Development Of A Surface Wave Transducer For The Steel Plate Inspection Based On The Electromagnetic Acoustic Technique

As a new ultrasonic testing method, Electromagnetic acoustic technology has been ahotspot in ultrasonic nondestructive testing field in recent years due to its non-contactcharacteristic and being free of couplant. In this thesis, an electromagnetic acoustictransducer(EMAT) is developed for surface wave scanning inspection on the steel plate basedon the signal-mode and no dispersion characteristics of surface wave. And the features of thescanning signals are discussed in detail.Firstly, according to the ferromagnetic properties of the steel plate, the testing principle ofthe tranducer with meander coil and vertical magnetization structure is investigated through themethod of simulation analysis and experimental verification. Then the theoretical calculationsteps of surface wave excitation parameters are given. Secondly, when the main structureparameters, such as spatial arrangement, lift-off and number of magnets, are determined by thesimulation analysis, a surface wave EMAT is developed with some lift-off conveniently for thescanning inspection in any direction on the steel plate surface. Finally, the scanning testingplatform is set up to conduct the experiments of slot testing, spherical hole testing and flatbottom hole testing. The detailed analysis on the scanning signals show that the steel platesurface can be tested based on interference enhancement of surface waves; when the transduceris placed in certain location from slots, the ultrasonic signal enhances10%~20%; for thespherical holes, one of the turning points that is easy to be get from the scanning signals isutilized to calculate the surface section diameters of spherical holes and the relative error iswithin17%; for the flat bottom holes, two of the turning points can be used to calculate thediameters of flat bottom holes and both the relative errors are within12%.The work in this dissertation enriches the methods of electromagnetic ultrasonic testingand is significant to promote the application of electromagnetic ultrasonic technique.