Transient Simulations of a Rectangular Waveguide Coupled to a Cylindrical Cavity

Posted Aug 29, 2024, 10:31 a.m. EDT Electromagnetics, RF & Microwave Engineering 2 Replies

Lucca Arnaud

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I am testing a simulation involving a rectangular waveguide coupled to a cylindrical cavity. The goal is to analyze how varying the port power from 0 to 1 kW every second affects the system. For this, I am running a transient simulation where the port power oscillates between these values every second.

Initially, I attempted to implement this by creating an analytical function that fluctuates between 0 and 1 each second. I then multiplied the port power by this function within the simulation. However, the simulation resulted in an error and did not run at all.

If anyone has experience with similar simulations or has successfully managed transient simulations with oscillating power inputs, I would greatly appreciate any insights or recommendations. I am particularly interested in tutorials or resources that might help resolve this issue and improve our simulation approach.

Please feel free to share your suggestions or direct me to relevant tutorials that could help address this problem.

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2 Replies Last Post Aug 29, 2024, 4:31 p.m. EDT

Robert Koslover Certified Consultant

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Posted: 2 months ago

You didn't mention your waveguide size or approx RF frequency, but I'm going to guess that if you are trying to do this on a time scale that follows the RF waves in detail, then, you have two vastly different time scales involved. From a purely RF perspective, your problem becomes (presumably) entirely steady state (that is, a second might as well be forever) unless your switching time is short enough for transient effects to actually matter. If so, but if you are only interested in the steady state situation, then just solve two problems: the ON condition and the OFF (ok, unlikely to be of much interest) condition. Hey, any chance you are working on modeling a microwave oven? After all, this is how microwave ovens behave. You can find some microwave oven model examples in Comsol supplied example files. Now, if you want to explore the transient filling/response of an RF cavity, then (once again) it is unlikely your cavity fill/empty time scales are anywhere near a second long. So, you would only be interested in either the filling or emptying process itself, during/about a single switching event (right?), in which case, a time-domain transient RF model is appropriate. But, you would only run it for a duration sufficient to cover the physics involved, i.e., nowhere near as long as a second. Indeed, maybe less than a microsecond. Those are my initial thoughts. Perhaps you should post your .mph file to the forum or explain in more detail what you are trying to accomplish?

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Dave Greve

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Posted: 2 months ago

Probably not a microwave as those are not usually cylindrical.

OP should explain what he is trying to learn. Keep in mind that the ring-down (and ring-up) time of a cavity is (very roughly) of the order of the Q multiplied by the period of the excitation. So for a high-Q cavity (say, tens of thousands) a simulation would require a very very long time. Certainly unrealistic, which is why OP should explain what he is after so we can help him find a better way.

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