Autonomous Industrial IoT for Civil Engineering Structural Health Monitoring

This article presents a wireless sensing node (SN) part of a wireless sensor network (WSN) dedicated to the deployment of a cyber-physical system intended for the Structural Health Monitoring of reinforced concretes. This low-power SN requires less than 21 mJ for a full processing: measurement, data formatting, and transmission of a 17-bytes LoRaWAN frame; id est 39~\mu \text{J} per transmitted bit. It is designed to be buried in reinforced concrete and is battery-free and energy autonomous for long-term deployment by a radiative electromagnetic wireless power transfer (WPT) approach. The SN is cold-start compatible down to a power of-17 dBm available at the output of the antenna. It is able to wirelessly transmit data over at least tens of meters thanks to the LoRaWAN wireless communication technology. Moreover, it is wirelessly, remotely, and omnidirectionally powered and controlled by a communicating node (CN) over meters, with the respect of regional regulatory constraints (equivalent isotropic radiated power (EIRP) of +33 dBm allowed in the 868-MHz industrial, scientific and medical (ISM) frequency band). By being a generic platform, this SN can employ various sensors to measure relevant parameters for the targeted application, id est: temperature, relative humidity, mechanical deformation through the strain, and electrical resistivity whose the variation allows to estimate the corrosion rate. By simultaneously using the same 868-MHz ISM frequency band for the wireless communication and the WPT, the SN meets the simultaneous wireless information and power transfer paradigm with a unique antenna and without interferences. Thus, the tested system allows the deployment of the subnetwork of two CNs and several SNs (currently four) to cover a surface/volume of several meters, currently up to 11 m around each CN indoors. Finally, this system can be easily deployed for other applications requiring energy autonomous WSNs, especially in harsh environments, such as reinforced concretes, space, underground mining, power plants, etc.