This is my version of the Micro Ultrasonic Levitator project from Make Magazine.
The bracket part that I uploaded is sized about right for the object to float in the middle of the ultrasonic transducers. One of the transducers needs to be wired with the opposite polarity of the other. If they are wired with the same polarity the objects will not float directly in the middle of the transducers (and the distance would need to be changed). When the transducers are wired with the same polarity the objects will float a little above and below the midpoint between the transducers.
The 6-32x1/2" machine screws (and nuts) on the bracket allow the transducers to be adjusted up and down a bit then fastened in place when the optimum position is found.
This item can be modified using the Thingiverse customizer to make the gap whatever you would like to try.
Here is a link to a short Instagram video of the levitator in action. https://www.instagram.com/p/Bo7lbjCgkxV/
I also included a picture of the electronic parts I used to make the levitator .