Study On Three-dimensional Magnetically-Coupled Inductive Wireless Power Transmission System For Capsule Endoscopy

A wireless power transmission(WPT) system transfers the electrical power wirelessly from a site(transmitter) to another site(receiver) in the form of electromagnetic waves. Its basic principle is inductive couple between the primary coils and the secondary ones. It is proved that WPT is a popular and promising method to solve the power supply problem of implantable devices. A capsule endoscopy(CE) is an advancing technology for direct inspection of the entire gastrointestinal tract. To improve the quality of inspection, some important specifications of CE such as the image resolution, the frame rate and the working time need to be increased. Furthermore, a multifunctional medical robot CE can perform the vivo semi-surgery, active motion, biopsy or drug delivery function. To realize these super functions, a CE system demands additional power supply to make the conventional power source(battery) method impractical. To overcome this problem, WPT is proved to as a most effective measure instead of batteries to provide the necessary and steady power.The present paper aims to accomplish the detailed work as follows.Firstly, the basic structure and principles of the wireless power transmission system are discussed. Electric energy conversion circuits, resonant compensation topologies and the electromagnetic inductive coupling technology are specially studied. The three dimensional structures of the wireless power transmission model are analyzed. To the transmitter coil, a full-bridge inverter was proposed and a double RCD snubber network is used to reduce over voltage and switching losses of MOSFETs was introduced. To deal with freedom of motion, three secondary orthogonal coils and one primary coil are adopted to guarantee magnetic coupling for an arbitrary orientation. A series resonating circuit is typically employed at the TC and RC to obtain resonance to compensate the reactive power of the whole WPT.Secondly, the designs of the primary power rectifier circuit, inverter control circuit, and full-bridge inverter circuit with PWM are successively introduced. The physical circuit of the power generator is built to supply high frequency AC energy, and the performance parameters of the power generator have been studied through experiments. It proves that the circuit can satisfy power supply of the capsule endoscopy.Thirdly, the mismatch phenomenon of the WPT system is studied which is mainly caused by variations of the environmental and coil parameters, and the reasons of the frequency mismatch are analyzed. Then, the system energy efficiency and output power expressions under every detuning case are worked out. Then, the corresponding experiments are carried out to verify the theory. The frequency tracking method is studied based on the phase difference between the primary voltage and current of the WPT. The frequency tracking method based on microcomputer control unit(MCU) is designed. The experiments have shown the effectiveness of the frequency tracking system with MCU.