A Recent Approach towards Fluidic Microstrip Devices and Gas Sensors: A Review

This paper aims to review some of the available tunable devices with emphasis on the techniques employed, fabrications, merits, and demerits of each technique. In the era of fluidic microstrip communication devices, versatility and stability have become key features of microfluidic devices. These fluidic devices allow advanced fabrication techniques such as 3D printing, spraying, or injecting the conductive fluid on the flexible/rigid substrate. Fluidic techniques are used either in the form of loading components, switching, or as the radiating/conducting path of a microwave component such as liquid metals. The major benefits and drawbacks of each technology are also emphasized. In this review, there is a brief discussion of the most widely used microfluidic materials, their novel fabrication/patterning methods.

Hydrothermal Synthesis of Hierarchical SnO2 Nanostructures for Improved Formaldehyde Gas Sensing

The indoor environment of buildings affects people’s daily life. Indoor harmful gases include volatile organic gas and greenhouse gas. Therefore, the detection of harmful gas by gas sensors is a key method for developing green buildings. The reasonable design of SnO2-sensing materials with excellent structures is an ideal choice for gas sensors. In this study, three types of hierarchical SnO2 microspheres assembled with one-dimensional nanorods, including urchin-like microspheres (SN-1), flower-like microspheres (SN-2), and hydrangea-like microspheres (SN-3), are prepared by a simple hydrothermal method and further applied as gas-sensing materials for an indoor formaldehyde (HCHO) gas-sensing test. The SN-1 sample-based gas sensor demonstrates improved HCHO gas-sensing performance, especially demonstrating greater sensor responses and faster response/recovery speeds than SN-2- and SN-3-based gas sensors. The improved HCHO gas-sensing properties could be mainly attributed to the structural difference of smaller nanorods. These results further indicate the uniqueness of the structure of the SN-1 sample and its suitability as HCHO- sensing material.

SnO2-TiO2 and SnO2-MoO3 Based Composite Gas Sensors to Develop an E-nose for Peruvian Pisco Varieties Differentiation

There is great interest in the development of a simple system that could identify adulteration or counterfeiting of Peruvian Pisco (a grape-based alcoholic drink). In this study, sensors based on SnO2-TiO2 and SnO2-MoO3 composites with different weight composition ratios were synthesized and characterized. These sensors were tested with aqueous solutions of EtOH/MetOH and Pisco samples of Italia and Quebranta varieties in order to explore their capacity to identify variations in these beverages. The response profile of the most sensitive sensors showed an enhanced response to alcoholic samples with greater content of ethanol up to a concentration of 45%v/v, while the increased content of methanol in the range of 0.1 to 0.3 % v/v diminished the intensity of the sensor response. Differences in the composition of methanol and ethanol in the Pisco varieties studied (Italia and Quebranta) were correlated to the capacity of the composite-based sensors to differentiate them with greater performance. Sensors based on SnO2-TiO2-1/2 composites showed greater reproducibility of their response profile over time in comparison to SnO2-TiO2-1/1 and SnO2-MoO3 composites. The PCA showed that composite sensors were able to differentiate Pisco samples according to their variety.