Explain about the Acoustic tablet

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