The most common technology for infrared involves emitting infrared light across the surface of the touch screen and using an array of vertical and horizontal light sensors to detect interruptions in the light. The touch screens are very transparent and can be quite durable and are often found in military applications. This technology is susceptible to debris on the surface or anything that will disrupt the light waves traveling across the surface. One recent introduction with an integrated infrared screen is the 8000i from Northstar. This marine navigation system is able to maintain a bright display, is not affected when a boat starts bouncing around on the water, remains cool during long use, and can even be operated if the user is wearing gloves.
Surface acoustic wave touch screens operate similar to infrared, except instead of infrared light, they send acoustic waves across the touch surface. When a finger touches the surface, waves are absorbed and a series of transducers and reflectors detects the point. The surface needs to be made of glass and is susceptible to scratches or debris on the surface. The touch surface can be rugged and the technology will sense most any object and work over wide temperature extremes.
Optical imaging uses a system of imaging sensors and infrared light across the touch surface to sense touch. Cameras are used to detect changes in the light on the surface, or shadows, and locate the touch. One intriguing application was the Microsoft Surface introduced in 2007. This new application makes a coffee table into a touch sensitive computer that can sense touch commands as well as the presence of objects and technology products resting on the surface. For example, the screen can sense a digital camera and download the images stored on the camera right onto the “desktop” of the screen. This download of images appears as a pile of virtual pictures ready to be arranged with the user’s fingers.
The two most popular bending wave technologies are 3M’s dispersive signal technology and Elo’s acoustic pulse recognition. These applications use transducers at the edges to detect bending waves disrupted by the user’s touch on a glass plate and a digital signal processor determines touch location. The touch surface can be very rugged and the transparent touch panels are as clear as glass. The dispersive signal technology can eliminate problems related to on-screen contaminants and surface damage. The acoustic pulse recognition can be scaled from a PDA size to 42" and offers palm rejection during signature capture. Palm rejection is a touch screen’s ability to differentiate a stylus from other objects that might come in contact with the screen, such as the palm of your hand.
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