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calculating the resistance of a wire

Posted Apr 20, 2015, 8:45 a.m. EDT Low-Frequency Electromagnetics, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.0 6 Replies

Aden
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Hi
Can anyone help me with calculating the resistance of a wire using AC/DC Module>Electrostatics(es)?
it's totally simple using Electrical Currents(ec) physics, how about (es)?

Thanks
6 Replies Last Post Apr 24, 2015, 2:39 p.m. EDT
Daniel Connelly
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Posted: 10 years ago Apr 20, 2015, 4:14 p.m. EDT
I was waiting for someone to answer this, but what I can add is there's generally two ways to determine resistance:

1. to solve a stationary problem with a small bias, solving current, and then take the ratio of voltage to current, taking care to adjust for if you've used any symmetric boundaries (eg simulating 1/2 the structure means you need to divide the resulting ratio by 2).
2. to do a small-signal analysis and find the admittance term for one of the terminals @ DC at zero bias. The resistance = 1 / the admittance. Again you need to adjust for any symmetric boundaries.

Maybe someone else can give more information.
I was waiting for someone to answer this, but what I can add is there's generally two ways to determine resistance: 1. to solve a stationary problem with a small bias, solving current, and then take the ratio of voltage to current, taking care to adjust for if you've used any symmetric boundaries (eg simulating 1/2 the structure means you need to divide the resulting ratio by 2). 2. to do a small-signal analysis and find the admittance term for one of the terminals @ DC at zero bias. The resistance = 1 / the admittance. Again you need to adjust for any symmetric boundaries. Maybe someone else can give more information.
Aden
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Posted: 10 years ago Apr 21, 2015, 5:06 a.m. EDT

I was waiting for someone to answer this, but what I can add is there's generally two ways to determine resistance:

1. to solve a stationary problem with a small bias, solving current, and then take the ratio of voltage to current, taking care to adjust for if you've used any symmetric boundaries (eg simulating 1/2 the structure means you need to divide the resulting ratio by 2).
2. to do a small-signal analysis and find the admittance term for one of the terminals @ DC at zero bias. The resistance = 1 / the admittance. Again you need to adjust for any symmetric boundaries.

Maybe someone else can give more information.



Dear Daniel

thanks for your reply.
Actually I have a simple DC Model (a cylinder), calculating the resistance exactly as you said like taking the ratio of voltage to current and then comparing the result with my analytical calculations.
However, I am interested in trying out the same model in different physics in order to find out the probable changes in the resistance value.
so you suggest trying the signal analysis rather than (es)?

Thanks
[QUOTE] I was waiting for someone to answer this, but what I can add is there's generally two ways to determine resistance: 1. to solve a stationary problem with a small bias, solving current, and then take the ratio of voltage to current, taking care to adjust for if you've used any symmetric boundaries (eg simulating 1/2 the structure means you need to divide the resulting ratio by 2). 2. to do a small-signal analysis and find the admittance term for one of the terminals @ DC at zero bias. The resistance = 1 / the admittance. Again you need to adjust for any symmetric boundaries. Maybe someone else can give more information. [/QUOTE] Dear Daniel thanks for your reply. Actually I have a simple DC Model (a cylinder), calculating the resistance exactly as you said like taking the ratio of voltage to current and then comparing the result with my analytical calculations. However, I am interested in trying out the same model in different physics in order to find out the probable changes in the resistance value. so you suggest trying the signal analysis rather than (es)? Thanks
Daniel Connelly
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Posted: 10 years ago Apr 21, 2015, 9:58 a.m. EDT
In the resistor library example there's a parameter: ec.R11 which is the resistance extracted using small-signal analysis. This is the small-signal resistance of contact 1.
In the resistor library example there's a parameter: ec.R11 which is the resistance extracted using small-signal analysis. This is the small-signal resistance of contact 1.
Aden
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Posted: 10 years ago Apr 23, 2015, 5:09 a.m. EDT
Good point. Thanks Daniel ;)
Good point. Thanks Daniel ;)
Aden
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Posted: 10 years ago Apr 24, 2015, 5:58 a.m. EDT
Hello again Daniel :)
just one more question! :)
you know I only have the option of calculating the parameter ec.R11, when I have the ground as boundary condition.
can't we calculate it when having a positive and negative Voltage terminals?

Thanks
Hello again Daniel :) just one more question! :) you know I only have the option of calculating the parameter ec.R11, when I have the ground as boundary condition. can't we calculate it when having a positive and negative Voltage terminals? Thanks
Daniel Connelly
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Posted: 10 years ago Apr 24, 2015, 2:39 p.m. EDT
The meaning of R11 in the AC sense is ∂V1 / ∂I1 with all other terminals held constant. This is presumably 1 / ( ∂I1 / ∂V1) with all other terminals held constant. It's a small signal determination, operating on incremental changes, and so the voltage on other terminals as long as those nodes is constant doesn't matter.

Resistance (and admittance) are matrixes, so you can also calculate, for example, gmn ≣ ∂Im / ∂Vn for terminals m and n. That means if I change the voltage on terminal n with all other terminals held constant than what is the change in the current at terminal m. An example is transconductance in transistors.

The meaning of R11 in the AC sense is ∂V1 / ∂I1 with all other terminals held constant. This is presumably 1 / ( ∂I1 / ∂V1) with all other terminals held constant. It's a small signal determination, operating on incremental changes, and so the voltage on other terminals as long as those nodes is constant doesn't matter. Resistance (and admittance) are matrixes, so you can also calculate, for example, gmn ≣ ∂Im / ∂Vn for terminals m and n. That means if I change the voltage on terminal n with all other terminals held constant than what is the change in the current at terminal m. An example is transconductance in transistors.

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