followed this: https://www.youtube.com/watch?v=HTgBzRgAFNs
the logic is that when you send a 40khz. wave, and invert another one right opposite, the pressure from the two affect the air molecules in between in such a way that a particle can be suspended between them.
nasif helped me desolder ultrasonic speakers / receivers from the module that they come on, by suggesting to use the heat gun. a transducer (such as a speaker or a mic) can be used for different purposes (because they do the same thing).
i fiddled around a lot with different ways to make this happen, but ended up following the youtube tutorial for the base build.
first figured out tracking waves by using a function generator sending a signal to the oscilloscope.
video 1:
nataly helped me take this one. video 2:
schematic: https://edisonsciencecorner.blogspot.com/2020/06/blog-post_18.html