Industrial ultrasonic imaging and microscopy
Industrial ultrasonic imaging and microscopy
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工业超声成像和显微镜
DOI：
10.1088/0022-3727/29/6/001
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
R. Gilmore
中科院分区：
文献类型：
--
作者：
R. Gilmore
超声成像和扫描声显微镜是用来描述在不同的放大倍率和频率类似的成像过程的术语。这两个过程通过获取高频声波与材料相互作用的空间相关测量来形成图像。除了干涉测量（称为V(z)）和更高频率扫描声学显微镜使用的千兆赫频率外，很难确定它们之间的操作差异。这一点尤其正确，因为几乎所有商用超声成像系统都使用产生聚焦光束的换能器，并且可以显示放大的高分辨率图像。超声c扫描成像主要是由超声无损检测行业发展起来的。这种发展是渐进和进化的。在50年的时间里，越来越好的宽带换能器、电子设备和扫描仪被开发出来，以便在越来越高的频率上工作，现在范围从1.0到100兆赫。相反，扫描声学显微镜在20年前突然出现在斯坦福大学的校园里。第一台扫描声学显微镜工作在千兆赫兹频率，使用微波电子学产生声波脉冲，每个脉冲有许多波长。三个因素控制声图像的分辨率：声波束直径或其点扩散函数（PSF）；构成图像的像素的大小和间距；被解析特征的信噪比（对比度）。光束直径（PSF）由超声波脉冲的频率和光束的焦点收敛（或焦距与直径比Z/d）控制。在耦合流体中，Z/d由换能器直径和透镜决定，而在材料中，Z/d由材料的超声速度决定。像素是构成扫描图像的计算机显示的彩色或灰度正方形。按照奈奎斯特的标准，这些图像的分辨率是像素大小和间距的两倍。因此，为了支持超声光束的分辨率，像素必须不大于光束直径的一半。最后，所研究的特征的对比度必须（至少）在图像噪声产生的背景之上有一个清晰的灰色阴影。噪音可能是由材料或电子器件引起的。为了支持工业超声检查材料，本讨论将强调成像和显微镜之间的相似之处而不是不同之处。聚焦透镜的作用，脉冲频率，和被成像的材料，相对于声学图像的最终分辨率，将被详细考虑。它将表明，在分辨率的进一步改进可以实现与图像处理。最后，在金属、陶瓷、复合材料、附着方法、涂层和电子组件方面的应用研究将用于演示成像/显微镜在无损检测中的具体作用。
Ultrasonic imaging and scanned acoustic microscopy are terms used to describe similar imaging processes at different magnifications and frequencies. Both processes form images by acquiring spatially correlated measurements of the interaction of high-frequency sound waves with materials. With the exception of the interference measurement, called V(z), and the gigahertz frequencies used by the higher frequency scanning acoustic microscopes, it is difficult to establish operational differences between them. This is especially true since almost all commercial ultrasonic imaging systems use transducers producing focused beams and can display magnified high-resolution images. Ultrasonic C-scan imaging was developed largely by the ultrasonic nondestructive testing industry. The development was gradual and evolutionary. Over a 50-year period, better and better broadband transducers, electronics and scanners were developed for operation at progressively higher frequencies, now ranging from 1.0 to 100 MHz. Conversely, scanning acoustic microscopes made a relatively sudden appearance 20 years ago on the campus of Stanford University. The first scanning acoustic microscopes operated at gigahertz frequencies and used microwave electronics that produced acoustic tone bursts with many wavelengths per pulse. Three factors control resolution in an acoustic image: diameter of the acoustic beam or its point spread function (PSF); size and spacing of the pixels making up the image; signal-to-noise ratio (contrast) of the feature being resolved. The beam diameter, or PSF, is controlled by the frequency of the ultrasonic pulse and the focal convergence of the beam (or focal length to diameter ratio Z/d). In the coupling fluid, the Z/d ratio is determined by the transducer diameter and lens, but in the material, Z/d is established by the materials ultrasonic velocities. Pixels are the squares of colour or greyscale that make up computer displays of scanned images. Following Nyquist's criterion, the resolution of those images is twice the size and spacing of the pixels. It follows, therefore, that in order to support the resolution of an ultrasonic beam, the pixels must be no larger than half that beam diameter. Finally, the contrast of the feature being studied must be (at least) a clear shade of grey above the background produced by the image noise. The noise can be due to the material or the electronics. Written to support industrial ultrasonic inspection of materials, this discussion will emphasise the similarities between imaging and microscopy rather than the differences. The roles of the focusing lens, the pulse frequency, and the material being imaged, with respect to the final resolution of an acoustic image, will be considered in detail. It will be shown that additional improvements in resolution can be achieved with image processing. Finally, applications studies in metals, ceramics, composites, attachment methods, coatings, and electronic assemblies will be used to demonstrate specific roles for imaging/microscopy in nondestructive testing.