I still need to find out more but here is a little bit that I just copied and pasted here
"The key to root development in an aeroponic environment is the size of the water droplet. In commercial applications, a hydro-atomizing spray is employed to cover large areas of roots utilizing air pressure misting.
A variation of the mist technique employs the use of ultrasonic nebulizers or foggers to mist nutrient solutions in low-pressure aeroponic devices.
Water droplet size is crucial for sustaining aeroponic growth. Too large of a water droplet means less oxygen is available to the root system. Too fine of a water droplet, such as those generated by the ultra-sonic mister, produce excessive root hair without developing a lateral root system for sustained growth in an aeroponic system.
Mineralization of the ultra-sonic traducers requires maintenance and potential for component failure. This is also a shortcoming of metal spray jets and misters. Restricted access to the water causes the plant to lose turgidity and wilt."