The application of the Mie theory for the evaluation of laser diffraction measurements is appropriate for spherical particles of pure materials with the following properties:
opaque particles |
expected size distribution: 90% below 2µm |
| transparent particles | expected size distribution: 90% below 200µm |
The Mie theory is not suited for non-spherical particles, for mixtures of various materials, and for particles with unknown refractive index.
sensors: |
HELOS family | MYTOS family |
| measuring ranges: | all measuring ranges | all particle sizes |
| range of relative complex refractive index | refraction coefficient 0.1 <= n <= 5.0 |
absorption coefficient 0.0; 1E-5<= k <= 8.0 |
| evaluation: | MIEE | Mie Extended Evaluation Mode |
The basis for applying the Mie theory is the publication by G. Mie[2] in 1908, in which an exact solution of Maxwell's equations was formulated for scattering of electromagnetic waves by spherical particles. This solution is known as the Mie theory. A detailed description is presented in [3].
For the application of Mie theory, the complex refractive index, n of the particles and the refractive index nm of the (non-absorbing) fluid must be known.
The complex refractive indes ist defined by: |
n = np - i * kp |
The relative complex refractive index is defined by: |
m =n/nm |
where |
|
np |
the refractive index of the particle, describes reflection and refraction, |
nm |
the refractive index of the fluid, |
kp |
the absorption coefficien of the particle, describes the absorption, |
i |
the imaginary unity. |
