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Isolation of ultrasonic scattering by wavefield baseline subtraction

机译：通过波场基线减法分离超声散射

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Wavefield imaging generally refers to the measurement of signals over a two-dimensional rectilinear grid that originate from a spatially fixed source. Subtraction of such wavefields is investigated as a means of separating scattered signals from the total wavefield; that is, baseline wavefield data acquired from a defect-free specimen are subtracted from analogous data acquired after introduction of a defect. The wavefields considered here are generated by a 5 MHz angle-beam probe and measured over an area of the accessible specimen surface using a laser vibrometer. The primary challenge in isolating the scattered waves is imperfect temporal and spatial alignment of the two wavefields. Two methods for aligning the wavefields in space and time prior to performing baseline subtraction are presented and their efficacy is evaluated using data acquired before and after introducing notches that originate from a through-hole. Although perfect baseline subtraction is not achieved, the improvement in performance after alignment using either method allows for scattered waves from small defects to be separated and visualized, even when their amplitudes are much smaller than those of the incident waves.
机译：波场成像通常是指在二维直线网格上对信号的测量，该二维直线网格源自空间固定源。研究了将这种波场相减作为从总波场中分离散射信号的一种方法。也就是说，从引入缺陷之后获得的类似数据中减去从无缺陷样本获得的基线波场数据。此处考虑的波场由5 MHz角波束探头产生，并使用激光振动计在可触及样品表面的区域进行测量。隔离散射波的主要挑战是两个波场的时间和空间对准不完善。提出了两种在执行基线减法之前对齐空间和时间中的波场的方法，并使用引入源自通孔的凹口之前和之后获得的数据评估了它们的功效。尽管无法实现完美的基线减法，但是使用两种方法进行对准后的性能提高都可以将小缺陷的散射波分离并显示出来，即使其幅度远小于入射波的幅度。

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