Hello to everybody, So far, I´ve tried to modify a code, which I´ve found here:
Nx = 128; % Number of samples collected along first dimension
Nt = 1024; % Number of samples collected along second dimension
table = dlmread('table.txt');
table = table(:,2:129);
dx = 0.009; % Distance increment (i.e., Spacing between each column)
dt = 1/(150e3*40); % Time increment (i.e., Spacing between each row)
x = 0 : dx : (Nx-1)*dx; % distance
t = 0 : dt : (Nt-1)*dt; % time
Nyq_k = 1/dx; % Nyquist of data in first dimension
Nyq_f = 1/dt; % Nyquist of data in second dimension
dk = 1/(Nx*dx); % Wavenumber increment
df = 1/(Nt*dt); % Frequency increment
k = 0:dk:Nyq_k-dk; % wavenumber
f = 0:df:Nyq_f-df; % frequency
figure;
fft2result = fft2(table)*dx*dt;
imagesc(f,k,abs(fft2result));
colorbar;
Where "table" is a matrix of following dimension 1818x128. Each column represents the time record of displacement perpendicular to the plate. There are 128 points altogether with spacing of 9 milimeters. The plate thickness is equal to 8 milimeters and the frequency of the excitation signal is 150 kHz. After executing the above mentioned code, I will obtain following representation:
I cannot explain, why there are two significant areas instead of one and also, why the frequency is so high. I am also attaching the file with the signals.
