# can the imaginary part of complex permittivity be negative?

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#### mtxx

##### Junior Member level 3
The complex permittivity has a real and imaginary part.
Er = Er' + i Er"

the real part is usually referred as the dielectric constant, this must be a positive value,

but the imaginary part, is it always positive as well?

it should be right?
since Q, the quality factor should be a positive value as well.

#### hshah8970

##### Full Member level 2
For mediums that exhibit energy loss for the signal, the imaginary permittivity is positive.
For mediums that have energy gain, imaginary permittivity is negative.

drkirkby

Points: 2