Biography
Enrollment Date: 2011
Graduation Date：2014
Degree：M.S.
Defense Date：2014.05.27
Advisors：Xiang Xie
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research on the Key Technology of Wireless Power Transfer in Human Body Environment
Abstract:
The emergence of wireless capsule endoscopy brings the endoscopy technology into a new era. The wireless capsule endoscopy can not only examine the small intestine, but also bring less pain to the patients. With the increasing demand in clinic, the wireless capsule endoscopy need to include more functions. However, those additional functions will need more space or more power that can hardly be accepted in the wireless capsule endoscopy powered by the button cells. Fortunately, using wireless power transfer (WPT) technology to power the wireless capsule endoscopy is a promising way to meet those challenges. In this paper, a high-efficiency and portable WPT system is proposed.
In the WPT system, the segmented transmitting coil structure is adopted. According to the position of the capsule, the transmitting coil which is the nearest to the capsule is selected to send wireless power. Such working mechanism ensures higher coupling coefficient between the transmitting coil and receiving coil. The whole system can be powered by a battery like the laptop battery. As the result, the proposed WPT system reduces the radiation problem caused by the low transfer efficiency, and the patients can move freely. Furthermore, the optimal segmentation number of this new structure is achieved through theoretical analysis.
After considering the body loss, circuits’ loss, and the coil loss, the operating frequency of the system is optimized. And a more accurate formula for the parasitic capacitance of the solenoid is achieved in the frequency optimization.
The contents of this article also include the software and hardware design of the WPT system. The whole system is controlled by a MCU, and the control instruction is based on the feedback from the wireless capsule.
The innovations of this thesis are as follows:
Firstly, a new segmented power transmitting coil structure is proposed, and this segmented transmitting coil ensures the highest transfer efficiency.
Secondly, the parameters of the segmented transmitting coil are optimized theoretically, and the optimal height of each segmentation maximizes the worst transfer efficiency.
Thirdly, an optimal operating frequency of the system with lowest power loss is achieved after considering the body loss, the circuits’ loss, and the coil loss.
Fourthly, a formula for the parasitic capacitance of a solenoid is deduced in the process of calculating the solenoid’s quality factor, and this formula is more accurate than other methods.
Fifthly, based on the above four innovations, the minimum, average, and maximum AC-AC transfer efficiency of the proposed wireless power transfer are 5.62%, 10.4% and 24.8% with air core receiving coil, and 26.3%, 38.9% and 51.9% with a Mn-Zn ferrite core receiving coil respectively. Compared with other organizations, this proposed system has the highest transfer efficiency.