1558-1748 (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2020.2964676, IEEE Sensors Journal IEEE SENSORS JOURNAL, VOL. XX, NO. X, 1 RFID Coupled Passive Digital Ammonia Sensor for Quality Control of Packaged Food Saranraj Karuppuswami, Student Member, IEEE, Saikat Mondal, Student Member, IEEE, Deepak Kumar, Student Member, IEEE, Premjeet Chahal, Senior Member, IEEE Abstract—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. Index Terms—Ammonia sensor, Food volatiles, LC tank, Polyaniline, RFID, Supply chain, Wireless. I. I NTRODUCTION E NHANCING traceability with quality information of food products has become a prerequisite for improving the performance of global food supply chains [1]. Currently, Internet-of-Things (IoT) based tracking and tracing infras- tructures such as Radio Frequency Identification (RFID) and Electronic Article Surveillance (EAS) are used for retrieving product traceability information across the food supply chain [2]. Unfortunately, these techniques are aimed at providing just the product traceability information and do not shed any light on the nature of the product. The evolution from ”traceability- centric” to a ”value-centric” supply chain with real-time qual- ity information is vital to improve product management for the producer and consumer alike [3]. This evolution is possible due to the application of controllability factor across the food supply chain through sensors that provide additional quality information that prevents spoilt, expired, or contaminated food S. Karuppuswami, S. Mondal, D. Kumar, and Dr. Premjeet Chahal are with the Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI, 48823 USA e-mail: chahal@egr.msu.edu. products from reaching the end user and aids in promoting good health and well-being, as well as preventing food-borne illness, and reducing product recalls. Ideally, the quality control sensors must be affordable, user- friendly, and simple to implement without elaborate time- consuming processes or change in the infrastructure. These sensors monitor the supply chain end-to-end and are the first line of defense against contamination or tampering of food products as well as preventing economically motivated adulteration. There are a number of quality indicators that are of interest and are monitored to determine the quality index of the food package. The indicators can be physical, chemical or environmental such as pH, dielectric constant, pressure, temperature, etc [1]. One such commonly monitored indicator is the volatile or aroma being emitted from different stages of the packaged food over time [4]. Vapor monitoring should be in real-time across the supply chain in order to quickly identify and remove the food products which fail the quality test [5]. In literature, a number of well-established aroma monitoring techniques have been extensively studied such as mass spec- trometry, head space solid-phase micro extraction, colorimetric analysis, gas chromatography, and electronic noses [6]–[10]. Although, these techniques are well-established, a number of common limitations exists such as requirement of expensive equipment with a laboratory environment (non-field operable), complicated and time extensive data analysis, and requirement of skilled labor. For example, gas chromatography requires specialized containers as well as carrier gases leading to a non-field operable laboratory set up [6]. Head space extraction technique uses a sorbent to trap the volatiles following by desorption into a chamber for performing complex mass spec- trometry that requires skilled technicians [8]. An affordable, real-time, and non-contact sensor that can be easily integrated as part of the food package overcoming the limitations of the traditional vapor monitoring techniques is needed to promote the value-centric nature of the supply chain. Recently, battery-free wireless sensors in the microwave frequency regime are used for providing a non-contact, real- time sensing solution for detecting packaged food vapors and gases [11]. In our previous work, Inductor-Capacitor (LC) based resonant tanks have been proposed for aroma profiling of food along the supply chain [5], [12]. The basic operating principle of these tags is to detect change in impedance of the sensor tag due to adsoprtion, absorption or condensation of gas molecules onto the sensor substrate. For absorption, two different techniques are commonly used, substrate absorption