I wonder whether this has any practical use. Touch screens already remove physical feedback and it's very hard to use them with your eyes closed when you can't confirm your actions in any other way than looking, unless you have accessibility software.
Now, with this "invisible touch screen", not only can you not see the phone, but instead of moving your fingers on a smooth surface, you use something that is neither smooth or comfortable and it certainly isn't the same shape as an iPhone screen.
Besides all that, when the technology can detect any gesture, why limit ourselves to arbitrarily tapping our hand. It would be a lot more useful to just bind a few simple gestures to features that you use often.