Low-Cost, High-Accuracy, and Long-Communication-Range Energy-Harvesting Beat Sensor With LoRa and Ω–Antenna for Water-Level Monitoring

This article proposes a low cost of U.S. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\$}72.5$ </tex-math></inline-formula> BoM with a small size of water-level monitoring Internet-of-Things (IoT) sensors without ultrasonic-level sensors. The power consumption for sensing and RF transmission is minimized to less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~\mu {\textrm {W}}$ </tex-math></inline-formula> in the manner of the beat sensor (BS) IoT system so that power is supplied by energy-harvesting power supply using a card-size solar cell. Communication range can be reached 2 km using LoRa WAN and Quasi-isotropic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula>-antenna. The system continuously measures the water level at a pond for 21 days without a battery, and the root mean square error (RMSE) of the water-level measurement (WLM) reaches 2.5 mm. The practical evaluations show that this proposal can apply to several IoT systems for monitoring water levels.