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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Is phasor used for Electromagnetic waves, transient of RF module?

Posted 2013年9月24日 GMT-4 21:42 RF & Microwave Engineering, Parameters, Variables, & Functions Version 4.3b 2 Replies

Mengkai Liu
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After completing a simulation, I tried plot imag(temw.Ex) and actually got somthing. It seems that even in a transient analysis, the EM waves are still complex, not real. But actually the concept of phase is ill defined for a transient analysis because a wide range of frequencies exist. Also in the help documents, a phasor is said to be used for harmonic field, Electromagnetic waves, frequency domain. So what does a complex field mean in a transient analysis? This also gives rise to another problem. When I specify surface current by Jx=sigma*Ex, should I use real(sigma*temw.Ex) or simply sigma*temw.Ex? Also for a continuous wave source, should I use cos(omega*t) or exp(i*omega*t)?
2 Replies Last Post 2013年10月1日 GMT-4 16:00
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago 2013年9月25日 GMT-4 08:27
Hi,

also a transient electromagnetic field can be seen as a composition of harmonic signals, each being a complex quantity. So the sum is of course also a complex quantity. It is just more difficult to assign a specific meaning to it.
What you do with the complex components depends on your application. For example in communication technology we use so-called I/Q demodulators to decompose an electronic signal into the real and complex components by multiplying sine and cosine functions to it. This facilitates further signal processing, such as complex FFT.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
Hi, also a transient electromagnetic field can be seen as a composition of harmonic signals, each being a complex quantity. So the sum is of course also a complex quantity. It is just more difficult to assign a specific meaning to it. What you do with the complex components depends on your application. For example in communication technology we use so-called I/Q demodulators to decompose an electronic signal into the real and complex components by multiplying sine and cosine functions to it. This facilitates further signal processing, such as complex FFT. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology
Mengkai Liu
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Posted: 1 decade ago 2013年10月1日 GMT-4 16:00
Got it. Thank you!
Got it. Thank you!

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