X-ray radiography has long been recognized as a valuable tool for detecting internal features and flaws. Recent developments in microfabrication and composite materials have extended inspection requirements to the resolution limits of conventional radiography. Our work has been directed toward pushing both detection and measurement capabilities to a smaller scale. Until recently, we have used conventional contact radiography, optimized to resolve small features. With the recent purchase of a nano-focus (sub-micron) x-ray source, we are now investigating projection radiography, phase contrast imaging and micro-computed tomography (μ-CT). Projection radiography produces a magnified image that is limited in spatial resolution mainly by the source size, not by film grain size or detector pixel size. Under certain conditions phase contrast can increase the ability to resolve small features such as cracks, especially in materials with low absorption contrast. Micro-computed tomography can provide three-dimensional measurements on a micron scale and has been shown to provide better sensitivity than simple radiographs. We have included applications of these techniques to small-scale measurements not easily made by mechanical or optical means. Examples include void detection in meso-scale nickel MEMS parts, measurement of edge profiles in thick gold lithography masks, and characterization of the distribution of phases in composite materials. Our work, so far, has been limited to film.
Propagation phase-contrast micro-computed tomography allows laboratory-based three-dimensional imaging of articular cartilage down to the cellular level
