- V. I. Ovod, "Modeling of multiple scattering from ensemble of spheres in a laser beam", submitted to J. Particle & Particle Systems Characterization, 1998.
This paper details the results of upgrading an effective numerical technique (derived for multiple-scattering simulations in photon correlation/cross-correlation with a plane-wave light source) for the modeling of multiple scattering in a laser beam. The off-axis shape coefficients of an arbitrary beam are computed starting from the set of known beam-shape coefficients for an on-axis location by using the addition theorem for the spherical vector wave functions of the first kind. The discussed technique is verified by comparison with localized approximation for a focused Gaussian beam and with Barton's spheres-arbitrary beam interaction theory. An additional advantage of the proposed technique (self-testing of the computation accuracy by comparison of the off-axis beam-shape coefficients evaluated from two different on-axis origins) is demonstrated.
- V. I. Ovod, "Modeling of multiple scattering suppression by a one-beam cross-correlation system", Applied Optics, 37, pp. 7856-7864, 1998.
This paper details the results of adapting a rigorous algorithm, derived for multiple-scattering simulations in photon correlation spectroscopy, for the modeling of multiple-scattering suppression by a cross-correlation system employing one laser beam and two slightly tilted detectors.
The practical significance of the proposed numerical technique is shown for the optimization of an arbitrary design configuration of cross correlation and for prediction of the ideal performance possible with that design. It is shown that the behavior of the coherent factor modeled versus the angle between detectors is in agreement with experimental data and analytical investigation. This factor allows mapping of the spatial extent of the single-scattering and the multiple-scattering speckles. The map holds important information about the optimal displacement of detectors for a given measurement setup and it allows comprehensive investigation of the scattering component suppression even when their magnitudes are small.
- V. I. Ovod,
D. W. Mackowski
, and R. Finsy, "Modeling of the effect of multiple scattering in Photon Correlation Spectroscopy: Plane-wave approach", Langmuir, 14, pp. 2610-2618, 1998.
A technique for numerical modeling of the time autocorrelation function (ACF) of the electric field scattered from a concentrated dispersion, which is illuminated by a plane-wave, has been developed as an approach to estimate the particle dynamics and multiple scattering effects in Photon Correlation Spectroscopy (PCS) measurements. Systematic error of the modeling of the particle dynamics and the error of the ACF estimation was investigated for Brownian free particles. It has been found that systematic error and the decreased dynamic delay-time range of the ACF exponential behavior for free particles are caused by low and high frequency oscillations of integrated functions.
An optimization of the numerical model has been carried out in order to reach a required magnitude of the systematic error and a maximum of the dynamic delay-time range by a minimum of calculation expenditures. The dynamics of an ensemble of particles was generated by a stochastic technique. Practical application of the proposed technique was shown by modeling of the first-order ACF for the depolarized component of the back-scattered electric field. Influence of multiple scattering by interacting spheres on this ACF was investigated for different sphere diameters and dispersion concentrations by using a rigorous multiple scattering technique. This model can be used to further develop photon correlation spectroscopy for the characterization of particles in concentrated and turbid media: in a following paper, the multiple- scattering suppression by one-beam cross-correlation is simulated taking into account geometrical parameters of a setup.
- V. I. Ovod, M. Stintz, and E. Heidenreich, "Modified conventional plane-wave scattering approach to estimate performance characteristics of laser particle-size analyzers", Journal of Modern Optics, 45, pp. 299-314, 1998.
A technique is derived for the rapid engineering simulation of the influence of the main instrumental parameters of a laser particle-size analyzer on its response function and other main performance characteristics. The technique is based on the modified conventional (classical) plane-wave approach. From the methodological point of view, this method incorporates a set of nondimensional coefficients describing the change of the amplitude, duration and shape of a pulsed signal for different particle trajectories in a Gaussian beam with a circular or elliptical cross-section. The above-mentioned performance characteristics as well as the distortion of the signal shape caused by the bandwidth limitation of a photodetector are investigated taking into account the nondimensional coefficients. It was shown that the technique is valid for the modeling of measurements of attenuation and/or near-forward scattering by single particles in the broad practical range of particle diameters. Correctness of the modified technique has been confirmed experimentally and theoretically by comparison with the exact generalized Lorenz-Mie theory. Application expediency of the technique for the rapid investigation of performance characteristics of laser particle-size analyzers is illustrated.
