Study On Micro Flow Sensor System And Its Applications

Micro Air Vehicles (MAVs) are attracting more and more attentions nowadays.Since MAVs are small-sized, light-weighted and low-speeded, it is difficult to controlMAV that is prone to be disturbed by wind. Real-time mesurements of aerodynamicparameters are needed for the autopilot to improve the stability and wind resistance. Asfor vessel designs, drag reduction designs are necessary, the shear stresses on the fluid-solid boundaries are decisive factors to their performances and need to be measured.However, magnitude of fluid-solid boundary shear stress is low so that researchersusually test the total drag force instead of shear stress distribution which contains moreinformation for vessel optimal design. In the dissertation, we research on flexible hotfilm flow sensors with thin film thermal resistors made by using magnetron sputteringon polyimide (PI) substrate and PI-based flexible PCB, and further research on theirapplications in MAV aerodynamic parameters measurement and underwater fluid-solidboundary shear stress measurement.A new temperature compensation technique for thermal anemometers is presentedin this paper. The compensation is realized by using a temperature sensor independentof the flow sensor in the bridge circuit of the anemometer and adopting a novel designapproach to the resistors of the bridge for balancing out the temperature drift. Thetemperature sensor does not have to possess an equal temperature coefficient ofresistance to that of the flow sensor. The temperature compensation in a dynamicmeasurement does not affect the measurement of velocity fluctuations when thetemperature fluctuations are of lower frequencies than the bandwidth of the temperaturesensor. The compensation method was theoretically proved and experimentally tested indifferent temperature and flow conditions. Results showed that the drift of theanemometer induced by the temperature variation could be effectively eliminated from22%to less than0.6%over a range of ambient temperatures (35°C~90°C) using theproposed compensation method.Measurement of two-dimensional (2-D) flow vector using combined hot filmsensors is researched. After the flow direction sensitivity of individual hot film isanalyzed, a new method of measuring2-D surface flow with micro thermal flow sensorconsist of integrated fan-shaped CTD hot films is designed with corresponding data fusion technics. Three-sector self-heating sensor design is proven to be the simplest planfor360°2-D flow vector measurement. Three-element and four-sector design are putinto test within range of0~30m·s-1and360°, results show that for three-sector design,root mean square (RMS) errors are0.65m·s-1for flow speed and2.69°for direction.For four-sector design, RMS errors are0.59m·s-1for flow speed and0.96°for direction.Measurement error of similar sensors with different number of sectors is also analyzed.A novel and practical methodology by which the aerodynamic parameters areinferred using micro hot-film flow sensor array mounted on the surface of the wing isproposed. An artificial neural network is used to model the coupling relationshipbetween readings of the sensor array and aerodynamic parameters. Result of windtunnel experiments is analyzed, where RMS errors are0.27m·s-1for aero speed,0.87°for angle of attack and0.27°for sideslip. Hot film sensors for fluid-solid boundaryshear stress measurement and mini mass flow measurement are also analyzed.