This 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 (s_d)
For a given total signal duration of s_d, 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 (d_t)
The time step, d_t, will be given by:
where f_max is the highest frequency to be simulated.
Number of time samples (N_t)
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 f_min to f_max. 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.
Related content
Altair Feko: How to Calculate the Time Response for a Given Input Signal in POSTFEKO
