Performance analysis of wireless power transfer system based on resonating slot antenna for bio implant devices

Abstract

The method of wireless power transmission which uses magnetic resonance is similar to magnetic induction method that is used for electric shaver and cell-phone power transmission. These two methods use the magnetic field to transmit the power to the receiver. Magnetic induction method has high power transmission efficiency. But, power transmission range of this method is very short. On the other hand, magnetic resonant method has relatively high power transmission efficiency and long transmission range. However, most of magnetic resonant wireless power transmission system use low resonant frequency(about MHz). It is hard to integrate the wireless power transfer system which uses low resonant frequency to bio implant devices because of antenna size. There is another problem of the wireless power transfer system using coil antenna. If we use coil antenna to transmit the power to the receiving devices, the central axis of transmit and receive antenna should be matched to transmit the power efficiently. If not, power transfer efficiency is rapidly decreased. Also, wireless power transfer system using coil antenna is hard to integrate the circuit. In this thesis, we select the slot antenna to transmit the power because slot antenna is easily to be integrated to the circuit. Then, we determined the resonant frequency as 910.4 MHz which is one of the ISM band(Industrial Scientific Medical band) frequency from 902 MHz to 928 MHz. High resonant frequency helps us to miniaturize the antenna because antenna size is determined from the wave length at the resonant frequency. Slot antenna size is generally represented as $\lambda/2$. But, it can be reduced to $\lambda/4$ by using half-slot antenna. So, the size of half-slot antenna is about 9 cm at the resonant frequency 910.4 MHz. To reduce the size of the antenna, we insert C shape structure in the main slot and use the sub-slot to make the current path much longer. From this process, we successfully miniaturize the ant...