I am thinking some kind of subspace force beam that comes down from the transporter emitter on the ship to the beam-in point (and subspace, because I don't see the ship punching microholes in whatever materials are line-of-sight between the ship and the beam-in point), then said beam widens out to some two-foot radius and creates a human-sized cylinder, then the transported matter is sent down via the subspace wave to be recomposited as human.
Have we discussed in the BBS how this all works?
For some reason I always assumed that's what the annular confinement beam was for - but I looked it up on Memory Alpha and aparently I was wrong.
But such a component to the transporter beam *must* exist...I remember an early Enterprise episode where they triend to beam up a crewmember in a windstorm and he arrived with all sorts of leaves and debris incorporated into his body...later transporters would'nt do that, otherwise Checkov & Terrel would have arrived on Ceti-Apha 5 full of sand! (Not to mention everybody who attemped to travel via transporter dying of painful embolisms!)
I always figured that tube of light you see in the TMP & Generations beaming effect was a visible version of that "shield"...