Research On The Experiments Of Electromagnetic Acoustic Transducer Testing Mechanism

Electromagnetic Acoustic Transducer (EMAT) is a global leading technology in the field of non-destructive testing (NDT). The features of EMATs, such as high accuracy, contactlessness, need-no-couplant, make them particularly suitable for the nondestructive inspection under high temperature, moving objects and phased-array-controlled operation. They also can easily generate ultrasonic waves at different modes. All these merits make them attract more and more attention from researchers. However, EMATs also have their blemishes, such as low transduction efficiency resulting in weak signal, which should be overcome during inspection.Firstly,based on the review of EMAT technology development history and its application actuality, this thesis discusses the mechanism of electro-acoustic transduction phenomenon of an EMAT, analyses theoretical basis of ultrasonic generation with EMAT due to Lorentz force, magnetization force and magnetostriction force. EMAT has been compared with piezoelectric acoustic transducer in this thesis. This thesis discusses the impedance matching technology which has an important effect for EMAT and introduces a method of designing EMAT testing system. Secondly,an EMAT receiving experiment is designed in the dissertation and it is showed that experimental data approximated to the calculation are assuredly generated by EMAT. Lastly,EMAT ultrasonic generation in different specimens have also been experimentized, after EMAT coil designed, impedance networking matched and bias magnetic field chosen. Rayleigh wave, Lamb wave and shear vertical wave can be generated in aluminum specimens and Lamb wave can be generated in stainless steel specimen with meander-line coil EMAT. It is also showed that the spiral pancake EMAT can generate bulk wave in aluminum specimens. Ultrasonic generation and reception with EMAT has been achieved by experiments in this dissertation and it can be referenced to next experiments and instrument development.If the appropriate mode of ultrasonic is chosen, the proper elements of EMAT are assembled, the impedance networking is well matched, the precision of EMAT is suitable, the EMAT technology will be applied to the actual inspection. Because of the inherent advantages of EMAT, EMAT testing technology has a bright application future.