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I am trying to model the frequency response of a force (dielectrophoresis) that is based on gradient of an electric field.

One of the components is the CM factor which has a frequency component, but the other factor is $\Delta E^2 $ I was wondering if this is affected by frequency? If the magnitude is $20\: \mathrm{v/m}$ at DC is it the same in AC conditions. If not, how does it change with frequency?

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Force on what? Can you clarify your question with a picture of some sort or maybe a more descriptive problem setup? –  BMS Dec 4 '13 at 21:02
    
When you talk about magnitude of a DC current, it is well understood. But for AC, you have to clarify if it is peak to peak or rms value. Either way, it would not depend on frequency at all. –  mcodesmart Dec 4 '13 at 21:40
    
Related (duplicate?) : physics.stackexchange.com/questions/63845/… –  jinawee Dec 4 '13 at 22:01
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2 Answers

The magnitude does not change with frequency, because the formula for an even wave is

$$ \Psi(x) = A\cdot e^{i(kx - \omega t)} $$

Where $A$ is the amplitude and $\omega$ is the frequency. So, if you change the frequency, the amplitude does not change.

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For LaTeX you surround the block with $$ \\LaTeX Lines $$ or $LaTeX Inline$ for inline. I also submitted an edit for your post to fix that. As far as the question, would the field not change because in AC the charge movement change would produce a change in the electromagnetic field, and this change would depend on the frequency of the current? –  danielu13 Dec 4 '13 at 21:10
    
@danielu13: Thank you for the help! Can you rewrite your answer a bit? I do not understand completely what you mean... –  arc_lupus Dec 4 '13 at 21:13
    
This makes sense for just the electric field, but what about the gradient of an Electric field? $\delta E / \delta x $ –  user35262 Dec 4 '13 at 23:06
    
Correction to my deleted comment: The absolut value of the gradient becomes bigger everywhere except for the maxima and minima when you increase the frequency. –  arc_lupus Dec 5 '13 at 6:30
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Electric field is associated with any electrical signal or electromagnetic process. A plane wave carries no information, and is normally modulated (Amplitude modulation, phase modulation etc.) with respect to time, and any modulation means a frequency dependent amplitude, which will in turn mean a frequency dependent force.

I hope, this answer goes in the right direction.

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