Optimal Array Beamforming for Microwave Power Transmission in Complex Environment

Wireless power transfer (WPT) is a popular research field in recent years and can be categorized into three approaches: inductive coupling, laser beaming, and microwave power transmission (MPT). MPT system operates at the microwave and transfers the energy over more than a few wavelengths. It has its unique advantages of supplying power to non-accessible and mobile receivers. The overall efficiency, which is the ratio between available DC power at the receiver and supplied DC power at the transmitter, depends on both circuit design and wave propagation. As a comprehensive theory of MPT system is not available, this chapter starts with the study of MPT system from the perspectives of mathematical formulation and the experiment in the indoor environment, in Sect. 3.1. The preliminary study leads to the conclusion that highly directional wireless transmitter is very useful in the MPT system for achieving high transmission efficiency. For this reason, phased array antennas with beamforming functionality are usually used to direct the electromagnetic wave toward mobile receivers, and adaptive array algorithms are implemented to enable wireless power focusing in the complex environment. Section 3.3 presents a novel beamforming algorithm, which is proven to give the optimal transmission efficiency and applies to the arbitrarily positioned unequal array based on our problem formulation. To verify this algorithm, Sect. 3.4 validates it with numerical electromagnetic simulation in different cases. The numerical comparison in these examples shows that this algorithm gives higher transmission efficiency over other optimal beamforming algorithms discussed in Sect. 3.2.

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