The pixel size is determined by the thin-film-transistor LCD manufacturing process used to make amorphous-silicon sensors, which is also more expensive than CMOS manufacturing. For example, amorphous-silicon, CMOS, and CCD detectors are all readily available in multimegapixel area arrays however, pixels in amorphous silicon are much larger (tens or hundreds of microns). The size of the object under test, resolution, required sensitivity, and throughput are all important factors when selecting an x-ray sensor for a machine-vision application. This quality is both the great advantage and Achilles heel of x-ray imaging. The lack of x-ray optics is explained by their unique quality-they pass through most substances without refracting, as visible photons do, when passing through materials with differing optical properties. Exceptions include the need for photon-conversion materials and the relative dearth of focusing optics for x-ray systems.Ĭonverting x-ray photons to visible photons is critical for two reasons: materials that convert x-ray photons directly to electrical energy are expensive to manufacture, and x-ray photons, especially high-energy x-ray photons, damage standard detector materials, such as the crystalline and amorphous-silicon substrates used in area- and linear-array sensors. Like visible machine-vision systems, x-ray AOI systems use an illumination source, detector, frame grabber or direct digital interface such as USB, image processor, and standard machine-vision software and algorithms. Hardware for x-ray AOI and visible AOI is similar in many ways. The unique properties of x-ray radiation are enabling new machine-vision systems that can find obscured defects in solid objects in industries such as electronics, pharmaceuticals, automotive, and food processing. The dangers and complexity of x-ray imaging have kept these systems from a wider variety of applications however, increased understanding of x-ray sources and safety is quickly pushing x-ray automated optical imaging (AOI) into product-inspection, quality-control, and process-control systems. Based on amorphous-silicon, CCD, or CMOS sensors, x-ray automated optical imaging systems serve more industries.Īlthough x-ray imaging systems have been around since the early 1900s, medical diagnostics has been the dominant application.
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