Study On Digital Holographic Measurement Method Of Particle Field

The testing and diagnosis of particle field are important in science and engineering and the like fields. Digital holographic measurement of particle field is a technology that combines digital technology and traditional optical holography, and hologram of the particle field is recorded directly by CCD digitally and then reconstructed numerically in computer. And intensity as well as phase information of 3D particle field can be achieved. The parameter information of the size, position and velocity and so on of particle can be obtained through analysis of the numerically reconstructed image and the measurement of particle filed is then completed. Therefore, digital holography has shown its potential and advantage in measuring particle field, and so developed into a new instrument for practical field measurements.The subject, based on the the reseach of the basic theory of digital holography, centers about the method of digital holographic measurement of particle field and its application in practical spray particle field. The main work as follows has been done in this paper.1. The basic theory of digital holography for particle field measurement is studied.2. A new method for particle size and position measurement of digital holography by Hough transform is proposed. And particle threshold extraction is studied, and the two focus judging criteria, namely the gray level gradient focus judging criteria and gray combining image focus judging criteria are also presented to act as the rule by which to judge if the particle is in focus or out of focus, and the method of determining particle position along an optical axis is given. Computer simulations of the 2D and 3D particle fields are performed and the experiment is conducted for diameter 90μm standard particle field. And the measurement results are that the particle diameter is 92.54μm, and the absolute error 2.54μm, and the 3D particle distribution given. The research results show that the method presented in this paper is feasible.3. Experiments of digitally recording dynamic spray field with CW laser and high-speed CCD have been carried out. The method for particle measurement presented in the paper is used to measure and analyze diesel spray and ethanol spray under different pulse width of the injector and different measuring points, and the 3D distribution of particle field, and weight distribution and SMD variation curve of the spray field are obtained. From the experiment results, it can be seen that the digital holography can be applied to spray field of the internal combustion engine.4. The trajectory of particle that is moving throughout a 3D space is obtained by processing and reconstructing sequence holograms recorded consecutively. And then the velocity of diesel spray and ethanol spray are measured by processing the reconstructed trajectory image with the method of particle measurement proposed in the paper. The experimental results testify that the digital holographic measurement method of particle field proposed in this paper can realize the velocity measurement of spray field.5. The automatic measurement software of particle field has been completed in Matlab and Visual C++ 6.0, and image processing software package for automatic and high-speed particle information extraction has been developed.