| Summary: | A simple adaptive 1-D frequency-scanning method is proposed for radiative wireless power transfer (WPT) systems in low-power wireless sensor networks (WSNs). As a proof of concept, a directive leaky-wave antenna that scans 1-W output RF power in the angular range from ±10° at 2.4 GHz to ±37° at 2.5 GHz, is used to power a WSN covering an area of 1.2 m <inline-formula> <tex-math notation="LaTeX">$\times1.2$ </tex-math></inline-formula> m. It is shown that, using a frequency-scanned antenna, a wider area than using a non-scanned directive antenna can be powered without additional expensive equipment. The WPT protocol is described, showing that any sensor in the WSN can select the optimum transmission channel in the 2.4-GHz band, based on the received signal strength indicator measurements, as the coordinator performs a scheduled frequency hopping phase. This maximizes the WPT beaming efficiency and the transferred dc power. The optimum channel selection can be performed periodically, which makes the system robust against channel state changes.
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