Research On Capacitive Testing Technology For Ablation Degree Of Spacecraft Outer Protection Material

When flying in the atmosphere,high-speed aircraft will be subject to atmospheric friction to produce high-temperature ablation.The ablation material on the outer surface plays a role of heat insulation when friction and ablation occurs with the atmosphere,and protects the aircraft itself.Aiming at the ablation detection of composite thermal ablation materials on the outer surface of high-speed aircraft,an electrical capacitive tomography method based on planar array capacitive sensors is proposed.Combining the detection principle of traditional electrical capacitance tomography,the detection principle of the planar array capacitance sensor is analyzed,and the mathematical model of the array capacitance sensor is constructed by analyzing the electric field theory.For the forward and inverse problems involved in the sensor in electrical capacitance tomography,combined with the mathematical model of the planar array capacitive sensor,the mathematical expressions of the forward and inverse problems are derived,and the solution method is given.Use simulation software to model the array capacitance sensor,and calculate the electric field intensity distribution in the three-dimensional space of the measured field and the capacitance between the plates through the finite element division method of the measured field space,and further use the mathematical software to design.The data of the sensor is calculated and processed,and the sensitivity distribution matrix of the planar array capacitive sensor at different spatial positions in the measured field is obtained.Combined with theoretical analysis,finite element simulation is performed by changing the sensor structure parameters to complete the optimized design of the array capacitance sensor.The design of the micro-capacitance acquisition system of the array capacitance sensor focuses on the analysis of the principle and characteristics of the C/V conversion circuit and the array switch control circuit in the measurement circuit,and combines theoretical analysis to optimize the error of the circuit under non-ideal conditions.Combine the sensor’s excitation collection mode to complete the embedded program design of the lower computer,and complete the specific work flow design of each part of the function.The electric field intensity data of the sensor calculated by finite element simulation is used to calculate the spatial sensitivity distribution in the measured field of the sensor,layer the spatial sensitivity matrix and analyze the sensitivity distribution characteristics of each layer.The capacitance imaging experiment is designed,combined with the layered sensitivity matrix to reconstruct the image of the sensor’s measurement results.The imaging results are basically consistent with the theoretical results,which verifies the correctness of the sensor detection principle and the feasibility of the detection method.