# How can I implement a frequency-dependent resistor in Simulink?

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Angelis Karlos on 17 Oct 2017
Commented: Bruno Neri on 21 Nov 2017
Hello,
I have an electrical circuit describing a mechanical system, in which there is a frequency-dependent resistor, following a formula of R=R_0*sqrt(f). I was wondering how I can define such a resistor in Simulink. I have made the model using Simulink components, not physical ones.
Thanks, Angelis Karlos

David Ding on 19 Oct 2017
Hi Angelis,
My understanding is that you have an electrical circuit in Simulink, and you would like to model a variable resistor dependent on some frequency value.
There are only two places where you can find a variable resistor in Simulink. One is under RF Blockset and the other is under Simscape. In both cases, the usage of the variable resistor is the same. The resistor block will have three ports: positive node, negative node, and the inport where the resistance is determined.
For the RF Blockset, you may find the "Variable Resistor" block under RF Blockset -> Circuit Envelope -> Elements". You may feed the "R" port of that block with the resistance defined as per your formula, using a MATLAB function block, for example.
If you are using Simscape, the "Variable Resistor" block is found under Simscape->Foundation Library->Electrical->Electrical Elements. The usage is similar to that in the RF Blockset.
Thanks,
David
Bruno Neri on 21 Nov 2017
Hi David, I have kind of the same problem, but I didn't really unterstand your answer.
I have to implement the resistance of an Inductor at one of my simulations. But the value of the resistance given by the manufacturer changes according to the frequency. I'd have to implement it up to the 50th Harmonic. And all of the components are connected to the system. Which means, that resistance would have different values for different frequencies at the same simulation. I could "call" the resistance values from a vector since I already them.
Is that possible to implement?