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Variable Frequency Microwave

Posted 05.06.2014, 06:08 GMT-4 RF & Microwave Engineering, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3b 2 Replies

Silvernine
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Hello! I just started using COMSOL and I have been working on simulating a microwave wave guide with a dielectric material and been using a static frequency of 8.5 GHz and all my analysis related to that have been done. I now wanted to have an analysis to see the effect of a variable frequency wave generator upon a dielectric material. Basically instead of just putting 8.5 GHz through the wave guide, the microwave generator will put a microwave frequency that varies with time from 8.2 GHz to 12.4 GHz and then back again to 8.2 GHz. The problem is still a Frequency-Transient problem.

Initially I set my frequency (f0) as a parameter with the expression of 8.5[GHz]. I deleted that and instead created a new variable "f0". I also created a new parameter "t = 0[s]" so that COMSOL knows that "t" has been initiated. The new function was a triangle waveform "wv1". The expression for "f0" then becomes "10.3+(2.1*wv1(t[1/s]))[GHz]". However, it seems I'm missing something else as I keep getting an error:
Failed to find consistent initial values.
Last time step is not converged.

How should I proceed. I have read various threads and tried many different ways but I have not succeeded. Perhaps there is a smoother way of approaching this?

Thank you.
2 Replies Last Post 10.06.2014, 17:17 GMT-4
Robert Koslover Certified Consultant
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Posted: 1 decade ago 07.06.2014, 19:30 GMT-4
If all you want to do is explore different frequencies, don't introduce a time parameter at all. Just do a frequency domain problem and specify a range of frequencies. But if you truly must have an explicit time dependence, then you'll need to use the transient formulation, in which case you should specify a time-dependent waveform as your input. Note that such a waveform is technically an FM (frequency modulated) waveform. Look up frequency modulation at en.wikipedia.org/wiki/Frequency_modulation .
If all you want to do is explore different frequencies, don't introduce a time parameter at all. Just do a frequency domain problem and specify a range of frequencies. But if you truly must have an explicit time dependence, then you'll need to use the transient formulation, in which case you should specify a time-dependent waveform as your input. Note that such a waveform is technically an FM (frequency modulated) waveform. Look up frequency modulation at http://en.wikipedia.org/wiki/Frequency_modulation .
Silvernine
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Posted: 1 decade ago 10.06.2014, 17:17 GMT-4
Thank you very much! That is a much better and simpler way than what I attempted.
Thank you very much! That is a much better and simpler way than what I attempted.

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