Fred, We've been talking about magnetic flux which is the surface integral of the normal component of flux density vector B. Right? Given that, please check your statements. Sainath ---------Included Message---------- >Date: Mon, 21 Jul 2003 12:35:22 +0800 >From: "Wen Fred-Q16099" <fred.wen@xxxxxxxxxxxx> >Reply-To: "Wen Fred-Q16099" <fred.wen@xxxxxxxxxxxx> >To: "'gigabit@xxxxxxxxxx'" <gigabit@xxxxxxxxxx> >Cc: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx> >Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 > >Sainath, > >The integral (maximum or minimal) depends on the loop of the surface edge, not >the surface itself. Given a fixed loop, the integral will not vary on various >surface. Its principle comes from the physics law that tells us the integral on >a closed surface is always ZERO. > >Fred > >> -----Original Message----- >> From: Sainath Nimmagadda [mailto:gigabit@xxxxxxxxxx] >> Sent: Sunday, July 20, 2003 1:40 PM >> To: andrew.c.byers@xxxxxxxxxxxxxx >> Cc: si-list@xxxxxxxxxxxxx >> Subject: [SI-LIST] Re: si-list Digest V3 #194 >> >> >> Andy, >> >> I disagree with your correction(about integrating magnetic >> flux lines). >> Please do a simple dimensional check. >> >> Yes, there is this correct inductance value which we get in >> the limiting >> case when we capture all the flux. This is also the maximum >> inductance. >> Lower inductance values are possible depending on the chosen >> surface and >> the minimum can go as low as zero, like you said. So, there is a >> distribution ranging from zero to the correct value. I believe the >> significance of this and its SI application opens up new >> directions... >> >> >> For SI application involving return current paths, I wonder >> how the idea >> of minimum(zero) inductance path stuck around so long. >> >> Sainath >> >> ---------Included Message---------- >> >Date: Fri, 18 Jul 2003 17:29:15 -0700 >> >From: <andrew.c.byers@xxxxxxxxxxxxxx> >> >Reply-To: <andrew.c.byers@xxxxxxxxxxxxxx> >> >To: <gigabit@xxxxxxxxxx> >> >Cc: <si-list@xxxxxxxxxxxxx> >> >Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> > >> >Sainath, >> > >> >First of all, with your surface, either above the microstrip >> or below, >> you >> >are capturing magnetic field lines, not "flux lines". You integrate >> these >> >field lines over the area of the surface to produce a scalar number >> which is >> >your magnetic flux. A lot of times people get Flux and Field >> confused. >> Flux >> >is a scalar number, while field is a vector. >> > >> >So, like you say, if you capture all the field lines on your >> surface, >> you >> >should calculate the true flux and therefore the correct inductance. >> Calling >> >it a "maximum" or "minimum" does not really fit here. If you were to >> use a >> >surface where you did not account for all the field lines, the >> inductance >> >you calculate would indeed be smaller than the correct value. But it >> would >> >be wrong. I guess you could say that "maximum" inductance >> calculation >> is >> >correct, and "minimum" inductance calculation would be zero (you >> capture >> >none of the field lines). >> > >> >Any 2D cross section of an interconnect system should have >> one correct >> >inductance value. As you move along in the 3D direction of >> propagation, >> the >> >2D cross sections will change and your inductance at that >> point might >> change >> >too. Once again this is assuming no internal inductance and a single >> mode. >> >With internal inductance, your total inductance becomes frequency >> dependent. >> >The Ramo, Whinnery, Van Duzer book points this out as well. >> > >> >Andy >> > >> >-----Original Message----- >> >From: Sainath Nimmagadda [mailto:gigabit@xxxxxxxxxx] >> >Sent: Friday, July 18, 2003 6:07 PM >> >To: Byers, Andrew C >> >Cc: si-list@xxxxxxxxxxxxx >> >Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> > >> > >> >Andy, >> > >> >Yes, the inductance value should remain