Research Of The Metal Long-distance Detection Technology Based On Electromagnetic Ultrasonic Guided Wave

Ultrasonic testing is now an important nondestructive detection method, with China’srapid industrial development, ultrasonic testing has more extensive application. At present,large atmospheric tanks have been used for a long time in chemical raw materials and oilstorage in our country. It can cause oil leakage, fire and explosion and other major accidentsonce it has been damaged. Since the tank bottom is more difficult to detect than the other tankparts, at present, most nondestructive testing technique can only detect the tank bottom, theelectromagnetic ultrasonic technology can realize the non-contact nondestructive testing inthis respect. The main problem of the electromagnetic ultrasonic detection is that theconversion efficiency of the electromagnetic ultrasonic transducer is low and signal is weak.This paper has researched the theories of the electromagnetic ultrasonic in more detail, itresearched the electromagnetic ultrasonic excitation principle of the steel plate theoretically.The mathematical modeling analyzed the lorenz force mechanism of electromagneticultrasonic, the magnetization force mechanism, the magnetostrictive force mechanism. Thispaper researched the propagation characteristics of ultrasonic guided wave on the steel plate,and it respectively analyzed the multi-mode characteristics and dispersion characteristics in theprocess of propagation. In order to improve the conversion efficiency of the electromagneticultrasonic transducer further, the formulas of electromagnetic ultrasonic transducer conversionefficiency can deduce the relationship between static bias magnetic field and conversionefficiency. Aiming at the disadvantage of the low conversion efficiency of the conventionalstructure, this paper proposed a method to improve the conversion efficiency on the steel plate,and it enhanced the result in the magnetic field calculating by COMSOL finite elementsoftware. The simulation results showed that the conventional structure can effectivelyimprove the conversion efficiency and realized the long distance detection of defects on thesteel plate. By optimizing the permanent magnet and the exciting coil of the transducer probe,it can finally determining the combination of the optimization parameters of each transducerprobe.After testing on the steel plate, the results showed that lamb wave would produce themode conversion phenomenon when it encountered the defects on the steel plate in the process of communication, the amplitude of the echo signal increased with the increase of the depth ofthe defects on the steel plate, the amplitude of the echo signal can be used to characterize thedepth of the defects on the steel plate. In condition, the opposite position of the excitationprobe and the receiving probe constant on the steel plate, the parameters of the detectionsystem matched with each other. By comparing the amplitude of echo signals, it can concludethat the attenuation of the SH wave generated by the process of propagation is larger, and itshowed that the lamb wave is more suitable for the long distance transmission of the steelplate. The optimized receiving probe of lamb wave can receive the echo signal of A0modelamb wave at18m position, the effective detection distance of the optimized lamb wavetransducer is as1.5times as the effective detection distance of the original model, this methodimproved the conversion efficiency of the transducer effectively.