Study on the Shielding Effect of Claddings with Transmitter–Receiver Sensor in Pulsed Eddy Current Testing

Abstract

The shielding effect caused by the cladding has a serious influence on pulsed eddy current testing (PECT) of ferromagnetic metallic structures. To analyze the shielding effect and reveal the essence for reducing the shielding effect, a non-coaxial transmitter–receiver sensor (TR sensor) is used, and the influence of the shielding effect caused by the cladding on the TR sensor is studied theoretically in this paper. Firstly, an analytical model for the TR sensor with rectangular cross-section coils is conducted by using the first integral mean value theorem. Then, on the basis of the analytical model, the expression of the shielding effectiveness is derived to quantitatively evaluate the shielding effect and the spatial frequency spectra is utilized to research the characteristics of the sensor. Based on these, the performances of the TR sensor for reducing the shielding effect are studied. Results show the TR sensor which is more sensitive to the smaller radial spatial frequency can be used to reduce the shielding effect caused by the galvanized steel sheet.