An investigation on transmitter and receiver diversity for wireless power transfer
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This thesis investigates near-field wireless power transfer using multiple transmitters or multiple receivers. First, transmitter diversity is investigated in terms of the power transfer efficiency (PTE). It is found that an improvement in the PTE can be achieved by increasing the number of transmitters. Furthermore, a region of constant PTE can be created with the proper arrangement of transmitters. Next, receiver diversity is investigated in detail. An improvement in the PTE can be also achieved by increasing the number of receivers. However, it is shown that when two or more receivers are closely located, the PTE is reduced due to mutual coupling between receivers. This is termed a ‘sink’ phenomenon, and it is investigated through measurement and simulation. Finally, to account for more general situations of multiple transmitters and multiple receivers, Monte-Carlo simulation is applied. The cumulative distribution function (CDF) is used to interpret the results of the Monte-Carlo simulation. The transmitter and receiver diversity gain can be found based on the CDF. Moreover, the sink phenomenon can be observed by analyzing the CDF curve. Several strategies for positioning receivers are introduced to reduce the sink phenomenon. The results of the Monte-Carlo simulation also show that a saturation in the transmitter or receiver gain is reached when the number of transmitters or receivers is increased. Therefore, increasing the number of transmitters or receivers beyond a certain number does not help increase the PTE.