Skin Effect

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


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 

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)))
	L = Length of wire
	D = Skin depth
	C = Conductivity of copper
	R = Radius of conductor
	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 
fields from adjacent wires?

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?

Thank you in advance.

Rob Davis (UK)