High temperature thin film thermal flowmeter sensor

High-temperature thin film flowmeters generally consist of a thermal resistance layer and a thin film thermometer layer. The thermal resistance layer of piezos discs transducer usually uses PZT material with a small thermal conductivity so that the thermometers are on both sides can obtain a large temperature difference, thereby obtaining a stronger signal and a higher sensitivity. The thin film thermometer layer is typically a thin film thermocouple or a resistance temperature transducer. Polyimide has high thermal resistance and good mechanical properties. The thin film thermal flowmeter as a thermal resistance layer can be used below 400°C. Silica of piezoelectric effect sensor has low thermal conductivity and good mechanical properties. Therefore, as the material of the thermal resistance layer of most high-temperature thin film thermal flow meters, this thermal flow meter can be used at the temperature of 900 °C. High temperature thin film flow meters can use precursor ceramic materials as RTD and thermal resistance layers. Precursor piezo ceramics have high-temperature thermal flow meter for aero-engine environment was fabricated with a SiN of 250 μm in the middle thermal barrier layer. The thermal flowmeter can be used at the temperatures around 1 400 °C.

Multi-functional integrated thin-film sensors are integrate with high-temperature thin-film strain piezoelectric tube transducer, thermometers, and thermal flow meters. It is challenging because the three sensors have different sensing principles, different structures, and different sizes. A multifunctional integrated thin-film sensor was designed to simultaneously measure strain, temperature, and heat flow, where Pt strain gage measures Pt-13Rh/Pt. thermocouple measures temperature, 2 layers of different thickness of alumina thermal resistance layer and 40 pairs of Pt A thermopile-type thermal flowmeter is consisting of a -13Rh/Pt thermocouple.which measures the heat flux. In order to break the working temperature of alloy materials, NASA has further developed a multi-function integrated thin-film sensor for TaN piezo ceramic materials.

The piezoelectric plate sensor uses a lift-off process for patterning a strain factor of 3.9, TCR of -93 × 10-6 ℃ -1, resistivity of 259 μΩcm, an apparent strain sensitivity of -24 × 10-6 ℃ -1. The TCR of piezo ceramic materials and alloys is negative,NASA has developed multi-functional high-temperature thin-film sensors for piezo ceramics . These piezoelectric rings transducer include high-temperature thin-film strain gauges, high-temperature thin-film thermocouples, and high-temperature thin film thermal flowmeters. The TCR of Pd-13Cr is positive. The two together constitutes a functional layer that makes the TCR positive and negative offset a portion, piezoelectric materials piezo tube transducer is reducing the overall TCR, thereby increasing the sensitivity. The multi-functional thin-film sensor has problems of spalling and diffusion, compatibility issues of the peeling process, and high-temperature expansion problems.