基于激光测振仪的兰姆波离面和面内位移检测

In-plane and Out-of-plane Displacement of Lamb Waves Test with Laser Vibrometer

激励模态和频响特性是超声导波传感器性能评估的两个重要指标,而传统的传感器,如压电传感器和电磁声传感器(Electromagnetic acoustic transducer,EMAT)等,受自身带宽和模态选择性的影响,无法有效地实现这两个参数的评估。激光测振仪可以测量结构中弹性波原始的离面和面内位移,且测量不受带宽的限制,因而是进行超声导波传感器激励模态测定和频响特性测量的理想方法之一。采用此种方法对一种周向一致激励兰姆波的EMAT进行测试,结果表明,此传感器在150～210 kHz的范围内能激励产生出单一S0模态兰姆波,在50～150 kHz范围内,A0模态与S0模态共存。利用激光测振仪检测离面和面内位移的方法,是进行传感器评估和兰姆波接收的有效方法,在超声导波的非接触测量、高温波导体检测及弹性波传播3D可视化方面也有广阔的应用前景。

Excited modes and frequency response are two key parameters of ultrasonic guided wave transducers evaluating.However,traditional transducers such as piezoelectric transducer and electromagnetic acoustic transducer（EMAT） can＇t measure these two parameters efficiently because of the limit of frequency bandwidth and mode selection of themselves.Laser vibrometer can be employed to measure the raw in-plane and out-of-plane displacement of elastic waves in the structure without the limit of bandwidth.Thus it could be one of the ideal methods to identity the excited modes and measure the frequency response curve.A kind of omnidirectional lamb wave EMAT is been inspected by this method.The results show that the transducer can produce purity S0 mode in 150～200 kHz and both A0 and S0 mode in 50～150 kHz.It can be predicted that the method using laser vibrometer to detect the in-plane and out-of-plane displacement is an efficient method of evaluating the transducer and receiving Lamb waves,and can be widely used in no-contact measurement,high temperature testing and 3D visualization of elastic waves propagation.