# Electromagnetic pulses

**URL:** <https://boards.straightdope.com/t/electromagnetic-pulses/157801>\
**Category:** Factual Questions\
**Created:** [February 27, 2003, 3:22am UTC](https://boards.straightdope.com/t/electromagnetic-pulses/157801 "2003-02-27T03:22:45Z")\
**Posts on this page:** 5\
**Page:** 2

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [February 27, 2003, 11:40pm UTC](https://boards.straightdope.com/t/electromagnetic-pulses/157801/21 "2003-02-27T23:40:45Z")

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Good point, **Desmostylus** , but for a pulse it might be more suitable to substitute omega(w) for (pi . f).

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [February 27, 2003, 11:42pm UTC](https://boards.straightdope.com/t/electromagnetic-pulses/157801/22 "2003-02-27T23:42:11Z")

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Also, shouldn’t it be **2** pi x f?

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**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\
**Post date:** [February 27, 2003, 11:54pm UTC](https://boards.straightdope.com/t/electromagnetic-pulses/157801/23 "2003-02-27T23:54:10Z")

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You could write it as sqrt( 2 / (w . mu . sigma)).

It’s exactly the same, but your way looks messier.

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<div class="post-metadata">

**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [February 28, 2003, 12:08am UTC](https://boards.straightdope.com/t/electromagnetic-pulses/157801/24 "2003-02-28T00:08:52Z")

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I was thinking of the convenience of plugging the rate of change directly into the equation rather than having to calculate a frequency. Plus, I’m pretty sure the formula would be different for an EMP, which would be roughly a square wave.

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**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\
**Post date:** [February 28, 2003, 12:29am UTC](https://boards.straightdope.com/t/electromagnetic-pulses/157801/25 "2003-02-28T00:29:18Z")

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I think the term you are looking for is “step function” rather than “square wave”.

But the model of the incident pulse doesn’t alter the properties of the shielding material.

Anyway, to compare some different materials, here’s a few skin depth examples at f = 1 MHz, with skin depths given in microns.

```auto

Silver 63
Copper 65
Gold 78
Chromium	81
Aluminum	84
Brass 95
Magnesium	108
Tungsten	118
Zinc 119
Cadmium 136
Nickel 140
Phosphor-Bronze	140
Tin 169
Beryllium	207
Lead 231
Monel 323
Manganese	327
Titanium	331

Silicon Iron	43
Permalloy	20
Hypernik	15
Mu-Metal	7
Supermalloy	3
Iron (purified)	16
Iron 50
Steel 93

```

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