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Basic knowledge

Objective Lens Coupling Technology

Usually, the CT equipment with a resolution up to micron dimension is called micro CT.

Traditional micro CT adopts flat panel detectors. In the structural design, direct imaging is achieved through geometric projection magnification, which mainly relies on a small X-ray source focal spot and a large geometric magnification ratio to achieve a high-resolution image. The figure below is a typical schematic diagram magnified by the geometric projection. When the bulb sample is far from the X-ray source (as shown in the figure above), the imaging resolution of the filament is lower; when the sample is close to the X-ray source (as shown in the figure below), the imaging resolution of the filament is significantly improved, but due to the bulb shell, the filament cannot be any closer to the X-ray source, so this is the highest resolution for geometric projection magnification. It can be seen that the geometric projection magnification cannot achieve high-resolution imaging at a long working distance. In other words, high-resolution imaging cannot be performed on large samples (the working distance is the distance from the X-ray source to the sample's rotation center).


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Schematic diagram of geometric projection magnification principle


       Imaging with Sanying’s objective lens coupling technology is based on optical secondary magnification (as shown in the figure below). The magnification factor of the system is the product of geometric projection magnification factor and optical magnification factor. It can be seen that the bulb sample can still achieve the highest resolution even at a long distance from the X-ray source. High-resolution imaging of a large sample at a long working distance is achieved.


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Schematic diagram of optical secondary magnification


The following figure shows the optical path of the objective lens coupling detector. The X-ray that penetrates the sample is transformed by the scintillator into continuous spatial visible light, and then the visible light is magnified through the conventional optical system of microimaging, and visible light signal is collected by the CCD camera.


  Optical path diagram of objective lens coupled detector



          In the micro CT equipment, the flat panel detector and the objective lens coupling detector are usually used together to give full play to their respective advantages and improve the overall technical performance of the equipment.



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