Thanos has been referenced several times as having 3 separate force fields at his disposal.
The tech forcefield is shown in this instance:
http://img246.imageshack.us/img246/66/energy8qa2.jpg
Notice how it is clearly separate from his body and sits out in front of him. Notice also how he moves his fingers in order to bring it up. This is his tech forcefield. It causes very little to no strain to use, and doesn't seem to tap into his personal power reserves much. His personal tech power also fuels his flight and teleportation abilities.
In instances where he teleports someone you will typically see him perform finger movements, this is linked into his personal technological arsenal.
For instance:
http://img370.imageshack.us/img370/4387/energy141bz3.jpg
http://img176.imageshack.us/img176/9791/energy142sq1.jpg
Here Thanos uses a huge forcefield, most likely tech:
http://img242.imageshack.us/img242/5219/energy25iz7.jpg
Here we see Thanos with prep having his forcefield survive Galactus' blast:
http://img139.imageshack.us/img139/6706/energy31uw6.jpg
The above instances are all clearly tech forcefields.
Here is another instance, when he blocks Thor wielding the power gem:
http://img92.imageshack.us/my.php?image=bbt38nq.jpg
It's clearly in the shape of a huge shield, unlike the surrounded field that he used previously, and indeed seems different than the skin-tight forcefield.
Now let's look at his personal skin-tight forcefields:
Here he takes a surprise blast from Silver Surfer. Notice it's the same tech setup as when he blocks the blast in the above picture, only this time he didn't anticipate. Notice the blast does nothing but make his armor smoke slightly, he isn't damaged in the least. This appears to be his "always-on" skintight forcefield. As this forcefield is invisible, it most likely is also tech related:
http://img95.imageshack.us/img95/9489/durability2nm6.jpg
Now lastly, lets look again at the fight with Drax, note that the forcefield is purple, unlike the invisible forcefields that he had before. This is the field Drax ripped through, since Drax had the counter life force to Thanos. Had Thanos known, he most likely would have erected a tech forcefield as well to protect against Drax, as it wouldn't have had the vulnerability to Drax that his own cosmic energy field had.
It would seem that he only rarely chooses to erect his personal cosmic forcefield, which is typically drawn as having a color to it, and usually only does it briefly as it uses his own power.
So basically he has 3 tech fields (a shield looking one, a dome type forcefield, and a skintight always-on forcefield similar to a green lantern's protection aura) and a 4th shield which he can put up that's created from his own power cosmic.