Up until now auto focus has been carried out either by DC motor or Ultra Sonic / Silent Wave Motors, however a new innovation noted by Monty Solomon and reported in todays New Scientist may offer another option, especially for ultra-compact lens systems. A company called '1 Limited' of Cambridge, UK has developed a sheet of piezoelectric ceramic material which can move whatever is placed on it (by using a grip and shift type movement), roll it into a cylinder and you could move a small camera lens up or down the cylinder (zoom or focus). At the moment this technology is aimed at camera phones however I have no doubt that it could be important for lens systems in ultra-compact cameras.