超声Lamb波二次谐波发生效率分析与模式选择

在导波模式展开分析方法的基础上,提出激发效率参量来定量表征超声Lamb波积累二次谐波的发生效率。以P92钢板为例,理论计算得到了与频散曲线对应的理论激发效率参量分布图谱,从图谱中选择理论激发效率参量大小不同的两种基频Lamb波模式:纵波型S1模式和交点型A2/S2模式,分别测量这两种基频Lamb波模式在钢板中传播时产生的二次谐波信号。理论计算和实验测量结果表明,这两种基频Lamb波模式的理论和实验激发效率参量的比值基本一致,且激发效率参量较大的纵波型S1模式能激发出效率更高的二次谐波信号。研究结果表明激发效率参量可以有效的用于Lamb波二次谐波发生效率的表征及模式选择。 

Excitation efficiency analysis and mode selection on second harmonic generation of ultrasonic Lamb waves

Based on the modal expansion analysis method, an excitation efficiency parameter is proposed to quantitatively describe the efficiency of accumulative second harmonic generation of Lamb waves. Theoretical excitation efficiency parameters corresponding to the disperse curves of Lamb wave are calculated in a given P92 steel plates. Two types of primary Lamb modes with different excitation efficiency parameters are selected for experimental comparison, which are called longitudinal velocity type S1 mode and intersection point type A2/S2 modes. Then, the second-harmonics generations of the selected two different primary Lamb waves are measured, respectively. The results show that there is a good agreement between the theoretical predictions and experimental verifications of the two different types of Lamb wave modes. It is found that the longitudinal velocity type S1 mode with a higher excitation efficiency parameter corresponds to the higher second harmonies of Lamb wave. Therefore, excitation efficiency parameter developed in this contribution could be an effective indicator for the mode selection of efficient second harmonic generation of Lamb waves.