Menu

Discussion Forum

New Discussion
查找

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Units Electromagnetic Waves, Frequency domain

Posted 2021年1月7日 GMT-5 05:45 Wave Optics Version 5.5 2 Replies

Johannes Schultz
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi, i am wondering about the unit declaration of the quantities using the Electromagnetic Waves, Frequency domain module of COMSOL. E.g., for the electric field V/m (correct unit in the time domain) is indicated by COMSOL but i am expecting Vs/m because we are in frequency space. Is the calculated field automatically transformed back (inverse fourier transformation) to the time domain after the calculation by COMSOL? It would be nice if someone could explain me this behaviour.

Thanks, JS

2 Replies Last Post 2021年1月8日 GMT-5 12:40
Lars Dammann COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 4 years ago 2021年1月7日 GMT-5 10:13

Hi,

COMSOL uses phasors in the frequency domain, so if you type as a voltage somewhere, this actually gets interpreted as . You can get the physical voltage back by inserting a time t and applying a real operator, so the expression above becomes . To phase shift the voltage, you can write e.g. which then becomes a sine function instead of a cosine, and so on.

So the magnitude of the complex values is really the amplitude of the harmonic signal and the complex phase is the phase shift relative to the global phase. So since it is an amplitude, we can measure it in V.

There is also a chapter on phasors in the reference manual or possibly the AC/DC user's guide, you can find it by just searching the help for "phasor".

I hope that makes it more clear, let me know if you have any questions.

Hi, COMSOL uses phasors in the frequency domain, so if you type 1V as a voltage somewhere, this actually gets interpreted as 1V\cdot e^{i\,\omega\, t}. You can get the physical voltage back by inserting a time t and applying a real operator, so the expression above becomes 1V\cdot\cos\left(\omega\, t\right). To phase shift the voltage, you can write e.g. -1iV which then becomes a sine function instead of a cosine, and so on. So the magnitude of the complex values is really the amplitude of the harmonic signal and the complex phase is the phase shift relative to the global phase. So since it is an amplitude, we can measure it in V. There is also a chapter on phasors in the reference manual or possibly the AC/DC user's guide, you can find it by just searching the help for "phasor". I hope that makes it more clear, let me know if you have any questions.
Johannes Schultz
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 4 years ago 2021年1月8日 GMT-5 12:40

Thanks a lot for the explanation. Now everything is clear.

Best, JS

Thanks a lot for the explanation. Now everything is clear. Best, JS

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content