Wireless power transmission-part III: Experimental study

The authors have carried out a comprehensive experimental study on Wireless Power Transfer (WPT) by using both the self-resonance coupling and near-field electromagnetic coupling between transmitting and receiving electrically-small loop antennas. For the first coupling mechanism, the frequency of the transmitted signal is kept same as the self-resonance frequency of the transmitting and receiving antenna system; however, for the second coupling mechanism, the frequency of the transmitted signal is kept well above the self-resonance frequency subject to obtain high radiation efficiency of the transmitting antenna. Experiments have been carried out to study the Power Transfer Efficiency (PTE) of the antenna system coupled in axial and radial orientations for both the abovementioned coupling mechanisms. Results show that the better PTE is achieved in axial coupling mode as compared to the radial coupling mode when the self-resonance coupling mechanism is used; but the usable frequency range (i. e. the bandwidth) is found to be very small less than 1 MHz for this coupling mechanism. The observation is reversed when near-field electromagnetic coupling mechanism is used and the bandwidth for WPT for this mechanism is also found to much broader similar to 50 MHz.