Analysis of Influencing Factors on the Conversion Efficiency of Laser-EMAT Ultrasound Detection with High-Temperature Carbon Steel Forgings

Abstract

A method to improve the conversion efficiency based on surface cooling technology was proposed to achieve a low signal-to-noise ratio (SNR) of laser-electromagnetic acoustic transducer (EMAT) detection with high-temperature forgings. A finite element model of the laser-EMAT ultrasonic testing process operated with high-temperature forgings was established to study the effects of the laser source parameters and temperatures on laser-excited ultrasonic waves and their radiated acoustic field. The ratio of the magnetostriction and Lorentz force to the ultrasonic reception efficiency of the EMAT at different temperatures was analyzed and verified experimentally. The results indicate that the surface cooling technology can improve the energy conversion efficiency when the carbon steel temperature exceeds the Curie temperature. With the help of surface cooling technology, the SNR of the longitudinal wave increases by 26.5 dB at 766°C, and the SNR of the shear wave improves by 12.1 dB at 655°C.