Abstract-For the class-E amplifier in a wireless power transfer (WPT) system, the design parameters are always determined by the nominal model. However, this model neglects the conduction loss and voltage stress of MOSFET and cannot guarantee the highest efficiency in the WPT system for biomedical implants. To solve this problem, this paper proposes a novel circuit model of the subnominal class-E amplifier. On a WPT platform for capsule endoscope, the proposed model was validated to be effective and the relationship between the amplifier's design parameters and its characteristics was analyzed. At a given duty ratio, the design parameters with the highest efficiency and safe voltage stress are derived and the condition is called 'optimal subnominal condition.' The amplifier's efficiency can reach the highest of 99.3% at the 0.097 duty ratio. Furthermore, at the 0.5 duty ratio, the measured efficiency of the optimal subnominal condition can reach 90.8%, which is 15.2% higher than that of the nominal condition. Then, a WPT experiment with a receiving unit was carried out to validate the feasibility of the optimized amplifier. In general, the design parameters of class-E amplifier in a WPT system for biomedical implants can be determined with the proposed optimization method in this paper.Index Terms-Biomedical implants, class-E amplifier, efficiency improvement, subnominal condition, wireless power transfer system, zero-voltage-switching (ZVS).
Capsule endoscopy is a new technique that allows complete exploration of the small intestine, and widely used all over the world, for its convenience and less pains compared with traditional endoscopy. However, the limited power supplies of batteries handicap the development of capsule endoscopy. This paper presents a novel wireless power transfer system for the capsule endoscopy utilizing the strongly coupled magnetic resonances theory. The wireless power transfer system consists of four coils, an excitation source and a load. In order to evaluate the system performance, experiments were carried out in which the working frequency is determined at 8.2MHz. The results demonstrate that the distance between two sets of transmission coils have great effect on the system efficiency and the maximal system efficiency can reach 26.14%. Therefore, this power supply system has a promising prospect on wireless power transfer for capsule endoscopy. Improving the quality factor of coils can effectively increase the efficiency of the system, which is the key to the future work.
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