Research On Wall Shear Stress Sensors And Its Readout Circuit

Wall shear stress is an important parameter reflecting fluid motion in the near-wall boundary layer,and it is also one of the essential measurement parameters in wind tunnel experiments.Due to the limitation of model volume in wind tunnel experiments,the micro-electromechanical system(micro-electromechanical system)sensor is considered one of the most promising sensors because of its small size,high sensitivity,and good stability.To solve the problem of the short duration(milliseconds)of the flow field and large impact load in a shock tunnel,a capacitive Microcapacitive wall shear stress sensor with a high-frequency response,high precision,and extensive range and a high-frequency Micro-capacitive detection circuit integrated with the head is developed,which can be used to detect wall shear stress in a shock tunnel.The main research work of this paper is as follows:(1)A high-frequency wall shear stress sensor is developed based on flat plate differential capacitance detection.The measurement principle is that after the floating probe senses the shear stress,the polar plates of the differential capacitance are displaced with the torsion beam by the force transfer rod,which causes the change of the flat plate capacitance value,and the shear stress is detected by measuring the change of the capacitance.Based on the numerical simulation,theoretical analysis,and finite element simulation results,the sensitive structure parameters of the sensor head are optimized robustly.The sensor has a sensitivity of 4Pa/f F in the range of 0-2000 Pa,a sensitivity of better than 1%,and an inherent frequency of higher than 3k Hz.Micro-capacitor chips are fabricated using the micro-electromechanical system technology,and floating probes and encapsulated shells are processed by precision lathe.(2)A sensor readout circuit and a PC signal acquisition system with weak dynamic differential capacitance resolution better than 3f F have been developed at a 3k Hz detection frequency.For the complex measurement environment of a shock tunnel,the sensor readout circuit and sensor head are designed in an integrated way to ensure the measurement accuracy,stability,and anti-interference ability of the weak capacitance detection circuit.The readout circuit is manufactured using the microstrip ceramic circuit process to ensure the assembly accuracy of the sensor.A PC-based data acquisition and processing system is developed,which realizes the realtime graphical display and data storage of the high-frequency output signal of the sensor.(3)Visual-based high-precision sensor micro-assembly and performance testing have been completed.Because the assembly error of the sensor will seriously affect the accuracy of shear stress measurement,in addition to controlling the processing accuracy of sensor components,including floating elements,micro-electro-mechanical chips,readout circuits,and encapsulated shells,it is essential to develop high-precision micro-assembly technology.This paper uses a micro-assembly process based on visual precision alignment to achieve high-precision sensor assembly,and the assembly error is controlled at a magnitude of 20μm.In order to obtain the performance parameters of the wall shear stress sensor of the micro-system,based on the principle of centrifugal force equivalence,the static calibration experiment of the sensor is completed by the rotating loading method.The performance parameters such as sensitivity,resolution,linearity,and repeatability of the sensor are obtained.The calibration results show that the sensitivity of the three sensors is 4.3Pa/f F,3.8Pa/f F,and3.6Pa/f F,respectively.The resolution is better than 10 Pa,and the linearity and repeatability are better than 0.2%.Finally,the sensor is tested in the shock tunnel environment,and the corresponding data are obtained.