An Energy-Efficient All-Dynamic Multi-Parameter Sensor for Battery-less Smart Nodes in Agricultural Internet-of-Things

The increasing demand for efficient and sustainable agricultural practices underscores the importance of Agriculture Internet-of-Things (Agri-IoT). This integration of technology in agriculture facilitates precise and efficient farming methods, contributing significantly to global food security and environmental conservation. For Agri-IoT optimization, it is essential to obtain information such as temperature, ambient humidity (AH) and soil moisture (SM) in an environment-friendly manner. The existing sensor node is powered by battery that can potentially pollute the soil and have limited lifespan. In this work, we present a sensor chip that can efficiently read in temperature, AH and SM in an all-dynamic manner. The multi-parameter chip operates in an event-driven manner, which only starts wireless transmission if an input event is detected. The event-driven operation further reduces the energy consumption of the sensor node. The low-energy sensor is combined with RF energy harvester and wireless transmitter to achieve battery-less data acquisition. The proposed sensor chip is fabricated in 65-nm CMOS technology and occupies a chip area of 0.612mm ² . The measured temperature accuracy is ±1°C over the range of -40 to 85°C with a single-point calibration. The measured ambient humidity ±3.8 %RH over the 10-90 %RH range. Besides, it can support soil moisture monitoring over the range of 10-50 % gravimetric water content. The power consumption of the multi-sensor interface circuits is 4.8 μW at a supply voltage of 0.8 V.