A touch screen is a display which can detect the presence and location of a  touch within the display area. The term generally refers to touch or contact to the  display of the device by a finger or hand. Touch screens can also sense other passive  objects, such as a stylus. However, if the object sensed is active, as with a light pen,  the term touch screen is generally not applicable. The thumb rule is: if you can interact  with the display using your finger, it is likely a touch screen - even if you are using a  stylus or some other object. Up until recently, most touch screens could only sense one point of contact at a time,  and few have had the capability to sense how hard one is touching.
This is starting to  change with the emergence of multi-touch technology - a technology that was first  seen in the early 1980s, but which is now appearing in commercially available  systems. The touch screen has two main attributes. First, it enables you to interact with what is  displayed directly on the screen, where it is displayed, rather than indirectly with a  mouse or a touchpad. Secondly, it lets one do so without requiring any intermediate  device, again, such as a stylus that needs to be held in the hand. Such displays can be  attached to computers or, as terminals, to networks. They also play a prominent role in  the design of digital appliances such as the personal digital assistant , satellite  navigation devices and mobile phone
There are a number of types of touch screen technology
A resistive touch screen panel is composed of several layers. The most important are  two thin metallic electrically conductive and resistive layers separated by thin space.  When some object touches this kind of touch panel, the layers are connected at certain  point; the panel then electrically acts similar to two voltage dividers with connected  outputs. This causes a change in the electrical current which is registered as a touch  event and sent to the controller for processing.  Surface acoustic wave SAW technology uses ultrasonic waves that pass over the touchscreen panel. When  the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic  waves registers the position of the touch event and sends this information to the  controller for processing. Surface wave touch screen panels can be damaged by  outside elements. Contaminants on the surface can also interfere with the functionality  of the touch screen.
A capacitive touch screen panel is coated with a material, typically indium tin oxide that conducts a continuous electrical current across the sensor. The sensor therefore  exhibits a precisely controlled field of stored electrons in both the horizontal and  vertical axes - it achieves capacitance. The human body is also an electrical device  which has stored electrons and therefore also exhibits capacitance. When the sensor's  'normal' capacitance field (its reference state) is altered by another capacitance field,  i.e., someone's finger, electronic circuits located at each corner of the panel measure  the resultant 'distortion' in the sine wave characteristics of the reference field and send  the information about the event to the controller for mathematical processing.  Capacitive sensors can either be touched with a bare finger or with a conductive  device being held by a bare hand. Capacitive touchscreens are not affected by outside  elements and have high clarity. The Apple iPhone is an example of a product that uses capacitance touchscreen technology.
An IR touchscreen panel employs one of two very different methods. One method  uses thermal induced changes of the surface resistance. This method is sometimes  slow and requires warm hands. Another method is an array of vertical and horizontal  IR sensors that detect the interruption of a modulated light beam near the surface of  the screen.
Optical imaging
A relatively-modern development in touchscreen technology, two or more image  sensors are placed around the edges (mostly the corners) of the screen. Infrared  backlights are placed in the camera's field of view on the other sides of the screen. A  touch shows up as a shadow and each pair of cameras can then be triangulated to  locate the touch. This technology is growing in popularity, due to its scalability,  versatility, and affordability, especially for larger units.
Dispersive signal technology
Introduced in 2002, this system uses sensors to detect the mechanical energy in the  glass that occur due to a touch. Complex algorithms then interpret this information  and provide the actual location of the touch. The technology claims to be unaffected  by dust and other outside elements, including scratches. Since there is no need for  additional elements on screen, it also claims to provide excellent optical clarity. Also,  since mechanical vibrations are used to detect a touch event, any object can be used to  generate these events, including fingers and stylus. A downside is that after the initial  touch the system cannot detect a motionless finger. 1.1.2 DEVELOPMENT
Virtually all of the significant touchscreen technology patents were filed during the  1970s and 1980s and have expired. Touchscreen component manufacturing and  product design are no longer encumbered by royalties or legalities with regard to  patents and the manufacturing of touchscreen-enabled displays on all kinds of devices  is widespread.
The development of multipoint touchscreens facilitated the tracking of more than one  finger on the screen, thus operations that require more than one finger are possible.  These devices also allow multiple users to interact with the touchscreen  simultaneously. With the growing acceptance of many kinds of products with an integral touchscreen  interface the marginal cost of touchscreen technology is routinely absorbed into the  products that incorporate it and is effectively eliminated. As typically occurs with any  technology, touchscreen hardware and software has sufficiently matured and been  perfected over more than three decades to the point where its reliability is  unassailable. As such, touchscreen displays are found today in airplanes, automobiles,  gaming consoles, machine control systems, appliances and handheld display devices  of every kind. The ability to accurately point on the screen itself is taking yet another  step with the emerging graphics tablet/screen hybrids.

