The field is a phasor, which contains amplitude and phase information of the field but is independent of
t.
The time dependency of a time-harmonic field can be written in two ways: ejωt or
e−jωt. In COMSOL Multiphysics, the former sign convention
ejωt is used.
where ε' and
ε'' are two material parameters that are named as the
real part and
imaginary part of the relative permittivity, respectively. Inserting the complex relative permittivity in the frequency domain Maxwell–Ampère’s law gives
where the term ωε0ε'' contributes to energy loss that is indistinguishable from the loss quantified by the electrical conductivity
σ. With the sign convention used here, a positive material parameter
ε'' corresponds to a loss although the imaginary part of the complex number
ε' –
jε'', evaluated as
imag(ε' –
jε''), is negative. See
Modeling Losses in the Frequency Domain for details.