# FDTD Frequency Settings

A number of settings related to the time interval are available when using the FDTD solver.

On the Source/Load tab, in the Settings group, click the  Frequency icon. On the Solution frequency dialog, click the Advanced tab. Click the FDTD tab to show the finite difference time domainsettings.
Automatically determine the time interval to be considered
Select this option to automatically determine the time interval1 based on the time signals used by configuration sources, the size of the computational domain and the material properties. An estimate is made for the propagation time required for the time signal to pass through the domain.
Specify the time interval in number of periods
Select this option to specify the maximum time interval and / or minimum time interval in sinusoidal periods. A period is defined as $\frac{1}{{f}_{centre}}$ , where ${f}_{centre}$ is the average between the upper and lower frequencies in the requested band.
Specify time interval in seconds
Select this option to specify the absolute maximum time interval and / or minimum time interval in seconds.
Specify convergence threshold
Select the Specify convergence threshold check box to specify the convergence threshold for the FDTD simulation. For example, to specify a threshold of -100 dB, enter a value of 1e-5. The simulation terminates if the threshold is reached and the simulation time is larger or equal to the minimum simulation time.
1 A time interval is the time duration for which the model is simulated.