interactive whiteboard-Technologies

Interactive whiteboards may use one of several types of sensing technology to track interaction on the screen surface: resistive, electromagnetic, infrared optical, laser, ultra-sonic, and camera-based (optical).

Resistive — Resistive touchscreens are composed of two flexible sheets coated with a resistive material and separated by a microthin air gap. When contact is made to the surface of the touchscreen, the two sheets are pressed together, registering the precise location of the touch. This technology allows one to use a finger, a stylus, or any other pointing device on the surface of the board.
Active Electromagnetic Board — These interactive whiteboards feature an array of wires embedded behind the board surface interacts with a coil in the stylus tip to determine the (X,Y) coordinate of the stylus. Styli are either active (require a battery or wire back to the whiteboard) or passive (alter electrical signals produced by the board, but contain no batteries or other power source). In other words, there are magnetic sensors in the board that react and send a message back to the computer when they are activated by a magnetic pen.
Passive Electromagnetic Board - In contrast to an active electromagnetic board this one does not contain the sensing technology in the board itself, but in the pen. Tiny magnetic fibers are embedded in the whiteboard and form a pattern that an electromagnetic coil in the pen is able to sense. Therefore the pen is able to calculate its location on the whiteboard and sends this information to a computer.
Capacitive — Just like the electromagnetic type, the capacitive type works with an array of wires behind the board. In this case however the wires interact with fingers touching the screen. The interaction between the different wires (laminated in a patented X- and Y-axis manner) and the tip of the finger is measured and calculated to a (x, y) coordinate. Other types include Projected Capacitive, which uses an Indium Tin Oxide (ITO) [20]grid sandwiched between clear film and the newest type using Transparent Electrodes replacing the ITO. 
Optical:
Infrared light curtain — When pressed to the whiteboard surface, the finger or marker sees the infrared light. Software then manipulates the information to triangulate the location of the marker or stylus. This technology allows whiteboards to be made of any material; with this system no dry-erase marker or stylus is needed.
Laser light curtain — An infrared laser is located in each upper corner of the whiteboard. The laser beam sweeps across the whiteboard surface—much like a lighthouse sweeps light across the ocean—by using a rotating mirror. Reflectors on the stylus or marker reflect the laser beam back to the source and the (X,Y) position can be triangulated. This technology may be combined with a hard (usually ceramic on steel) surface, which has long life and erases cleanly. Markers and styli are passive, but must have reflective tape to work.
Projector/Laser light curtain — A dual infrared laser device is positioned in the top middle area of a flat surface. The laser beam sweeps across the surface creating an invisible curtain. The projector, usually an ultra short throw projector) has a built in camera with an infrared filter that scans the projected area. When a pointer, finger or marker disrupts the laser curtain, an X,Y position can be traced. This is one of the few optical technologies that do not require a reflecting frame in the perimeter of the projected area to work.is located in each upper corner of the whiteboard. The laser beam sweeps across the whiteboard surface—much like a lighthouse sweeps light across the ocean—by using a rotating mirror. Reflectors on the stylus or marker reflect the laser beam back to the source and the (X,Y) position can be triangulated. This technology may be combined with a hard (usually ceramic on steel) surface, which has long life and erases cleanly. Markers and styli are passive, but must have reflective tape to work.
Frustrated total internal reflection — Infrared light bounces within a flexible and transparent surface. When the surface is deformed through a finger press the internal reflection is disrupted and the light escapes the surface where it is then sensed by cameras. Image processing software turns the light spots observed by the cameras into mouse or pointer movements.
Camera Pen and Dot Pattern – These interactive whiteboards have a microscopic dot pattern embedded in the writing surface. A wireless digital pen contains an infrared camera that reads the dot pattern to determine the exact location on the board. The digital pen uses this pattern to store the handwriting and upload it to a computer. The accuracy is high since the coordinates are usually fixed at about 600 dots per inch. With the electronics in the pen, the whiteboard is passive (containing no electronics or wiring). This is licensed as Anoto technology.
Wii Remote IWB — A Wii Remote is connected to a computer through its Bluetooth connection capabilities. Using open-source software and an IR-Pen (a pen made with a momentary switch, power source and an Infrared Led) any surface (desk/floor/wall/whiteboard/LCD) can be turned into an Interactive Whiteboard. The Wii Remote has a very accurate Infrared Light tracking camera. Once calibrated, the Wii Remote detects a mouse click at the screen location of the IR-Pen. The Wii remote was first adapted for use as an interactive whiteboard by Johnny Chung Lee.
DST [Dispersive Signal Technology] A touch causes vibrations which create a bending wave through the substrate, which is detected by corner-mounted sensors. Using advanced digital signal processing and proprietary algorithms, an accurate touch location is identified. A touch is activated by a finger or stylus touching the glass substrate and creating a vibration. The vibration radiates a bending wave through the substrate, from the point of contact and spreading out to the edges. Sensors in the corners convert the vibrational energy into electrical signals. Through advanced Digital Signal Processing, we are able to apply dispersion correction algorithms which analyze the signals and report an accurate touch.
Ultrasonic:
Ultrasonic only — These devices have two ultrasonic transmitters in two corners and two receivers in the other two corners. The ultrasonic waves are transmitted by the whiteboard surface. Some little marks in the whiteboard borders create reflecting waves for each ultrasonic transmitter at different and recognizable distances. Touching with a pen or even the finger in the whiteboard causes these point waves to be suppressed, and the receivers communicate the fact to the controller.
Hybrid Ultrasound and Infrared — When pressed to the whiteboard surface, the marker or stylus sends out both an ultrasonic sound and an infrared light. Two ultrasonic microphones receive the sound and measure the difference in the sound's arrival time, and triangulate the location of the marker or stylus. This technology allows whiteboards to be made of any material, but requires a suitably adapted active dry-erase marker or stylus.