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How can I remove negative values from vector (Half-Wave Rectification)

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jaylynn markey
jaylynn markey on 3 Nov 2020
I need help removing the negative values from a vector. I I started with an EMG signal and converted the signal from the time domain to the frequency domain using fft. Next I applied a bandpass filter from 25-400 Hz to get a filtered signal. Now I need to apply a half wave rectification. I would like to use a for loop to remove the ngative values from v_mag_filtered. I'd appreciate the help, I'm a bit rusty on MATLAB
% Time Signal
max_index = 10000;
freq = 960;
t_step = 1/freq;
for i = 1:max_index
t(i) = (i-1)*t_step;
v(i) = EMG(i) * 1E-6;
end
% Power spectrum
for i = 1:max_index
freq_range(i) = (1/t_step)*(i-1)/max_index;
end
v_freq = fft(v,max_index); %complex vector of ECG singal
v_mag = 2*v_freq.*conj(v_freq)/(max_index)^2; %phase information of complex number removed
x = freq_range(1:max_index/2);
y = v_mag(1:max_index/2);
%band pass filter
v_freq_filtered = v_freq;
for i = 1:max_index
if ((freq_range(i)<25))
v_freq_filtered(i) = 0.0;
end
if ((freq_range(i)>400))
v_freq_filtered(i) = 0.0;
end
end
v_mag_filtered = 2*v_freq_filtered.*conj(v_freq_filtered)/(max_index)^2;

Answers (3)


Star Strider
Star Strider on 3 Nov 2020
Try this:
t = linspace(0, 6*pi, 1E+5);
s = sin(t);
idx = s >= 0; % Conditional Logical Index
s_hwr = s.*idx; % Signal With Half-Wave Rectification
figure
plot(t, s_hwr)
grid
ylim([-1 1])
This will work regardless of your signal. Since ‘EMG’ is not provided, I use ‘s’ instead here.
  2 Comments
Star Strider
Star Strider on 4 Nov 2020
Sure!
I chose 3 cycles to provide a representative waveform, and elements to produce a smooth plot. All of these (in this example) are arbitrary, so choose whatever values you want (within reason, and within the available memory capacity of your computer) to experiment with.

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m.venkata manohar reddy
m.venkata manohar reddy on 1 Aug 2021
Find the Fourier series of the function obtained by
passing the sinusoidal voltage v(t) = v0 cos(100πt)
through a half wave rectifier given in figure that clips
the negative waves

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