So I am trying to estimate blood velocity using Doppler ultrasound. We have a complex signal y(t)= i (t) + j* q(t). i(t) and q(t) contain unwanted high frequency components created by the demodulation process and low frequency signals that are reflections from stationary tissues. I need to design a bandpass filter to remove these unwanted signals. The higher cutoff frequency of the bandpass filter is can be set at 10000 Hz and the lower frequency at 100 Hz. I am trying to calculate the Fourier transform of y(t) using a time window t(0)-tau<t<t(0) +tau to estimate instantaneous blood speed at t= t(0). This is my matlab code so far:(adsbygoogle = window.adsbygoogle || []).push({});

it=xt.*cos(2*pi*f0*t);

ht=9900*sinc((9900)*(t)).*exp(((20000*pi-200*pi)/2+200*pi)*j*t);

ift=conv(it, ht*ts);

qt=xt.*(cos(2*pi*f0*t)-sin(2*pi*f0*t));

qft=conv(qt, ht*ts);

cft(ift, ts,1)

The above is my lowpass filter. Then I used numerical convolution to calculate an approximate output of the filter output i(t) and q(t) when the input is i(t) and q(t) respectively:

for k=1:50

yt=ift+j*qft;

yk =yt(1:length(t)).* ((t>=.02 .*k - .02) - (t>= .02 .*k + .02)) ;

[Yw, w] = cft(yk, ts, 1 ); % calculate the Fourier transform, where

[maxY w_index] = max(abs(Yw)); % find the peak in ||xw||

omega_m(k) = w(w_index); % omega_m(k) is the Doppler shift frequency

end

but when I multiply y(t) by p(t-t0) I get 0 for my w0 and blood velocity is zero everywhere..What am I supposed to do?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Complex signal construction

Loading...

Similar Threads for Complex signal construction |
---|

Coupling signals to a stripline transmission line |

Carrier Signals and demodulation of audio waveforms |

Why do we normalise a signal (function)? |

On Radio Waves |

Complex Exponentials Signal processing |

**Physics Forums | Science Articles, Homework Help, Discussion**