| T O P I C R E V I E W |
| Jennes |
Posted - Mar 24 2015 : 00:44:53
I hope my question is not to trivial for the experts. I didn't get an answer so far. Am I completely on the wrong track?
So here is my setup:
.units meters
*
*ground plane definition
*
g1 x1=0 y1=0 z1=0.0
+ x2=0.25 y2=0 z2=0
+ x3=0.25 y3=0.25 z3=0
+ thick=0.005 seg1=30 seg2=30
+ sigma=3.6e+07 nhinc=1
*+ nin1 (0.125,0.01)
*+ nout1 (0.125,0.0150)
+ hole circle (0.125,0.125,0,0.005)
* The nodes for a wire through the hole
N1 x=0.125 y=0.125 z=0.2
N2 x=0.125 y=0.125 z=-0.2
* The elements connecting the nodes
E1 N1 N2 w=0.001 h=0.001
* Short together the end of the L shaped trace (N3) and its corresponding
* point on the ground plane directly beneath (nin)
.equiv nin n1
.equiv nout n2
* compute loop inductance from beginning of L (N1) to its corresponding
* point directly underneath (nout)
*.external N1 nout
.external nin nout
*
*
.freq fmin=1 fmax=2e4 ndec=10
.end
I would like to induce a current from nin to nout, this current has a frequency f which seems to not a problem for a quasi static solution, right? I get values from the simulation but those seem to be strange... 0.00689655H, or 6.7mH?
Thanks for a hint.
Best regards,
Jens
Best wishes,
Jens |
| 5 L A T E S T R E P L I E S (Newest First) |
| Enrico |
Posted - Apr 06 2015 : 10:45:22
I'm sorry, but FastHenry2 does not support mu values different from one. Ferromagnetic material support is not included.
Best Regards,
Enrico |
| Jennes |
Posted - Apr 04 2015 : 19:24:36
Thanks a lot for your patience in this topic. This is, by the way, what I expected from an aluminium plane which I used here. Just given by sigma.
Now my next question: As you said, the magnetic field goes through the plate but how do I assign mu for a strong ferromagnetic material?
Say I have mu_r>>1?
I didn't see an exmaple setting mu_r. Thanks!
Best wishes,
Jens |
| Enrico |
Posted - Mar 31 2015 : 20:03:36
Let's start considering how things work at low frequency in capacitance case. Basic electromagnetic theory tell us that at low frequency, when the fields are static, the electric field does not penetrate into conductors. The rationale is, if we had an electric field inside the conductor, the free charges would start moving towards the surface, so there wouldn't be any equilibrium. Therefore, due to the accumulation of charges on the surface, we have a shielding effect for the electric field.
The same concept however is not true for magnetic fields, if we are considering materials with relative permettivity (#956;r) approaching one (that is, non-ferromagnetic materials). In this case, the field penetrates the conductors, without being significantly disturbed.
However, when the frequency increases, things start to change, because of the proximity effect. That is, eddy currents are induced on nearby conductors. However, you need a (relatively) high frequency to see this effect in action.
FastHenry2 could be used to perform simulated experiments to clarify the theory and work with some quantitative results.
First simulate the lone wire. Then add a ground plane near to the wire. Note that you don’t need to create a port on the ground plane to see its effect on the wire.
Running FastHenry2, it can be observed that at low frequencies the results are the same with or without the insertion of the ground plane. However, when the frequency increases, also the high-frequency effects start playing a significant role. As a consequence, in the presence of the ground plane, the high-frequency resistance increase and inductance drop are more pronounced.
In your case, the gnd plane however hardly plays any effect.
First, the frequency at which you run the simulation is too low.
Second, a gnd plane placed in that position is not really coupled to the loop. The gnd plane will not model current flowing along the z-axis, that would be the only one receiving some coupling from the wire passing through the hole, and the other parts of the loop are too far. You can see the effect with a gnd plane near the loop, e.g.
g1 x1=0 y1=0.04 z1=-0.3
+ x2=0.70 y2=0.04 z2=-0.3
+ x3=0.70 y3=0.04 z3=0.3
+ thick=0.03 seg1=50 seg2=50
+ sigma=3.6e+07 nhinc=10
Said that, there is also another point worth clarifying in your last post. If it is true that the magnetic fields are not shielded by materials with (almost) unitary mr, it is still possible to reduce the loop impedance of a conductor. To this goal let's take the example of two wires over a ground plane. The loop impedance depends on where the 'return' path for the current is located; therefore, if you insert a third conductor between the two conductors and connect it at both ends to a ground plane, a current can flow to reduce the magnetic field. But since you must be able to make current actually flow in your conductors, you cannot appreciate this effect completly from the inductance matrix but it is better seen with a circuit simulator. This concept, however, is very delicate, since shielding depends on where the foreseen 'return' path for the current flowing in your lines is (i.e. in a nearby gnd plane, as could happen in a PCB, or very far on some other conductor, as could happen in a dense connector).
