How do Touch Screens work?
Development of touch screens can be traced back to 1960s and was steadily developed and has captured imagination of both scientists and users. EA Johnson was the first person to develop the idea of using resistive touch screens for air traffic control applications. Bent Stumpe in CERN developed the technology with transparent screens in 1970s. This technology was incorporated into several instruments over the years. Multi-touch technology was developed in University of Toronto by mid-1980s, first using optical technology and later using capacitance technology.
The first software designed for touch screen instruments was revealed in 1986. IBM Simon, unveiled in 1993, was the first cell phone that used touch screen technology. After its first use as an interface for a consumer instrument, touchscreen technology was further developed and refined, and currently include a repertoire of multi-touch and pressure sensitive technologies.
Touchscreens come in several varieties. Resistive touchscreens are composed of two thin transparent and electrically resistive layers that are separated by a thin space. They are connected to electrodes, and based on the flow of electric current the point of contact between the screens can be detected. They offer poor screen contrast, but can be used in many situations since it is the contact between the two layers that is detected.
Capacitive touchscreens are commonly used in cell phones and tablets, but they do not sense electrically insulating objects touching the screen - for example, they do not sense fingers if rubber or latex gloves are worn. This is because they senses a change in electrostatic field when an electrical conductor (like human skin) touches a thin metal layer (like indium tin oxide) applied on a resistant material like glass (surface capacitance).
If a grid of electrical conductor is used, it forms a uniform electrostatic field (projected capacitance) over the surface and can result in accurate determination location of contact. This accuracy is enhanced when multi-touch screens have capacitors are placed at the intersections in the grid. New touch screens such as super AMOLED screens use this technology with the capacitors embedded in the glass itself, reducing the distance between the surface and the image.
Surface acoustic touchscreen technology uses ultrasonic waves that are passed over the screen, and the point of touch is determined by determining absence of this layer of waves when the screen is touched. Another technology called infrared grid uses infrared LED and photodetector pairs that senses perturbation of the grid. Infrared grid technology offers ease of use as any disturbance near the screen will be identified irrespective of electrical resistance.
Another variation of this theme is used in Microsoft pixelSense where infrared cameras detect leakage of light from an acrylic sheet when it is pressed. Optical imaging technology that utilizes infrared light sources and infrared cameras, and measures touch by detecting shadows is gaining popularity because of its versatility and scalability. Several other touchscreen technologies that offer precision and ease of use are being developed by different manufacturers. Touchscreen devices interpret touch commands by integrating the touch signal to the command menu which is made visible to user as an image on the screen.
Due to the widespread use of touchscreens and relatively low cost of their manufacture, they are gaining popularity around the world. Used in different instruments ranging from restaurant menus to heavy and precision equipment control panels, they have changed the way we interact with the world. An important aspect of touch screen development has been ergonomics. For example, continuous vertical touchscreens results in so called gorilla arms due to muscle fatigue. Development of multi-touch screens has made this technology available for even more uses including gaming and graphics related applications.
Touch has been incredibly successful on our phones, tablets, airport kiosks and cash machines. Why not on our computers? Will microsoft be successful with touch screen on their windows 8 operating system? Learn more at scientificamerican.com
What is the physics behind touchscreens? Read more at www.rtcmagazine.com
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Edited by: Rajesh Bihani ( Find me on Google+ )