It does not have to be designed to push people, it just needs to generate forces required to push them, and be light weight. They don't exist because of the Physics, as I repeatedly keep saying. There is a direct correlation between the size of the fan, the forces it generates, and its weight (area = Pi times radius squared).
More area = more air = more force = more required horse power = farther the air will travel = heavier device.
If it was possible to make a light weight fan with the characteristics you describe, they would. It would have many uses in aerospace and industry.
In the world today the devices that generates the most thrust to weight ratio's are:
- Rocket engines (would fry some one before it would push them)
- Jet Engines. (They can produce the thrust but are weight prohibiting when they get big enough to push someone over.)
- Industrial fans (Same issue as Jet Engines).
Added:
Laser scanners are quit common, easy to build, and come in many forms.
http://en.wikipedia.org/wiki/3D_scannerSince the CT's and T's have unique silhouettes you would recognize the differences in silhouettes. Neural networks exist to recognize people through pattern recognition and can be trained to recognize different patterns:
http://en.wikipedia.org/wiki/Facial_recognition_systemhttp://en.wikipedia.org/wiki/Pattern_recognitionhttp://en.wikipedia.org/wiki/Prior_knowledge_for_pattern_recognitionHere is a real world example of a robotic sentry gun designed for use on the boarder of South Korea, complete with video:
http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=762