Battery-Free NFC Sub-ppm Gas Sensor for Distributed Gas Monitoring Applications at Room Temperature

This work proposes a low-cost battery-less near-field communication (NFC) tag for gas sensing based on a resistive gas sensor. A proof-of-concept tag is designed using commercially available off-the-shelf (COTS) components. The energy required for the tag operation comes from the magnetic field generated by the reader, and all the electronics are powered by connecting them to the energy-harvesting output of the NFC integrated circuit. Read ranges up to 25 mm have been obtained with commercial NFC-enabled smartphones. The reading of resistance variations due to the presence of gas is performed using a low-consumption timer. The oscillation frequency of this timer depends on the resistance of the gas sensor and is measured by a microcontroller integrated into the tag. This method does not require any gain adjustment for operation, allowing the use of sensors with different resistance ranges. Low-cost room temperature sensors have been integrated for NO2 detection in both ppb and ppm ranges using laser-induced graphene (LIG). A detection limit of up to 36 ppb has been achieved. The smartphone transmits the data to a cloud database, allowing users to analyze and post-process the information.