Modelling a RC circuit

Hi, I'm trying to model a RC circuit with two R's and one C in parallel. R1,R2,C are vectors which change at a function of time.

I'm calculating the total impedance of the system and then applying an AC current I=I_0*sin(w*t).

My goal is to measure the voltage, I've tried working in the time- domain and also in the frequency domain but I'm having trouble calculating the voltag. it is expected that I will get a sine wave with a phase shift from the current signal , but from some reason it not what I'm getting.

Also, I want to plot the two signal , the input current and the output voltage on the same graph as a function of time so I could see the time shift between them, I'm guessing that the problem I have with that is that the imaginary part of V is not plotted in matlab and that is the part that is responsible for the phase shift. Is there a way to get pass that?

Here is the code that I wrote :

Fs=2000000;

f=10000;%[Hz]Current frequency 

t=[0:(1/Fs):0.1-(1/Fs)];%[sec] one cardiac cycle

w=2*pi*f;%[rad/sec]

Cm1=linspace(343*10^-12,448*10^-12,100000);

Cm=[Cm1,Cm1(end:-1:1)];%[F] Myocardium capacitance through one cardiac cycle

Gm1=linspace(173*10^-6,226*10^-6,100000);

Gm=[Gm1,Gm1(end:-1:1)];%[S] Myocardium conductivity through one cardiac cycle

Gb1=linspace(810*10^-6,402*10^-6,100000);

Gb=[Gb1,Gb1(end:-1:1)];%[S] Blood conductivity through one cardiac cycle

%Calculating the admittacne

Y=Gb+Gm+1i*w*Cm;

Y_fft=fft(Y);

%Generating the current applied

I_0=15*10^-6;%[A]

I=I_0*sin(w*t);

I_fft=fft(I);

V_fft= I_fft./Y_fft;

v=ifft(V_fft);

plot(t(1:5000),v(1:5000),t(1:5000),I(1:5000));

Thank you so much for you help!

if you think I should rather work with Simulink let me know (:

Answer 1

[Rick Rosson]

The circuit is not time-invariant. Yet you are applying techniques, such as the DFT, that apply only to time-invariant systems.

[aviran]

You are right. so is there a way to solve a circuit like that? maybe in the time domain?

[Ruben Díaz Granero]

Hi! I've a similar problem operating with the FFT but instead of trying to analyze an output singal I want to obtain the impedance. Nevertheless is the same problem. Do you find any solution?

Thanks!