Study Of Coplanar Capacitive Nondestructive Detecting Sensor

NDE (Nondestructive evaluation) technology is to obtain the detected material information by sensors and to convert the information into the parameter of the defects to evaluate under the premise of not damaging the work piece or material’s use and performance.A new method of coplanar capacitive sensor nondestructive evaluation technology which is simple in construction and easy to operate has been studied to detect and locate the anomalies or damage of non-metallic plate.Firstly, the effect of the structural parameters of two electrode coplanar capacitive sensor to sensor’s effective capacitance is analyzed by finite element simulation. As follows:1) the effects of the sensor electrode width and electrode spacing to two electrode coplanar capacitive sensor’s effective capacitance are obtained. We obtain that the larger the electrode width and the smaller the electrode spacing, the greater the coplanar capacitive sensor’s effective capacitance, especially the electrode spacing’effect to sensor’s effective capacitance.2) The relationships between effective detect depth and the sensor electrode width, electrode spacing are achieved.Then, the effect of the structural parameters of three electrode coplanar capacitive sensor to sensor’s effective capacitance is analyzed by finite element simulation. As follows:1) the effects of the non-metallic plate’s thickness and inhomogeneous distribution of relative permittivity to effective capacitance are analyzed.2) The effective detection range of three-electrode coplanar capacitive sensor in horizontal and vertical direction is analyzed.3) The damage of non-metallic plate is preliminarily detected and located.4) The effect of damage depth and damage region with sensor’s capacitance in the non-metallic plates is studied.Finally using AD7150/AD7745/AD7746and STC89C52RC MCU to design the external detecting circuit is to research the effect of the damage information to coplanar capacitive sensor’s effective capacitance. Both of the simulation and the preliminary experimental results show that, the method of coplanar capacitive sensor nondestructive evaluation technology to detect and locate the anomalies or damage of non-metallic plates is feasible and effective.