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RE: PET ( or MYLAR )


From: "Payne, Will E" <will.e.payne-at-lmco-dot-com>

FROM : Will Payne

Jim, you are of course right on both counts.  I was extrapolating from the
meager info I had available to me.  However, on the second count, my
intuition is now justified by the following data from "Reference Data for
Radio Engineers, 4th Edition" (1957) list of Material Properties :

Polyethylene DE-3401 with 0.1% antioxidant additive : 

   FREQ Epsilon TAN Epsilon

  60 Hz   2.26   <.0002
  1 kHz   2.26   <.0002
  1 MHz   2.26   <.0002
100 MHz   2.26   <.0002
  3 GHz   2.26   <.00031
 25 GHz   2.26   <.0006

Dielectric Strength (0.033") is 1200 V/mil at 25C.
Softening point is 95 - 105 C
Moisture absorption 0.03%

> ----------
> From: 	Tesla List[SMTP:tesla-at-pupman-dot-com]
> Sent: 	Wednesday, August 26, 1998 22:07
> To: 	tesla-at-pupman-dot-com
> Subject: 	Re: PET ( or MYLAR )
> 
> Date: Wed, 26 Aug 1998 18:48:19 -0700
> From: Jim Lux <James.P.Lux-at-jpl.nasa.gov>
> 
> Tesla List wrote:
> > 
> > Well, if 6u PET holds 600v then 9 mil PET should hold 900 kV, no?
> No... thin layers have higher dielectric strength (per unit thickness)
> than thick layers. A phenomenon that has surprised many. Ruby mica has
> such a high dielectric strength partly because it is composed of many
> very uniform very thin layers stuck together.
> 
> 
>  I should
> > be able to get a pop bottle to  stand up to a 15 kV Tesla coil, even
> with 15
> > kV of LF riding ont he 15 kV of 60 Hz.  I notice the CRC handbook lists
> the
> > dielectric constant of PET the same value for all three frequencies in
> their
> > table.  Thats gotta be a good sign for low dissipation.  I dont have a
> > microwave oven for dielectric loss testing right now.
> 
> A microwave oven is 2450 MHz, many, many decades above the 100 kHz or so
> for a TC. Loss at microwave frequencies may not be all that well
> correlated with loss at low frequencies.  And, the change (or lack of
> change) in epsilon (the dielectric constant) doesn't have much to do
> with the change in loss factor. There are a number of substances with
> dielectric constants that are relatively constant over frequency (around
> 2.5) that have remarkably high losses at some frequencies.
> 
>