1558-1748 (c) 2018 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.2018.2881487, IEEE Sensors Journal > Sensors-23475-2018 < 1 Abstract— This paper presents an inkjet printed differential passive microwave planar resonator-based sensor for toxic vapor detection at room temperature. Two devices are presented, with 5 (D1) and 50 (D2) layers of composite sensitive film (PEDOT:PSS- MWCNTs). Each one consists of two band-pass resonators with the fundamental modes around 2.5 and 2.7 GHz. Theoretical and experimental results are presented, both devices show sensitivity to ethanol vapor ranging from 500 to 1300 ppm according to the magnitude and resonant frequency shifts of their scattering parameters (S-parameters). Limitations due to a continuous drift on both the reference and the sensitive channels are discussed. Though further improvements are needed, such sensor is a good candidate for integration into real-time multi-sensing platforms adaptable for the Internet of Things (IoT). Index Terms— chemical gas sensor, composite polymer carbon nanoparticles, flexible microwave resonator, inkjet printing, passive transducer. I. INTRODUCTION oxic compounds in the atmospheric environment involve various particles and mixtures of complex gases, such as volatile organic compounds (VOCs). Several classifications of carcinogenic agents exist, in particular those of the European Union (EU), the International Agency for Research on Cancer (IARC) and the Institut National de Recherche et de Sécurité (INRS). They provide information on the carcinogenic risk of listed chemical substances in the workplace. For example, the occupational exposure limit value for ethanol is 500 ppm in Germany and 1000 ppm in France and the USA [1]. Powerful systems, that allow the real-time detection of these chemical agents in the form of prevention tools to alert the people concerned, are therefore urgently needed. Manuscript received March 30, 2018; revised August 29, 2018; accepted November 05, 2018. This work was supported in part by the French National Research Agency under project ANR-13-BS03-0010 and in part by the “Investments for the future” Programme IdEx Bordeaux, reference ANR-10- IDEX-03-02. H. Hallil, P. Bahoumina, K. Pieper, J. L. Lachaud, D. Rebière and C. Dejous, are with Univ. Bordeaux, Bordeaux INP, CNRS, IMS UMR 5218 F-33405 Talence, France (e-mail: hamida.hallil-abbas@u-bordeaux.fr, corinne.dejous@ims-bordeaux.fr). A. Abdelghani, K. Frigui, S. Bila and D. Baillargeat are with Univ. Limoges, CNRS, XLIM UMR 7252 F-87060 Limoges, France H. Hallil, Q. Zhang and P. Coquet are with NTU, THALES, CNRS, CINTRA UMI 3288 Singapore 637553, Singapore P. Coquet, E. Pichonat and H. Happy are with Univ. Lille, CNRS, IEMN UMR 8520 F-59652 Villeneuve d’Ascq, France Currently, most of the microsystems available for this purpose are based on non-differential chemiresistor gas sensors using metal oxides or carbon materials as a sensitive element [2], [3]. However, this kind of sensor often operates at high temperatures and therefore requires a large amount of energy. Although, recent studies based on chemiresistive sensors functionalized with carbon and composite materials have been conducted at room temperature and recorded a normalized sensitivity to ethanol among the very best ones, from 3.7 to 24×10-4 /ppm [4]. Nevertheless, these sensors operate at low frequencies and require significant instrumentation for the conversion of measured quantities. Such characteristics limit the possibility of energy autonomy or deployment of these sensors in harsh environments. To overcome these weaknesses, studies based on microwave transducers have been conducted this decade. Indeed, electromagnetic transducers can operate at room temperature [5] [6] [7]. Being a passive device and with possible high- frequency wireless operation, they can be further deployed as autonomous devices. They are thus appropriate for networking and communicating operation, being usable for real-time detection and providing exploitable information directly. In addition, due to its planar structure, the device can be manufactured collectively on flexible substrate by low cost inkjet printing technology [8] [9]. Bailly et al. used a geometry based on conductor-backed coplanar waveguide (CBCPW) microwave antenna on which a hematite sensitive layer is deposited and demonstrated the high sensitivity of this sensor for detecting ammonia at concentrations ranging from 100 to 500 ppm [10]. The variables selected for this study are the real and imaginary parts of the reflection coefficient, Γ. This study shows that the microwave based on rhombohedra exhibited a sensitivity of 4.6 × 10 −7 /ppm for the real part and 3.4 ×10 −7 /ppm for the imaginary part of |ΔΓ|. Very recently, Park et al. also published a study based on a double split-ring resonator (DSRR) as microwave resonator coupled with PEDOT:PSS conducting polymer film for humidity detection [11]. They show that as the RH changes, the transmission parameter S21 change simultaneously, both its magnitude and its resonance frequency of 2.45 GHz. Furthermore, the sensor exhibits great repeatability in the range from 40% to 60%, with a frequency shift of -8.15 MHz, or a sensitivity of 1.7×10 −4 /%RH, and a shift of the magnitude estimated to 0.07dB. These results demonstrate the feasibility of microwave sensors for Differential passive microwave planar resonator-based sensor for chemical particle detection in polluted environments Hamida Hallil, Member, IEEE, Prince Bahoumina, Katrin Pieper, Jean Luc Lachaud, Dominique Rebière, Aymen Abdelghani, Kamel Frigui, Stéphane Bila, Member, IEEE, Dominique Baillargeat, Member, IEEE, Qing Zhang, Philippe Coquet, Emmanuelle Pichonat, Henri Happy and Corinne Dejous, Member, IEEE T