Here are some animations and figures from my presentation at the COMSOL Conference in Cambridge last year, showing how sound fields can be manipulated using topology optimization. You can cite [1] if you want to recreate any of these.
Criss-cross splitter:
De-multiplexor:
Mode Converter I - 01-to-02 mode:
Mode Converter II - Evanescent_01-to-00 mode:
Mode Converter III - 3D complex mode to 00 mode (Before and after):
Cloacking:
Tweeter Phase Plug:
You can of course read much more about the details in the paper and presentation.
[1] R. Christensen, "Acoustic Topology Optimization – Implementation and Examples", COMSOL Conference 2019 Cambridge, https://www.comsol.dk/paper/acoustic-topology-optimization-implementation-and-examples-81961