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EM Waves -> Frequency domain -> Scattered field: Direction of energy flow
Posted Aug 6, 2016, 12:02 p.m. EDT 1 Reply
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I am looking at energy flow calculated using the scattered field formulation, but the direction i get is opposite of what i expected. As a simple example, lets consider a plane wave with the electric field polarized along the y-axis propagating in the +z direction, e.g. [1]
E_b = [0, E0*exp(i*kz*z), 0]
where kz = 2*pi/lmb (in air) and E0 is the field amplitude. Now, since the wave in propagating in the +z direction, i would expect the energy flow also be in the +z direction. However, the calculated energy flow in COMSOL is in the -z direction, see attached MWE.
Can anybody enlighten me what i have done/understood incorrectly?
[1] en.wikipedia.org/wiki/Plane_wave#Complex_exponential_form
E_b = [0, E0*exp(i*kz*z), 0]
where kz = 2*pi/lmb (in air) and E0 is the field amplitude. Now, since the wave in propagating in the +z direction, i would expect the energy flow also be in the +z direction. However, the calculated energy flow in COMSOL is in the -z direction, see attached MWE.
Can anybody enlighten me what i have done/understood incorrectly?
[1] en.wikipedia.org/wiki/Plane_wave#Complex_exponential_form
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1 Reply Last Post Aug 8, 2016, 9:07 a.m. EDT
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Posted:
8 years ago
After some more research i found out that the definition of a forward propagating wave differs between different fields of science. Indeed the usual definition for a physicist (like me) is
E_b = [0, E0*exp(i*kz*z), 0],
but engineers and mathematician tend to use a slightly different convention
E_b = [0, E0*exp(-i*kz*z), 0].
Apparently COMSOL adapts this convention and hence the energy flow is opposite of what a physicist would expect.
E_b = [0, E0*exp(i*kz*z), 0],
but engineers and mathematician tend to use a slightly different convention
E_b = [0, E0*exp(-i*kz*z), 0].
Apparently COMSOL adapts this convention and hence the energy flow is opposite of what a physicist would expect.