Ray, Mathematically speaking if L1(or L2) is less than L2(orL1)by more than a factor of k square i.e. if L1 <(k^2*L2) then clearly L12 will be larger than L1. So for a conductor with small self inductance, lying in vicinity of an inductive path can make their mutual go above self inductance. Siddharth. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Ray Anderson Sent: Friday, October 28, 2005 3:21 PM To: si-list@xxxxxxxxxxxxx Cc: Ray Anderson Subject: [SI-LIST] Can L12 ever exceed L1 or L2 ?? A question for the E&M gurus on the list: =20 Are there any conditions (pathological or not) that the mutual inductance between two conductors can be greater than the self inductance of either one? =20 Since L12 =3D k * sqrt(L1*L2) and the coupling factor k must be -1 < k < = 1 then this would seem to imply that L12 must be less than or equal to geometric mean of the self inductances. However this leaves open the possibility the Lm could be > than one or the other which flies in the face of the commonly made assertion that Lm must be less than either. It seems that there must be other qualifying statements to made regarding the relationship to the self and mutual inductances. =20 Going back to some of the basic fundamental relationships (such as Grover's formulas) I can convince myself that for circular conductors L12 must be less than or equal to either L1 or L2, but how about the mutual coupling between some other structures say a signal trace and large planar structure that isn't intended to be be a signal return path but very well may be ? =20 I've got a field solver reporting Lm being 2 to 3 times Lself on one particular problem. I'm trying to determine if the solver is having a difficult time dealing with the particular geometries involved or if it is indeed possible despite the common wisdom to the contrary. =20 Any comments one way or the other are appreciated. =20 Regards, =20 -Ray =20 =20 Raymond Anderson Senior Signal Integrity Staff Engineer Product Technology Department Advanced Package R&D Xilinx Inc. =20 =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu