A New Eddy Current Detection Technology Based On Self-resonance Circuit

In recent years,with the rapid development of aviation,more and more materials have been used in the manufacture of aviation equipment.Among them,as a traditional aviation metal material,aluminum alloy is still the most used in aviation equipment manufacturing.And carbon fiber reinforced polymer(CFRP),as an emerging composite material,has attracted more and more attention in the aviation field.Therefore,the research of non-destructive testing methods for these two main aviation materials has also attracted more and more attention.Eddy current testing(ECT),as a mature,highly efficient non-contact non-destructive testing technology,has been widely used in non-destructive testing of aluminum alloy materials and CFRP.Unlike aluminum alloy materials,the conductivity of CFRP is very low,so the application of traditional eddy current testing on such low-conductivity materials is mainly high-frequency detection.However,high-frequency detection is more susceptible to various interference factors,and the background noise is relatively high,which brings great inconvenience to practical applications.For this problem,a new type of eddy current detection technology based on self-resonant circuit is proposed in this paper.In this technology,an LC resonator composed of an eddy current coil and a capacitor in parallel is used as an eddy current detection probe,and a special excitation circuit is designed to make the LC resonator always in a high-quality resonance state.Compared with the traditional eddy current detection technology,the proposed new eddy current detection technology improves the detection sensitivity through the design of special circuits and the optimization of the eddy current signal detection method,which can overcome the problem of low conductivity of CFRP,and can realize CFRP defect detection at a lower frequency.And this technology is also suitable for the detection of aluminum alloy materials,and its applicability is stronger than other eddy current detection technologies.First of all,the impedance model of the eddy current testing probe of the new eddy current testing technology is solved in this paper.On this basis,the detection characteristics of the new eddy current detection technology are analyzed,and application models for CFRP and aluminum alloy materials are established respectively.Then,based on the detection characteristics of the technology,a self-resonant eddy current detection system was designed and developed comprehensively using circuit design and computer technology.Finally,the built-up self-resonance eddy current inspection system was used to carry out the defect inspection experiments of CFRP and aluminum alloy materials.The following conclusions can be obtained from the experimental results:①For CFRP,the detection effect of the self-resonant eddy current detection system at 500kHz is similar to that of the traditional eddy current detection system at 10MHz;② In the case of using a self-resonant eddy current detection system,500kHz is high enough to achieve accurate detection of common defects of CFRP,including cracks,delamination and impact damage;③ For high-conductivity materials such as aluminum alloys,using the resonance frequency as the detection signal of the self-resonant eddy current detection system can provide better detection results.