Realization of SSH model through electrical circuits -- how to measure impedance?

Question

I am trying to reproduce the results given in this paper. The authors create a circuit whose $I-V$ equations are similar to the Hamiltonian of the SSH model. And then through impedance measurement, they prove the existence of edge-states in the circuit. I am trying to simulate the circuit in LTspice and having some problem in impedance measurement. This is the circuit that realizes the SSH-model (green wires can be ignored):

I have created a circuit till node 10 (this circuit is used to do the actual experiment):

I want to measure the impedance between nodes 1 and 10. Is $frac{V_1-V_{10}}{I_1}$ the correct expression? I don't think this is correct as all the current $I_1$ that enters node 1 may not leave node 10, some of it may go into ground. I want to know the correct expression for impedance or is my approach for impedance measurement is totally wrong?
Also, is this question more suitable for Electrical Engineering Stack Exchange?

Laurie · Answer

Thevenin" theory states (Wikipedia)
"a) Any linear electrical network containing only voltage sources, current sources and resistances can be replaced at terminals A-B by an equivalent combination of a voltage source Vth in a series connection with a resistance Rth.
b) The equivalent voltage Vth is the voltage obtained at terminals A-B of the network with terminals A-B open circuited.
c) The equivalent resistance Rth is the resistance that the circuit between terminals A and B would have if all ideal voltage sources in the circuit were replaced by a short circuit and all ideal current sources were replaced by an open circuit.
d) If terminals A and B are connected to one another, the current flowing from A to B will be Vth/Rth. This means that Rth could alternatively be calculated as Vth divided by the short-circuit current between A and B when they are connected together."
The theorem applies exactly for AC circuits too, just substitute impedance for resistance.
You could follow d) above and using LTspice, simulate a short between nodes 1 and 10 and measure the current Ishort.
The impedance between nodes 1 and 10 is
(V1 - V10)/Ishort

Realization of SSH model through electrical circuits -- how to measure impedance?

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