Any idea how hard the ultrasound radiation pressure (used in the tactile holograms) would be to make? I guess you just need transducers, and some software to t

Any idea how hard the ultrasound radiation pressure (used in the tactile holograms) would be to make? I guess you just need transducers, and some software to time them correctly? That's unbelievable to me. They say they can't get very powerful though or stray sound would damage your hearing. I wonder if there's any way around that? i.e., different frequencies?