New sdm = dc (see patent)

Don't think so - all batteries and battery-powered devices (like DSLRs) use DC (to use AC it would need to be plugged directly into the wall). I think you may be confused between the two "DC"s involved here: one is direct current, the type of power used by the camera and lens. The other is (and I am cribbing from a post I think of Stefan's in another thread here!) a "DC brushless motor" which is the SDM replacement.

The DCs are the same. To run a brushless (synthetic commutator) motor, the DC is effectively converted to multi phase AC.

Cut and pasted from the following page,

http://www.pentax.co.uk/en/group/14/product/21977/body/specifications/Photo_Lens...

Is this the answer to your question?

"* This lens is compatible with the PENTAX K-5, K-r, K-7, K-x, K-m, K2000, K20D, K200D, K100D Super and K10D (with firmware v. 1.30 or above installed). When mounted on other camera bodies, the focus mode is automatically switched to manual."

Here is an animation of a brush-less DC motor.
http://www.townbiz.com/animations/4-pole_bldc.html

It's been a long time but I believe the DC in the Pentax use the same principle.
Only the rotor (the bit that turns) isn't surrounded by the stator (the bit that doesn't turn).

Yep, that's the answer. I wasn't sure at what point the existing SDM lenses converted the DC supply from the camera batteries to an AC one to drive the motor - whether it was converted by the camera or by the lens.