Discussion Forum

Hi,

We are calculating the optical force within metal scatterers in a PEC bounded structure 2D model. The model is bounded by PEC with PMLs on the left and right sides. We define the background field Eb = E0exp(-jk*x) in the y direction and solve for the scattered fields (Please see the attached mph file).

The problem here is that the size of the mesh element can have significant impact on the integral of the force density. Please see the attached jpeg file. The x-axis indicates the maximum mesh element size in the model, which is the wavelength (633nm) over a number # (You may change the parameter, mesh_d, in the mph to have the same figure). The surface integral 1 calculates the gradient term (integral of the derivative of the solutions) and the surface integral 2 gives the Poynting term. The total is equal to the sum of the gradient and Poynting terms. We can see that the gradient term switches from negative value to positive value when varying the maximum meshing size.

https://www.comsol.com/blogs/how-identify-resolve-singularities-model-meshing/

This article explains that some issues may happen when singularities exist. In the conclusion, point 3 says that it is acceptable when calculating the integral of some quantity including the derivative of the solutions. However, we still have significant errors when applying different meshing. We also removed the sharp corners by filleting the scatterers, but the problem remains, especially for the gradient term.

Do you have any solutions toward this issue? Thanks.