Selection of materials for multilayered structures to be used in packageless sensors
Recently a multilayered structure with a low-velocity layer sandwiched between two high-velocity materials, one of which also works as a supporting substrate and another one as a coat isolating the wave from the influence of undesired external factors, was suggested for application in packageless sensors [1,2]. The thickness of a middle piezoelectric layer must be sufficient to confine the wave within this layer. The suggested combinations of materials included ZnO or GaN as a waveguiding layer, sapphire or diamond as a supporting substrate and Al2O3 (alumina) or AlN as a coating. In the present work, two previously reported structures were analyzed and compared to find the selection criterion for optimal combination of materials enabling high coupling of the useful mode and suppression of parasitic modes.
AlN/ZnO/diamond structure combining isolated and surface acoustic waves
In order to generate surface acoustic waves (SAW) and waveguiding layer acoustic waves (WLAW) simultaneously, a multilayer structure of AlN/ZnO/diamond has been proposed. This structure has been investigated theoretically (two-dimensional finite element method) and experimentally. The nature of the excited modes and their order were identified by modeling and confirmed experimentally by measuring the frequency response of the device in the air and in contact with the liquid. The demonstrated structure can be used to realize a packageless sensor or resonator, using the WLAW alone. A temperature compensated gas or liquid sensor can also be realized by combined usage of the SAW and the WLAW.
Turbine blade temperature calculation and life estimation - a sensitivity analysis
Abstract The overall operating cost of the modern gas turbines is greatly influenced by the durability of hot section components operating at high temperatures. In turbine operating conditions, some defects may occur which can decrease hot section life. In the present paper, methods used for calculating blade temperature and life are demonstrated and validated. Using these methods, a set of sensitivity analyses on the parameters affecting temperature and life of a high pressure, high temperature turbine first stage blade is carried out. Investigated uncertainties are: (1) blade coating thickness, (2) coolant inlet pressure and temperature (as a result of secondary air system), and (3) gas turbine load variation. Results show that increasing thermal barrier coating thickness by 3 times, leads to rise in the blade life by 9 times. In addition, considering inlet cooling temperature and pressure, deviation in temperature has greater effect on blade life. One of the interesting points that can be realized from the results is that 300 hours operation at 70% load can be equal to one hour operation at base load.