MULTI TOUCH

IntroductionMulti-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 iPhoneIn 2007 Microsoft introduced MS, a

functional multitouch table-top computer based on a standard PC platform.

TechniqueThe 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

                                                           

FTIRif 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.

FTIRUnder "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’sAcrylicCameraprojector 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

AdvantagesMulti 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.

ApplicationPersonal computers, Laptops, Tabletops, Graphics

Tablets. It supports both LCD and CRT monitors.Telephones, Watches, PDAs, Mobile phones.Advanced multi touch Gaming with high graphics supportGovernmental, office and business purposesAn enhanced multimedia experience including audio, video

and photo sharingEnhanced dining experienceConcierge serviceConcept mappingCollaboration 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.

THANK YOU