7.4     Energy simulation stop criterion

In electromagnetic simulation, the compromise between simulation time and results accuracy has always been important issue. Typically the computation process is stopped by the user upon the decision that the simulation results, e.g. S-parameters have stabilised. In practise it is rather difficult to define a general method for determining a priori the number of FDTD iterations limit, at which the computations can be stopped (also automatically) to assure accurate results in all possible cases. Exemplary method was introduced for Amigo but unfortunately, it may fail in some cases.  

The effective solution here is monitoring the electromagnetic (EM) energy in the calculation model and stopping the simulation when it decays to a certain level. This allows reducing the number of performed FDTD iterations without reducing computational accuracy. This solution is available in QuickWave as Energy Stop Criterion feature. The Energy Stop Criterion is enabled for pulse excitations with finite duration time. For such excitation, energy available in the circuit decays in time and after reaching some threshold level, further FDTD computation does not contribute to any significant increase of results accuracy and the simulation can be stopped.

The Energy Stop Criterion feature allows user to determine the relative energy threshold level, at which the computation should be suspended. The user is also provided with a mechanism of monitoring the S-parameters fluctuation level, where the level of those changes may be used as an additional stop criterion. QuickWave delivers also some kind of security procedure that may be enabled by the user and which allows suspending the calculations after N iterations, corresponding to the duration (expressed in FDTD iterations) of defined number of exciting pulses, despite the required energy decay was not achieved.

Detailed discussion about all options available for Energy Stop Criterion is given in Energy Stop Criterion.

If the Energy Stop Criterion feature has been enabled, its subsequent stages are logged in the Simulator Log window.

The Energy Stop Criterion feature is currently not supported for projects with excitation defined through the text file as described in User defined signal excitation.