Reconfigurable intelligent surface (RIS) is a promising technology for RF wireless power transfer (WPT) as it is capable of beamforming and beam focusing without using active and power-hungry components. In this paper, we propose a multi-tile RIS beam scanning (MTBS) algorithm for powering up internet-of-things (IoT) devices. Considering the hardware limitations of the IoT devices, the proposed algorithm requires only power information to enable the beam focusing capability of the RIS. Specifically, we first divide the RIS into smaller RIS tiles. Then, all RIS tiles and the phased array transmitter are iteratively scanned and optimized to maximize the receive power. We elaborately analyze the proposed algorithm and build a simulator to verify it. Furthermore, we have built a real-life testbed of RIS-aided WPT systems to validate the algorithm. The experimental results show that the proposed MTBS algorithm can properly control the transmission phase of the transmitter and the reflection phase of the RIS to focus the power at the receiver. Consequently, after executing the algorithm, about 20 dB improvement of the receive power is achieved compared to the case that all unit cells of the RIS are in OFF state. By experiments, we confirm that the RIS with the MTBS algorithm can greatly enhance the power transfer efficiency.

中文翻译：

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可重构智能表面辅助无线电能传输系统：分析与实现

可重构智能表面 (RIS) 是一种很有前途的射频无线功率传输 (WPT) 技术，因为它能够在不使用有源且耗电的组件的情况下进行波束成形和波束聚焦。在本文中，我们提出了一种多瓦片 RIS 波束扫描 (MTBS) 算法，用于为物联网 (IoT) 设备供电。考虑到物联网设备的硬件限制，所提出的算法只需要功率信息即可启用 RIS 的光束聚焦能力。具体来说，我们首先将 RIS 划分为更小的 RIS 瓦片。然后，对所有 RIS 瓦片和相控阵发射器进行迭代扫描和优化，以最大限度地提高接收功率。我们精心分析了所提出的算法并构建了一个模拟器来验证它。此外，我们已经建立了一个真实的 RIS 辅助 WPT 系统测试平台来验证算法。实验结果表明，所提出的MTBS算法能够适当地控制发射机的传输相位和RIS的反射相位，从而将功率集中在接收机上。因此，在执行该算法之后，与RIS的所有单位单元都处于OFF状态的情况相比，接收功率实现了大约20dB的改进。通过实验，我们证实了采用 MTBS 算法的 RIS 可以大大提高功率传输效率。