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?