Torsional wave focusing in cylindrical structures with the conformal gradient-index phononic crystal lens
Torsional wave focusing in cylindrical structures with the conformal gradient-index phononic crystal lens
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DOI：
10.1063/5.0050295
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发表时间：
2021-05
影响因子：
3.2
通讯作者：
G. Okudan;H. Danawe;D. Ozevin;S. Tol
中科院分区：
文献类型：
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作者：
G. Okudan;H. Danawe;D. Ozevin;S. Tol
研究了柱面结构与共形梯度折射率声子晶体(GRIN-PC)透镜集成的扭转波聚焦问题。该机械透镜改变了沿轴向传播的波的折射特性，使得扭转波能以增大的幅度聚焦在所需的点上。在本文中，我们的主要目标是利用GRIN-PC概念来放大基本扭转波模，即T(0，1)，它特别适合于管道的导波超声检测，并且可以将重要的结构信息扩展到远距离管道。为此，我们首先通过耦合压电力学和固体力学模型的多物理模拟对d35压电换能器阵列进行了研究，确定了实现扭转平面波激励的最佳换能器数目。通过二维傅立叶变换和不同轴向位置的圆管圆周切向位移历史数据验证了纯T(0，1)激励的正确性，并通过实验进行了验证。接下来，我们设计、制造了用于T(0，1)模聚焦的共形GRIN-PC，并对其进行了数值和实验研究。测量结果表明，在GRIN-PC透镜的存在下，扭转波模的振幅在焦点处放大了39%。
We present torsional wave focusing in cylindrical structures integrated with conformal gradient-index phononic crystal (GRIN-PC) lenses. The mechanical lens modifies the refractive characteristics of propagating waves along the axial direction such that the torsional wave energy focuses at a desired point with an increased amplitude. In this paper, our main goal is to exploit the GRIN-PC concept for amplification of the fundamental torsional wave mode, namely, T(0,1), which is especially favorable in the guided wave ultrasonic testing of pipelines and can extend important structural information over long-range pipelines. To this end, we first study d35 piezoelectric transducer arrays through multiphysics simulations coupling piezoelectric and solid mechanics models and determine the optimal number of transducers to achieve the excitation of torsional plane wave. Two-dimensional Fourier transform as well as the tangential displacement histories around the pipe circumference at various axial positions verify the pure T(0,1) excitation, which is validated with experiments. Next, we design, fabricate, and numerically and experimentally study the conformal GRIN-PC for T(0,1) mode focusing in a range of ultrasonic frequencies, from 30 to 50 kHz. Measurements show that the amplitude of the torsional wave mode is amplified by 39% at the focal point with the presence of the GRIN-PC lens.