS and CDD, a new type of CMOS image sensor, OV6922, has been selected considering the size, the frame rate and the power consumption, and the matched lens and illumination model have been designed. According to the control requirement, the Micro Control Unit(MCU), PIC12F509, is used to realize the communication with OV6922 by SCCB protocol and the detailed control circuit and software is designed. By comparing two modulation modes of amplitude modulation and frequency modulation, the analog frequency modulation circuit is proposed which has the advantages of strong anti-jamming capability, high energy utilization and wide bandwidth. Limited by the inner space of capsule endoscopy, the helical antenna working in the normal mode is designed and the structure parameters are optimized by HFSS simulation software. The external video receiving system is proposed which could realize the video receiving, storage, and browsing. Meanwhile the real-time display function allows the doctors monitoring the status of capsule endoscopy.The WPT modes and the basic theory of electromagnetic induction are studied, and the inductive coupling energy transmission technology is adopted to realize the power supply. The research on the structure and the key technologies of the inductive coupling power transmission system has been launched. The key technologies include energy transform technology, resonant compensation technology and electromagnetic inductive coupling technology. Based on the working environment, the realizing solution and control strategy of the wireless power have been determined. A loosely coupled transformer model and a modified generalized spatial model have been established to optimize the system and analyze the stability. Using the models, the system disturbance parameters are proposed and quantified. The verification method by m analysis tool aiming at the robust stability of inductive coupling power transmission system has been proposed.Based on the experiment study, the wireless powered video capsule endoscopy system has been optimized and verified. The working performance of illumination model, wireless communication model and video capture model has been tested. In the in-vitro experiment, the image sensor has captured the video of intestinal tract and the external video recorder has received the video signal, stored in the SD card and displayed in real-time, which verified the design of the video part. In the WPT system, the wireless power transmitting and receiving part have been respectively optimized through the experiment study. The working performance of different structure of transmitting coil have been tested and used to evaluate the system robust stability. An optimized method for wireless power receiving part has been proposed and the optimal model for capsule endoscopy has been obtained. The integrated video capsule endoscopy, measured 11 mm in diameter and 28 mm in length, has the ability to obtain NTSC video in the frame rate of 30f/s and its work hours is unlimited due to the WPT system which has the transmission efficiency of 4.4%. At last, in the living pig experiment, the wireless powered video capsule endoscopy successfully captures the GI tract images which proves the reliability and feasibility of the whole system. |
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