MULTI TOUCH

Introduction Multi-touch is a human-computer interaction technique. Consists of a touch screen as well as software that recognizes multiple simultaneous touch points. Multi touch using Frustrated Total Internal Reflection Enables high-resolution multi touch sensing on rear-projected interactive surfaces. interact with more than one finger at a time and also able to accommodate multiple users simultaneously

Developments In 2007 Apple unveiled the iPhone In 2007 Microsoft introduced MS, a functional multitouch table-top computer based on a standard PC platform.

Technique The technique used in multi touch is frustrated total internal reflection (FTIR). It was introduced by Jefferson Y. Han who founded a company Perceptive Pixel. Han envisions large collaborative spaces that will allow multiple users to work and interact. Perceptive Pixel’s technology is currently being utilized, in the form of the Multi-Touch Collaboration Wall.

Frustrated Total Internal Reflection (FTIR) Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary no light can pass through, so effectively all of the light is reflected. The critical angle is the angle of incidence above which total internal reflection occurs.

FTIR critical angle is given by: Where n2 is the refractive index of the less dense medium, and n1 is the refractive index of the denser medium

FTIR if the angle of incidence is greater than the critical angle, then the light will stop crossing the boundary and be totally reflected back internally. This occur when light travels from a medium with a higher refractive index to one with a lower refractive index. Side effect of total internal reflection is the propagation of an evanescent wave across the boundary surface. evanescent wave travel along the boundary between the two materials. This wave leads to a phenomenon known as frustrated total internal reflection.

FTIR Under "ordinary conditions" evanescent wave transmits zero net energy If a third medium with a higher refractive index than the second medium is placed and it will pass energy across the second into the third medium.

Requirements Hardware IR led’s Acrylic Camera projector computer

Acrylic with led’s at its edges

Software several languages /programming environments are used Eg;Processing (P5), Flash, C, C++, Java

Working infrared light is beamed inside the acrylic and reflects internally. as a finger touches the acrylic surface, the internal reflection of the IR-light, is interrupted. The images that are generated by the camera contain white blobs Every blob corresponds to certain coordinates Software can by analyzing these coordinates perform certain tasks

Working Multiple points are obtained on the camera Each point is a pixel position Each point locations are identified and all operations are performed

(a) IR view of a touch (b) Pixel positions located on screen

Advantages Multi touch based on FTIR is a simple and inexpensive technique. enables high-resolution graphics It acquires true touch image information at high spatial and temporal resolutions. It is scalable to large installations. Larger shared-display systems

Disadvantages being camera-based, it requires a significant amount of space behind the interaction surface as an optical system, it remains susceptible to harsh lighting environments.

Application Personal computers, Laptops, Tabletops, Graphics Tablets. It supports both LCD and CRT monitors. Telephones, Watches, PDAs, Mobile phones. Advanced multi touch Gaming with high graphics support Governmental, office and business purposes An enhanced multimedia experience including audio, video and photo sharing Enhanced dining experience Concierge service Concept mapping Collaboration and instruction on Interactive Whiteboards

Conclusion There are many ways to make a multi-touch screen. Some of the early designs measured the change in electrical resistance or capacitance on a surface when fingers touched it. But these devices have limited resolution, are relatively complex, and don't easily and inexpensively scale up to large dimensions. Multi-touch technologies have a long history. This technique using FTIR is simple and easy to implement. It provides any resolution displays supported with high graphics.The applications being both made and proposed are plenty in number.

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