Battery-free smart-sensor system for real-time indoor air quality monitoring

Abstract Indoor air pollution is one of the serious issues that affect public health nowadays. Therefore, indoor air quality needs to be monitored by a real-time system for early air pollution warning. Until now, most wireless sensors used for air quality monitoring have required power supply from a battery for sensor operation and wireless data communication. This battery, which is attached to a sensing module, makes the wireless sensing module larger and requires regular replacement efforts and high costs. The present study proposes a novel battery-free sensor module to measure the concentration of volatile organic compounds, ambient temperature, relative humidity, and atmospheric pressure for monitoring air quality in indoor environment. The proposed system comprises a smart-sensor tag, and a radio frequency (RF) energy harvester. The sensing circuit, designed using ultra-low power sensors and a microcontroller unit (MCU), consumes low average power of only 0.5 mW. The MCU collects data from the sensors and writes the sensing data to the memory in the form of an Electronic Product Code (EPC) Class 1 Generation 1 compliant identification (ID) of the tag. The RF energy harvester with a highly efficient buck–boost converter and a 50-mF supercapacitor for real-time saving of the collected power can sufficiently collect the available RF energy from the reader within a maximum distance of ∼250 cm from the reader to supply power for sensing and wireless communication operation of the smart-sensor tag. Therefore, the proposed smart-sensor module can be a battery-free sensor device for monitoring environment parameters in indoor condition. Experiments are conducted to validate and support the developed system for real-time air quality monitoring and warning.