The Aircraft Composite Detection Methods Based On Capacitive Sensing Mechanism

Aerospace composite materials with features of light weight, high strength, resistanceto wear, etc., are widely used in the structure of the new aircrafts. Because the failure formsand fatigue life due to the damage mechanism of composite are significantly different frommetal materials structure, non-destructive health monitoring of composite becomes essentialfor flight safety and prediction of the material residual fatigue life.Electrical capacitance tomography(ECT), as a new non-destructive testing technology,has emerged in recent years based on capacitive sensing mechanism. ECT has advantages inadaptability, low prices, fast speed, non-destructive visual measurement, etc.Based on planar array capacitive sensor, ECT system is built for non-destructivetesting of aircraft composite materials. To verify the validity and reliability of the ECTsystem, studies of excitation modes, sensor design and optimization, as well as the design ofhardware platform structures and other relevant aspects are carried out as follows.(1) Analysis the soft field characteristics of ECT. Three-dimensional plane arraysensors are created by COMSOL software. Use these simulation data to reconstruct ECTimages in Matlab and also compare different damage models. Optimize the parameters ofthe sensor design, including geometric shape of electrodes, the spaces between theelectrodes, the thickness of the substrate, a shield electrode etc. And then analyze thecorresponding influences, such as signal strength of the sensors, detection depth, sensitivityand other performances.(2) Different excitation and measurement methods are discussed. Parity incentivemodel is proposed, and the performance and imaging results of the sensor under singleexcitation mode, dual-excitation mode and parity excitation mode sensor are compared andanalyzed.(3) ECT hardware detection system based on Xilinx Spartan-3ANFPGA chip isdesigned. Excitation signal source is built by FPGA DDS module and the D/A converterchip. Micro-controller (MCU) based on FPGA embedded soft core structures is designed tocontrol analog switches, multiplexers, programmable amplifiers, and the communication units. At the same time, digital quadrature demodulation on the data coming from A/Dconversion is completed by FPGA. Finally, design and debug ECT system hardware circuitbased on PCB board and complete online debugging of the hardware system.