In vitro durability tests of cardiovascular devices are often used to evaluate the potential for fretting damage during clinical use. Evaluation of fretting damage is important because severe fretting can concentrate stress and lead to the loss of structural integrity. Most international standards call for the use of phosphate buffered saline (PBS) for such tests although there has been little evidence to date that the use of PBS is appropriate in terms of predicting the amount of fretting damage that would occur in vivo. In order to determine an appropriate test media for in vitro durability tests where fretting damage is being evaluated, we utilized an in vitro test that is relevant to cardiovascular devices both in terms of dimensions and materials (nitinol, cobalt-chromium, and stainless steel) to characterize fretting damage in PBS, deionized water (DIW), and heparinized porcine blood. Overall, tests conducted in blood were found to have increased levels of fretting damage over tests in DIW or PBS, although the magnitude of this difference was smaller than the variability for each test media. Tests conducted in DIW and PBS led to mostly similar amounts of fretting damage with the exception of one material combination where DIW had greatly reduced damage compared to PBS and blood. Differences in fretting damage among materials were also observed with nitinol having less fretting damage than stainless steel or cobalt-chromium. In general, evaluating fretting damage in PBS or DIW may be appropriate although caution should be used when selecting test media and interpreting results given some of the differences observed across different materials.
In the scope of very high‐frequency (VHF) and ultra high‐frequency (UHF) terrestrial communication or broadcasting systems planning, the use of point‐to‐area propagation prediction methods is expected. The benchmarking of such models on different scenarios is very helpful to assist the system planner in choosing those most suited to the site in hands. In this sense, this study provides a comparative performance analysis of the International Telecommunication Union radio communication sector (ITU‐R) recommendations P.526, P.1546, and P.1812 and a few other models on a site marked by the presence of irregular terrain covered by forest. A set of measurements at 563 MHz at different spots in Rio de Janeiro city with such features was taken as reference. The best prediction performance was achieved by the P.526 and P.1812 methods, in addition to a wedge diffraction model, with path loss mean errors between −5 and 3 dB, and standard deviations between 8.7 and 9.2 dB. Such results were observed when the presence of the forest layer was incorporated adding a representative clutter height.
In this study an irregularly shaped microstrip patch antenna was designed, simulated, and optimized for air-to-ground communication (ATG) applications. The process started with the design of a rectangular patch antenna with the traditional transmission line and cavity methods, followed by a simulation with the finite-difference time-domain method (FDTD) in conjunction with a genetic algorithm (GA). The aim of the study was to design an efficient patch antenna. The designed antenna is resonating at 14.25 GHz with 35 dB return loss. The 10 dB bandwidth of the antenna is 3.7 GHz.
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