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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 ``` ``````# 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 () 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&amp;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/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`
`(93% * 1.001) + (7% * 2.3) = 0.931 + 0.161 = 1.092` Measuring: Spencer Webb found the Er very close to 1.0. ``````