The Internet-of-Things (IoT) is predicted to bring a revolution in the way we monitor our health, environment, and infrastructure and allow enhancements in efficiency, performance, and services. However, a critical issue is how to power IoT devices as they become more numerous and smaller. Batteries add weight, size, and require replacement and add maintenance cost when there are billions of IoT devices. It is therefore prohibitive and unsustainable to use batteries.
In this talk, I will show how to solve the power challenge to implement battery-free IoT by two promising technologies including wireless power transfer (WPT) and reconfigurable intelligent surfaces (RIS). In WPT, the RF energy transmitted from a dedicated source will be received and converted into DC energy to power IoT devices. To increase the output DC power, I propose waveform and beamforming optimization for multi-sine multi-input and multi-output (MIMO) WPT systems. Simulation results show that the proposed multi-sine MIMO WPT system can significantly increase output DC power. Prototype and experimental measurement of the WPT systems with limited feedback technology are also provided. On the other hand, RIS consists of a large number of reconfigurable scattering elements and each element is able to adjust the phase shift of its scattered RF wave so that passive beamforming can be implemented. RIS can be used to increase the received power in WPT and also used to reduce the energy consumed by wireless communications in battery-free IoT. To enhance RIS performance, I propose novel RIS architectures which I denote as fully and group connected reconfigurable impedance networks. Simulation results show that the received signal power can be effectively increased by using the proposed RIS architecture. In addition, a preliminary prototype of RIS and experimental measurements are also provided to demonstrate the increased signal power.