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Wireless sensor elements integrated with miniaturized antennas are useful in various applications such as wearable chemical and environmental sensors and Internet-of-Things (IoT) sensor nodes. A major problem in antenna operation is detuning of the antenna bandwidth due to loading by the sensor element. In this article, we report on the integration of an interdigitated capacitor (IDC), acting as a sensor, into an aperture coupled patch (ACP) antenna, such that weak coupling is established between the IDC and the rectangular patch resonator. Because of low mutual coupling, during the sensing process the antenna is not detuned out of its operational bandwidth and its performance is not compromised by the presence of the sensor and vice versa. A sensing material (barium titanate film) is deposited on the IDC located at the edge of the microstrip line used to slot-feed the ACP antenna. A change in the material permittivity is transduced into a variation of resonant frequency of the antenna. We describe the design and fabrication of the IDC sensor-integrated ACP antenna and demonstrate the measured sensing performance at different temperatures and relative humidity concentrations. [ABSTRACT FROM AUTHOR]

ZnO nanomaterials with different shapes were synthesized, characterized and tested in the selective monitoring of low concentration of CO and NO2 in air. ZnO nanoparticles (NPs) and nanofibers (NFs) were synthesized by a modified sol-gel method in supercritical conditions and electrospinning technique, respectively. CO and NO2 sensing tests have demonstrated that the annealing temperature and shape of zinc oxide nanomaterials are the key factors in modulating the electrical and sensing properties. Specifically, ZnO NPs annealed at high temperature (700 °C) have been found sensitive to CO, while they displayed negligible response to NO2. The opposite behavior has been registered for the one-dimensional ZnO NFs annealed at medium temperature (400 °C). Due to their adaptable sensitivity/selectivity characteristics, the developed sensors show promising applications in dual air quality control systems for closed ambient such as automotive cabin, parking garage and tunnels. [ABSTRACT FROM AUTHOR]

Abstract 2D-SnS 2 flakes were synthesized via a wet chemical route and deposited as a thin film onto the Pt-interdigitated contacts of a ceramic substrate with aim to fabricate a conductometric sensor. The 2D-SnS 2 sensing film was then annealed "in situ" under controlled conditions at different temperatures up to 400 °C. The morphological, microstructural and electrical properties of the sensing film, before and after the thermal treatment, were characterized by "in situ" techniques. SEM analysis has shown that the 2D flake morphology was maintained after thermal treatments, whereas Raman and EDX analysis have highlighted the partial/total modification of the SnS 2 phase towards the SnO 2. As a consequence of the formation of 2D-SnS 2 /SnO 2-x mixed phases, a dramatic change of the electrical properties of the sensing film has been also observed. Conductometric gas sensors based on hybrid SnS 2 -SnO 2-x nanoflakes were then obtained by simple self-annealing treatments of 2D-SnS 2 film directly on the sensor substrate. The fabricated sensors were tested toward ammonia (NH 3) as target gas. Results evidence that increasing the annealing temperature of the 2D-SnS 2 sensitive film, the electrical resistance of the sensing layer decreases while the response towards ammonia increases, showing the maximum at an annealing treatment of 250 °C. This behaviour was explained on the basis of the morphological, microstructural and electrical modifications observed, highlighting the role of 2D-SnS 2 /SnO 2-x mixed phases in determining the sensing properties towards ammonia. Highlights • Synthesis of two-dimensional (2D) SnS 2 flakes by a wet chemical route. • Formation of SnS 2 -SnO 2-x heterostructures by self-annealing of SnS 2 sensing layer on a sensor substrate. • Effect of annealing temperature on the electrical and NH 3 sensing properties of the sensing layer. • SnS 2 -SnO 2-x mixed phases show improved NH 3 sensing properties than pure SnS 2 or SnO 2 phases. [ABSTRACT FROM AUTHOR]