Eddy-current testing by flexible microloop magnetic sensor array

Abstract

A flexible microloop magnetic sensor array has been developed for nondestructive evaluation in nuclear power plants and its fundamental characteristics have been investigated. A flexible micro-eddy current testing (micro-ECT) probe consists of a pancake-type exciting coil of the diameter of 3.2 m and a flexible microloop magnetic sensor array with an area of 14 2 14 mm 2 and a thickness of 125 m. The array has 16 microloop sensors made of copper formed on a flexible polyimide film by sophisticated photolithography. Each coil has 40 turns (8 m line and 8 m space) within an area of 2 2 2 mm 2 . The flexible sensorarray enables the micro-ECT probe to be applied to an arbitrary geometric configuration. The purpose of this work is to detect and reconstruct flaws in conductive tubing of a steam generator in a pressurized nuclear power reactor by using the flexible micro-ECT probe with higher spatial resolution than that of a conventional ECT probe. The spatial resolution of flaw detection was 3 mm and the detectability of an outer 20% flaw made by electric discharge machining was confirmed. The reconstruction of circumferential and axial flaws using the electromotive force and phase measured with the sensor array is described. Threedimensional eddy current and magnetic field analysis was also performed for comparison with measured data. Finally, a design study of a practical and robust micro-ECT for a realistic tube configuration with respect to detectability was carried out.

Induction coil sensors—a review

“…For testing the spatial distribution of the magnetic field by means of coil sensors the flexible microloop sensor array has been developed [26]. The array consists of 16 microloop sensors with an area of 14 × 14 mm 2 and a thickness of 125 µm.…”

Feasibility investigation of fault diagnosis using electromagnetic analysis of planar structures

“…Its advantages include the flexibility ofattachment to a complex surface, high sensitivity and easy construction [74]. In recent years, the planar coil sensor has become an area ofinterest in many researches including analytical modeling of various sensor dimension designs [74][75][76] and magnetic field detection applications [77][78][79]. It has been reported that planar coil sensors have been successfully implemented in the ECT technique to inspect the PCBs [60,[80][81][82].…”

Support vector machine and optimised feature extraction in integrated eddy current instrument

“…It has been proved as an effective tool for quantitative characterisation of hidden corrosion and cracks in multilayered aircraft structures [4,5], leading to the development of instruments for aircraft inspection [5][6][7][8][9]. For in-situ inspection for aerospace structures, various EC techniques are required, because each method has specific advantages, in multi-frequency excitation it is easy to classify defects at different depths [10], sensor arrays can inspect a large area [11] and alternating current field measurement (ACFM) can be used to evaluate defect depth [12]. Therefore, there is an increasing interest in developing an integrated portable EC instrument [13] with low cost and increased functionality.…”