A Battery-free Asset Monitoring System based on RF Wireless Power Transfer

In the Internet of Things (IoT) era, asset monitoring represents an appealing implementation of Wireless Sensor Networks due to the enormous benefits associated with being able to monitor and record the exact position and transportation conditions of assets, personal objects, and the like. This kind of infrastructure enables the provision of increasingly advanced services, including the ability to measure the movement speed of a monitored asset using relatively inexpensive nodes with sensing capabilities and wireless transmission and reception. These nodes would ideally employ battery-free sensors that do not require any maintenance, but conventional power supply management systems cannot satisfy this requirement. In response to the heightening demand and interest surrounding Battery-free tags, this article proposes a system inside a Wireless Sensor Network infrastructure that uses battery-free tags to identify an asset and monitor its speed. The battery-free tags are powered by RF energy through Wireless Power Transfer, and the speed of an asset proceeding at constant speed is achieved by measuring the time that the tag takes to traverse a series of hot-spots interspersed at specific distances. Our discussion shall include the performance characteristics and key features of a system on chip (SoC) specifically designed to power a node through RF WPT. The outcome is a strategy and a model for designing the infrastructure by providing the optimum number of hot-spots needed to perform the identification of an asset and measure its speed. Validation of the model has been performed through specific tests and experimental results have been provided.