D. F. Nicoli
, J. S. Wu, Y. J. Chang, V. I. Ovod, and K. Hasapidis, "Zeta potential analysis of colloidal systems by ELS, with combined DLS sizing capability", International Labmate, pp. 20-22, 1997.
It has been illustrated that Electrophoretic light scattering (ELS) is a powerful technique which provide a quantitative measure of the charge on colloidal particles in liquid suspension. This technique can be implemented immediately following production of colloidal particles, as a means of estimating their stability against subsequent aggregation.
ELS is especially useful when combined with DLS technology for multi-angle, high-resolution particle size analysis in the same instrument package. The combined multi-angle particle size analysis by DLS and low-angle zeta potential analysis by ELS are realized valid now in a new NICOM 370ZLS instrument. Practical application of this instrument is demonstrated by measurements of variety colloids.
- V. I. Ovod, "Hydrodynamic focusing of the flow of particles in light scattering counters", J. Particle & Particle Systems Characterization, 12, pp. 207-211, 1995.
To reduce errors when measuring sizes of particles in light-scattering counters and phase-Doppler analyzers, the hydrodynamic focusing of particle trajectories in relation to the center of the measurement zone is used. This focusing is effected in a special running-type chamber. Equations describing the mechanical energy of liquid flows running through a running-type chamber have been compiled. By solving a system of such equations, relatively simple equations for engineering calculations of the coefficient of hydrodynamic compression of particle trajectory in relation to the center of the measurement zone have been obtained. Results of experimental research are given and the application of the proposed technique for designing improved running-type chamber with one and two "sheaths" is demonstrated.
- V. I. Ovod,
, "Single-multiple scattering technique to simulate a time-dependent signal of a pulse laser radar with separately located illuminating and receiving platforms", Journal of Modern Optics, 42, No 4, pp. 883-893, 1995.
A technique for calculating the time-dependent signal of a laser radar with a narrow angle of the field of view and separately located receiver and laser is proposed. The laser is assumed to have a short pulse and the results are valid for relatively uniform meteorological situations. This technique is based on the use of a single-multiple scattering model of the aerosol space and "weighted" influence energetic coefficients of elementary volumes of aerosol space, taking account of spatial, energetic, temporary and other parameters of a radiation source and receiver. Taking into consideration a number of approximations, a relatively simple engineering technique to estimate a laser radar signal is described.
- V. I. Ovod, "Monodispersion of the investigated flow in the sorting unit of particle size optical and electrical analyzer", J. Particle & Particle Systems Characterization, 12, pp. 42-45, 1995.
The use of the compact cylindrical piezoelectric transducer in the jet dispersion unit of the sorting system of an optical or electrical particle size analyzer is discussed. Solving two equations for the shift distribution in a piezoelectric transducer with a running fluid chamber, important expressions for the vibrational velocity of acoustic terminal, mechanical impedance, force factor, resonance frequency of dispersion unit and length of the stable part of the jet are obtained. The practical application of this technique is illustrated by calculation of design parameters for an industrial dispersion unit used in an H-50 cytophotometer (Ortho Instruments, USA). Good agreement between theoretical and experimental results is shown.
- V. I. Ovod, "Calculation of the calibration characteristics of optical analyzers of the particle size taking into account of the spectral characteristics of radiation source and photodetector", Sov. J. Opt. Technol., 57, No 12, pp. 29-33, 1990.
The paper details the results of numerical modeling which allow one to increase the measurement accuracy of optical sensors for particle sizing by means of adjusting the choice of spectral characteristics for the radiation source and photodetector.
- V. I. Ovod, "Calculation of the calibration characteristics of fiber diameter optical analyzers taking into account of the spectral characteristics of radiation source and photodetector", Journal of Applied Spectroscopy, 53, No 3, September, pp. 470-475, 1990.
The paper presents the results of theoretical investigations which allow one to increase the accuracy of optical analyzers of the diameter of extended cylindrical objects (fibers) by means of adjusting the choice of spectral characteristics for the radiation source and photodetector.
- V. I. Ovod, "Estimate of the threshold sensitivity of laser particle analyzer ", Measurement Techniques, 33, No 3, pp. 279-283, 1990.
This paper deals with theoretical investigations of the threshold sensitivity of particle-size laser analyzers (LA) based on the light-scattering phenomena. The results obtained permit the relatively simple determination of the structural LA parameters for which the acceptable performance characteristics of LA could be achieved.
