Multi-touch technology is an advanced human-computer interaction technique that recogonises multiple touch points and also includes the hardware devices that implement it, which allow users to compute without conventional input devices . Multi-touch consists of a touch screen (screen, table, wall, etc.) or touchpad, as well as a software that recognizes multiple simultaneous touch points, as opposed to the standard touchscreen which recognizes only one touch point at a time. Multi touch using Frustrated Total Internal Reflection is a simple, inexpensive, and scalable technique for enabling high-resolution multi- touch sensing on rear-projected interactive surfaces. Different applications for multi-touch interfaces both exist and are being proposed. Some uses are individualistic eg iPhone, iPod touch, MacBook Pro, MacBook Air. The use of multi-touch technology is expected to rapidly become common place.
TOUCH SCREEN
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
TECHNOLOGIES
There are a number of types of touch screen technology
Resistive
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.
Capacitive
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.
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