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docs:become [2020/04/22 23:04] pklapetek |
docs:become [2020/04/23 08:17] pklapetek |
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| source is now inside the NFFF domain. This leads to a diffraction effect due to finite source size, which is however small and has minor impact on the result. | source is now inside the NFFF domain. This leads to a diffraction effect due to finite source size, which is however small and has minor impact on the result. | ||
| - | The results show that the correspondence between the 19 apertures manual model and the periodic model with evaluating 19 near-field repetitions for the far field calculation are comparable to about 4 percents. Better correspondence could be obtained if the manual domain would be further extended (as seen from the smaller domain calculations trends). | + | The results show that the correspondence between the 19 apertures manual model and the periodic model with evaluating 19 near-field repetitions for the far field calculation are comparable to about 4 percents. Better correspondence might be obtained if the manual domain would be further extended or if the periodic calculation is run with bigger distance between the individual elements (boundaries, objects, integration domains) as observed always with NFFF. |
| {{:docs:validation.png?800|}} | {{:docs:validation.png?800|}} | ||
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| The **Become benchmark grating** was setup the same way as the above test example. | The **Become benchmark grating** was setup the same way as the above test example. | ||
| The grating was now formed by silver, using the PLRC metal handling approach. | The grating was now formed by silver, using the PLRC metal handling approach. | ||
| + | We have only increased the size of buffer between the computational domain border | ||
| + | and the studied structure which is well known approach how to improve simulations response. | ||
| All the other parameters we kept from the previous case. Normalization was again | All the other parameters we kept from the previous case. Normalization was again | ||
| done via reflection from a perfect electric conductor surface. | done via reflection from a perfect electric conductor surface. | ||
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| The image below shows the normalized angular dependence of the diffraction from the (finite size) grating. | The image below shows the normalized angular dependence of the diffraction from the (finite size) grating. | ||
| - | {{:docs:result_twomethods.png?800|}} | + | {{:docs:result_twomethods_biggerbuffer.png?800|}} |
| - | When inspected in detail, it can be seen that there is a difference of about 3 percents between | + | When inspected in detail, it can be seen that there is only a difference of about 0.2 percents between the two methods output for the first diffraction maximum, which was confirmed as |
| - | the two methods output for the first diffraction maximum, similarly to the PEC case. | + | a positive effect of bigger distance of the computed structure from boundaries. |
| - | Again we expect that this difference is given by the difference in models - big single calculation | + | A bigger problem is, that the diffracted intensity is about 0.140 of the incident intensity, |
| - | has to work with limited source size and repeated calculations work with infinitely periodic field | + | |
| - | even if they are not infinitely periodic. | + | |
| - | A bigger problem is that the diffracted intensity is about 0.147 of the incident intensity, | + | |
| which is less than expected (the expected value is 0.186). Something has to be wrong. | which is less than expected (the expected value is 0.186). Something has to be wrong. | ||
| Line 108: | Line 107: | ||
| To compare its impact on results, here is a list of different metal model settings and results: | To compare its impact on results, here is a list of different metal model settings and results: | ||
| - | * the fitted metal setting: 6 1.03583 0 1.37537e+16 1.25733e+14 2.1735 -0.504659 7.60514e+15 4.28131e+15 0.554478 -1.48944 6.13809e+15 6.62262e+14 means n=(0.129 + 3.87i) and leads to first order diffraction intensity of 0.147 | + | * the fitted metal setting: 6 1.03583 0 1.37537e+16 1.25733e+14 2.1735 -0.504659 7.60514e+15 4.28131e+15 0.554478 -1.48944 6.13809e+15 6.62262e+14 means n=(0.129 + 3.87i) and leads to first order diffraction intensity of 0.140 |
| - | * default metal setting: 6 0.89583 0 13.8737e15 0.0207332e15 1.3735 -0.504659 7.59914e15 4.28431e15 0.304478 -1.48944 6.15009e15 0.659262e15 means n=(0.036 + 4.147i) and leads to first order diffraction intensity of 0.150. | + | * default metal setting: 6 0.89583 0 13.8737e15 0.0207332e15 1.3735 -0.504659 7.59914e15 4.28431e15 0.304478 -1.48944 6.15009e15 0.659262e15 means n=(0.036 + 4.147i) and leads to first order diffraction intensity of 0.143. |
| The easiest way how to check the metal properties is to calculate the reflectance of a bulk. | The easiest way how to check the metal properties is to calculate the reflectance of a bulk. | ||
| This uses very similar geometry to our calculation (TSF source, periodic and CPML boundaries), | This uses very similar geometry to our calculation (TSF source, periodic and CPML boundaries), | ||
| so we can expect that there are not many additional potential error sources when comparing to our calculation. | so we can expect that there are not many additional potential error sources when comparing to our calculation. | ||
| - | |||
| - | First of all, error in the reference value (PEC reflection) is below 0.001 percent. This certainly | ||
| - | cannot affect our results. | ||
| Reflectance of the default metal for this particular voxel spacing and other settings is 0.983 | Reflectance of the default metal for this particular voxel spacing and other settings is 0.983 | ||
| Reflectanceof the fitted metal model is 0.9587. | Reflectanceof the fitted metal model is 0.9587. | ||
| Result from the Filmmetrics reflectance calculator is 0.9678, which is something in between. | Result from the Filmmetrics reflectance calculator is 0.9678, which is something in between. | ||
| - | This is probably also not the source of problem (however might be compared to reflectance | + | Finally, error in the reference value (PEC reflection) is below 0.001 percent. This certainly |
| + | cannot affect our results. | ||
| + | So, this all is probably also not the source of problem (however might be compared to reflectance | ||
| coming from FEM). | coming from FEM). | ||
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| ===== Summary ===== | ===== Summary ===== | ||
| + | |||
| + | So far the result is not the expected value, which needs to be investigated first. Many of the convergence studies, or studies of impact of different simulation settings on the results were performed already or could be easily re-run when this is more clear. | ||
| The sensitivity of 2D calculations results on the settings (computational domain size, time step, near-to-far field transformation, et.c) is in the order of few percent, the dominant effect of this uncertainty is the near-to-far field transformation. This does not affect the cases when these conditions are kept same in a series of calculations (so relative changes can be calculated with much higher accuracy), however it certainly affects the absolute values, e.g. when comparing a single calculation to completely different calculation or experimental data. | The sensitivity of 2D calculations results on the settings (computational domain size, time step, near-to-far field transformation, et.c) is in the order of few percent, the dominant effect of this uncertainty is the near-to-far field transformation. This does not affect the cases when these conditions are kept same in a series of calculations (so relative changes can be calculated with much higher accuracy), however it certainly affects the absolute values, e.g. when comparing a single calculation to completely different calculation or experimental data. | ||
docs/become.txt · Last modified: 2020/04/24 12:27 by pklapetek
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