Multi-touch is a human-computer interaction technique and the hardware devices that  implement it, which allow users to compute without conventional input devices e.g.,  mouse, keyboard. Multi-touch consists of a touch screen like screen, table, wall or  touchpad, as well as software that recognizes multiple simultaneous touch points, as  opposed to the standard touchscreen i.e. computer touchpad, ATM, which recognizes  only one touch point. This effect is achieved through a variety of means, including but  not limited to: heat, finger pressure, high capture rate cameras, infrared light, optic  capture, tuned electromagnetic induction and shadow capture.

Multi-touch technology dates back to 1982, when the University of Toronto developed the first finger pressure multi-touch display. The same year, Bell Labs at  Murray Hill published what is believed to be the first paper discussing touch-screen  based interfaces.
Bell Labs
In 1984 Bell Labs engineered a multi-touch screen that could manipulate images with  more than one hand. The group at the University of Toronto stopped working on  hardware and moved on to software and interfaces, expecting that they would have  access to the Bell Labs work.
A breakthrough occurred in 1991, when Pierre Wellner published a paper on his  multi-touch Digital Desk, which supported multi-finger and pinching motions.
Finger works
In 1998, FW, a Newark-based company run by University of Delaware academics  John Elias and Wayne Westerman, produced a line of multi-touch products including  the iGesture Pad and the TouchStream keyboard. Westerman published a dissertation  in 1999 on the subject. In 2005, after years of maintaining a niche line of keyboards and touch pads, Finger works was acquired by Apple Computer.

Various companies expanded upon these discoveries in the beginning of the twenty- first century. Mainstream exposure to multi-touch technology occurred in the year  2007, when Apple unveiled the iPhone and Microsoft debuted surface computing. The  iPhone in particular has spawned a wave of interest in multi-touch computing, since it  permits greatly increased user interaction on a small scale. More robust and  customizable multi-touch and gesture-based solutions are beginning to become  available, among them TrueTouch, created by Cypress Semiconductor. The following  is a compilation of notable uses of multi-touch technology in recent years. Microsoft Surface In 2001 Steve Bathiche and Andy Wilson of Microsoft began work on an idea for an  interactive table that mixes both physical and virtual worlds. Research and  Development expanded rapidly in 2004, once the idea caught the attention of  Microsoft Chairman Bill Gates. In 2007 Microsoft introduced MS, a functional multi- touch table-top computer based on a standard PC platform including an Intel Core 2  Duo processor, Windows Vista, and 2 GB of RAM
Perceptive Pixel
PP is a company founded by New York University consulting research scientist  Jefferson Y. Han that creates wall displays and tables that can accommodate up to 20  fingers. Han introduced the FTIR technique to multi touch screens. The displays use  light emitting diodes along with infrared light to determine the point of contact. Han  envisions large collaborative spaces that will allow multiple users to work and  interact. PPâ„¢s technology is currently being utilized, in the form of the Multi-Touch  Collaboration Wall, by CNN and an unspecified government contractor everyday  programs with ease and most importantly more than one user can operate the system  at any given time.
Apple iPhone, iPod touch, MacBook Air, and MacBook Pro In 2005, Apple acquired Fingerworks. In 2007 they introduced the iPhone, marking  the first time multi-touch technology was used on a phone. The iPhone includes such  components as a web browser, music player, video player, and a cell phone without  the use of a hard keypad or stylus. Following the release of the iPhone, Apple also expanded its use of multi-touch  computing with the new iPod Touch, as well as the new MacBook Air. Multi-touch  was later added to the 2008 MacBook Pro line in the form of a trackpad. Apple is  currently in the process of trying to patent its Multi-touch technology and to  trademark the term "multi-touch".

The use of multi-touch technology is expected to rapidly become common place. For  example, touch screen telephones are expected to increase from 200,000 shipped in  2006, to 21 million in 2012. Developers of the technology have suggested a variety of  ways that multi-touch can be used including:
·         Enhanced dining experience
·         Concierge service
·         Governmental use
·         Concept mapping
·         Collaboration and instruction on Interactive Whiteboards

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 the total internal reflection occurs. When light crosses a boundary between materials with different refractive indices, the  light beam will be partially refracted at the boundary surface, and partially reflected.  However, if the angle of incidence is greater (i.e. the ray is closer to being parallel to  the boundary) than the critical angle ” the angle of incidence at which light is  refracted such that it travels along the boundary ” then the light will stop crossing  the boundary altogether and instead be totally reflected back internally. This can only  occur where light travels from a medium with a higher refractive index to one with a  lower refractive index. For example, it will occur when passing from glass to air, but  not when passing from air to glass.
The critical angle is the angle of incidence above which total internal reflection  occurs. The angle of incidence is measured with respect to the normal at the refractive  boundary. The critical angle is given by: where n
is the refractive index of the less dense medium, and n
is the refractive index of the denser medium

An important side effect of total internal reflection is the propagation of an evanescent  wave across the boundary surface. Essentially, even though the entire incident wave is  reflected back into the originating medium, there is some penetration into the second  medium at the boundary. Additionally, the evanescent wave appears to travel along  the boundary between the two materials. This wave can lead to a phenomenon known  as frustrated total internal reflection.
Under "ordinary conditions" it is true that the creation of an evanescent wave does not  affect the conservation of energy, i.e. the evanescent wave transmits zero net energy.  However, if a third medium with a higher refractive index than the second medium is  placed within less than several wavelengths distance from the interface between the  first medium and the second medium, the evanescent wave will be different from the  one under "ordinary conditions" and it will pass energy across the second into the  third medium.

