Wang Chia-Fu, Wee Junghyun, Peters Kara
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA.
Sensors (Basel). 2022 Nov 2;22(21):8426. doi: 10.3390/s22218426.
This paper demonstrates that a graded-index (GRIN) phononic lens, combined with a channel waveguide, can focus anti-symmetric Lamb waves for extraction by a detector with strong directional sensitivity. Guided ultrasonic wave inspection is commonly applied for structural health monitoring applications; however, obtaining sufficient signal amplitude is a challenge. In addition, fiber Bragg grating (FBG) sensors have strong directional sensitivity. We fabricate the GRIN structure, followed by a channel waveguide starting at the focal point, using a commercial 3D printer and mount it on a thin aluminum plate. We characterize the focusing of the A mode Lamb wave in the plate, traveling across the GRIN lens using 3D laser Doppler vibrometry. We also measure the extraction of focused energy using an FBG sensor, examining the optimal sensor bond location and bond length in the channel of the waveguide for maximum signal extraction. The measured amplification of the ultrasound signal is compared to theoretical predictions. The results demonstrate that significant amplification of the waveform is achieved and that selecting the location of the FBG sensor in the channel is critical to optimizing the amplification.
本文表明，渐变折射率（GRIN）声子透镜与通道波导相结合，可聚焦反对称兰姆波，以便由具有强方向灵敏度的探测器进行提取。导波超声检测通常应用于结构健康监测；然而，获得足够的信号幅度是一项挑战。此外，光纤布拉格光栅（FBG）传感器具有很强的方向灵敏度。我们使用商用3D打印机制造GRIN结构，随后制造从焦点开始的通道波导，并将其安装在薄铝板上。我们使用三维激光多普勒振动测量法表征板中A模兰姆波穿过GRIN透镜的聚焦情况。我们还使用FBG传感器测量聚焦能量的提取，研究波导通道中用于最大信号提取的最佳传感器粘结位置和粘结长度。将测量得到的超声信号放大倍数与理论预测值进行比较。结果表明，实现了波形的显著放大，并且在通道中选择FBG传感器的位置对于优化放大至关重要。
