Discussion Forum

If you select and use the scattered field formulation, you will normally specify a "background field" (most often, a plane wave). When the computation is complete, the resulting field is the superposition of this background field and any fields that are scattered by the target (typically whatever structures that you put into your computational volume). If you plot the "full field," you will see that resulting overall field. If you plot only the scattered field, then the background field (which is what illuminated the wave-scattering target(s)) is not itself included. And, of course, you can also choose to simply plot just the background field. The scattered field formulation is useful for radar cross-sections, antenna as a receiver, and wave-obstacle scattering problems.

Hi, Robert, I would like to ask you about the definition of the incident wave source of the scattering field. I want to simulate the motion of the microsphere in the optical tweezers system. I used "ewfd - scattering field - gaussian beam - plane wave expansion" to define the incident field, the spot of the Gaussian beam focus at the (0,0,0). But when I use "parametric sweeping" to make the microsphere move in the light field, the spot of the Gaussian beam will also change. Why does this happen? It puzzled me. As shown in the multi-section diagram of the microsphere in the attachment, the spot position at (0,0,0), but when the microsphere moves to the position of (0,5,0), the spot focus is also around (0,5,0). Why does this happen? Sincerely, Miao Peng

Hmm. Based on the image you provided, you appear to be plotting the total electric field magnitude. Now, I don't know much about optical tweezers and microspheres, but if you want to see a plot of the background field (i.e., the gaussian beam), then you should plot that instead. To do that, I suggest that you look in the pull-down menus for the various output field plotting options and see what happens when you choose them (I expect that the background field will be in the list of options) instead. I can only assume that the total field has its magnitude concentrated around the microsphere, and thus it makes some sense to me that this could be seen as "moving" with it. That's my guess, anyway. Good luck.

Hi, Robert, thanks for your kindness help. According to your suggestion, I have made the background field multi-section diagram. I analyzed the change of the spot of Gaussian beam in two cases: without scatterers put in (in uniform water medium), with scatterers put in. The scatterer is a silica microsphere with a diameter of 1 um. Your assume that the total field has its concentrated energy around the microsphere, and thus it makes some sense to me that this could be seen as "moving" with it. But the same thing happens when there are no scatterers. That is, I made the center position of the whole geometric model change (in the absence of scatterers ), and the position of the spot was set as (0,0,0). With the change of the geometric center, the spot of the Gassian beam would also change. I put this phenomenon in the attachment with the form of video, and I hope to get your help. Sincerely, Miao Peng