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Abstract

The invention provides a method and a system for measuring geometric properties, such as diameter, shape and surface roughness of single rough particles by an optical method. The particle may be immersed in a gaseous or liquid fluid. A volume of the fluid, containing the particles to be measured, is illuminated by a beam of coherent electromagnetic radiation, resulting in a distribution of scattered radiation with a speckle structure. This distribution is detected with a one-dimensional or two-dimensional image detector. An autocorrelation function RI(r) of the detected intensity distribution is calculated, and from the position .delta.r of its first zero the diameter d.sub.P of the scattering particle is evaluated based on I, the wavelength of the electromagnetic radiation, and Z.sub.0, the distance from the particle to the detector. The system to perform this method comprises a radiation source, which is preferably a laser, to illuminate a measuring volume, and an array or matrix detector arranged to receive the backscattered light. The detected intensity distribution is converted to binary data and a signal processing unit calculates the autocorrelation function of the detected intensity distribution to yield the particle size. In a preferred embodiment of the invention, the radiation scattered from a particle is relayed to the detector by an optical system comprising a set of lenses, a polarizer and a pinhole. The surface roughness of the particle under investigation is estimated from the contrast of the measured intensity distribution. The shape of the particle follows from an evaluation of the calculated diameter values along a set of angular directions .phi.=0 . . . .pi..

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First Claim