A capacitive touchscreen panel consists of an
insulator such as
glass, coated with a transparent
conductor such as
indium tin oxide (ITO).
[2][3] As the human body is also a conductor, touching the surface of the screen results in a distortion of the local
electrostatic field, measurable as a change in
capacitance. Different technologies may be used to determine the location of the touch. The location can be passed to a computer running a software
application which will calculate how the user's touch relates to the
computer software.
Projected capacitance
Projected Capacitive Touch (PCT) technology is a capacitive technology which permits more accurate and flexible operation, by
etching the conductive layer. An
XY array is formed either by etching a single layer to form a grid pattern of
electrodes, or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid (comparable to the
pixel grid found in many
LCD displays).
Applying voltage to the array creates a grid of
capacitors. Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location.
[5] The use of a grid permits a higher resolution than resistive technology and also allows
multi-touch operation. The greater resolution of PCT allows operation without direct contact, such that the conducting layers can be coated with further protective insulating layers, and operate even under screen protectors, or behind weather and vandal-proof glass.
PCT is used in a wide range of applications including
point of sale systems,
smartphones, and public information kiosks.
Visual Planet's ViP Interactive Foil is an example of a kiosk PCT product, where a gloved hand can register a touch on a sensor surface through a glass window.
[6] Examples of consumer devices using projected capacitive touchscreens include
HTC's
HD2,
G1, and
HTC Hero,
Apple Inc.'s
iPhone and
iPod Touch,
Motorola's
Droid,
Palm Inc.'s
Palm Pre and
Palm Pixi and more recently the
LG KM900 Arena,
Microsoft's
Zune HD,
Sony Walkman X series,
Sony Ericsson's Aino and now
Vidalco's Edge, D1 and Jewel phones.
