Tetrahedron impedance planar network -- What is the impedance magnitude between nodes 1 & 2?

This is an AC circuit operating at a frequency of 1 MHz 2 π \frac{1\text{MHz}}{2\pi} . The inductors are 1 mH and the capacitors are 1 nF.

Simplifying assumptions: the components are pure, ideal components, there is no mutual inductance between the inductors and the wiring is negligible.

The device impedance formulae are simple and the frequency was chosen to give integer impedance magnitudes, in the sense that a unit circle in the complex plane has a magnitude of 1 1 around the entire circle. The standard unit for inductors is a Henry and for capacitors is a Farad. Convert the units used above to those units before computing the device impedances.

Kirchhoff's circuit laws and some matrix algebra (simultaneous equations) work should yield the result. If you did the phase angle version of this problem, then you have no more work to do.


The answer is 500.

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2 solutions

With the impedances entered as conductances, the graph is:

The computation method: resistance = With [ { Γ = PseudoInverse [ With [ { wam = WeightedAdjacencyMatrix [ $#$1 ] } , DiagonalMatrix [ Tr/@ wam T ] wam ] ] } , Outer [ Plus , Diagonal [ Γ ] , Diagonal [ Γ ] ] Γ Γ T ] & ; \text{resistance}=\text{With}\left[\left\{\Gamma =\text{PseudoInverse}\left[\text{With}\left[\{\text{wam}=\text{WeightedAdjacencyMatrix}[\text{\$\#\$1}]\},\text{DiagonalMatrix}\left[\text{Tr}\text{/@}\text{wam}^T\right]-\text{wam}\right]\right]\right\}, \\ \text{Outer}[\text{Plus},\text{Diagonal}[\Gamma ],\text{Diagonal}[\Gamma ]]-\Gamma -\Gamma ^T\right]\&; .

The result: ( 0 500 250 + 250 i 250 250 i 500 0 250 250 i 250 + 250 i 250 + 250 i 250 250 i 0 500 250 250 i 250 + 250 i 500 0 ) \left( \begin{array}{llll} 0 & 500 & 250+250 i & 250-250 i \\ 500 & 0 & 250-250 i & 250+250 i \\ 250+250 i & 250-250 i & 0 & 500 \\ 250-250 i & 250+250 i & 500 & 0 \\ \end{array} \right) .

The impedance between nodes 1 and 2, the 500 in the second entry of the first row is the answer. The circuit between nodes 1 and 2 is pure resistive.

graph theory approach seems interesting. can you please tell me easy self explanatory graph theory book for Electrical engineering which has lot of examples.

veeresh pandey - 2 years ago

This method is direct application of Kirchhoff's current and voltage laws stated in matrix form. The single line of code above is the entire description of the computation. You can research each function call by going to https://reference.wolfram.com/language/ and using the search box. This method only work on planar graphs, i.e., can be drawn on a piece of paper without connection lines crossing.

ok . thanks :)

veeresh pandey - 2 years ago
Veeresh Pandey
May 27, 2019

convert middle star to delta then see magic (two branches become open circuit due to infinite impedence of them leaving one branch behind which is between nodes 1 and 2 thus giving 1k||1k=0.5k=500 ohm )

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