This paper addresses the concept of a wirelessly powered and battery-free wireless sensor for Cyber-Physical Systems dedicated to Structural Health Monitoring applications in harsh environments. The proposed material architecture is based on a smart mesh Wireless Sensor Network composed of Sensing Nodes and Communicating Nodes. The Sensing Nodes are used to sense the physical world. They are battery-free and wirelessly powered by a dedicated radiofrequency source via a far-field Wireless Power Transmission system. The data collected by the Sensing Nodes are sent to the Communicating Nodes that, between others, interface the physical world with the digital world through the Internet. A prototype of the Sensing Node -using a LoRaWAN uplink wireless communication and a temperature and relative humidity sensor-has been manufactured and experiments have been performed to characterize it. The experimental results prove that the periodicity of measurement and communication can be controlled wirelessly by using only the Wireless Power Transmission downlink. In this paper, we highlight the performance of this complete implementation of a wirelessly powered and battery-free wireless Sensing Node -not yet integrated or miniaturized-designed for implementing complete Cyber-Physical Systems and based on Simultaneous Wireless Information and Power Transfer. Finally, an investigation of comparable implementations of battery-free Sensing Nodes for Cyber-Physical Systems is carried out.

This paper addresses the practical implementation of a wireless sensors network designed to actualize cyber-physical systems that are dedicated to structural health monitoring applications in the construction domain. This network consists of a mesh grid composed of LoRaWAN battery-free wireless sensing nodes that collect physical data and communicating nodes that interface the sensing nodes with the digital world through the Internet. Two prototypes of sensing nodes were manufactured and are powered wirelessly by using a far-field wireless power transmission technique and only one dedicated RF energy source operating in the ISM 868 MHz frequency band. These sensing nodes can simultaneously perform temperature and relative humidity measurements and can transmit the measured data wirelessly over long-range distances by using the LoRa technology and the LoRaWAN protocol. Experimental results for a simplified network confirm that the periodicity of the measurements and data transmission of the sensing nodes can be controlled by the dedicated RF source (embedded in or just controlled by the associated communicating node), by tuning the radiated power density of the RF waves, and without any modification of the software or the hardware implemented in the sensing nodes.

This paper presents a multifunctional battery-free wireless sensing node (SN) designed to monitor physical parameters (e.g., temperature, humidity and resistivity) of reinforced concrete. The SN, which is intended to be embedded into a concrete cavity, is autonomous and can be wirelessly powered thanks to the wireless power transmission technique. Once enough energy is stored in a capacitor, the active components (sensor and transceiver) are supplied with the harvested power. The data from the sensor are then wirelessly transmitted via the Bluetooth Low Energy (BLE) technology in broadcasting mode to a device configured as an observer. The feature of energy harvesting (EH) is achieved thanks to an RF-to-DC converter (a rectifier) optimized for a low power input level. It is based on a voltage doubler topology with SMS7630-005LF Schottky diode optimized at −15 dBm input power and a load of 10 kΩ. The harvested DC power is then managed and boosted by a power management unit (PMU). The proposed system has the advantage of presenting two different power management units (PMUs) and two rectifiers working in different European Industrial, Scientific and Medical (ISM) frequency bands (868 MHz and 2.45 GHz) depending on the available power density. The PMU interfaces a storage capacitor to store the harvested power and then power the active components of the sensing node. The low power digital sensor HD2080 is selected to provide accurate humidity and temperature measurements. Resistivity measurement (not reported in this paper) can also be achieved through a current injection on the concrete probes. For wireless communications, the QN9080 system-on-chip (SoC) was chosen as a BLE transceiver thanks to its attractive features: a small package size and extremely low power consumption. For low power consumption, the SN is configured in broadcasting mode. The measured power consumption of the SN in a deep-sleep mode is 946 µJ for four advertising events (spaced at 250 ms maximum) after the functioning of sensors. It also includes voltage offset cancelling functionality for resistivity measurement. Far-field measurement operated in an anechoic chamber with the most efficient PMU (AEM30940) gives a first charging time of 48 s (with an empty capacitor) and recharge duration of 27 s for a complete measurement and data transmission cycle.

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.

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.

This paper addresses the concept of a smart-node wireless network designed for structural health monitoring applications. The network architecture is based on a smart mesh composed of sensing nodes and communicating nodes. The sensing nodes are used to implement the so named communicating material/communicating concrete and collect physical data for structural health monitoring purposes. These data are sent to the communicating nodes that interface the smart-node network with the digital world through the Internet. The sensing nodes are batteryless and wirelessly powered by the communicating nodes via a wireless power transmission interface. Experimental results have been obtained for a simplified sensing node using a LoRaWAN uplink wireless communication (from the sensing node to the communicating node) proving that the functionality of the sensing nodes can be controlled wirelessly by using only the wireless power transmission downlink.