Multi touch is designed using the FTIR technology. FTIR describes the internal  reflection of light .It is force-sensitive, and provides unprecedented resolution and  scalability .Large enough to accommodate both hands and multiple users.This  phenomenon is also used in fingerprint and robot sensors.Allows us to create  sophisticated multi-point widgets for applications HARDWARE
The basic design has a hardware and software part. Hardware requires basically IR  ledâ„¢s,acrylic,camera,projector and a computer. Infra red light has a higher wavelength  than that of visible light .Therefore it has more intensity and will be felt everywhere  inside the denser medium. Acrylic is the denser medium .It is a synthetic fiber having  half the density of glass.An infra red camera or a webcam is used to catch IR light . A IR block filter of the camera has to be removed since it blocks IR light. It also consists  of a projector and a computer. The object has to be projected on top of the acrylic  from a computer . Thus acrylic is a virtual display. The IR LEDâ„¢s about 10-20 are  arranged on both sides of the acrylic along its edges .The camera below the acrylic  and the projector located behind to acrylic. SOFTWARE
Computer applications are necessary to communicate between a multi touch display  and a computer.These applications can be developed within several languages /  programming environments.For example: Processing (P5), Flash, C, C++, Java and  others. Because of the usability of certain APIâ„¢s and the relatively simple visualisation  possibilities, P5 or Flash 9, in combination with Actionscript 3.0 will make a great  combination

FTIR describes the internal reflection of light, inside a certain material. In our case, it  will be infrared light, that internally reflects inside is a piece of acrylic, also known as  plexiglas.This way, infrared light is beamed inside the acrylic and reflects internally.In  a simple way, you can say that, IR-light bounces inside the acrylic, from one side to  another.As soon as a finger touches the acrylic surface, the internal reflection of the  IR-light, is interrupted.The infrared light scatters on the finger tips.Infrared light is  invisible to the human eye, but by placing an infrared camera behind the acrylic your  fingertips will be visible on the infrared camera.The images that are generated by the  camera, contain white blobs (caused by the fingertips). These blobs will be analyzed by software. Every blob corresponds to certain  coordinates. Software can by analyzing these coordinates perform certain tasks, for  example move, resize or rotate objects.  Multiple points are obtained on the camera .Each point is a pixel position. Either a  single pixel or a group of pixel . Each point locations are identified and all operations  are performed .Suppose if we want to zoom a picture we use 2 fingers and move it in  or out to perform zoom in and zoom out respectievely . Two coordinates will be  located on the camere .The difference is found which is put as the offset and it is  either added or subtracted with the locations to zoom out and zoom in respectievely.

·         Multi touch based on FTIR is a simple and inexensive technique .It  constructs a multi touch display with the available and less costly  materials .
·         Scalable technique that enables high-resolution graphics .It provides  support to any resolution possible as all multiple points could be  generated on a camera

·         It acquires true touch image information at high spatial and temporal  resolutions.The actual finger print of the touch is obtained .This could  be used to determine the force sensitivity on displays , either too hard  or soft touches can be analysed.
·         It is scalable to large installations.Any kind of applications can be  made to suit multi touch using FTIR . Allows us to create sophisticated  multi-point widgets for applications
·         Larger shared-display systems ie it is well suited for use with rear- projection like wall screens,table tops .All this lead to high resolution  graphics.

A myriad different applications for multi-touch interfaces both exist and are being  proposed. Some uses are individualistic e.g., iPhone, iPod touch, MacBook Pro,  MacBook Air, HTC Diamond . However, multi-touch technology is mainly used to  incorporate collaboration into the computing experience .
A multi touch display can be used in
·      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
Applications for a multi touch display are never ending . We can even convert a  computer to a mere piece of display attached to a wall or a

Touch screens are the interface for the 21 st century. Touch screens address the  conflicting demands for smaller portable electronics with larger displays, by  eliminating traditional buttons without sacrificing screen size. The recent release of  the iPhone has created a buzz around touch screen interfaces and its multi-touch  acrobatics have caught the eye of many industry leaders. 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 .  A drawback of the approach is that, being camera-based, it requires a significant  amount of space behind the interaction surface, though we primarily expect  application scenarios where rear-projection would have been employed anyway (e.g.  interactive walls, tables). Also, as an optical system, it remains susceptible to harsh  lighting environments.

1 comment:

  1. i want multi touch technology to seminar topics.. i send to mail


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