It's pretty simple - you have a space surrounded by vertical-facing, powerful extractors. Smoke doesn't leave the area, as it is caught in the downward currents.

On some, there are also ashtrays with extractors around them, as well as reservoirs (with liquid to put the cigarettes out). BAA seems to think you're better off with their awful ashtrays, though.

The writing on the extractors is Japanese, so I can only assume this is the country of origin...