Model On Time-space Domain Amplitude Of SH Guided Wave And Design Method Of SH Electromagnetic Acoustic Transducer

Non-destructive testing(NDT)is a widespread and effective method of ensuring the reliability of structures and equipment made of metal materials.Guided wave technology has been widely studied because of its advantages such as long detection distance,high efficiency,and full coverage.Shear Horizontal(SH)guided waves,among guided waves,have the advantages of simple dispersion characteristics,defect sensitivity,and a wide application range,and are utilized in a variety of scenarios.Electromagnetic acoustic transducers(EMATs)are often utilized to generate SHguided waves because they are versatile in configuration and require no couplant.The time-domain parameters of the excitation signal and the spatial-domain parameters linked to the spatial distribution of the EMAT components,together known as the time-space parameters of EMATs.At present,the relationship between the time-space parameters of SH guided wave EMATs(SH-EMATs)and the amplitude of SH guided waves is still unclear,making it difficult to analyze and predict the excitability of each SH guided wave mode,resulting in a lack of theoretical guidance for SH-EMAT design.The time-space domain amplitude model of SH-EMATs is a model for calculating the amplitude of each SH guided wave mode according to the time-space parameters of the SH-EMAT.The SH-EMAT optimization,SH guided wave mode and wavelength control can all benefit from the time-spatial domain amplitude model.It is difficult to directly calculate the amplitude of each SH guided wave mode according to the time-space parameters of SH-EMATs.Therefore,from the perspective of equivalent surface stress,this paper first calculates the equivalent surface stress excited by SH-EMATs,and then establishes the timespace domain amplitude model of SH guided waves based on the equivalent surface stress,so as to establish the relationship between time-space parameters of SHEMATs and the amplitude of each SH guided wave mode.The traditional singlefrequency and single-wavelength transducer design method is extended to the timespace domain on this foundation,and the SH-EMAT design method based on timedomain control and spatial-domain control is thoroughly investigated.In order to determine the equivalent surface stress excited by SH-EMATs,a method for calculating the equivalent surface stress is proposed for periodic permanent magnet SH-EMATs(PPM-SH-EMATs)and magnetostriction-based SH-EMATs(MSH-EMATs).The theoretical model of the EMAT coil considering the relative permeability of the material is established,then the dynamic magnetic field and eddy current in the material excited by the coil are obtained.The equivalent surface stress of the Lorentz force excited by the PPM-SH-EMAT is calculated,and the equivalent surface stress of the magnetostrictive force excited by the M-SH-EMATs is calculated by taking the nonlinearity of magnetostriction into account.The factors affecting the amplitude and spatial distribution of equivalent surface stress are analyzed on this basis.The time-space domain amplitude model of SH guided waves based on equivalent surface stress is established to address the present difficulty of calculating the amplitude of each SH guided wave mode using the time-space parameters of the equivalent surface stress.The equivalent surface stress boundary condition of SHEMATs is established,and the time-space parameters of surface stress are analyzed.On this basis,the time-space domain amplitude coefficients of each SH guided wave mode under transient and continuous excitation in two-dimensional and threedimensional spaces are calculated.Simulation and experiment are used to measure the validity of the time-space domain amplitude model of SH guided waves.In order to control the amplitude of each SH guided wave mode,an SH-EMAT design method based on time-domain control is studied.Influence of frequency and its band of excitation signal on the amplitude of each SH guided wave mode generated by the PPM-SH-EMAT is analyzed to demonstrate that the amplitude of each SH guided wave mode can be effectively controlled by only changing the timedomain parameters of the excitation signal.Then,by altering the frequency and frequency band of the excitation signal,the amplitude of the SH1 mode is considerably reduced,resulting in the excitation of a single SH0 mode.In order to realize the excitation of multi-wavelength SH guided waves,an SHEMAT design method based on spatial-domain control is studied.Based on the analysis of the relationship between the surface stress distribution and the spatial distribution of SH-EMAT array elements,the spatial sampling model of EMATs is proposed,which provides a theoretical basis for designing the spatial distribution of EMAT array elements.Then,using pulse modulation technology as the basis,a spatial-domain control-based design strategy for EMAT array elements is proposed.Finally,the spatial parameters of the multi-wavelength SH-EMAT are designed,and multi-wavelength SH guided waves excitation and reception are accomplished.