Simultaneous Retrieval Of Particle Size And Refractive Index By Extended IPI Technique

The size and refractive index of a particle are important parameters of particle measurement.Because the particles' real part of the refractive index and its size are closely related to the scattered light characteristics.Therefore,in the measurement of particle size based on light scattering,in order to make the scattered light not affected by the refractive index of particles,it is necessary to select the appropriate scattering angle.However,in physical or chemical reactions such as heating and combustion,the refractive index changes with the change of particle size,thus affecting the accuracy of particle size measurement.Therefore,a method that can simultaneously measure particle size and refractive index is of great significance to accurately measure the parameters of particle field.In this paper,extended interferometric particle imaging(IPI)technique and its application in particle field are studied.The main work as follows has been done:1.A method of measuring particle size and refractive index simultaneously is proposed based on the extended IPI,in which opposite two-sheet illumination at dual scattering angles is laid out for the experiment.The size of a particle is evaluated by the interference fringe recorded at the scattering angle of 90° and then the refractive index is calculated by the fringe pattern recorded in the side scattering region when combined with droplet size determined.2.The image processing algorithms for the images collected by the extended IPI experiment system are studied,including the particle positioning algorithm based on the gradient-matched algorithm,the defocused particle image matching algorithm based on the invariance of relative position and the fringe frequency extraction algorithm based on the Fourier transform.The effect of double laser beam interference on the imaging of refractice index measurement system is analyzed and verified by experiments.3.The experimental optail system was designed and built for simultaneous measurement of particle size and refractive index.The water droplets with a size of19.7?m and a refractive index of 1.33,polystyrene microspheres with a size of51?m and a refractive index of 1.59,and glass beads with a size of 56.9?m and a refractive index of 1.90 were measured.The size and refractive index of particles are calculated by the interferometric fringe figure processing algorithm.The size measurement relative errors of three kinds of particels are 0.86%,0.65% and 0.46%,respectively.The refractive index measurement relative errors are 1.11%,0.35%and 0.27%,respectively.The experimental results demonstrate the feasibility of using the extended IPI experimental system to simultaneously measure particle size and refractive index.4.Measurements were made at the water spray field,the ethanol spray field and the water spray field with standard particles.The size and refractive index of droplet in different area of spray field were calculated.The average size of the water droplet was 52.95 ?m and the average refractive index was 1.3232±0.0036.The average size of the ethanol droplet was 48.63 ?m and the average refractive index was1.3595±0.0012.