If we use the axisymmetric model for the coil, the FEMM results is very close to the value calculated using the formula for a current loop.From: Tomislav Borzic <tborzic@xxxxxxxxx> Reply-To: femm@xxxxxxxxxxxxxxx To: femm@xxxxxxxxxxxxxxx Subject: [femm] inductance Date: Tue, 13 Nov 2001 07:12:23 -0800 (PST)
Hello everybody, I am (again) coming with small problem. It is about inductance. I am callculating inductance of a coil. 1. one turn 2. four turns.
In case (1) I use formula L= (mi0/pi)*(1/4 + ln(D/r0) where is: mi0=4*pi*e-7 D- diameter of coil ( like this: 0-----D----0, where 0 is conductor and D is space between them) r0= radius of conductor
I know this is formula for two paralell conductors and inductance between them but with some assumptions it can work. so in this case, r0=0.05m, D=0.8m,I+ = 1A, I-=-1A, my callculations give 1.2 e-6 H/m, FEMM 1.16 e-6 H/m, so it is ok. I used AJ block integral (A j dV/2 = energy) BUT, if I take four turns of wire, inductance should be 16 times higher because inductance of coil rises with n^2. (n = number of turns) I can not achieve acceptable solution.
*.fem file is attached. plase help thanks tomislav.
current loop: L=N^2*R*mu0*Ln(R/r) where R=radius of loop r=radius of wire
Using your dimensions: R=4cm r=0.0005cm 4 turns then L = 167.2nH
Using FEMM: Let J=1.0 then integral(A.J)=6.236e-9 I = 0.1954 Amps/turn
Regards, Jim
_________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
Attachment:
smallcoil2.FEM
Description: Binary data