Development and characterization of fast responding pressure sensitive microspheres

Characterization of multi-dye pressure-sensitive microbeads

The response times of pressure-sensitive particles to passing shockwaves were measured to investigate their ability to accurately determine pressure changes in unsteady flows. The particles tested were loaded with novel pressure-sensitive dyes such as Pt (II) meso-tetra(pentafluorophenyl)porphine, Pt(II) octaethylporphine, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl))iridium III, and iridium(III) bis(4-phenylthieno[3,2-c] pyridinato-N,C2')acetylacetonate. For this work, porous silicon dioxide pressure-sensitive beads (PSBeads) were used. Two synthetic procedures were used to fabricate the particles. In the first, a one-step method loaded dyes during the synthesis of microbeads, in the second a two-step method synthesized the microbeads first, then loaded the dyes. The shock tube facility was used to measure the response times of microbeads to fast pressure jumps. The study involved testing multiple luminophors loaded in microbeads with various size distributions. Response times for the silica-based microbeads ranged between 26 μs and 462 μs (at 90% of the amplitude response), which are much faster than previously reported polystyrene-based microbead response times, which range from 507 μs to 1582 μs (at 90% of the amplitude response) [F. Kimura, M. Rodriguez, J. McCann, B. Carlson, D. Dabiri, G. Khalil, J. B. Callis, Y. Xia, and M. Gouterman, "Development and characterization of fast responding pressure sensitive microspheres," Rev. Sci. Instrum. 79, 074102 (2008)].

Invited review article: Unsteady and pulsating pressure and temperature: a review of experimental techniques

Unsteady flow of liquids and gasses are important in many scientific, engineering, and biological contexts. Measurement of the characteristics of unsteady and pulsating flows is more difficult than that of static flows. Time constants of the sensors must be understood, sampling rates must satisfy basic signal processing criteria and synchronization of the measurements with the flow may be necessary. Because of development of more advanced measurement devices, there has recently been a growing interest in unsteady and pulsating flow measurements and the number of papers in this field has increased in recent years. This paper reviews the current state of the art in sensors and measurement techniques for the characterization of pressure and temperature in unsteady and pulsating flows including an analysis of the advantages and limitations of each technique.