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Surface acoustic wave (SAW) devices are key components for sensing applications. SAW propagation under a periodic grating was investigated in this work. The theoretical method used here is the space harmonic method. We also applied the results of SAW propagation studied in this work to design a two-port resonator with an Al grating on ST-cut quartz. The measured frequency responses of the resonator were similar to the simulation ones. Then, the chemical interface of polyaniline/WO3 composites was coated on the SAW sensor for ammonia detection. The SAW sensor responded to ammonia gas and could be regenerated using dry nitrogen.

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Experiments have been performed with two coaxial atomizers, the first with an annular stream of air surrounding a central jet of water and the second a commercial airblast atomizer with air swirl. They quantify the deterministic unsteadiness of the droplet flow caused by the break-up process in terms of the mean and temporal fluctuations of the droplet surface area and provide links between atomizing air and liquid flow conditions and the amplitude of the droplet flow unsteadiness with distance from the nozzle exit. Time dependent measurements of droplet surface area in the spray were obtained by image processing of high speed photographs to detect the temporal fluctuations of the attenuation of the incident light and by a Mie scattering technique to detect the intensity of the light scattered by droplets illuminated by a laser sheet. Mie scattering was preferred, because of improved measurement accuracy and lower cost. The spray unsteadiness due to the break-up process was quantified in terms of the spectrum of the energy of the fluctuations of the droplet surface area within a frequency range associated with the break-up process. With the coaxial atomizer, the energy of the deterministic unsteadiness varied between 50% and 65% of the total energy of the spectrum and remained in the droplet flow at least up to 150 liquid jet diameters downstream of the break-up region and its energy increased with the reduction of the air or liquid flowrates, although higher energy was correlated with faster attenuation with the downstream distance from the exit plane, caused by the redistribution of droplets by the gas flow turbulence.