When a fan blows air across a room, the airflow typically decelerates and spreads out. Now in a new study, scientists have demonstrated the opposite: an airflow created by a carefully controlled ultrasound array can maintain its narrow shape and accelerate as it moves away from the source. The researchers explain that it's as if the airflow is being pushed along by a sequence of invisible fans floating in mid-air. They expect that the accelerating air stream could have unprecedented applications, such as the ability to perform and control chemical reactions in mid-air.
One of the most interesting features of the beam is that that tilting the ultrasound array is not required to control the beam direction. Instead, the beam is electronically steerable by tuning the wavefronts, which forms a tilted beam without tilting the array.
https://phys.org/news/2017-08-scientist ... d-air.html
This is on a very small scale, only a foot or so, but it leads one to wonder about future possibilities. Could it one day be capable of influencing weather? Remember how ineffective the first LASERs were in comparison to what they can do today.