Acoustic tablet:

Acoustic (or sonic) tablet utilize sound waves to detect a stylus position. Either strip microphones or point microphones might be utilized to detect the sound emitted by an electrical spark from a stylus tip. The position of the stylus is determined by timing the arrival of the produced sound at the different microphone positions. An advantage of two-dimensional acoustic tablets is that the microphones may be placed on any surface to form the "tablet" work area. This may be convenient for various applications such as digitizing drawings in a book.

Three-dimensional digitizers utilize sonic or electromagnetic transmissions to record positions. One electromagnet transmission technique is similar to that utilized in the data glove. A coupling among the transmitter and receiver is utilized to compute the location of a stylus as it moves over the surface of an object. As the points are choose on a non-metallic object, a wireframe outline of the surface is displayed on the computer screen. Once the surface outline is made, it may be shaded with lighting effects to generate a realistic display of the object. Resolution of this system is from 0.8 mm to 0.08 mm, based on the model.