Online measurement techniques for multi-parameters of particles based on defocus imaging
The imaging technique for particle online analysis can obtain parameters,including velocity,particle size,number,and concentration of the particle phase in sparse two-phase flow,and their three-dimensional distribution.This technique is non-invasive,simple to operate,and provides intuitive results.However,the limited depth of field in the imaging system can lead to defocus blur,which hinders its application in online particle measurement.In fact,the degree of defocus blur of the particle image contains the depth position information of particles,and the use of defocus blur to measure key particle parameters has attracted increasing attention from researchers.This paper reviews the development history of multi-parameter measurement of particles by defocusing image method.The principle of depth measurement of 3 typical defocus methods(special diaphragm method and astigmatism method based on a single camera,and two-imaging distance method based on two cameras)is briefly described.The advantages and disadvantages of different methods are analyzed.It is pointed out that with the support of advanced image processing algorithms,such as deep learning,defocus imaging method will be more widely used in the field of online particle measurement.
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