On Mar 4, 2008, at 9:51 AM, Robert Rehammar wrote:
> So it seems to be the case here that different amounts of energy
> enters
> from the source depending of in what dielectric it sits. How can I
> understand this?
This is a property of Maxwell's equations that has nothing to do with
Meep per se, but seems to be one of the most common confusions of Meep
users.
When you specify a source, you are specifying a current in Maxwell's
equations. The same current, however, radiates different amounts of
power depending on the surrounding geometry/material.
One way of looking at this is that the radiated power depends on the
local density of states (in fact, the two are directly proportional
for a fixed dipole current source), and the local density of states
varies with geometry/material. (In a homogeneous material with index
n, in d dimensions, if I recall correctly the density of states goes
as n^{d-1}.)
Equivalently, what you are looking at in the radiation from a
localized current is essentially the Green's function, and the Green's
function depends on geometry.
Equivalently, the current you are putting into Maxwell's equations is
*free* charge current. There are also *bound* charges associated with
the polarization of the materials. A given free current in vacuum
corresponds to less power input/output than the same current in a
dielectric material, because in the latter case you have to supply
energy to move both the free charges and the bound charges.
Regards,
Steven G. Johnson
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