We have an interesting Electromagnetism lecturer who likes to set slightly odd problems to keep us entertained, this week's involves calculating the electric field at a point 1cm inside your head due to a mobile phone operating at 1.8 GHz, given that the electric field strength at the surface of your head is 20 Volts per metre. He assures us that the dielectric constant of brain tissue is 51.3, has a conductivity of 1.6 ohm^-1 m^-1 and that brain tissue is not typically magnetic...

Skin depth of brain tissue at this frequency is about 1.19cm, so there's definitely a (reduced) field there, but I can't figure out the simple task of working out its magnitude there.

Thought this might entertain a few..

## Electric Field Due To A Mobile Phone...

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- danpilon54
**Posts:**322**Joined:**Fri Jul 20, 2007 12:10 am UTC

### Re: Electric Field Due To A Mobile Phone...

how is skin depth defined? How could you use that information to find the strength?

hint: exponential decay.

hint: exponential decay.

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### Re: Electric Field Due To A Mobile Phone...

Skin depth is simply,

[math]\delta = \sqrt{\frac{2}{(\mu \omega \sigma)}}[/math]

And the electric field is:

[math]E = E_{0}exp(-\frac{x}{\delta})exp(i(\frac{x}{\delta}-wt))[/math]

Where the wave decays by a factor equal to the first exponential?

Using everything, I come up with:

[math]E_{0}exp(-\frac{x}{\delta})[/math]

As the new value for the field? But the field should be zero at the skin depth, and that won't come out of the above expression, so I've clearly got a little confused along the way...

[math]\delta = \sqrt{\frac{2}{(\mu \omega \sigma)}}[/math]

And the electric field is:

[math]E = E_{0}exp(-\frac{x}{\delta})exp(i(\frac{x}{\delta}-wt))[/math]

Where the wave decays by a factor equal to the first exponential?

Using everything, I come up with:

[math]E_{0}exp(-\frac{x}{\delta})[/math]

As the new value for the field? But the field should be zero at the skin depth, and that won't come out of the above expression, so I've clearly got a little confused along the way...

### Re: Electric Field Due To A Mobile Phone...

The field can never reach zero if it experience exponential decay. The definition of skin depth is the point where you have e

^{-1}of the initial field.If there is no answer, there is no question. If there is no solution, there is no problem.

Waffles to space = 100% pure WIN.

### Re: Electric Field Due To A Mobile Phone...

Oh excellent, clearly misunderstood the term while we were being lectured. Thanks very much

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