Energy autonomous LPWAN node for walls and bridges : 4 seasons results

Measuring and monitoring the state of infrastructure built with concrete, such as buildings or bridges, is important to prevent damages or other serious issues. Some requirements for monitoring devices are long operation lifetime, robustness against adverse temperatures or weather conditions, low maintenance costs. Providing access over long distances to the measurement data is a welcome feature. Due to harsh temperature conditions and maintenance costs, batteries might not always be a recommended energy source. One approach is to harvest energy in the operating environment using Thermoelectric Generators (TEG). This energy harvesting method takes advantage of the temperature differences between ambient air and concrete to convert thermal energy into electrical energy. This work presents the results of a yearlong investigation of an energy autonomous long range wireless node installed on a bridge and powered by harvesting energy from temperature differences. The work concentrates on the reliability of the energy source and shows that, apart from a few days in November and December, sufficient energy can be harvested to transmit several LoRaWAN compatible messages per day with sensor data as payload

Energy autonomous wireless sensing node working at 5 Lux from a 4 cm2 solar cell

Harvesting energy for IoT nodes in places that are permanently poorly lit is important, as many such places exist in buildings and other locations. The need for energy-autonomous devices working in such environments has so far received little attention. This work reports the design and test results of an energy-autonomous sensor node powered solely by solar cells. The system can cold-start and run in low light conditions (in this case 20 lux and below, using white LEDs as light sources). Four solar cells of 1 cm2 each are used, yielding a total active surface of 4 cm2. The system includes a capacitive sensor that acts as a touch detector, a crystal-accurate real-time clock (RTC), and a Cortex-M3-compatible microcontroller integrating a Bluetooth Low Energy radio (BLE) and the necessary stack for communication. A capacitor of 100 μF is used as energy storage. A low-power comparator monitors the level of the energy storage and powers up the system. The combination of the RTC and touch sensor enables the MCU load to be powered up periodically or using an asynchronous user touch activity. First tests have shown that the system can perform the basic work of cold-starting, sensing, and transmitting frames at +0 dBm, at illuminances as low as 5 lux. Harvesting starts earlier, meaning that the potential for full function below 5 lux is present. The system has also been tested with other light sources. The comparator is a test chip developed for energy harvesting. Other elements are off-the-shelf components. The use of commercially available devices, the reduced number of parts, and the absence of complex storage elements enable a small node to be built in the future, for use in constantly or intermittently poorly lit places

Autonomous wireless sensors for walls and bridges

We have been working on methods to provide enough energy for the monitoring of civil infrastructure such as walls or bridges. In this presentation we will discuss the status of that work. More specifically, we will show and discuss measurements resulting from the use of TEGs to harvest energy in order to power wireless sensors in such environments

Battery-free LPWAN nodes for bridges and walls

This presentation builds on an early work where we evaluated the potential of harvesting energy from concrete walls using temperature differences. We have now built and installed several LPWAN nodes that are powered solely from TEGs, using small temperature differences. With efficient harvesting, those nodes can scavenge sufficient energy to sense parameters in the civil infrastructure environment and communicate with gateways that are several kilometres away. This brings battery-free monitoring of walls and bridges one step closer to reality. After giving an overview of the technologies involved and discussing the basis of TEG harvesting, we will present first results and early conclusions of several weeks of measurement activity

Energy Autonomous Wireless Sensing Node Working at 5 Lux from a 4 cm2 Solar Cell

Harvesting energy for IoT nodes in places that are permanently poorly lit is important, as many such places exist in buildings and other locations. The need for energy-autonomous devices working in such environments has so far received little attention. This work reports the design and test results of an energy-autonomous sensor node powered solely by solar cells. The system can cold-start and run in low light conditions (in this case 20 lux and below, using white LEDs as light sources). Four solar cells of 1 cm2 each are used, yielding a total active surface of 4 cm2. The system includes a capacitive sensor that acts as a touch detector, a crystal-accurate real-time clock (RTC), and a Cortex-M3-compatible microcontroller integrating a Bluetooth Low Energy radio (BLE) and the necessary stack for communication. A capacitor of 100 μF is used as energy storage. A low-power comparator monitors the level of the energy storage and powers up the system. The combination of the RTC and touch sensor enables the MCU load to be powered up periodically or using an asynchronous user touch activity. First tests have shown that the system can perform the basic work of cold-starting, sensing, and transmitting frames at +0 dBm, at illuminances as low as 5 lux. Harvesting starts earlier, meaning that the potential for full function below 5 lux is present. The system has also been tested with other light sources. The comparator is a test chip developed for energy harvesting. Other elements are off-the-shelf components. The use of commercially available devices, the reduced number of parts, and the absence of complex storage elements enable a small node to be built in the future, for use in constantly or intermittently poorly lit places