Comparison of conventional and collapsed region operation of capacitive micromachined ultrasonic transducers

We report experimental results from a comparative study on collapsed region and conventional region operation of capacitive micromachined ultrasonic transducers (CMUTs) fabricated with a wafer bonding technique. Using ultrasonic pulse-echo and pitch-catch measurements, we characterized single elements of 1-D CMUT arrays operating in oil. The experimental results from this study agreed with the simulation results: a CMUT operating in the collapsed region produced a higher maximum output pressure than a CMUT operated in the conventional region at 90% of its collapse voltage (3 kPa/V vs. 16.1 kPa/V at 2.3 MHz). While the pulse-echo fractional bandwidth (126%) was higher in the collapsed region operation than in the conventional operation (117%), the pulse-echo amplitude in collapsed region operation was 11 dB higher than in conventional region operation. Furthermore, within the range of tested bias voltages, the output pressure monotonously increased with increased bias during collapsed region operation. It was also found that in the conventional mode, short AC pulses (larger than the collapse voltage) could be applied without collapsing the membranes. Finally, while no significant difference was observed in reflectivity of the CMUT face between the two regions of operation, hysteretic behavior of the devices was identified in the collapsed region operation.     

Effects of microwave and conventional baking on the oxidative stability and fatty acid composition of puff pastry

The effects of microwave and conventional baking on the fatty acid and trans fatty acid compositions of puff pastries, which contain high amounts of hydrogenated fat, were investigated. In addition, free fatty acids, peroxide value, and induction time for oxidative stability by the Rancimat method have been compared for microwave- and conventionally baked puff pastries. The data indicate there were considerable changes in acidity, peroxide value, and Rancimat induction time in both microwave- and conventionally baked samples. Although the content of saturated fatty acid such as palmitic and stearic and the ratio of saturated to unsaturated fatty acids did not change significantly, an apparent increase was determined in trans oleic acid levels by both baking methods. In addition, a significant decrease in linoleic acid content of the samples was found by microwave baking.     

Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) system

This article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF₆], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time-dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume-of-fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.     

Enhancing magnetic levitation and guidance force and weight efficiency of high-temperature superconducting maglev systems by using sliced bulk YBCO

We aimed to enhance the magnetic force efficiency of Maglev systems without increasing total weight. For this aim, we divided YBCO bulks into three slices horizontally to utilize the YBCO-permanent magnetic guideway (PMG) interaction surface as much as possible. We used whole YBCO above PMGs with different magnetic pole directions (PMG-A and PMG-B) in two lying positions of transversal and longitudinal and investigated levitation and guidance force performances. It is determined that levitation and guidance forces by using YBCO in transversal lying mode are bigger compared to the longitudinal mode. For sliced YBCO, the maximum levitation force increased by 69% and 78%, while the guidance force enhancements are determined as 212% and 91%, compared to the whole YBCO above PMG-A and PMG-B, respectively. The levitation and guidance force density with respect to the total mass of unit a set of slices YBCO increased by 92% and 106%, respectively, compared to the whole YBCO above PMG-B in transversal mode. Since the higher levitation force and the lower total weight of the onboard unit are important parameters in point of the energy efficiency in Maglev and other levitation applications, the result of this study supplies useful data for the engineers and industrial partners.