Risa

Ask whatever you like, I apparently have no depths to which I will not sink to embarrass myself lol

That being said I'm not sure how they work precisely. I don't know if they've ever talked about that much on screen and I am pretty sure it's not in the TNG Tech Manual. Not sure about others. I know that Reed described it as a 'stable EM barrier' and that they are generated from transmitters throughout various junctions and corridors. However forcefields are also just miniature versions of the shields we see around ships. Those are generated using a high concentration of gravitons to generate layers of disruptive energy that cocoon the ship in it's protective shield. Presumably the same sort of technology is being used but on a significantly smaller scale and with less overall power.