From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Wednesday, April 15, 1998 2:52 PM
To:  tesla-at-pupman-dot-com
Subject:  Dielectric

Hi all,
          As there have been a few queries on dielectric properties 
lately I've resurrected this classic post that Ed Harris sent to the 
list several years ago.


------- Forwarded Message Follows -------
<header snip>

update 8/1/1995
Compiled by Ed Harris 
174 W 18th Ave
Columbus, OH 43210
New inclusions to the old stuff:
Info on magnet wire coatings!

>From all the discussion on this group about building ones own capacitors 
and what types of materials make good coil forms, I became interested in 
obtaining some hard (or semi-hard) data on different types of polymers. I 
was also interested when someone (?) asked whether ABS was a good material 
for coil forms - I had no idea. It seems that it is much preferable to PVC.

I thought I'd share the results of my library searches:

First, I'd like to list some of the plastics with their chemical name and 
their abreviations. Trade names are listed if they are well known.

chemical name                   abreviation     aka             notes
-------------                   -----------     ---             ------
polyethylene                    PE              polythene-British!

                                                        CH2-CH2 monomer

                                HDPE                    High density PE
                                LDPE                    Low density PE

polypropylene                   PP                      replace one H in PE
                                                        by CH3

polyvinyl chloride              PVC                     replace one H in PE
                                                        by one Cl atom

polyvinylidene chloride         CPVC PVDC               replace two H in PE
                                                        by two Cl

polystyrene                     PS                      replace H in PE by
                                                        a benzene ring

polyvinyl flouride              PVF                     replace H in PE by
                                                        F atom

polyvinylidene flouride         PVDF            Kynar   repace two H in PE 
                                                        by two F atoms
                                                        *wire wrap insul.

polymethyl methacrylate         PMMA            Plexiglas
                                                Perspex (British)

polytetraflouroethylene         PTFE            Teflon  replace all H in PE
                                                        by F atoms

polychlorotrifloroethylene      PCTFE           Kel-F   replace 3 H in PE
                                                        with F one with Cl

polyamide 6                     PA 6            Nylon 6

polyamide 66                    PA 66           Nylon 66

polyamide-imide                 PAI             Torlon

polyurethane                    PUR

polycarbonate                   PC              Lexan

Polyacetal                      POM             Delrin

polyethlene terephthalate       PET             Mylar   co-polymer of PE

cellulose actetate butyrate     CAB             Butyrate

cellulose nitrate               CN              "Laquer" *typical constituent

acrylonitrile-butadiene-styrene ABS             Cycopac ter-polymer of 
                                                * warning Jim Oliver says
                                                this name may apply to
                                                may many diff materials

polyimide                       PI              Kapton

polyvinyl formal                ?               Formvar wire coating

OK, there are zillions of others, but these are the ones I picked because I 
heard of them before...
A couple of comments: Notice that there are many polymers which share a 
common structure with polyethylene, all that changes is replacing one or 
more of the H atoms in (PE) with some other atom or group of atoms. Then 
there are plastics which are called co-polymers or ter-polymers. A co-
polymer is just taking two different monomers and sticking them together in 
a unit cell before polymerizing. Example: PET. Likewsie, a ter-polymer is 
just sticking three monomers into a unit cell and then polymerizing. A very 
common example is ABS which is used as sewar and drainage pipe.

Now for the useful stuff. What are the electrical properties of some of 
these polymers? The most useful properties in my mind are the dielectric 
constant (or permittivity), the dielectric strenght, and the dissipation 
factor. All of these properties are dependent on temperature and frequency, 
but amazingly they also depend somewhat on the actual thickness of the 
material (as in thin films).

----A couple of notes:
All three properties mentioned above depend on frequency, but it turns out 
that for many non-polar polymers (ie PE) that the dielectric constant and 
dissipation factor do not depend much on frequency. I'll show some data for 
some of the plastics I could find. However, nobody seems to have data on 
the frequency dependence of the dielectric strength. It is best just to 
assume that this was done at DC.

One property which is not well known for polymers is that the breakdown 
electric field or dielectric strength (VOLTS/INCH etc...) depends on the 
actual thickness of the film. Typically, as the film gets thinner, the 
dielectric strength goes up!!! For example, LDPE has a strength of 800volts 
per mil at 80 mils, but this goes up to 1400volts/mil at 20mils!! 
Polystyrene exceeds even this! I have personally done measurements on LDPE
which show DC breakdowns of 3000Volts/mil at 2mils... 