the same for both >> cases. Also, >> >> >we are capturing all the magnetic flux lines in both cases. >> > >> >Now comes the real question. When you capture all the flux lines, is >> the >> >inductance going to be maximum? or minimum? >> > >> >Sainath >> > >> >---------Included Message---------- >> >>Date: Fri, 18 Jul 2003 09:50:57 -0700 >> >>From: <andrew.c.byers@xxxxxxxxxxxxxx> >> >>Reply-To: <andrew.c.byers@xxxxxxxxxxxxxx> >> >>To: <gigabit@xxxxxxxxxx> >> >>Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> >> >> >>Sainath - >> >> >> >>With the case of the surface above the microstrip, the inductance >> >value >> >>should remain the same. The integrating distance will be >> from the top >> >> >of the >> >>microstrip to infinity, and the B-field will be diminishing in >> >magnitude as >> >>you get further and further from the microstrip. The integral to >> >infinity >> >>will be equivalent to some series, and can be solved easily to a >> >finite >> >>number. >> >> >> >>Another way of looking at it - all of the fields that wrap under the >> >>microstrip will also wrap above it. You just have to have a big >> enough >> >>surface to catch them all. In practice, a surface that is about 3-4 >> >times >> >>the height of the dielectric should catch most of the fields. This >> >whole >> >>infinite surface stuff is just for theoretical robustness. >> >> >> >>By the way, there is a paper that demonstrates this in FDTD >> simulation. >> >I >> >>believe it is in the 1997 EPEP conference - its written by Melinda >> >Piket-May >> >>and Roger Gravrok. I might be off by a year of two... if you have >> >those >> >>conference proceedings look for it. I can dig more for the >> name if you >> >> >would >> >>like. >> >> >> >>andy >> >> >> >>-----Original Message----- >> >>From: Sainath Nimmagadda [mailto:gigabit@xxxxxxxxxx] >> >>Sent: Thursday, July 17, 2003 11:44 PM >> >>To: Byers, Andrew C >> >>Cc: si-list@xxxxxxxxxxxxx >> >>Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> >> >> >> >> >>Hi Andy, >> >> >> >>Thanks again. I get the themes that inductance is a one >> number affair >> >> >>and current returns through the least inductance path. Is there a >> >>contradiction in these themes? >> >> >> >>Let me borrow the following from your previous mail. >> >> >> >>"If you were to put your integrating surface on the other >> side of the >> >> >>trace, extending up from the top of the trace, you >> theoretically would >> >> > >> >>have to make the area of the surface extend to infinity to >> "catch" all >> >> > >> >>the field lines." >> >> >> >>For this case, is the inductance of the microstrip going to be >> >>infinity(because of infinite surface)? or any other value? remains >> same >> > >> >>as what it was for the integrating surface below the trace? >> >> >> >>Sainath >> >> >> >> >> >> >> >> >> >>---------Included Message---------- >> >>>Date: Thu, 17 Jul 2003 17:37:12 -0700 >> >>>From: <andrew.c.byers@xxxxxxxxxxxxxx> >> >>>Reply-To: <andrew.c.byers@xxxxxxxxxxxxxx> >> >>>To: <gigabit@xxxxxxxxxx> >> >>>Cc: <si-list@xxxxxxxxxxxxx> >> >>>Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> >>> >> >>>Hello Sainath, >> >>> >> >>>Clearing up some terminology here. >> >>> >> >>>"Least inductance" refers to the path that the current will travel >> >>because >> >>>it has the least inductance of all possible paths in the system. >> >>Current >> >>>will never choose an alternate path of "most inductance". >> BUT you can >> >> > >> >>have a >> >>>different design in which the "path of least inductance" >> is longer. >> >>For >> >>>example a two wire line with no ground plane where the wires are >> >>extremely >> >>>far apart. Huge loop, huge inductance. But still the smallest loop >> for >> > >> >>that >> >>>system. For a microstrip, a path of More Inductance would >> be if there >> >> > >> >>were a >> >>>gap in the ground plane under the microstrip line. The >> current