Speed detection of battery-free nodes based on RF Wireless Power Transfer

In the Internet of Things (IoT) era, Wireless Sensor Networks (WSNs) are rapidly increasing in terms of relevance and pervasiveness thanks to their notable real-time monitoring performance across several fields, including industrial, domestic, military, biomedical, commercial, environmental, and other sectors. A highly attractive implementation of WSNs is asset tracking with accurate data regarding the location and transportation conditions of goods, equipment, and the like. One highly promising application of WSNs along these lines is the remote speed monitoring of goods, ideally with battery-free sensor nodes that do not require any maintenance. This, however, represents a major challenge in power supply management. The goal of this paper is to investigate Radio Frequency (RF) Wireless Power Transfer (WPT) architecture to power a battery-free measurement system with time-domain readouts, for the speed detection of a moving sensor tag within a Wireless Sensor Network infrastructure. The performance characteristics and key features of a System-on-Chip (SoC) specifically designed to power a node through RF WPT will be discussed. The aim is to provide a strategy and a model to estimate the speed of a specific battery-free sensor that is powered by a transmitting hot-spot. Specific tests and experimental results are provided.