I hope to have shed some light in this topic.
Best Regards,
Enrico
|
| Jennes |
Posted - Mar 27 2015 : 19:17:04
quote:
Originally posted by Enrico
The original file you modified had a wire in close proximity with the gnd plate, so the current loop of which FasterCap could calculate the inductance was well defined.
In your case, you have a wire which is perpendicular to the gnd plane. So you are not forming a loop. Please remember that inductance is a propriety of a closed loop. We can also define a concept of partial inductance, however this should be used only to partition a loop, and is not corresponding to a physical case (in a nutshell, the partial inductance of a segment is equivalent to the inductance of a loop defined by the segment, two lines perpendicular to the segment starting at the end points, and closed at infinity).
Thanks a lot for your reply. Nevertheless, so far I am in the dark...
First my code:
*This is the input deck to calculate effective inductance
*This plane has a dimension of 0.25 X 0.25
*
.units meters
*.default nhinc=5
*
*ground plane definition
*
g1 x1=0 y1=0 z1=0.0
+ x2=0.20 y2=0 z2=0
+ x3=0.20 y3=0.15 z3=0
+ thick=0.03 seg1=50 seg2=50
+ sigma=3.6e+07 nhinc=10
*+ nin1 (0.125,0.01)
*+ nout1 (0.125,0.0150)
+ hole circle (0.10,0.075,0,0.005)
* The nodes for a wire through the hole
N1 x=0.1 y=0.075 z=0.2
N2 x=0.1 y=0.075 z=-0.2
N3 x=0.6 y=0.075 z=-0.2
N4 x=0.6 y=0.075 z=0.2
* The elements connecting the nodes
E1 N1 N2 w=0.001 h=0.001
E2 N2 N3 w=0.001 h=0.001
E1 N3 N4 w=0.001 h=0.001
E1 N4 N1 w=0.001 h=0.001
* calculate between n1 and n2, loop is closed
.equiv nin n1
.equiv nout n2
* compute loop inductance from beginning of L (N1) to its corresponding
* point directly underneath (nout)
.external nin nout
*
*
.freq fmin=2e4 fmax=2e4 ndec=1
.end
I created a loop (in my eyes) but the result is exactly the same if I am commenting out the plane. Seems the wire doesn't see the plane...
seems the inductance is calculated for the wire only?!
It seems I can't place LaTex here but I try to describe the problem... I would expect that the wire current (dI/dt=I0*sin(omega*t)) induces eddy current in the plate.
This leads to energy loss by Ohm resistance as well as a magnetic field in counter direction to the inducing current.
What I would like to have is the plate as an inductor...
The capacity is of second order for me.
Thanks a lot for further support, I think I get something wrong...
Best wishes,
Jens |
| Enrico |
Posted - Mar 24 2015 : 18:41:13
The original file you modified had a wire in close proximity with the gnd plate, so the current loop of which FasterCap could calculate the inductance was well defined.
In your case, you have a wire which is perpendicular to the gnd plane. So you are not forming a loop. Please remember that inductance is a propriety of a closed loop. We can also define a concept of partial inductance, however this should be used only to partition a loop, and is not corresponding to a physical case (in a nutshell, the partial inductance of a segment is equivalent to the inductance of a loop defined by the segment, two lines perpendicular to the segment starting at the end points, and closed at infinity).
For a good introduction to the concept I suggest you to read M. Kamon paper "Fast Parasitic Extraction and Simulation of Three-Dimensional Interconnect via Quasistatic Analysis", PhD thesis at the Massachusetts Institute of Technology, Feb 1998, pages 53-55. You can freely download the thesis from the MIT web page (see Links under the Services web page) or via Google Scholar.
One additional clarification: FastHenry2 results are in H (but if you directly read the Zc.mat output file, watch out that here the results are multiplied by 2*pi*f. You can find a detailed description in the User's guide).
Best Regards,
Enrico
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