would >> >> >>be >> >>>forced to diverge around the gap. This path would be more >> inductive >> >>than a >> >>>solid ground plane, but the current would still be >> following the path >> >> > >> >>of >> >>>least inductance for that particular case. >> >>> >> >>>The main challenge in most systems I've dealt with is making sure >> >that >> >>>return current paths have the least inductance possible. >> The simplest >> >> > >> >>way to >> >>>do this is go differential. Then you carry your virtual >> ground with >> >>you >> >>>everywhere. If single ended, then be very conscious about >> where the >> >>return >> >>>currents flow and try to provide a short path. Plenty of >> threads on >> >>this >> >>>list about that. >> >>> >> >>>Not sure if this clears up your last question, hope it >> helps though. >> >>> >> >>>- Andy >> >>> >> >>> >> >>> >> >>>-----Original Message----- >> >>>From: Sainath Nimmagadda [mailto:gigabit@xxxxxxxxxx] >> >>>Sent: Thursday, July 17, 2003 4:01 PM >> >>>To: Byers, Andrew C >> >>>Cc: si-list@xxxxxxxxxxxxx >> >>>Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> >>> >> >>> >> >>>Andy, >> >>> >> >>>Thanks. I appreciate the extra effort to explain detail of >> >>integration. >> >>>In short, you've explained the current loop formed by a >> signal path >> on >> > >> >> >> >>>trace and signal return path beneath the trace and on the ground >> >plane. >> >> >> >>>Such a return path, with its minimum loop area, is widely known to >> >>>provide the path of "least" inductance for high-frequency >> currents(for >> > >> >> >> >>>example, Black Magic book). If inductance is thought of as one >> number, >> > >> >> >> >>>what does "least inductance" refer to? Which is the path of "most" >> >>>inductance for the microstrip? No doubt, I'm missing somethig. >> >>> >> >>>Sainath >> >>> >> >>>---------Included Message---------- >> >>>>Date: Thu, 17 Jul 2003 10:02:49 -0700 >> >>>>From: <andrew.c.byers@xxxxxxxxxxxxxx> >> >>>>Reply-To: <andrew.c.byers@xxxxxxxxxxxxxx> >> >>>>To: <gigabit@xxxxxxxxxx>, <beneken@xxxxxxxxxxxx> >> >>>>Cc: <si-list@xxxxxxxxxxxxx> >> >>>>Subject: RE: [SI-LIST] Re: si-list Digest V3 #194 >> >>>> >> >>>>Sainath, >> >>>> >> >>>>As Thomas pointed out, inductance is the ratio of >> magnetic flux to >> >>>current >> >>>>in the conductor. Magnetic flux is the integral of B dot >> dA, or the >> >> >>>magnetic >> >>>>field [dot product] the surface you are integrating over. >> The "dot >> >>>product" >> >>>>is the same as multiplying the B-field by the area by the >> cosine of >> >> >>>the >> >>>>angle between the B-vector and the normal to the area. So if the >> >>>B-vector is >> >>>>perpendicular to the area surface, then the B-vector is >> parallel to >> >> >>the >> >>>unit >> >>>>normal vector of the area surface, cosine of this zero >> degree angle >> >> >is >> >> >> >>>1, >> >>>>and you simply multiply B*area. Here's an example to illustrate. >> >>>> >> >>>>You have a rectangular metal trace over a ground plane, length in >> >the >> >>>>z-direction, height in the y, width in the x. Stretch a >> rectangle in >> >> > >> >>>the yz >> >>>>plane between the trace and the ground plane. Make it any length >> >>>(smaller if >> >>>>you are simulating with EM tool). If we assume perfect conductors >> (ie >> > >> >> >> >>>no >> >>>>internal-conductor magnetic fields >> ---------End of Included Message---------- >> _____________________________________________________________ >> >> >> ------------------------------------------------------------------ >> 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 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 >> >> > ---------End of Included Message---------- _____________________________________________________________ ------------------------------------------------------------------ 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 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