We can use waves to model almost everything in the world from the thing we can see or touch to the things which we can’t.

Here, we try to model the waves itself.

Moving Waves

clear; close all; clc

a=1;    %amplitude

f=5;    %frequency

T=1/f;  %time period

w=2*pi*f;   %angular frequency

lb=2*T; %wavelength

k=2*pi/lb; %wavenumber

x=0:pi/200:10*pi;

t=0:0.01:2; %time

figure(1)

for i=1:length(t)

    y=a*sin(k*x-w*t(i));    %waveform

    plot(x,y)

    pause(0.1)

end

Screen Shot 2016-11-03 at 5.13.22 PM.png

Fourier Transform to analyse the amplitude spectrum

clear; close all; clc

fs=1000;    %sampling frequency

t=0:1/fs:1.5-1/fs;%time

f1=10;  %frequency1

f2=20;  %frequency2

f3=30;  %frequency3

%x=5*sin(2*pi*10*t+3);

x=1*sin(2*pi*f1*t+0.3)+2*sin(2*pi*f2*t+0.2)+3*sin(2*pi*f3*t+0.4);

plot(t,x)

figure(1)

grid on

xlabel('Time')

ylabel('Amplitude')

title('Plot of 2*sin(2*pi*f1*t+0.3)-3*sin(2*pi*f2*t+0.2)+5*cos(2*pi*f3*t+0.4)') 

X=fft(x);

fre=fs/length(t);

fre_hz=(0:length(t)/2-1)*fre;

X_mag=abs(X);   %X is complex

figure(2)

plot(fre_hz,X_mag(1:length(t)/2))

grid on

axis([0 40 -inf inf])

xlabel('Frequency (in hz)')

ylabel('Magnitude')

title('Magnitude spectrum of 5*sin(2*pi*10*t+3)')

screen-shot-2016-11-03-at-5-17-59-pm

screen-shot-2016-11-03-at-5-17-46-pm

Hilbert Transform and get the envelope of the waveform

clear; close all; clc

fs = 1e4;   %sampling frequency

t = 0:1/fs:1;   %time

f1=10;  

f2=20;

f3=30;

x=1*sin(2*pi*f1*t+0.3)+2*sin(2*pi*f2*t+0.2)+3*sin(2*pi*f3*t+0.4);

%x=5*sin(2*pi*10*t+3);

y = hilbert(x);

figure(1)

plot(t,real(y),t,imag(y))

% %xlim([0.01 0.03])

legend('real','imaginary')

title('Hilbert Function')

figure(2)

env=abs(y);

plot(t,x)

xlabel('Time')

title('Envelope')

hold on

plot(t,env)

legend('original','envelope')

screen-shot-2016-11-03-at-5-21-40-pm

Screen Shot 2016-11-03 at 5.21.53 PM.png

 

Application of Hilbert Transform: Edge Detection and comparison with the classical derivative method

clear; close all; clc

x = 0:0.1:100;

y = channel(x,[10 30 70]);  %channel function to define a trapezoidal channel

plot(x,y)

figure(1)

subplot(311)

plot(x,y)

grid on

title('Channel')

subplot(312)

deriv =diff(y); %dervative of the channel

plot(x(2:end),deriv)

title('Detection by derivative method')

grid on

subplot(313)

hil = hilbert(y);   %hilbert transform of the channel

env=abs(hil);

plot(x,env)

grid on

title('Detection by hilbert transform')

screen-shot-2016-11-03-at-5-25-10-pm

 

Channel Function

 

  • – Utpal Kumar, IES, Academia Sinica