Considering the fact that the acoustic attenuation increases with the carrier frequency, the attention shifts towards the low-frequency ultrasonic waves in the field of ultrasonic nondestructive testing and structural health monitoring of highly attenuative materials. However, low-frequency ultrasonic waves may sharply reduce the imaging resolution, although it can propagate longer distance. When an ultrasonic primary longitudinal wave tone burst propagates through an elastic solid with quadratic nonlinearity, it results in the generation of the quasi-static component (QSC). The QSC has advantages of low attenuation and better sound beam directivity, so it is expected to be a novel tool for non-destructive testing of highly attenuative materials. Therefore, aimed at detecting defects and improving the imaging quality in highly attenuative materials, a novel synthetic aperture focusing technique in the time domain combined with nonlinear ultrasonic QSC is proposed. In this study, experimental examinations were carried out to evaluate the imaging performance of the proposed method and low-frequency ultrasonic waves, in which a pulse-echo transducer is used to detect the QSC pulse generated by a primary longitudinal wave. The imaging results indicate that the proposed method has significant advantages over low-frequency ultrasonic waves in terms of visual presentation of defects. The effect of the duration of the tone burst on imaging quality is also investigated, and the results show that the imaging quality is optimal when the cycle number meets the requirement for the maximum response of QSC. This study would open new perspectives for the research on ultrasonic imaging in highly attenuative materials.

中文翻译：

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利用超声纵波准静态分量进行高衰减材料缺陷检测的合成孔径聚焦成像


考虑到声衰减随着载波频率的增加而增加，在高衰减材料的超声无损检测和结构健康监测领域，注意力转向低频超声波。然而，低频超声波虽然可以传播更远的距离，但可能会急剧降低成像分辨率。当超声一次纵波突发音通过具有二次非线性的弹性固体传播时，会产生准静态分量（QSC）。 QSC具有低衰减和更好的声束指向性等优点，有望成为高衰减材料无损检测的新型工具。因此，为了检测高衰减材料的缺陷并提高成像质量，提出了一种结合非线性超声QSC的新型时域合成孔径聚焦技术。在这项研究中，进行了实验检查来评估所提出的方法和低频超声波的成像性能，其中使用脉冲回波换能器来检测初级纵波产生的QSC脉冲。成像结果表明，该方法在缺陷的视觉呈现方面比低频超声波具有显着优势。还研究了突发音持续时间对成像质量的影响，结果表明，当循环数满足QSC最大响应要求时，成像质量最佳。这项研究将为高衰减材料超声成像的研究开辟新的视角。