Research On Key Technologies And Applications Of Resonant Sensors Based On Micromechanical Cantilever

Aiming at the urgent demands of current measurements in electrical equipments and new energy power generation as well as in-situ measurements of fluid density/viscosity in the fields of industrial control,petroleum exploration and internal combustion engines,a resonant sensor based on micromechanical cantilever was investigated in this work,including its basic theories,design and optimization,fabrication,performance tests and applications.Finally,the goals of in-situ measurements of current and fluid density/viscosity were achieved.The following are the main results obtained in this work:(1)A formula between the deflection of a microcantilever with various widths and surface stress was found.An analytical equation for computing the fundamental resonant frequency of a microcantilever with various widths was proposed.Moreover,an equation for overall microcantilever sensitivity was established to optimize the structure of the microcantilever and further enhance the overall microcantilever sensitivity.(2)An equation for calculating the density sensitivity was found when a microcantilever was used to measure fluid density and was operated under the first flexural mode.Further,an equation for computing the critical width of the rectangular microcantilever was deduced.Through fluid-structure interaction analysis,the density sensitivity as well as the quality factor of the microcantilever could be improved by optimization of the microcantilever's structure and operating mode.The improved quality factor could enhance the measurement range of fluid viscosity.(3)The principles of quality factor,resonant frequency and the sensor output were proposed to guide the design of the resonant microcantilever sensor.Magnetic actuation was used to drive the sensor into resonance while piezoresistive detection was used to sense the sensor's motion.(4)The layout of the sensor chip was designed and the fabrication process was also determined.Based on bulk micromachining technology,the microcantilever sensor chip was manufactured and finally the package of the sensor was carried out.(5)The experimental setup of the microcantilever sensor was established.The softwares for data collection and processing were also developed.The equivalent electrical circuit models of the microcantilever operating under four different resonant modes were established.The effects of instrument parameters and working conditions for the sensor on the resonant frequency of the sensor were studied.A resonant frequency tuning mechanism of the sensor by varying the DC bias current of Wheatstone bridge or the AC oscillating voltage was presented.(6)Based upon the experimental setup of the microcantilever sensor,the resonant microcantilever sensors with different microcantilever shapes operating under different resonant modes were employed to measure the density and viscosity of the organic reagents.The experimental results showed that,the biggest deviation between the experimental data and reference data was less than 2.00% in the density range of 620.83 kg/m~3–866.87 kg/m~3.The best accuracy of sensor was less than 11.00% in the viscosity range of 217.9 ?Pa·s–961.8 ?Pa·s.And the viscosity measurement accuracy could be improved by utilizing the microcantilever sensor's higher resonant mode.The working principle of measuring the DC current by using the resonant microcantilever sensor was addressed.The measurement accuracies and current sensitivities were obtained through experiments when the resonant microcantilever sensor was operated under different resonant modes.The experimental results showed that the best accuracy was 0.92% and the biggest current sensitivity was –6.702 Hz/m A~2 in the current range of 0.5 m A–4.0 mA.