Hi,
I'm trying to simulate a localized sound field in air using the sound from ultrasound techniques (http://en.wikipedia.org/wiki/Sound_from_ultrasound). I've got two ultrasonic sources, one at 20 kHz and one at 21 kHz. Looking at the frequency spectrum of a sensor placed at the point where the two waves meet it does not give the expected result which is a harmonic at the difference frequency of 21 kHz - 20 kHz = 1 kHz.
the grid is set up as follows:
c0_min = 343;
f_max = 25e3;
x_size = 1;
y_size = 1;
points_per_wavelength = 2;
dx = c0_min/(points_per_wavelength*f_max);
dy = dx;
Nx = round(x_size/dx);
Ny = round(y_size/dy);
kgrid = makeGrid(Nx, dx, Ny, dy);
The medium is set up as follows:
medium.sound_speed = 343;
medium.alpha_coeff = 2.4*10^(-7);
medium.alpha_power = 1.4484;
medium.density = 1.045;
medium.BonA = 0.4;
[kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed);
The sensor data looks like this: http://imgur.com/T9zuyN4
A FFT of this data looks like this: http://imgur.com/ZB2eFQ4
Is it possible to simulate the nonlinear effects with k_wave? If so what am I doing wrong?