We were at school together <a href=" http://fuq.in.net/#tolerant ">fuq.</a> We perceive the waves as vibration on theskin, and by varying the modulation frequency or pulsing the feedback, different 'textures' can be created. And by giving each feedback point a different modulationfrequency, different feedback is produced, allowing different textures to be applied to the user at the same time, potentially allowing for a range of mid-air sensations.