don_quixote
Junior Member level 2
ac resistance vs dc resistance
Hello everyone,
I'm using Ansoft Q3D to do some extraction tasks and found out that Q3D gives lower AC resistance value than DC resistance value. This really confused me because all what i learned tell me that the resistance of a conductor @ high frequency is going to increase due to the skin effect and/or proximitty effect (like what's being said in Howard Johnson's HSSP book). If it does not increase (e.g. the wire cross section is smaller than the skin depth) at lease it shouldn't decrease.
I searched on the internet and found this on Ansoft HF forum:
Now i'm even more confused because Richard from Ansoft says "higher AC than DC resistance shouldn't happen in real life....". Since this is so a fundamental issue i guess many of you can help me.
Any input is appreciated.
Thank you,
don_quixote
Hello everyone,
I'm using Ansoft Q3D to do some extraction tasks and found out that Q3D gives lower AC resistance value than DC resistance value. This really confused me because all what i learned tell me that the resistance of a conductor @ high frequency is going to increase due to the skin effect and/or proximitty effect (like what's being said in Howard Johnson's HSSP book). If it does not increase (e.g. the wire cross section is smaller than the skin depth) at lease it shouldn't decrease.
I searched on the internet and found this on Ansoft HF forum:
DC Resistance versus AC Resistance in Q3D
by: eustacec
email: eustacec@nus.edu.sg
12/17/2002 5:55A
Hello, I have a question on quick3d. I have run a simulation which shows that the DC resistance value is HIGHER than the AC resistance. Can this happen? and Why. Theoretically, the AC resistance is due to the skin effect, and it will always be bigger than DC. 2nd situation where I have 2 different conductors in series. Copper + Solder. How does this impact on the DC and AC? Your reply is appreciated. Thank you. Cheers.
Re: DC Resistance versus AC Resistance in Q3D
by: Richard Remski
email: remski@ansoft.com
3/3/2003 11:41A
The AC solver doesn't 'know' what skin depth is, so it assumes that the current is in the 'surface' of the conductor only. This curve is valid for frequencies up where the skin depth is less than the real conductor thickness, but is going to be incorrect at really really low frequencies. The DC solution on the other hand does assume currents thru the whole thickness, so its answer is more 'valid' for those very, very low frequencies. So no, higher AC than DC resistance shouldn't happen in real life....if you see it that's an indication that for the frequency you're looking at is in that transition region where the AC assumptions are breaking down. RTR
Now i'm even more confused because Richard from Ansoft says "higher AC than DC resistance shouldn't happen in real life....". Since this is so a fundamental issue i guess many of you can help me.
Any input is appreciated.
Thank you,
don_quixote