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The current research projects of the department focus on the characterization of drop size using Mie Scattering Imaging and Holography as well as the online measurement of the refractive index and/or refractive index gradient using rainbow spectroscopy.

Since optical characterization methods are in the focus of our work, which are continuously developed further on the basis of simulation calculations, we are working on two complementary scattered light simulation methods. The Nullfield Method with Discrete Sources (NFM-DS) has been developed into an effective and powerful method to calculate the light scattering of complex particles and particle systems (fibers, disks, particles with inclusions, composite particles). In cooperation with a research group at Moscow State University, Moscow, research is being conducted at the Discrete Sources Method (DSM) to characterize nanoparticles. For this purpose, the non-local effects occurring below a particle size of 5 to 10 nm must be considered in theory.

The Department of Powder and Particle Measurement Technology deals with particle measurement issues in process engineering. In the following, the main areas of work are briefly described.

 

 

Drop charaterization

The current research projects of the department focus on the characterization of drop size using Mie Scattering Imaging and Holography as well as the online measurement of the refractive index and/or refractive index gradient using rainbow spectroscopy. These developments are used to investigate the combustion of single drops, which are generated by a specially developed piezoelectric drop generator.


Aerosol charaterization

nullIn addition, methods for the optical characterization of nanoparticles, nanocomposite particles and their aggregates are developed, which are based on the evaluation of scattering patterns or use spectroscopy. Since the focus is on optical characterization methods that are continuously being further developed on the basis of simulation calculations, two complementary scattered light simulation methods are being worked on.


The Nullfield Method with Discrete Sources

Efficient numerical simulation programs are needed to understand the scattered light interactions in optical particle measurement technology and to develop new measurement methods. The Nullfield Method with Discrete Sources (NFM-DS) has been developed into an effective and powerful method to calculate the light scattering of complex particles and particle systems (fibers, discs, particles with inclusions, composite particles). The well-known T-Matrix method for the calculation of light scattering of particles is advantageous compared to other methods, because all information about the scattering process is contained in a calculated T-Matrix. Calculated T-matrices can thus be further used for further calculations (such as orientation determination).


Invariant Imbedding T-Matrix Method

In order to be able to simulate the light scattering of other complex particles (such as overlapping spheres), the Invariant Imbedding T-Matrix Method is currently being developed. Within the project, the Invariant Imbedding T-Matrix Method is systematically investigated from theory, algorithms and implementation to find new recursive algorithms and to make the method more efficient. A complete 3D variant of the method will be developed and implemented, which is currently not yet available and thus goes far beyond the current state of research.


Discrete Sources Method

In cooperation with a research group at Moscow State University, Moscow, research is being conducted at the Discrete Sources Method (DSM) to characterize nanoparticles. For this purpose, the non-local effects occurring below a particle size of 5 to 10 nm must be considered in theory.


Total internal reflection microscopy (TIRM)

Since its invention in the mid-1980s, Total Internal Reflection Microscopy (TIRM) has become an extremely sensitive technique for measuring the interaction between colloidal particles and a planar surface. Resolution down to the femtonewton range is achieved. For the analysis of the measured signals with the TIRM method, a precise knowledge of the particle-wall distance dependence of the intensity of the scattering is required. The Nullfield Method with Discrete Sources (NFM-DS) is used to simulate the necessary TIRM calibration curves and to simulate the optical imaging of a non-spherical particle in an evanescent field.


ScattPort

In current international research, an efficient and rapid exchange of information is required. Novel software and Internet technologies as well as the possibility of rapid dissemination of information via the Web offer scientists easy access to information of all kinds. However, much valuable information is often hidden and therefore hardly accessible to the community. In order to continuously provide the stray light community with current sources and keep them up to date, an information portal (ScattPort) was set up as part of a project funded by the German Research Foundation.  A workshop on light scattering is held regularly at the beginning of each year (Bremen Workshop on Light Scattering).