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Multi-touch Screen Technology

Written By: 

Preeti Jain


While we are all fascinated by the touchscreen-market gimmick cajoling us with its ‘Touch away’ tagline, are we actually only at an inch’s distance? This ‘no-distance’ de facto makes sense at the front end only. When given a hawk’s eye, there is another world inside waiting to be discovered, waiting to satiate your knowledge for technology. What is Multitouch Screen TechnologyWell, for the smart gadgets with smart people in the smart world, it’s an uncanny missing out a discussion on Touchscreen Technology, specifically undertaking the Multitouch Technology.
The multi-touch or the plural touch is an interactive technique which allows users to interact with the digital environment inside the gadget, directly or indirectly with his fingers or palm. Multi-touch devices include smart phones, touch tables, computer tables, public kiosks, walls, and ‘touchpad’. Well these inverts in touchpad bring us to a minute line of demarcation between touchscreen and touchpad. While in a touchscreen, the screen being manipulated lies directly underneath the user-interactive surface, in a touchpad the touch surface does not overlays the screen.
Evolution of Multi-Touch Technology:
It’s not often when one devises a new technology by observing rife, regular principles of science working around. But this man did, and did it in a manner which left his audience biting their nails over his first presentation at TED. In 2006, Jeff Han; the then research scientist at NYU came up with his Multi-Touch table based on the principle of Frustrated Total Internal Reflection (FTIR). He observed that in a glass of water, the light reflects differently on the areas where the hands contact the glass. Here, visible light is entrapped inside the glass owing to total internal reflection. Whenever a finger or palm touches the glass, light diffuses or gets frustrated at the point of contact. This effect is called FTIR. In 2007, Apple Inc. came up with its revolutionary multi-touch technology in mobile phones; the iPhone. The mobile phone is a soft-touch based interface. iPhone uses capacitive coupling to sense multiple touch points. Apple’s rivalry Microsoft also released, in the same year the astounding Microsoft Surface based on DI Technology. Some other breakthrough in multi-touch technology include MERL’s Diamond Touch, TISCH, Fraunhofer multi-touch table, Microsoft wall, Thinsight, N trig andSurface2.0.
Multitouch Screen Technology


Multi-Touch Technologies:
Various techniques are involved in the development of human interface Multitouch devices. They are either sensor based or camera (computer vision optics) based.
·         Optical  Sensing Multi-touch Technology
Optical Sensing or the camera based sensing is the most widely used technique for multi-touch devices these days. Here, cameras are used as sensors to detect the presence of any object or human finger on the touch surface. The major hardware for optical technology comprise an infrared light source, cameras or optical sensors for touch detection and a Led/ LCD or projector for display or visual feedback. Well, two types of lights are involved in designing a Multitouch surface; visible light and Infrared light, both carrying an inevitable significance. Visible light which lies between 300nm- 700nm on the electromagnetic spectrum is used to illuminate the display or to provide a visual feedback to the user on a LCD or projector. However, IR light is used to locate the presence of a touch or object over the surface. The typical wavelength catering to near IR is around 700nm to 1000nm which is a little beyond the visible region perceptible to human eye. A single Led or Led ribbon is used as IR light source. The digital camera is trained to detect only the IR light (by using a filter to block visible light), avoiding any visible light to be seen by the camera. Therefore, only the human interventions on the touchscreen which are illuminated by IR are visible to the camera and not the visible feedback.
Let us now have a look at the major optical technologies governing the multi-touch era:
1.      Frustrated Total Internal Reflection (FTIR) - The FTIR principle is an extension to the concept of total internal reflection (TIR). Whenever light rays enter from a denser to rarer medium at an angle less than or equal to the critical angle, TIR is said to occur. The light is then found to be entrapped inside the medium. When a separate body with a higher refractive index comes in contact with the medium containing this entrapped light, the light gets frustrated at that point and bright luminescent spots are created (blobs). This frustrated light then escapes the medium and is scattered downwards towards the infrared camera which then tracks the image of touch point and relays it further for processing. The light used here is IR rays and the medium entrapping the IR is necessarily a sheet of acrylic.
Frustrated Total Internal Reflection (FTIR)
Layers in a FTIR system: An acrylic sheet of thickness varying from 6mm to 1mm is used. The acrylic sheets are rubbed with dry and wet sandpapers consecutively to remove scratches and to finish its sides. A baffle of wood or metal is used on the sides to prevent leakage of light from Led edges. The next layer calls upon the supply of a filtered data to the camera, i.e. only bright images (touches) should be visible to the camera. This is taken care by the diffuser. The next layer employed is specific to FTIR systems. It is known as the compliant layer. It is an additional layer added between the projector and the acrylic pane. It is a well known fact that performance of your touchscreen increases with the wetness of the touching fingers. The greasier your finger is, the better performance is obtained. Since it’s practically not possible not feasible that the fingers be wet or sweaty all the time, the silicone compliant layer dissolves the issue. It is made of material with refractive index slightly higher than the acrylic waveguide. It improves performance as in the layer is pressure sensitive, gives brighter bobs and protects the acrylic from scratches.


its so nice!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!smiley

good one


it is simply superb...........................




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i am working on LED LP....