Single-Frequency Self-Alignment RF Resonant Beam for Information and Power Transfer

TL;DR

RF-RBS tackles the low efficiency of RF wireless power transfer and near-field information transfer in IoT by leveraging a resonance mechanism between retro-directive antenna arrays at the BS and MT. It introduces a single-frequency design that uses phase-conjugate transmission and iterative power circulation to achieve self-alignment, outperforming traditional retro-directive beamforming by up to $16\%$. An analytical model encompassing EM propagation, resonance establishment, energy harvesting, and downlink communication predicts watt-level power delivery and a downlink spectral efficiency near $21$ bps/Hz in indoor settings. The work highlights practical potential for cable-free IoT operation and outlines future directions including safeguards, high-gain power amplifiers, phase shifters, RIS integration, and SWIPT-enabled deployments.

Abstract

Due to power attenuation, improving transmission efficiency in the radio-frequency (RF) band remains a significant challenge, which hinders advancements in various fields of the Internet of Things (IoT), such as wireless power transfer (WPT) and wireless communication. Array design and retro-directive beamforming (RD-BF) techniques offer simple and effective ways to enhance transmission efficiency. However, when the target is an array or in the near field, the RD-BF system (RD-BFS) cannot radiate more energy to the target due to phase irregularities in the target region, resulting in challenges in achieving higher efficiency. To address this issue, we propose the RF-based resonant beam system (RF-RBS), which adaptively optimizes phase and power distribution between transmitting and receiving arrays by leveraging the resonance mechanism to achieve higher transmission efficiency. We analyze the system structure and develop an analytical model to evaluate power flow and resonance establishment. Numerical analysis demonstrates that the proposed RF-RBS achieves self-alignment without beam control and provides higher transmission efficiency compared to RD-BFS, with improvements of up to 16%. This self-alignment capability allows the system to effectively transfer power and information across varying distances and offsets. The numerical results indicate the capability to transmit watt-level power and achieve 21 bps/Hz of downlink spectral efficiency in indoor settings, highlighting the advantages of RF-RBS in information and power transfer for mobile applications.

Figures (18)

• Figure 1: A typical application scenario of RF-RBS in IoT (e.g., WPT, wireless communication).
• Figure 2: Transceiver structure of RF-RBS.
• Figure 3: Round-trip iteration process and self-reproducing mode in RF-RBS.
• Figure 4: Power circulation between BS and MT.
• Figure 5: Single energy harvesting circuit. (a) Voltage doubling circuit. (b) RF equivalent circuit. (c) DC equivalent circuit.