Experimental investigation of Gaussian beam effects on the accuracy of a droplet sizing method

2D shape reconstruction of irregular particles with deep learning based on interferometric particle imaging

Interferometric particle imaging (IPI) technology is widely used in the measurement of various particles. Obtaining particle shape information directly by IPI is challenging because of the complex relationship between the speckle distribution of interference-defocused speckle patterns and the shape of the corresponding irregular particles. Considering this challenge, we implement a deep learning method based on the convolutional neural network (CNN) to reconstruct defocused images of sand particles with sparse features. We also introduce the negative Pearson correlation coefficient as the loss function. To verify the feasibility of our method, we implemented it to reconstruct defocused images obtained from IPI experiments. Finally, compared with another common CNN-based structure, we confirmed that our network structure has good performance in the shape reconstruction of irregular particles.

Fast and high-accuracy measurement of particle size and location from a linear interferogram

In this paper, we propose, to the best of our knowledge, a novel method of simultaneously detecting and evaluating the location and size of particles from a compression particle interferogram. The 2D position of the particle can be determined with high accuracy, as evaluated by the unidirectional gradient-match with the conjoint to centroid method. The fast-Rife method provides sub-pixel accuracy and high speed for estimating the fringe frequency from the Fourier spectrum of a particle interferogram. The capability mentioned above is well verified using synthetic and experimental data. The computational load falls almost 50%, and the relative error of the measured particle diameter is less than 1.12% for homogeneous solutions of polystyrene spheres of 50 µm and 70 µm. The results demonstrate that the method presented here is considerably promising for its application to a high-density particle field, such as spray, in accurately measuring both the particle size and its location.

On the feasibility of spray-dried eudragit-trehalose microparticles for enteric drug delivery

Enteric infections have long constituted a silent epidemic responsible for hundreds of thousands of deaths around the world every year. Because of the global rise in antibiotic-resistant bacteria and the slow development of new small-molecule antibiotics, alternatives such as bacteriophage therapy have become a much sought-after option in the treatment of enteric infections. However, the administration of therapeutics through the oral route to target gastrointestinal infections poses challenges to dosage formulation because these active ingredients, particularly relatively fragile biological entities, require protection from the stomach's harsh acids. Encapsulation of the therapeutics within a pH-responsive coating capable of surviving low pH conditions has the potential to provide such protection. In this study, we developed a spray-dried powder vehicle capable of withstanding low pH comparable to stomach conditions, using Eudragit® S100 as a protective particle coating and trehalose as a stabilizing excipient for a possible active component. A particle formation model and a monodisperse droplet chain technique were initially used to study the formation process of Eudragit-trehalose composite microparticles at different ratios and in different ratios of water-ethanol solvent, which showed formation of particles with Eudragit shells varying in thickness from 0.13 μm to 0.75 μm. Promising Eudragit-trehalose formulations were subsequently spray-dried and their survival in acidic and alkaline environments studied using a new shadowgraphic imaging method. The results demonstrated that Eudragit was capable of creating a protective shell in the particles irrespective of the type of solvent used to prepare the formulations. The trehalose cores of particles with higher than 5% w/w of Eudragit remained protected after one hour of exposure at pH 2, indicating the potential of Eudragit-trehalose formulations for enteric delivery of drugs.

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.

Interferometric laser imaging for droplet sizing revisited: elaboration of transfer matrix models for the description of complete systems

We report the development of an interferometric laser imaging for droplet sizing (ILIDS) numerical simulator. It is based on the use of generalized Huygens-Fresnel integrals associated to transfer matrices that describe the whole imaging setup. This simulator allows easy simulation of any kind of ILIDS setup. Simulations are shown to be in good agreement with experimental results. This simulator offers important perspectives in the design, realization, and calibration of ILIDS instruments, as airborne instruments, or in situ measurements in flows.

Fast in situ sizing technique for single levitated liquid aerosols

A fast in situ sizing technique for single levitated aerosol particles is presented. It makes use of the analysis of fast-Fourier-transformed vertically polarized Mie scattering patterns from single liquid aerosols levitated in a Paul-trap-type electrodynamic balance. The technique is shown to give reliable results for a test sphere of known physical properties. A first application to aqueous sodium chloride aerosol particles that changed size on humidity variation is presented, yielding good agreement with the full Mie theory.

Determination of size changes of optically trapped gas bubbles by elastic light backscattering

A technique for the determination of size changes of gas bubbles by means of Fabry-Perot resonances in elastic light backscattering and optical trapping is presented. A theoretical description of the interaction of a strongly focused laser beam with gas bubbles is also given. The differences in elastic light scattering for particles with a relative refractive index larger than one and for gas bubbles with a relative refractive index smaller than one are discussed in detail. The results of elastic light scattering experiments verify the theoretical considerations.

Interferometric laser imaging for droplet sizing: a method for droplet-size measurement in sparse spray systems

A full-field, time-resolved interferometric method for the characterization of sparse, polydisperse spray systems is reported. The method makes use of the angular intensity oscillations in the wide-angle forward-scatter region. A pulsed laser is used to illuminate a planar sheet through the spray, which is imaged, out of focus, from the 45°direction. The image consists of a set of out-of-focus spots, each of which represents an individual droplet, and superimposed on which is a set of fringes corresponding to the angular intensity oscillations of that droplet. Macrophotographic recording with high-resolution digitization for image analysis provides a full-field capability. The spatial frequency of fringes on each spot in the image plane is dependent on the diameter of the corresponding droplet in the object plane, and a simple geometric analysis is shown to be appropriate for the calculation of the spatial frequency of fringes as a function of droplet size. Images are analyzed automatically by a software suite that uses Gaussian blur, Canny edge detection, and Hough transforms to locate individual droplets in the image field. Fringe spatial frequency is then determined by least-squares fitting to a Chirp function. The method is applicable to droplets with diameters in the range of several millimeters to several hundred millimeters and number densities of up to 10(3) to 10(4). The accuracy of the method for droplet-size determination has been evaluated by measurements of monodisperse aerosols of known droplet size, and measurements of droplet-size distribution in a polydisperse aerosol produced by a gasoline fuel injector are also presented. An extension of the method, using high-speed photography to measure two components of velocity in addition to size and position, is discussed. A two-wavelength approach may also offer the capability to measure the concentration of model fuel additives in droplets, and the results of a feasibility study are described.

Light scattering by a coated sphere illuminated with a Gaussian beam

<p>The intensity of light scattered by a coated sphere illuminated with an off-axis Gaussian beam is calculated. Results are shown for different beam positions with respect to the sphere. As the beam is shifted further away from the surface of the sphere, the higher-Q morphology-dependent resonances become increasingly important in the backscatter spectra, and the angular scattering intensity becomes smoother.</p> <p>The scattered intensity depends on the beam position, the refractive indices of the core and coat, the radius of the core, and the thickness of the coat. As the beam is moved further away from the sphere, the effect of the core on the scattering intensity decreases. When the incident Gaussian beam is focused outside of a particle with a relatively small core, the scattering spectra and angular scattering patterns become similar to those of a homogeneous sphere having the refractive index of the coat. These calculated results suggest that measurements of spectral scattering and angular scattering patterns for several Gaussian beam positions could be useful for the characterization of coated spheres.</p>