[SI-LIST] Re: Definitions in IPC-T-50
- From: "Mirmak, Michael" <michael.mirmak@xxxxxxxxx>
- To: Jack Olson <pcbjack@xxxxxxxxx>, SI-LIST <si-list@xxxxxxxxxxxxx>
- Date: Wed, 16 Mar 2011 14:31:56 -0600
Jack,
As a matter of historical interest, the definition for Dielectric Constant you
quote from IPC-T-50 is worded very similarly to James Clerk Maxwell's
definition from his 1873 Treatise on Electricity and Magnetism, Vol. 1 (p. 55).
"This property of dielectrics... is also called the Dielectric Constant of the
substance. It is defined as the ratio of the capacity of an accumulator [older
term for capacitor] when its dielectric is the given substance, to its capacity
when the dielectric is a vacuum."
That historical connection may be why IPC-T-50's authors chose to use this
wording, though this is just speculation.
- MM
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Jack Olson
Sent: Wednesday, March 16, 2011 12:18 PM
To: SI-LIST
Subject: [SI-LIST] Definitions in IPC-T-50
Greetings,
IPC-T-50 (Terms and Definitions) is currently under revision, and as I was
browsing the latest entries (ok, I have a boring life...) I noticed the
definition they give for DIELECTRIC CONSTANT.
Dielectric Constant
The ratio of the capacitance of a configuration of
electrodes with a specific material as the dielectric
between them to the capacitance of the same electrode
configuration with a vacuum or air as the dielectric.
See â??Permittivity.â??
While that may be technically accurate, I wonder if it really helps the
reader understand the significance of the term.
As a member of the standards development committee I can submit
recommendations for the next publication, so is this a good definition or
could we do better?
I suppose I should also include the following:
Effective Relative Dielectric Constant
The relative permittivity (See â??Dielectric Constantâ??) of
a mixed media configuration, such as air and the solid
dielectrics used in microstrip, that has the equivalent
electromagnetic wave propagation characteristics of a
single dielectric medium.
Permittivity
The square root of the ratio of the electromagnetic
wave propagation characteristics of free space to that
of the dielectric medium. The permittivity, ï?¥, of a
material is, in general, a complex-valued (has real and
imaginary parts) parameter. The real and imaginary
parts of ï?¥ are given by ï?¥N and ï?¥O. See "Dielectric
Constant."
(the missing characters above look like a backwards "3")
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