Altair Feko: What are the guidelines for defining a time signal in POSTFEKO?

Esti
Esti
Altair Employee
edited October 21 in Altair HyperWorks

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 (image)

For a given total signal duration of image, the lowest frequency to be simulated is given by:

image

The total signal duration should allow for the response signal to decay sufficiently before the time signal repeats.

image 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 (image)

The time step image will be given by:

image

where image  is the highest frequency to be simulated.

 

Number of time samples (image)

The number of time samples is derived from:

image

 

Number of positive frequency samples

The number of frequency samples (positive) excluding zero is given by:

image

 

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 image to image. 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.

 

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