The developed technique and the software can be used in design of new laser analyzers/sensors for particle measurements in expanded ranges of their diameters.
- V. I. Ovod, "Calculation of the radiation flux, scattered by fiber, with the convergence of a focused laser beam taken into account", Sov. J. Opt. Technol., 57, No 1, pp. 17-20, 1990.
An improved technique is proposed to model calibration characteristics of laser instruments for in-situ measurement of fiber diameter. Increased calculation accuracy is achieved by taking account of the convergence of a focused Gaussian beam, represented by a superposition of collimated elementary beams, for each of which the rigorous scattering theory is valid separately. The proposed technique can be used for an arbitrary illuminating beam.
- V. I. Ovod, V. Ya. Shlyuko, "Correction of methodological errors of measurements in laser particle size analyzers", Measurement Techniques, 32, No 5, pp. 494-497, 1989.
In our previous papers we illustrated that the most substantial measurement errors in particle-size analysis by light scattering are the methodological ones. We investigated the methodological errors which are caused by the following: nonuniform illumination of the measurement zone by a focused beam, the possible deviation of the particle trajectories from the center of the measurement zone, the simultaneous appearance (coincidence) of several particles in this zone. This paper details the quantitative estimation of the total measurement error taking into account the above mentioned components. The developed technique is a part of the proposed metrological support of particle-size analyzers. This technique can be used in embedded software for error suppression in real time measurement of particle size.
- V. I. Ovod, "Effect of frequency properties of a photoreceiver on the calibration characteristics of laser particle-size analyzers", Sov, J. Opt. Technol., 56, No 3, pp. 129-131, 1989.
The signal waveform in the load resistance of a photoreceiver in a laser particle-size analyzer is investigated theoretically. A quantitative estimate is given for the degree of distortion of the recorded signal by the photoreceiver. Recommendations are made for the proper choice of photoreceiver with the specific parameters of the laser analyzer taken into account and also in order to carry out a correction of the measurement errors caused by the above-mentioned distortions.
- V. I. Ovod, "Calculation of parameters of scattering pulses recorded by fiber diameter laser analyzers", Optical and Spectroscopy, 64, No 2, pp. 402 - 406, 1988.
A technique is proposed to model calibration characteristics of laser instruments for in-situ measurement of fiber diameter. The technique is based on the rigorous simulation of light scattered by a cylindrical object. This technique is used for increasing sensitivity and measurement accuracy of a laser instrument by optimization of its constructive parameters.
- V. I. Ovod, "Calculation of calibration characteristics of laser particle analyzers", Sov. J. Opt. Technol., 54, No 4, pp. 199-202, 1987.
The calibration characteristics of light-scattering particle-size analyzers of various constructions are investigated by using proposed method. The software has been developed within the range, which includes large particles as well as strongly absorbing particles. A high accuracy is achieved for the calculations by using the continued fraction method (instead of traditional recursion formulas) for calculations of the ratios of Bessel functions of a complex variable. The measurement errors, resulting from ignoring the refractive index of the particle material, are determined.
- V. I. Ovod, V. Ya. Shlyuko, "Error in the determination of the particle-size distribution of a powder with a laser analyzer", Sov. Powder Metallurgy and Metal Ceramics, 25, No 12, pp. 956-960, 1986.
The paper details the results of accuracy increasing in particle size measurements performed by light-scattering instruments. Simple expressions have been obtained for log-normal distributed particles to estimate measurement errors cased by deflection of particle trajectories from the center of a laser beam. This technique takes into account the response function of the instrument and parameters of air- or hydrodynamic particle-stream focusing. The technique, which is in agreement with experiments used for error correction in real time.
- V. I. Ovod, V. Ya. Shlyuko, "Calculation of the calibration characteristics of scanning laser analyzers of fibers", Sov. J. Opt. Technol., 53, No. 11, pp. 642-645, 1986.
This paper presents the results of theoretical investigations of calibration curves of scanning laser analyzers for in-situ measurements of fiber diameter. These curves (response functions) represent the dependence of the duration of light pulses, scattered or absorbed by fibers, on their diameter. Simple equations were derived to estimate measurements errors caused by deflection of a fiber from the center of measurement zone. Theoretical results are in a good agreement with experiments.
