material system of high tempeture thin film piezo ceramic
Publish Time: 2018-06-29 Origin: Site
The typical thin film strain gauges and thermometers are used on the surface of piezo ceramic element.which are generally composed of multiple layers of piezo materials. The alloy substrate is followed by a transition layer, an insulating layer, a functional layer, and a protective layer, as is shown in FIG. 3 . The transition layer can enhance the bonding of the insulating ultrasonic piezo ceramic and the alloy substration; the insulating layer is the purpose of forming a good insulation between the functional layer and the alloy substration; the functional layer is generally an alloy or piezo ceramics.which belongs to the sensitive material layer for sensing strain or temperatu,protective layer is to improve the high temperature oxidation resistance of the functional layer, it is improving the life and stability of the transducer.
High-temperature thin-film thermal flowmeters generally consist of a thermal resistance 400Khz piezo transducer and a thermometer layer. The thermal conductivity of two kinds of thermal resistance materials with different thicknesses , the thickness of one piezo layer is 1mm, and the thickness of the other layer is 2mm. When there is heat flux, the temperatures are generated under the thermal resistance layer are T1 and T2 respectively. The thermal expansion coefficients of the 1Mhz piezoelectric material are different. During the heating or cooling process, thermal stress may be generated, so that the layers of different piezo materials crack. the sensitive material may oxidize and fracture, and thus the thin film sensor may fail. High-temperature strain gauges need to be stretched frequently. Because the tensile strengths of materials in different layers are different, stress concentration and cracks may occur between the piezoelectric effect sensor during operation, and finally the strain gauges will produce measurement errors and even fail. When it is designing a thin-film sensor, it is necessary to consider the coefficient of thermal expansion between the layers of materials, even the modulus of elasticity, so that the parameters of the adjacent piezo layers are as close as possible, thereby reducing the thermal mismatch and the tensile stress.