wiki/ PeFoamTapeEr

Calculating Er of Polyethylene Foam Tape

Here's what we're using for a dielectric: 4 lb/ft3 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.

Stuff Source Er Density
? http://www.berktek.com/technical/gen102.asp 2.3 solid, 1.64 "foam" NA
LDPE http://www.goodfellow.com/csp/active/static/A/ET31.HTML 2.2-2.35 @ 1 MHz 0.92 g/cm^3
HDPE http://www.goodfellow.com/csp/active/static/A/ET32.HTML 2.3-2.4 @ 1 MHz 0.95 g/cm^3
UHMW http://www.goodfellow.com/csp/active/static/A/ET30.HTML 2.3 @ 1 MHz 0.94 g/cm^3
? http://www.iewc.com/Tech18b.htm 2.3 solid, 1.5 foamed NA
HDPE http://www.kern-gmbh.de/cgi-bin/riweta.cgi?nr=1411&lng=2 2.4 @ 1 MHz 0.963 g/cm^3
LDPE http://www.sdplastics.com/polyeth.html 2.25-2.35 @ 1 KHz 0.0329-0.0334 lb/in^3
MDPE http://www.sdplastics.com/polyeth.html 2.25-2.35 @ 1 KHz 0.0334-0.0340 lb/in^3
HDPE http://www.sdplastics.com/polyeth.html 2.30-2.35 @ 1 KHz 0.0340-0.0348 lb/in^3
UMHW http://www.sdplastics.com/polyeth.html 2.25-2.35 @ 1 KHz 0.0340 lb/in^3
LDPE http://www.boedeker.com/polye_p.htm NA 0.033 lb/in^3
HDPE http://www.boedeker.com/polye_p.htm NA 0.035 lb/in^3
UHMW http://www.boedeker.com/polye_p.htm 2.3 @ 50 kHz 0.034 lb/in^3

Here's my choice: Er = 2.3 with a density of 0.0330 lb/in3 (57.0 lb/ft3). 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
(93% * 1.001) + (7% * 2.3) = 0.931 + 0.161 = 1.092

Measuring:

Spencer Webb found the Er very close to 1.0.


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