# Skin Effect

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From: 	Robert Davis[SMTP:RE.Davis-at-btinternet-dot-com]
Sent: 	Tuesday, July 29, 1997 4:35 PM
To: 	'tesla-at-pupman-dot-com'
Subject: 	Skin Effect

Hi,

I have the formula for skin depth as:

Depth (mm Copper) = 66/sqrt(freq)

Where the depth is the attenuation of current density from the surface
value/e.

Question 1:  Is the surface value the same as the DC resistive value for
copper wire of a given size?

Question 2:  From the above the dynamic resistance of a copper wire at a
given frequency appears to be:

Resistance = L/(Cr X ((PI X R^2) - (PI X (R-D)^2)))

Where:
L = Length of wire
D = Skin depth
C = Conductivity of copper

Is this correct?

Question 3:  The skin effect calculation assumes that there is only one
wire, skin effect being then caused by the magnetic field motion form the
oscilating currents in that wire, BUT we are winding coils with wires in
close proximity, does anyone have a correction factor to take into account

If this is the case then the thickness of insulation of wire used (assuming
the coil is close wound) will have some effect on the dynamic resistance of
the coil and hence the Q of the coil, I think proximity of other turns will
increase the dynamic resistance, is this correct?