A novel Lorentz force eddy current sensor for non-destructive testing of defects in flexible graphite sheets

Defects in flexible graphite sheets can significantly reduce their performance. However, existing detection methods, such as X-ray and ultrasonic testing, have limitations in real-time, non-contact, and comprehensive detection. To address these issues, this paper proposes a defect detection technique for flexible graphite sheets based on Lorentz force eddy current (LET) testing. The design and structural optimisation of the detection sensor were systematically studied through finite element analysis and an improved Multi-Objective Manta Ray Foraging Optimisation (IMOMRFO) algorithm. A corresponding detection system was subsequently developed. Experimental results demonstrate that the designed sensor and detection device can effectively identify defects larger than 500 μm in size at a speed of 7.5 m/s. Furthermore, the detection sensitivity is found to be directly proportional to the relative motion speed. This method offers a non-contact, high-speed defect screening capability, making it suitable for industrial production lines and filling an important gap in the quality control of flexible graphite materials.