Altair Feko: What are the guidelines for defining a time signal in POSTFEKO?
Altair EmployeeThis articles discusses the guidelines for defining a time signal in POSTFEKO.
The time signal that can be created depends on the simulated frequency range and frequency sampling.
Follow these basic guidelines when defining a time signal:
Total signal duration (
)
For a given total signal duration of 
, the lowest frequency to be simulated is given by:
The total signal duration should allow for the response signal to decay sufficiently before the time signal repeats.
The duration of the response signal decay is model dependent and only required when the signal is not intended as a repeating time signal pulse.
Time sampling (
)
The time step will be given by:
where 
is the highest frequency to be simulated.
Number of time samples (
)
The number of time samples is derived from:
Number of positive frequency samples
The number of frequency samples (positive) excluding zero is given by:
Bandwidth calculation of time signals
The total power content of the time signal is calculated as follows:
Pt = P1 + P2 + Pi + ... + Pn
where Pi = (SpectrumValue(F(i-1))^2 + SpectrumValue(F(i))^2) * 0.5 * (F(i) - F(i-1))
The bandwidth of the time signal is then calculated as follows:
- BW = [Fstart, Fend]
- where Fstart = Fi for the lowest frequency where Pi > 10% * Pt
- and Fend = Fi for the lowest frequency where Pi > 90% * Pt
In summary, the model should be simulated from 
to . The POSTFEKO power bandwidth calculation as described above gives an indication of the frequency range where most of the signal power is contained.
POSTFEKO will use this power bandwidth to give a warning when there is insufficient overlap between the simulated frequency range and the power bandwidth.