A self-frequency-conversion eddy current testing method

Eddy current testing (ECT) technology is currently one of the effective methods for non-destructive testing of aviation materials. In the application of ECT technology, a lower operating frequency is generally used for aviation metal materials, while carbon fiber reinforced plastics (CFRP) often require higher operating frequencies due to the low conductivity characteristic. However, multiple materials are often used simultaneously in aircraft manufacturing, including metallic materials and CFRP. Therefore, due to the difference in materials, the traditional ECT technology needs to be carried out in the ultra-large frequency range (1 kHz to 100 MHz) during the ECT inspection process of the aircraft, which will bring great difficulties to instrument development and actual operation. Concerning this issue, a self-frequency-conversion ECT method is proposed in this paper, and the corresponding ECT system was developed. The proposed method has two detection signals simultaneously, the current signal and the frequency signal, which are used to characterize the defects of CFRP and metal materials, respectively. Experimental studies on CFRP and aluminum alloys were carried out using the proposed method. The experimental results show that the proposed method can realize the defect detection of metal materials and CFRP in the conventional frequency range of 1 kHz to 1 MHz. Compared with the traditional ECT technique, the proposed method greatly reduces the operating frequency range and can provide better detection sensitivity, which is an ECT technology with great engineering application value.