I'm running the "Modelling Nonlinear Wave Propagation Example" in Matlab with a time varying source that produces linear sine sweep centered at 1 MHz and spanning 0.9 MHz. I want to see the higher order harmonics so I set up the time and grid parameters so that I have 674 MHz sampling rate and 101 MHz maximum supported frequency. When I look at the resulting spectrum of the sensor data, I see bunch of frequencies are squished around 95101 MHz. Please see this link (https://imgur.com/a/71uxjbq ) for the spectrum. To my understanding, aliasing doesn't seem to explain this. I'd still expect a decreasing pattern in higher frequencies even if they were aliased. Am I missing something? What could the reason be?
kWave
A MATLAB toolbox for the timedomain
simulation of acoustic wave fields
High frequencies are not aliased but instead compressed together?
(3 posts) (2 voices)
Posted 1 month ago #

Hi gk7,
Could you try running your simulation under linear conditions (don't define
medium.BonA
) to see if you still see the high frequencies? It could be related to your source definition rather than the nonlinearity. You have a very flat spectrum before the highfrequency peak, which doesn't immediately look like spectral blocking.Brad.
Posted 1 week ago # 
Hi Bradley,
I checked out the linear spectrum. As you suspected, it's flat except the main lobe at 1 MHz without high frequencies. How do I need to define the source to obtain proper results with nonlinear simulations?
Posted 6 days ago #
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