Research On Flexible Capacitive Three-dimensional Wind Sensors

According to the dimensions of measurement,wind sensors can be divided into onedimensional(1D)wind sensors measuring wind along the X-axis,two-dimensional(2D)wind sensors measuring wind in the XY-plane,and three-dimensional(3D)wind sensors measuring wind in the XYZ-space.Generally,2D wind sensors can basically meet the daily needs of agriculture,weather forecast and transportation.However,airflow in real life does not flow only in XY-plane,but also along Z-axis,which is called 3D wind.Actually,there are many important areas that require 3D wind measurement,such as wind speed measurement during aircraft ascent,turbofan control of wind turbines,and wind resistance optimization of vehicles.However,there are few studies on 3D wind sensors at present.In this regard,combined with the emerging flexible electronic device technology in recent years,a flexible three-dimensional wind sensor based on parallel plate capacitors is proposed.The main work and innovations of this thesis are described as follows:(1)A sensor scheme using flexible capacitor array to measure 3D wind speed is designed and verified.The sensor consists of eight flexible layers which are symmetrically distributed in the Z-axis,including two windward pillars,four electrode layers,and two supporting layers.There are four electrodes on each of the electrode layers,distributed in a 2 × 2 array.Every two opposing electrodes form a parallel plate capacitor,so the sensor contains a 2 × 2 × 2 capacitor array.The distance between the upper and lower electrodes changes with the deformation of the electrode layer caused by the wind,so the wind sensor can transform the 3D wind information into measurable capacitance information along X,Y,and Z axes.The wind direction is characterized by the change in trend of capacitance,and the wind speed is characterized by the change magnitude of capacitance.In order to verify the feasibility of the scheme,simulations are performed using the finite element method solver(COMSOL 5.5).The simulation variables include the wind speed along the X,Y,and Z axes.The results of the simulations showed the change in the distance between the upper and lower electrodes,which are consistent with the theoretical expectation.(2)A flexible capacitive 3D wind speed sensor based on the above scheme is fabricated and tested.According to the preliminary investigation,PDMS is chosen as the substrate material due to its plasticity and controllable Young’s modulus,and Cu is chosen as the electrode material due to its good electrical conductivity and low cost.The preparation process of the sensor includes the preparation of flexible substrate,the sputtering of electrode,and the bonding between substrates,involving 3D printing technology,magnetron sputtering technology,and plasma bonding technology respectively.The experiments mainly consist of two parts:calibrating the capacitance-wind speed curve of the sensor along the X,Y,and Z axes,and measuring the wind speed and direction in the XY,XZ,and YZ planes according to the calibration results.The measurement errors are calculated by comparing the measured values of 3D wind parameters(V,θ,φ)with the theoretical values.In the XY,XZ,and YZ planes,the average errors of V are 0.58m/s,0.41 m /s,and 0.53 m /s,respectively,the average errors of θare 2.68°,4.03°,and 5.65°,respectively,the average errors of φ are 6.63°,10.18° and 9.38°,respectively.(3)The existing flexible capacitive 3D wind speed sensor is analyzed and improved.According to the test results,three problems of the sensor are summarized: the measurement results of V are too large,the errors of θ and φ at specific angles are larger,and the measurement errors of φ are larger than θ.From the sensor model analysis,the basic reason of these problems is that the sensor has low sensitivity and poor anti-noise ability at low wind speed.In order to solve these problems,an improved scheme of adding groove structure to release stress is proposed.The test results in XY,XZ,and YZ planes show that the average errors of V are decreased by 15.52%,7.32%,and 28.30%,respectively,the average errors of θ are decreased by 8.21%,12.16% and 22.65%,respectively,and the average errors of φ are decreased by17.65%,26.42% and 25.27%,respectively.It can be seen that the scheme realizes the performance optimization of the wind speed sensor.In addition,the effects of temperature and humidity on the capacitances are studied respectively,which provides data support for the temperature and humidity compensation in the subsequent practical application of the sensor.