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# <a name="Calculating Er of Polyethylene F"></a> Calculating Er of Polyethylene Foam Tape

Here's what we're using for a dielectric: 4 lb/ft^3 white closed cell crosslinked polyethylene foam tape that is 0.062 -0.009/+0.018 in. thick. Not recommended for UV exposure, which means it doesn't have UV protectants in it. It's 3M (<http://www.3m.com/>) tape # 4466.

We can calculate the Er of the foam tape by estimating the density and Er of polyethylene in general.

Low density (LD), high density (HD) and ultra-high molecular weight (UHMW) polyethylene seems to have all about the same density, and about the same Er according to multiple sources on the internet.

<table border=1 cellpadding=0 cellspacing=0>
  <tr>
    <th bgcolor="#99CCCC"><strong> Stuff </strong></th>
    <th bgcolor="#99CCCC"><strong> Source </strong></th>
    <th bgcolor="#99CCCC"><strong> Er </strong></th>
    <th bgcolor="#99CCCC"><strong> Density </strong></th>
  </tr>
  <tr>
    <td> ? </td>
    <td><a href="http://www.berktek.com/technical/gen102.asp" target="_top">http://www.berktek.com/technical/gen102.asp</a></td>
    <td> 2.3 solid, 1.64 &quot;foam&quot; </td>
    <td> NA </td>
  </tr>
  <tr>
    <td> LDPE </td>
    <td><a href="http://www.goodfellow.com/csp/active/static/A/ET31.HTML" target="_top">http://www.goodfellow.com/csp/active/static/A/ET31.HTML</a></td>
    <td> 2.2-2.35 @ 1 MHz </td>
    <td> 0.92 g/cm^3 </td>
  </tr>
  <tr>
    <td> HDPE </td>
    <td><a href="http://www.goodfellow.com/csp/active/static/A/ET32.HTML" target="_top">http://www.goodfellow.com/csp/active/static/A/ET32.HTML</a></td>
    <td> 2.3-2.4 @ 1 MHz </td>
    <td> 0.95 g/cm^3 </td>
  </tr>
  <tr>
    <td> UHMW </td>
    <td><a href="http://www.goodfellow.com/csp/active/static/A/ET30.HTML" target="_top">http://www.goodfellow.com/csp/active/static/A/ET30.HTML</a></td>
    <td> 2.3 @ 1 MHz </td>
    <td> 0.94 g/cm^3 </td>
  </tr>
  <tr>
    <td> ? </td>
    <td><a href="http://www.iewc.com/Tech18b.htm" target="_top">http://www.iewc.com/Tech18b.htm</a></td>
    <td> 2.3 solid, 1.5 foamed </td>
    <td> NA </td>
  </tr>
  <tr>
    <td> HDPE </td>
    <td><a href="http://www.kern-gmbh.de/cgi-bin/riweta.cgi?nr=1411&amp;lng=2" target="_top">http://www.kern-gmbh.de/cgi-bin/riweta.cgi?nr=1411&amp;amp;lng=2</a></td>
    <td> 2.4 @ 1 MHz </td>
    <td> 0.963 g/cm^3 </td>
  </tr>
  <tr>
    <td> LDPE </td>
    <td><a href="http://www.sdplastics.com/polyeth.html" target="_top">http://www.sdplastics.com/polyeth.html</a></td>
    <td> 2.25-2.35 @ 1 KHz </td>
    <td> 0.0329-0.0334 lb/in^3 </td>
  </tr>
  <tr>
    <td> MDPE </td>
    <td><a href="http://www.sdplastics.com/polyeth.html" target="_top">http://www.sdplastics.com/polyeth.html</a></td>
    <td> 2.25-2.35 @ 1 KHz </td>
    <td> 0.0334-0.0340 lb/in^3 </td>
  </tr>
  <tr>
    <td> HDPE </td>
    <td><a href="http://www.sdplastics.com/polyeth.html" target="_top">http://www.sdplastics.com/polyeth.html</a></td>
    <td> 2.30-2.35 @ 1 KHz </td>
    <td> 0.0340-0.0348 lb/in^3 </td>
  </tr>
  <tr>
    <td> UMHW </td>
    <td><a href="http://www.sdplastics.com/polyeth.html" target="_top">http://www.sdplastics.com/polyeth.html</a></td>
    <td> 2.25-2.35 @ 1 KHz </td>
    <td> 0.0340 lb/in^3 </td>
  </tr>
  <tr>
    <td> LDPE </td>
    <td><a href="http://www.boedeker.com/polye_p.htm" target="_top">http://www.boedeker.com/polye_p.htm</a></td>
    <td> NA </td>
    <td> 0.033 lb/in^3 </td>
  </tr>
  <tr>
    <td> HDPE </td>
    <td><a href="http://www.boedeker.com/polye_p.htm" target="_top">http://www.boedeker.com/polye_p.htm</a></td>
    <td> NA </td>
    <td> 0.035 lb/in^3 </td>
  </tr>
  <tr>
    <td> UHMW </td>
    <td><a href="http://www.boedeker.com/polye_p.htm" target="_top">http://www.boedeker.com/polye_p.htm</a></td>
    <td> 2.3 @ 50 kHz </td>
    <td> 0.034 lb/in^3 </td>
  </tr>
</table>

Here's my choice: Er = 2.3 with a density of 0.0330 lb/in^3 (57.0 lb/ft^3). I picked the middle Er value, and the middle of the LDPE values. The reason for the LDPE is that I don't think they start with the HDPE for foam - so it's the "closest" to the foam in this table.

Calculating:

`4 lb/ft^3 / 57.0 lb/ft^3 = 0.070 = 7% PE, 93% air`<br />`(93% * 1.001) + (7% * 2.3) = 0.931 + 0.161 = 1.092`

Measuring:

Spencer Webb found the Er very close to 1.0.