Mary,
Probal\bly the truest definition I've come across is in IPC-2141 and some
of the other IPC specs. In IPC-2141 look at section 3.4.2 thru 3.4.3.
Here's a partial:
3.4.2 Relative permittivity (Dielectric Constant)
The relative permittivity, Er, of a substance is defined as the ratio of the
permittivity of the material to the permittivity of free space, which has a
value of 1.00. Dielectric constant is the term in common use in industry
even though "dielectric constant" varies with certain parameters. Factors
that influence the relative permittivity of a givcen material include the
electrical frequency at which the measurement is performed, temper-
ature, and extent of water absorption.
(snip)
The effective relative permittivity, Er', is the relative permittivity that s
experienced by an electrical signal transmitted along a conductive path.
etc,etc,etc
I've heard the arguements in interpertation before also, so I always keep
this spec handy.
Hope this helps,
Mitch Morey
Sr PCB Designer
ComStream Corp
San Diego CA 92121
Email: [log in to unmask]
Check out: www.comstream.com
>>> Doug McKean <[log in to unmask]> 02/09/98
01:54pm >>>
You're on.
Permittivity is also dielectric constant.
Ok, so what? Time for real simple terms.
Think of it like lens. It's the ability of a material
to *focus* an electric field (electric lines of force)
as a result of electric charges.
The higher the dielectric constant, the better the
capacitor. A material with a dielectric constant or
permittivity of 4 is four times better a capacitor
than say a capacitor with just air between the plates.
The *air* cap will have a voltage breakdown at 1/4
the voltage that the cap with a dielectric constant
has across it. Higher dielectric constants increases
the electrical strength of the material.
You can do the same type of analogy with permeability.
Permeability is the ability of a material to focus
*magnetic* lines of force. And so forth ...
That do it fer ya?
Regards, Doug
----------
> From: [log in to unmask]
> To: [log in to unmask]
> Subject: [DC] Permittivity
> Date: Monday, February 09, 1998 4:03 PM
>
> To: IPC
> Date: 2/6/98
> Re: Permittivity
>
> From: Mary Sugden [log in to unmask]
> The Copper Connection, Inc.
> Ph(408) 970-9838 Fx(408) 970-9184
> hhtp//www.copperconn.com
>
________________________________________________________________
>
> I would like to have a clear and consise definition for the term
> "permittivity" as it relates to dielectric materials. I have
> read no less than fifty different definitions and descriptions
> and still do not have a clear and consise definition. In
> several of the references, it simply states, ...see dielectric
> constant. However, the other descriptions and definitions of
> permittivity lead me to believe there is a subtle difference
> between the two terms. The definitions for relative dielctric
> constant are fairly clear and consistent between the various
> references I have used, but the definitions for permittivity are
> ambiguous and inconsistent.
>
> For the best definition, I will send the dude or dudette a
> nice bottle of California White Zinfandel
>
> _________________________ Shareware
____________________________
>
>
> "Will you teach your children what we have taught our children?
> That the Earth is our mother? What befalls the Earth, befalls
> all of the sons and daughters of the Earth.
>
> This we know; The Earth does not belong to man, man belongs to
> the Earth. All things are connected like the blood that unites
> us all. Man did not weave the web of life, he is merely a
> strand in it. Whatever he does to the web, he does to himself.."
>
> ...Chief Seattle In a letter to President Pierce, 1852
>
>
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