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EM Waves -> Frequency domain -> Scattered field: Direction of energy flow

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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


1 Reply Last Post 08.08.2016, 09:07 GMT-4

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Posted: 8 years ago 08.08.2016, 09:07 GMT-4
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.
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.

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