Abstract: A thickness detection method based on the dispersion characteristics of the Lamb wave is proposed to solve the detection problem of the boiler scale thickness.Firstly,the fluctuation model of Lamb wave in the aluminum-scale double-layer elastic structure is established,and the semi-analytical finite element method is adopted to solve the characteristic equation of Lamb wave in the model,and the dispersion curve of the Lamb wave which changed with the scale thickness is plotted.Secondly,a two-dimensional electromagnetic ultrasonic simulation model of aluminum-scale is established.The Lamb wave of S0 mode is excited by electromagnetic ultrasonic transducer in aluminum plate,and the waveform curve under different acquisition points is got.Finally,through the analysis of the dispersion curve and the waveform curve,the Lamb wave velocity of the low frequency S0 mode becomes slower with the increase of the thickness of the scale,and the Lamb wave velocity of the high frequency S0 mode becomes faster and the amplitude of the signal wave group decreases.The results show that the thickness of the boiler scale can be detected by S0 modal Lamb wave velocity and amplitude change.

Key words: Lamb wave, scale thickness, dispersion curve, semi-analytical finite element method