Zhang Haiyan, Zeng Lingtian, Fan Guopeng, Zhang Hui, Zhu Qi, Zhu Wenfa
School Institute for Advanced Communication and Data Science, School of Communication and Information Engineering, Shanghai University, Shanghai 200444, China.
School of Urban Railway Transportation, Shanghai University of Engineering Science, Shanghai 201620, China.
Sensors (Basel). 2020 Jan 31;20(3):775. doi: 10.3390/s20030775.
This paper describes an imaging method for near-field defect detection in aluminum plates based on Green's function recovery and application of instantaneous phase coherence weighting factors. The directly acquired acoustic information of near-field defects is usually obscured by the nonlinear effects due to the physical limitation of the acquisition system. Using the diffuse field to recover the Green's function can effectively retrieve the early time information. However, averaging operations of finite number in this process produces an imperfect imaging result. In order to improve the image quality, two kinds of instantaneous phased coherence weighting factors are used to weight the Green's function to reduce the background noise and improve the signal-to-noise ratio: the instantaneous phase coherence factor (IPCF), and the instantaneous phase weighting factor (IPWF). Experiments are conducted on two aluminum plates with two and four near-field defects, respectively. As a result, the background noise of amplitude images weighted by IPCF and IPWF is less than that of the conventional total focusing method (TFM). In addition, the IPCF image achieves a better signal-to-noise ratio (SNR) than that of IPWF, and the phase discontinuity in an IPWF image is suppressed through the IPCF.
本文介绍了一种基于格林函数恢复和瞬时相位相干加权因子应用的铝板近场缺陷检测成像方法。由于采集系统的物理限制，直接采集的近场缺陷声学信息通常会被非线性效应所掩盖。利用扩散场恢复格林函数可以有效地检索早期信息。然而，在此过程中有限数量的平均操作会产生不完美的成像结果。为了提高图像质量，使用两种瞬时相位相干加权因子对格林函数进行加权，以降低背景噪声并提高信噪比：瞬时相位相干因子（IPCF）和瞬时相位加权因子（IPWF）。分别在两块带有两个和四个近场缺陷的铝板上进行了实验。结果表明，由IPCF和IPWF加权的幅度图像的背景噪声小于传统全聚焦方法（TFM）的背景噪声。此外，IPCF图像比IPWF图像具有更好的信噪比（SNR），并且通过IPCF抑制了IPWF图像中的相位不连续性。
