jadi001:
the object being pinged is a potential human or not. So in this case, if the device could detect cloth, it will be fantastic as I couldn't really think of a situation where there would be cloths hanging around freely.
You guys don't use curtains and table cloths?
What I was really trying to distinct is hard surface and soft surface, since I am assuming there wouldn't be any humans walking around wearing an armor.
Lycra leggings, or the bare legs of people wearing shorts/miniskirts would probably read as hard object. A hard object with flat surfaces reflecting most of the sound away from it rather than back, may well read as a soft object.