Frequency response!!

Dear All,

I am a bit puzzled with obtaining the frequency response of my system! I am applying a voltage V(t) at a certain frequency f, and I have computed the resulting current as I(t). I want to get the frequency response from these two sine waves! lets say the real and imaginary part of the impedance.

Could you show me a simple procedure to get it!! should I use "system identification toolbox"? or are there any alternative ways!

Thanks in advance

[Jarrod Rivituso]

What format is your system in? Is it a Simulink model? Or an LTI object? Or something else?

[Foxbat]

Thanks, No, it is not a Simulink model! it is calculated from another software "Comsol" by using matlab (M-file). It is a physical system in which I am interested to get the frequency response. so as a result I have I(t) as output data and V(t) as input!

Answer 1

[Rajiv Singh]

Please see tfestimate (Signal Processing Toolbox), spa, spafdr, etfe (System Identification Toolbox) for functions that calculate the frequency response from time domain signals in a non-parametric (empirical) fashion.

Perhaps a more reliable way is to compute a dynamic linear model from the data and then obtain the frequency response by calling BODE or FREQRESP on it. For example:

z = iddata(I, V, Ts); % Ts is sample time

model = n4sid(z, 1:10); % state-space model or order between 1 and 10

H = freqresp(model, linspace(0, pi/Ts, 100)); % the frequency response

This requires System Identification Toolbox.

Answer 2

[Arnaud Miege]

If you have two time series, you probably need to use fft to convert the data into the time domain and compute the frequency response.

HTH,

Arnaud