As Internet of Things (IoT) devices proliferate, sustainable methods for powering them are becoming indispensable. The wireless provision of power enables battery-free operation and is crucial for complying with weight and size restrictions. For the energy harvesting (EH) components of these devices to be small, a high operating frequency is necessary. In conjunction with a large transmit antenna, the receivers may be located in the radiating near-field (Fresnel) region, e.g., in indoor scenarios. In this paper, we propose a wireless power transfer (WPT) system ensuring reliable supply of power to an arbitrary number of mobile, low-power, and single-antenna receivers, whose locations in a three-dimensional cuboid room are unknown. A max-min optimisation problem is formulated to determine the optimal transmit power distribution. We rigorously prove that the optimal transmit power distribution's support has a lower dimensionality than its domain and thus, the employment of a continuous aperture antenna, utilised in Holographic MIMO (HMIMO), is unnecessary in the context of the considered WPT problem. Indeed, deploying a discrete transmit antenna architecture, i.e., a transmit antenna array, is sufficient and our proposed solution provides the optimal transmit antenna deployment and power allocation. Moreover, for a one-dimensional transmit antenna architecture, a finite number of transmit antennas is proven to be optimal. The proposed optimal solution is validated through computer simulations. Our simulation results indicate that the optimal transmit antenna architecture requires a finite number of transmit antennas and depends on the geometry of the environment and the dimensionality of the transmit antenna array.

翻译：随着物联网设备的激增，为其提供可持续的供电方式变得不可或缺。无线供电技术可实现无电池操作，对于满足设备的重量和尺寸限制至关重要。为使这些设备的能量收集组件小型化，必须采用较高的工作频率。结合大型发射天线，接收器可能位于辐射近场区，例如在室内场景中。本文提出一种无线能量传输系统，确保为任意数量的移动、低功率、单天线接收器提供可靠供电，这些接收器在三维长方体房间内的位置未知。我们构建了一个最大-最小优化问题以确定最优发射功率分布。我们严格证明了最优发射功率分布的支撑集维度低于其定义域维度，因此在所考虑的WPT问题中，无需采用全息MIMO中使用的连续孔径天线。实际上，部署离散发射天线架构即发射天线阵列已足够，且我们提出的解决方案提供了最优的发射天线部署与功率分配方案。此外，对于一维发射天线架构，我们证明了有限数量的发射天线即为最优配置。通过计算机仿真验证了所提出的最优解。仿真结果表明，最优发射天线架构需要有限数量的发射天线，且其取决于环境几何形状与发射天线阵列的维度。