Reconfigurable intelligent surfaces (RISs) are considered a key enabler of highly energy-efficient 6G and beyond networks. This property arises from the absence of power amplifiers in the structure, in contrast to active nodes, such as small cells and relays. However, a certain amount of power is still required for RIS operation. To improve their energy efficiency further, we propose the notion of perpetual RISs, which secure the power needed to supply their functionalities through wireless energy harvesting (EH) of impinging transmitted electromagnetic (EM) signals. Toward this, we initially explain the rationale behind such RIS capability and proceed with a presentation of the main RIS controller architecture that can realize this vision under an in-band EH consideration. Furthermore, we present a typical EH architecture, followed by two harvesting protocols. Subsequently, we study the performance of the two protocols under a typical communications scenario. Finally, we elaborate on the main research challenges governing the realization of large-scale networks with perpetual RISs.

中文翻译：

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通过带内能量收集实现永久可重构智能表面：架构、协议和挑战

可重构智能表面 (RIS) 被认为是高能效 6G 及更高版本网络的关键推动者。与小型蜂窝和继电器等有源节点相比，该特性是由于结构中没有功率放大器而产生的。然而，RIS 运行仍然需要一定的电量。为了进一步提高其能源效率，我们提出了永久 RIS 的概念，它通过撞击传输的电磁 (EM) 信号的无线能量收集 (EH) 来确保提供其功能所需的电力。为此，我们首先解释这种 RIS 功能背后的基本原理，并继续介绍可以在带内 EH 考虑下实现这一愿景的主 RIS 控制器架构。此外，我们提出了一个典型的 EH 架构，然后是两个收集协议。随后，我们研究了两种协议在典型通信场景下的性能。最后，我们详细阐述了利用永久 RIS 实现大规模网络的主要研究挑战。