Journal Paper

Today, wireless sensor networks are used as the basis for deploying cyberphysical systems (CPS), particularly for internet of things applications. However, the main factor limiting the long-term and large-scale deployment of wireless sensor networks is the energy autonomy of the sensing nodes. Ambient energy harvesting and wireless power transfer techniques enable the design and the implementation of battery-free wireless sensing nodes that can become energy self-sufficient. Among those techniques the far-field electromagnetic wireless power transfer is an exciting solution enabling the remote powering of battery-free wireless sensing nodes over several meters in a wide range of environments. Main architectures of the sensing node and related concepts including CPS and simultaneous wireless information and power transfer are presented. Also, innovative solutions—including passive wake-up receivers and the use of feedback channels—are highlighted. State-of-the-art battery-free, wireless sensing nodes, wirelessly powered with electromagnetic waves, are described and compared, whether they communicate by backscattering or using standard, low-power communication protocols with a focus on energy efficiency, sustainability and security issues.