Should I use the RMS, the peak, or the instantaneous value to specify sources for electromagnetic fields?

Solution Number: 878
Title: Should I use the RMS, the peak, or the instantaneous value to specify sources for electromagnetic fields?
Platform: All Platforms
Applies to: AC/DC Module, RF Module, Acoustics Module, Batteries & Fuels Cells Module
Versions: All versions
Categories: Physics
Keywords: Testing log feature

Problem Description

Should I use the RMS, the peak, or the instantaneous value to specify sources for electromagnetic fields? How can I specify the phase angle?

Solution

The COMSOL Multiphysics formulation uses complex fields when solving time-harmonic problems. This means that the electric field E is given as



where is the complex electric field that you are entering, is the angular frequency, is time, and is the imaginary unit.

Whenever you specify a source field you can input a complex number Ec, where abs(Ec) is the peak value, and real(Ec) gives you the instantaneous value at .

This goes not only for the electric field, but for any time-harmonic input to your model. So, to define for instance an external current density, a magnetic field, an acoustic pressure, or an electric potential, with an RMS value of 1 and a phase angle of 30°, enter the expression:

sqrt(2)*exp(j*30*pi/180).


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