Team:TU Delft/Model/Q6
Modeling
Question 6:
How does the polysilicate layer covered cell scatters the light?
Far Field Scattering
Introduction
Parallel to the aforementioned model that investigated if focusing the light with bacteria covered in glass is possible we ran additional models to see how the electromagnetic field scatters from our structure further away from it. This is called the Far Field Effect and it describes the distribution of the scattered light’s power far away from the structure. Figure 1 below shows the main characteristics of a far a far field pattern.
From figure 1 two main characteristics of the far field scattering can be seen, the main lobe and the back lobes. The main lobe represents how most of the power is scattered and the minor lobes can be separated to the side lobes and back lobes, they represent the power scattered in undesired directions. Finally, we can see the Half-Power Beam Width (HPBW) that is the angle between the two directions where the intensity of the radiation is half of the beam and the First-Null Beamwidth (FNBW) representing the angular separation between the first nulls of the pattern. (Balanis, 2005)
The Far Field effect even though doesn’t tell us anything about the focal point of the lens gives us valuable information about how the light is scattering far away from the structure. Because we want to apply our biological microlenses to improve the light captured from optical sensors having all the light scattered backwards would be really bad. On the other hand, having a big main lobe with very small to none secondary lobes means that most of the light is scattered to the back side of the lens that is desired.
COMSOL model
The model described in the focusing study was used as a base to determine the scattering of the light. As shown in figure 2 the 3D model is identical to the focus study because we are investigating exactly the same structure under the same conditions. This time a far field domain was defined in the 3D model so we can see how the light is scattered very far away from the structure.
Figure 3 demonstrates the Far Field effect of the scattered light in a 3D plot. We can see that the main lobe is predominant and some very small side lobes can be seen and even less back lobes.
Figure 4 shows a 2D representation of the Far Field effect. Most of the far field graphs are in 2D because it is easier to read. Here it is easier to see that the main lobe is way bigger than the secondary. The secondary lobes are almost non existant.
Discussion
Conclusion
Parallel to the focusing study we investigated the way the light scatters from our polysilcate covered cell. We argued that the scattering pattern is as important for this application as the focusing because we need more ling trapped behind the microlens in the censor. The simulation results showed that the light scatters mostly forward from the lens with little to no back scattering. This means that there is almost no reflection from the microlenses and most of the power is scattered behind the cell. Additionally, we can see that the distribution is very thin forward meaning that there is no dispersion of the energy. Those results in addition with the focusing study indicate that the polysilicate covered cell are a very promising alternative for the conventional micro lenses.
References
- Balanis, C. a. (2005). Fundamental Parameters of Antennas. Antenna Theory : Analysis and Design, 27–114. http://doi.org/10.1007/978-
