The two main components of an electromagnetic interactive whiteboard are: input stylus (like digitising pen) and digitising grid. The digitised pen emits electronic signals through a transponder and make a contact with a computer system when it comes in contact with the gird's surface. Through this signal, the attached computer is able to figure out the x and y coordinates of the pen i.e. its exact location on the interactive whiteboard.




The digitised grid is touch sensitive and is made up of several layers: the top layer, middle layer and the ground layer. When a stylus is used on the surface of the touch sensitive grid, the top layer gets physically depressed. Consequently, the top layer depresses the middle layer, the middle layer depresses the ground layer of the grid and the ground layer sends an electronic signal to the digitized pen which in turn transfers the signal to the attached computer. In general the electromagnetic interactive whiteboard is quite precise.




Source: Electromagnetic Interactive Whiteboard