how to calculate the capacitance between the two lines?

hi friends,

I want to calculate the capacitance between the two lines as shown in Fig (a) and (b).
the width of the two lines are W1 and W2, and the distance between the two lines is H. the thickness of the two lines can be ignored.
my problem is how to calculate the capacitance between the two lines at the two conditions? Is there any analytical expression to get the capacitance?

Thanks a million.

Due to the fringing field, this is not trivial.

I do not know if a numerical solution also helps? You can calculate this with the free TNT/MMTL field solver.

http://mmtl.sourceforge.net/

http://www.westbay.ndirect.co.uk/capacita.htm

thanks for volker and vfone, your advices are helpful.