An Ultra-Low-Power Strain Sensing Node for Long-Range Wireless Networks in Carbon Nanotube-Based Materials

The application of flexible electronics to device-engineering technologies has enabled the manufacture of low-cost, lightweight, extensible, and foldable sensors. However, despite the efficient response of composite materials for the detection of signal stimuli reported in the state-of-art literature, there is an area of opportunity for the implementation of ultra-low-power wireless sensor networks (WSN) with novel flexible materials in precision medicine, structural health monitoring, environmental sensing, wearables and applications based on the Internet of Things (IoT). This article proposes a portable strain sensing node based on multiwall carbon nanotubes (MWCNTs)/polypropylene(PP) composites for Long-Range (LoRa) wireless networks with IoT connectivity. The nanostructured sensor node with 4 wt% MWCNTs shows high piezoresistive sensitivity with gage factors of ~ 4.5. A system identification problem is conducted following a constrained optimization model, which estimates the sensor errors due to nonlinearity and system parameters, providing a stable strain response with high accuracy. An energy management strategy is also implemented for the efficient integration of a microcontroller unit in combination with a wireless LoRa communication transceiver, enabling the utilization of flexible composite materials into a wireless nanostructured sensing network with ultra-low-power consumption of 0.8705 mW. The experimental results of the MWCNT/PP strain sensing node show the feasibility for a variety of IoT-WSN applications.