RFID Coupled Passive Digital Ammonia Sensor for Quality Control of Packaged Food

In this paper, an RFID coupled batteryless digital sensor tag is proposed for detecting Ammonia in packaged food. An interdigitated capacitive sensor coated with a thin film of Polyaniline(PANi) that has a higher affinity towards Ammonia is used as a sensing element. To determining the sensitivity of the sensing element, (i) Wireless Near field Short range technique (Capacitance change), and (ii) Direct Probing (Resistance change) techniques are evaluated. The short range technique consists of an inductor coupled to the interdigitated capacitor to form an LC tank and the resonance (capacitance) change due to Ammonia loading is read using a pick-up coil. The direct probe technique uses two wires to measure the resistance across the interdigitated capacitor as a function of Ammonia concentration. Among the two techniques, for demonstrating long range sensing with digitization, direct probing is chosen as this is more stable and can detect a minimum of 3 ppm of Ammonia at room temperature with a response time of 30 min and recovery time of 60 min. The long range approach consists of an RF front end with an antenna and an energy harvester and a low power digital backend that converts the sensor data into bits for transmission. The entire system is passive in nature and does not require an external power supply for operation making it a low cost and simple solution that can be easily integrated as part of the RFID infrastructure. The ID integrated sensor tags are used for a myriad of quality control applications across the food supply chain spectrum.