Udo Geckle

Surface acoustic wave-based (SAW) sensors are of great interest due to their high sensibility and fast and stable responses. They can be obtained at an overall low cost and with an intuitive and easy-to-use method. The chemical sensitization of a piezoelectric transducer plays a key role in defining the properties of SAW sensors. In this study, we investigate the structural and adhesion properties of a new class of coating material based on polyurethane polymeric composites. We used dark-field microscopy (DFM) and scanning electron microscopy (SEM) to observe the microstructure of polyurethane composite coatings on piezoelectric sensor elements and to analyze the effects of the chemical resistance and adhesion test (CAT) on the coating layers obtained with the polyurethane polymeric composites. The results of the microscopy showed that all polyurethane composite coatings exhibited excellent uniformity and stability after chemical adherence testing (CAT). All of the observations were correlated with the results of the ultrasonic analysis, which demonstrated the role of polyurethane as a binder to form the stable structure of the composites and, at the same time, as an adhesion promoter, increasing the chemical resistance and the adherence of the coating layer to the complex surface of the piezoelectric sensor element.

We discuss the fabrication of gas-analytical multisensor arrays based on ZnO nanorods grown via a hydrothermal route directly on a multielectrode chip. The protocol to deposit the nanorods over the chip includes the primary formation of ZnO nano-clusters over the surface and secondly the oxide hydrothermal growth in a solution that facilitates the appearance of ZnO nanorods in the high aspect ratio which comprise a network. We have tested the proof-of-concept prototype of the ZnO nanorod network-based chip heated up to 400 °C versus three alcohol vapors, ethanol, isopropanol and butanol, at approx. 0.2–5 ppm concentrations when mixed with dry air. The results indicate that the developed chip is highly sensitive to these analytes with a detection limit down to the sub-ppm range. Due to the pristine differences in ZnO nanorod network density the chip yields a vector signal which enables the discrimination of various alcohols at a reasonable degree via processing by linear discriminant analysis even at a sub-ppm concentration range suitable for practical applications.