- V. I. Ovod, "Calculation of characteristics of optical
analyzers of particles with allowance for convergence of nonuniform illuminating beam", Sov. J. Opt. Technol., 53, No 10, 1986.
An improved technique is proposed to model calibration characteristics of laser instruments for particle size measurements. Increased calculation accuracy is achieved by taking account of the convergence of a focused Gaussian beam, represented by a superposition of collimated elementary beams, for each of which the rigorous scattering theory is valid separately. The proposed technique can be used for an arbitrary illuminating beam.
- V. I. Ovod, V. Ya. Shlyuko, "Raising the resolving power of optical and electrical particle analyzers by using divergent deflecting plates", Measurement Techniques, 29, No 1, 65-68, 1986.
Increasing of measurement accuracy and performance of optical and electrical particle analyzers as well as increasing of practical application of the analyzers are achieved by additional option, i.e. by the space sorting of particles in real time. An engineering technique is developed to design the optimal module for particle sorting in space depending on a chosen particle parameter (for example, depending on particle diameter). Performance of the sorting module are improved by using two plates diverging at a certain angle by comparison with parallel ones with fixed dimensions and with given charging and deflecting voltages. The actual parameters of the sorter built in accordance with the proposed technique are in good agreement with the theoretical ones.
- V. I. Ovod, V. Ya. Shlyuko, "High-speed laser analyzer of particle size distribution", Sov. Powder Metallurgy and Metal Ceramics, 24, No 7, pp. 505-509, 1985.
Technique and software are developed to model calibration characteristics of laser flow analyzers operating under conditions of measurement of the duration of light pulses, which arescattered or absorbed by a single particle crossing a laser beam. The information contained in this paper can be employed both in design of new models of laser particle analyzers and in the calibration and estimation of measurement errors of industrial instruments of this type.
- V. I. Ovod, V. Ya. Shlyuko, "Correction of the characteristics of laser analyzers taking account of the radiation flux density distribution", Sov. J. Opt. Technol., 52, No 5, pp. 261-263, 1985.
An engineering technique based on the plane-wave approach is derived to estimate the effects of circular and elliptical Gaussian beams on response functions of optical instruments for particle sizing. This technique can be used to design particle measurement instruments with improved performance characteristics.
- V. I. Ovod, "Effects of coincidence on the measurement error in optical and electrical particle analyzers", Measurement Techniques, 28, No 3, pp. 279-282, 1985.
The paper deals with engineering technique to estimate errors in particle-size measurement instruments caused by coincidence of two or more particles in an electrical or optical field.
Simple equations are derived for the error correction in measurements of log-normal distributed particles. Proposed technique can be used both in embedded software of particle size analyzers and in optimization of design parameters of an analyzer.
- V. I. Ovod, V. Ya. Shlyuko, E. I. Moshkovskiy, A. B. Lyashenko, "A rapid method for determining the particle-size distribution of powders", Sov. Powder Metallurgy and Metal. Ceramics, 23, No 11, pp. 825-828, 1984.
Light scattering instrument is developed for particle size measurements in fine particle technology. Practical significance of this instrument is demonstrated by measurements of titanium carbide powders of particle sizes 3-5, 2-3, and 1-2 micrometers. It is shown that the distribution functions of the particles of titanium carbide powders produced by comminution in a ball mill and subsequent liquid centrifugal classification into 3-5, 2-3, and 1-2 micrometers fractions obey the logarithmic normal law. Measurement results obtained by light scattering instrument are in a good agreement with microscope analysis.
- V. L. Isakov, V. I. Ovod, V. A. Dropha, S. D. Kasmin, E. V. Kolosov, "Analysis of statistical characteristics of the distribution of lymphoma NK/Ly cells obtained by the laser flow cytometry", Experimental Oncology, 6, No 1, pp. 73,74,78, 1984.
Laser cytometer, developed for early cytological diagnostic, was used for investigation of distributions in volumes of NK/Ly ascyte lymphome cells in different periods after inoculation. With the age of tumour the primary peak of distribution shifts to an area corresponding to large cells, but from the sixth day there appears an additional peak of distribution due to an accumulation of a pool of nonproliferating quiscent G0(R1) cells. The obtained data are in good agreement with results of sedimentation fractionation of NK/Ly lymphoma cells. Discrepancies in statistical characteristics of distributions, found by the both methods, are not more than 20%.