Design Of Non-metallic Composite Array Impedance Measurement System

A variety of new, advanced non-metallic composite materials have been widely used in the fields of aerospace, automotive, electrical and electronics, construction, fitness equipment and others. Effected by the environment, raw materials, accumulated fatigue, impact,corrosion, and other physical and chemical and other factors, composite material may easily form defects in the process of molding and application. Acoustic impedance method is one of those methods which are widely applied. But it need to continuously move the single probe point by point to test. It is not suitable for the detection of large composite materials because of low detection efficiency. Therefore, designing an system for testing of non-metallic composite material performance, that is efficient, convenient and strong applicability will have very important significance.This paper, based on the analysis of the relevant domestic and international research,combining wave propagation composite acoustic impedance measuring principle, introduces a non-metallic composite array impedance measurement system. The system consists of hardware and software system. The hardware includes: an array of electromagnetic vibration excitation- acquisition resonator, excitation signal generator, excitation signal conditioning circuit, multiplexer control switch, data acquisition, receiving signal conditioning circuit,power supply, and so on; the software system, includes: system control: excitation signal generator control, multi-channel array switches control, data acquisition control module and so on; signal analysis processing software, that includes: FIR and IIR digital filter, a median filter, the wavelet threshold de-noising tookit, the improved CEEMD noise threshold tookit,correlation analysis Time Delay Estimation(TDE), CEEMD TDE, amplitude and frequency analysis, S transform time-frequency analysis software, and the software system is developed based on LabVIEW. The system has the ability of single excitation-single acquisition and single excitation-multiple acquisition. When working in single excitation-single acquisition mode, the system will use a single excitation and a single reception; working in single excitation-multiple acquisition mode, the system will use a single excitation and multiple receiver, and the excitation and receiver module can be setted via a flexible software system.The system is based on the detection principle that when the internal structure of the object isdifferent, the force generated different impedance, resulting in that the acoustic impedance properties of the material will change. The system excites the measured object by multiple probes and obtains probes' response signals of the object, then analyzes relation of the array excitation and response signals, achieves the inspection of the internal performance for the composite material.Finally, the reliability and stability of the excitation performance, vibration obtaining performance and flexible operation mode control function of system is tested and analyzed. In addition, the designed system was applied to detect the defect of composite board: 1) For non-damage standard board, an array of absorbers were used to pick up the vibration response with swept-sine excitation, and the frequency response change rule with the detection distance and the impedance characteristic values of the plate have been analyzed; 2) a simple defect detection test with the same layout program and detector array has been operated to test the impedance characteristics of the injury plate, which take advantage of the difference of the array impedance values to show defects. The results show that the designed system is feasible and reliable.