Composites Research Center, R & D E(E), DRDO, Dighi, Pune 411 015, India.
Composites Research Center, R & D E(E), DRDO, Dighi, Pune 411 015, India.
Ultrasonics. 2014 Jul;54(5):1401-8. doi: 10.1016/j.ultras.2014.02.014. Epub 2014 Feb 26.
Proper alignment of air-coupled ultrasonic transducers for generation and reception of Lamb waves is vital in order to acquire a high amplitude wave group. Any misalignment with either the transmitter or the receiver or both adversely influences the amplitude of a Lamb mode. This paper reports a systematic attempt to quantify the reduction in the amplitude of the fundamental anti-symmetric Lamb mode (Ao) in a metal plate caused by misalignments in air-coupled probes. Three different types of misalignments - linear, orientation and synchronised orientation were deliberately introduced in the transducers, and experiments were performed on a 6mm thick aluminium plate. Amplitudes of Ao mode measured at various configurations were normalised with that of Ao mode, captured in a reference configuration. Suitable curves fitted over the experimental data points revealed that Gaussian curves represent appropriately the variations in normalised amplitudes of Ao mode. Moreover, analytical expressions were derived to predict the difference in arrival times of Lamb mode(s) due to orientation and synchronised orientation misalignments.
为了获得高振幅的波群，对空气耦合超声换能器进行正确的声束对准对于产生和接收兰姆波至关重要。发射器或接收器或两者的任何不对准都会对兰姆模式的幅度产生不利影响。本文系统地尝试量化由于空气耦合探头中的不对准而导致金属板中基本反对称兰姆模式 (Ao) 的幅度降低。在换能器中故意引入了三种不同类型的不对准-线性、方向和同步方向，并在 6mm 厚的铝板上进行了实验。在各种配置下测量的 Ao 模式的幅度与参考配置中捕获的 Ao 模式的幅度进行了归一化。对实验数据点进行拟合的合适曲线表明，高斯曲线适当地表示了 Ao 模式归一化幅度的变化。此外，还推导出了分析表达式来预测由于方向和同步方向不对准而导致兰姆波（多个）到达时间的差异。
