fluctuating autoshutoff level

- July 26, 2023 at 6:07 am
  
  Yixuan Zhang
  Subscriber
  
  I am using varfdtd to simulate a vernier resonator. The simulation size is about 100um * 100um. I set the simulation time very long(200000fs), and also enable the autoshutoff level min of 1e-05. When I run the simulation, the autoshuoff level decreases to around 4~8e-3 very quickly and then start to fluctuate and decrease very slowly. After 12 hrs, the autoshutoff level can only decrease to about 0.0008. does this phenomenon make sense?
- July 28, 2023 at 5:59 pm
  
  Guilin Sun
  Ansys Employee
  
  This is most likely that such device has some strong resonance, which needs long time for the resonant signal to decay.
  If you do not need very accurate transmission and reflection at the resonance, you can use "time apodization" in the monitor.
  Please also check if the PML is thick enough. Occasionally PML may also cause fake resonance. However in such case changing the simulation span the resonace will shift, which can be differentiated from the real resonance.
  Please refer to this post for more:
  Ansys Insight: Slow convergence in FDTD