Finally what is dissipation factor? It is a measure of how lossy the 
material is to alternating electric fields (as in Tesla coils and tank 
capacitors). It is defined by 

        --- = tangent (delta)   = DF

where Ir is the resistive or dissipative current and Ic is the capacitive 
or displacement or reactive current. Delta is the phase angle between 
these currents  (in the complex plane). Another expression which contains 
the same information is the Power Factor. For those familiar with this term 
they are related by:


For small DF, then PF is approximately equal to DF. Obvisously, one would 
like to have DF as small as possible for low loss, high Q systems. In fact, 
for the purposes of approximation, the Q of a capacitor with low DF or PF 
is simply Q=1/DF=1/PF

Absolute power lost in the system is:
1. goes up with the square of the voltage gradient (electric field)
2. goes up linearly with the volume of the dielectric in the field
   ( make your coil forms thin)
3. goes up linearly with increasing dielectric constant
   ( don't use barium titanate primary caps!)
4. generally increases with frequency

polymer         dielectric      dielectric      dissipation
                constant        strength        factor
                50Hz / 1Mhz     (Kv/cm)         50Hz / 1Mhz (x10^-3)
--------        -----------     -----------     -----------
LDPE            2.29 / 2.28     370             .15 / .08
HDPE            2.35 / 2.34     --              .24 / .20
PP              2.27 / 2.25     240             .40 / .50
PVC-plasticized 4-8  / 4-5      270             80  / 120
PS              2.5  / 2.5      200-300         .1-.4/.05-.4
ABS             2.4-5/2.4-3.8   ~400            3-8 / 2-15
PMMA            3.3-3.9/2.2-3.2 140             40-60/4-40
POM             3.7 / 3.7       400             5 / 5
PTFE            2.1  / 2.1      480             .2 / .2
PCTFE           2.3-2.8/2.3-2.5 550             1 / 20
PA-6            3.8 / 3.4       400             10 / 30
PA-66           8 / 4           600             140 / 80
PC              3.0 / 2.9       380             .7 / 10
PET             4.0 / 4.0       420             2 / 20
PI              3.5 / 3.4       560             2 / 5
PUR-linear      5.8 / 4.0       >300            120 / 70
PUR-thermoset   3.6 / 3.4       240             50 / 50
PUR-thermoplas  6.6 / 5.6       300             30 / 60
CAB             3.7 / 3.5       400             6 / 21
Silicone        3.6             200             5-13 / 7        

Another comparison:

polymer         Dielectric constant / Dissipation Factor (x10^-3)

                100 Hz          1000 Hz         1 Mhz           10 Mhz

ABS             2.8/5           2.8/6           2.8/8           2.8/7
PMMA            3.6/62          3.2/58          3.1/40          2.9/33
PC              3.1/1           3.1/1.3         3.1/7           3.1/11
PE              2.3/.1          2.3/.1          2.3/.1          2.3/.1
PA-6            4.2/31          3.8/24          3.8/31          4.0/20

Magnet wire coatings from Phelps-Dodge:
All data pertain to 18 gauge magnet wires
Build= thickness of coating

Coating                 What's it made of       Build           DC 
----------              -----------------       -----           breakdown

Thermaleze-T (TZT)      polyester-imide         2.8mils         11kV

Armored Polythemaleze                           3.05mils        11kV
(APTZ)                  modified polyester&
                        modified polyamide-imide

Imideze (ML)            Aromatic polyimide      2.9mils         12kV

Formvar                 modified polyviynyl     3.0mils         10kV

Sodereze                modified polyurethane   2.9mils         8.5kV

Nyleze                  Polyurethane            2.9mils         8.5kV 
                        & polyamide

* Note: for the dielectric breakdown - These numbers are much bigger than 
for bulk materials because they are very thin coatings. As mentioned 
previously, the breakdown field increases as the thickness goes down.
{a similar effect happens in gases and liquids and was studied by Paschen}

Anyway, here's the dielectric constant/DF numbers for these matearials:

Material                Dielectric Const. / DF x 10^-3

                1kHz            100kHz          1Mhz            rating
TZT             3.7/5.6         3.56/16.4       3.58/21.5       3rd

APTZ            3.86/6.9        3.69/22.1       3.67/26.6       5th

ML              3.34/0.9        3.3/5.7         3.36/9.8        2nd to 

Formvar*        3.6/11.2        3.41/25.2       3.37/28.4       5th

Soldereze       3.85/11.3       3.66/20.7       3.66/23.1       4th

Nyleze          4.07/19.7       3.78/27.1       3.75/27.2       6th

* This shows that Formvar is far from an ideal coating for magnet wire
used in Tesla Coils when compared to something like Polyimide coatings

1. Polymer Engineering Principles, Richard C. Progelhof and James Throne
2. Plastics for Electronics, Martin T. Goosey
3. Handbook of Plastics in Electronics, Dan Grzegorczyk and George Feineman
4. SPI Plastics Engineering Handbook, Society of the Plasitics Industry
5. Electrical Engineer's Handbook, Pender - 4th Edition
6. Phelps-Dodge magnet wire product data

Plastics sources: probably best to check your local distributors, but there 
is a mail order company called US Plastic Corp -at-800-537-9724 (catalog). 
They have rod/sheet/tubing of PVC, PMMA, CAB, POM, PE, PS. Of particlular 
        Butyrate tubing up to 6 " diameter * lower loss coil forms
        Polystyrene tubing to 4 " dia * very low loss coil form
        4x8ft LDPE sheet 60mil or other * Capacitors

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12

      Many will recognize Richard Quick's sig at the bottom of the 
post on dielectrics I just sent. He originally reposted this piece to 
the list sometime after the original was posted. It was his update 
that turned out to be in my files. I am acknowledging his part in