About the refractive index problem of laser particle size analyzer

The Mie theory is a theory that considers the absorption of light by a substance and various electromagnetic effects to calculate the scattering intensity. Therefore the refractive index is an indispensable parameter for Mie calculations. Usually in software design, several models with different refractive index are calculated to be suitable for particles of different substances. The refractive index is therefore generated prior to testing and not as a result of particle size measurements.

    Therefore, when using a particle size analyzer to test, you first need to determine the refractive index of the sample. The average user simply does not know the accurate parameters of the refractive index of the product to be measured (according to the search, there is currently no instrument that can accurately measure the refractive index of the powder. The refractive index in the refractive index table It only represents the refractive index of the substance, not the refractive index of the powder. There is a big difference between the two), so I have to randomly choose one for calculation, and change to another if the calculation is not satisfactory. Isn't it doubtful how accurate such a refractive index is?

In fact, research results show that the accuracy of particle size measurement is not only related to the refractive index, but also to the particle shape, particle surface state, and particle concentration. The impact of the latter two is not less than that of the former. For this reason, Winner's instruments not only prepare 16 models of different refractive indexes, but also provide specialized software for comprehensive calibration of particle size. In order to be responsible to the user and avoid causing misunderstandings to the user, Winner Company did not indicate the refractive index in the test report because the refractive index cannot accurately represent the characteristics of the sample. It's just a pattern code used in calculations.

    Some people say that if there is no refractive index in the test report, it is not Mie theory. This statement is not comprehensive. Some instruments use the Fraunhofer diffraction theory (such as the German company Shinpartek), which of course does not require a refractive index. Although some instrument companies adopt the Mie theory, they are unwilling to indicate the refractive index due to considerations of responsibility to users. Obviously Winner belongs to the latter.