Multi-mode and multi-frequency guided wave imaging via chirp excitations
Multi-mode and multi-frequency guided wave imaging via chirp excitations
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DOI：
10.1117/12.880963
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发表时间：
2011-03
期刊：
影响因子：
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通讯作者：
J. Michaels;S. J. Lee;James S. Hall;T. Michaels
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文献类型：
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作者：
J. Michaels;S. J. Lee;James S. Hall;T. Michaels
导波成像提供了一种可视化和表征结构损伤的方法，在结构健康监测应用中显示出巨大的潜力。为了成功实施延迟求和和其他采用引导超声波的椭圆成像算法，需要一定程度的模式纯度，因为来自不期望模式的回波会导致掩盖损伤的成像伪影。但是还期望利用多个模式，因为不同的模式可以表现出对不同类型和取向的缺陷的增加的灵敏度。可以采用公知的模式调谐效应来使用相同的PZT换能器，以通过用不同频率的窄带音调突发激励换能器来生成和接收多个模式。然而，这个过程是不方便和耗时的，特别是如果需要大量的信号平均来实现令人满意的信噪比。此外，如果测量来自许多窄带短纯音激励的信号，则采集时间和数据存储要求两者可能是禁止的。在本文中，我们利用一个啁啾激励激励PZT传感器在一个广泛的频率范围内获得多模态数据与一个单一的传输，这可以显着减少测量时间和数据量。对来自线性调频脉冲激励的每个接收信号进行后处理，以获得对应于不同窄带频率范围的多个信号。选择具有最佳模式纯度和回波形状的窄带信号，然后用于生成目标结构中损伤的多个图像。实验证明了所提出的技术的有效性，使用铝板仪表与空间分布的压电传感器阵列和模拟损伤。
Guided wave imaging has shown great potential for structural health monitoring applications by providing a way to visualize and characterize structural damage. For successful implementation of delay-and-sum and other elliptical imaging algorithms employing guided ultrasonic waves, some degree of mode purity is required because echoes from undesired modes cause imaging artifacts that obscure damage. But it is also desirable to utilize multiple modes because different modes may exhibit increased sensitivity to different types and orientations of defects. The well-known modetuning effect can be employed to use the same PZT transducers for generating and receiving multiple modes by exciting the transducers with narrowband tone bursts at different frequencies. However, this process is inconvenient and timeconsuming, particularly if extensive signal averaging is required to achieve a satisfactory signal-to-noise ratio. In addition, both acquisition time and data storage requirements may be prohibitive if signals from many narrowband tone burst excitations are measured. In this paper, we utilize a chirp excitation to excite PZT transducers over a broad frequency range to acquire multi-modal data with a single transmission, which can significantly reduce both the measurement time and the quantity of data. Each received signal from a chirp excitation is post-processed to obtain multiple signals corresponding to different narrowband frequency ranges. Narrowband signals with the best mode purity and echo shape are selected and then used to generate multiple images of damage in a target structure. The efficacy of the proposed technique is demonstrated experimentally using an aluminum plate instrumented with a spatially distributed array of piezoelectric sensors and with simulated damage.