Re: [SI-LIST] : Dielectric loss

Nirmal Jain (
Thu, 18 Sep 1997 17:20:21 -0400

Dear Hans,

One straight forward explanation could be that the dielectric
has a finite conductivity and due to that there a conduction
current flowing in the dielectric, which causes losses in the
dielectric. The dissipation factor (loss tangent), tan delta
is given by (G/wC).

In a lossless dielectric, if the voltage changes sinsuoidally
the current leads the volatge by 90 degrees, which means
there is no loss. For real materials, there invaribaly is a
delay in polarization and the current leads the voltage
by 90-delta degrees where delta is loss angle.


Nirmal wrote:
> The term "lossy dielectric" implies an energy loss or joule heating in
> the dielectric material. Could someone out there explain the actual
> loss mechanism? Is is a paramagnetic or molecular vibration?, or?.. I
> understand the "loss tangent which is the ratio of the e" to e'
> (imaginary over real) but that does not explain the physical mechanism
> of the energy conversion. My book (quote: "it is obvious that the
> imaginary part is associated with power loss or dissipation within the
> dielectric"...) well, that is not so obvious to me! The book further
> implies that the loss is associated with the resonant frequency of
> polarization. The book, EM waves and radiating systems by E. Jordan,
> eloquently discusses "electronic polarization", and "microscopic
> bodies that contribute to the polarization effect".. but does not
> actually give a intuitive explanation.
> Thanx in advance
> Hans Mellberg

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