Research On The Key Technology Of EMAT In Flaw Detection Of Ferromagnetic Components

Ultrasound technology is one of the 5 common non-destructive testing techniques.Electromagnetic Acoustic Transducer(EMAT)is a new technique for non-destructive testing of ferromagnetic materials due to its advantages of no coupling agent and many excitation modes.In this paper,EMAT based on Lorentz force and magnetostrictive effect are studied because of the low energy conversion efficiency in multi-field coupling of EMAT.Designing launch and receive circuits to improve the detection accuracy and sensitivity,it is suitable for different probe structure and operating parameters and applied to component defects and stress detection.The main work is as following:1.The principle of EMAT based on Lorentz force and magnetostrictive effect is analyzed,the corresponding physical equation is deduced.2.The electromagnetic ultrasonic testing system was simulated.A variety of modes of ultrasound are studied,as well as the role of various modes in non-destructive testing.The influence of the coil structure on the ultrasonic mode is discussed.Through the simulation calculation,the physical parameters of the EMAT transmitting and receiving coil are optimized and the energy conversion efficiency of the electromagnetic ultrasonic transducer is improved.3.Full-bridge inverter circuit was designed based on FPGA,the use of resonant principle of the coil to achieve high-frequency,high-power excitation.The effects of pulse number and duty cycle on the ultrasonic signal are also studied.By designing the flyback converter,the structure of the system is optimized.In order to control the detection system through FPGA,the design of complete faint signal detection circuit is given because of the faint signal of EMAT,and the signal-to-noise ratio is improved.4.A series of experiments have been carried out of the defect detection on ferromagnetic materials.By the results of some experiments,the system parameters were further optimized.Finally,we completed the flaw detection experiment of the slab,verified the ability of defect location and depth testing of the system.