Simultaneous retrieval of particle size and refractive index by extended interferometric particle imaging technique.

A method is presented for simultaneously inferring both the refractive index and the size of a particle with extended interferometric particle imaging technique. The optical system of extended IPI with 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°, which is from the two reflected lights with two counter-propagating sheet illuminations. And then the refractive index is calculated by the fringe pattern recorded in the side scattering angle region with one of two-sheet illumination when combined with droplet size determined. Experiments on the polystyrene microsphere and water droplet suggest that the method presented herein is promising for many relevant applications, such as fuel combustion and environmental monitoring, in accurately measuring both the particle size and its refractive index.

Simultaneous location and size measurement of particles using extended glare-point imaging technique.

Interferometric particle imaging (IPI) is a robust and popular technique for measuring particle size and velocity. A method based on a template matching algorithm and an auto-correlation method is proposed to simultaneously extract the location and the separation of doublet images of a particle from an IPI focused image. The position coordinate (x,y) of the particle can be determined with high accuracy, as evaluated by using a serial particle mask. Furthermore, the method can be employed to achieve sub-pixel spacing extraction when combined with Gaussian interpolation. The algorithm is tested using synthetic and experimental data. The results suggest that the method presented here is promising for its application to a high-density particle field, in accurately measuring both the particle size and its location.

High-accuracy simultaneous measurement of particle size and location using interferometric out-of-focus imaging.

A method based on unidirectional gradient-matched algorithm and Fourier transform technique is proposed to simultaneously extract the location and the number of fringes/fringe spacing of a particle interferogram. The position coordinate (x,y) of a particle can be determined with high accuracy because of the elimination of the fringe within the particle fringe pattern. Furthermore, the method can be employed to achieve sub-pixel frequency extraction when combined with an improved Rife algorithm. The performance of the method has been verified by numerical simulations and experimental measurements. The results suggest that the method presented here is highly beneficial to applications such as spray, in accurately measuring both the particle size and its location.

Coated sphere scattering by geometric optics approximation.

A new geometric optics model has been developed for the calculation of light scattering by a coated sphere, and the analytic expression for scattering is presented according to whether rays hit the core or not. The ray of various geometric optics approximation (GOA) terms is parameterized by the number of reflections in the coating/core interface, the coating/medium interface, and the number of chords in the core, with the degeneracy path and repeated path terms considered for the rays striking the core, which simplifies the calculation. For the ray missing the core, the various GOA terms are dealt with by a homogeneous sphere. The scattering intensity of coated particles are calculated and then compared with those of Debye series and Aden-Kerker theory. The consistency of the results proves the validity of the method proposed in this work.