Hello,
First of all thank you so much for this useful toolbox.
I was wondering if k-wave has the capability to back propagate nonlinear waves for source identification and similar applications? Is it possible to reverse the harmonic generation phenomenon and end up with a single harmonic time signal at the source surface?
Thanks,
Hi ahmedsaliam,
Great question. Theoretically you can backpropagate nonlinearly steepened waves, so long as they haven't reached the point at which they have formed a shock, as then information loss occurs. In practice, the absorption needs to be considered. For purposes such as these, you can reverse the absorption to that it acts to amplify the signal, by using medium.alpha_sign = [-1 1], which puts a negative sign in front of the absorption term but leaves the dispersion alone.
Best wishes
Ben
Thanks for the reply Dr. Cox,
How would you go about reversing the effect of harmonic generation in terms of the K-wave environment and functions? Are there any provided examples that could be useful in this direction? (I couldn't find any myself)
Appreciate it!
Hi ahmedsallam,
The harmonic generation is the frequency-domain manifestation of the wave steepening. Time-reversing the waves, ie. using time series recorded over many points covering a surface as sources and inputting them in time-reversed order, will undo the steepening and so will undo the harmonic generation.
There are some time-reversal examples in k-Wave for photoacoustic sources, eg. http://www.k-wave.org/documentation/example_pr_2D_tr_circular_sensor.php which could be made nonlinear by setting a value for medium.BonA and making the initial pressure amplitude high enough.
Best wishes
Ben
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