TOUCH SCREEN TECHNOLOGIES

Resistive touch screens have a flexible top layer and a rigid bottom layer separated by insulating dots, with the inside surface of each layer coated with a transparent conductive coating.

Voltage applied to the layers produces a gradient across each layer. Pressing the flexible top sheet creates electrical contact between the resistive layers, essentially closing a switch in the circuit.

Projected capacitive technologies detect touch by measuring the capacitance at each addressable electrode. When a finger or a conductive stylus approaches an electrode, it disturbs the electromagnetic field and alters the capacitance. This change in capacitance can be measured by the electronics and then converted into X,Y locations that the system can use to detect touch.

3M Project Capacitive Technology (3M PCT) is based on mutual capacitance to create multi-touch interactive. Mutual capacitance is the intentional or unintentional capacitance between two "charge holding objects” (see illustration). Projected capacitance touchscreens intentionally create mutual capacitance between elements of columns and rows in the vicinity where each intersect the other. This allows the system electronics to measure each node (intersection) individually to detect multiple touches on the screen during one screen scan.

When a finger touches near an intersection, some of the mutual capacitance between the row and column is coupled to the finger which reduce the capacitance at the intersection as measured by the system electronics. This reduced capacitance crosses the "touch threshold" set by the electronics indicating a touch has occurred.

The DST Touch System determines the touch position by pinpointing the source of "bending waves" created by finger or stylus contact within the glass substrate. This process of interpreting bending waves within the glass substrate helps eliminate traditional performance issues related to on-screen contaminants and surface damage, and provides fast, accurate touch attributes.

Acoustic wave touch screens use transducers mounted at the edge of a glass overlay to emit ultrasonic sound waves along two sides. These waves are reflected across the surface of the glass and received by sensors. A finger or other soft tipped stylus absorbs some of the acoustic energy and the controller measures the amplitude change of the wave to determine touch location.

Infrared touch screens are based on light-beam interruption technology. Instead of an overlay on the surface, a frame surrounds the display. The frame has light sources, or light emitting diodes (LEDs) on one side and light detectors on the opposite side, creating an optical grid across the screen.

When an object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photo sensors.

Optical touch screen technology uses two line scanning cameras located at the corners of the screen. The cameras track the movement of any object close to the surface by detecting the interruption of an infra-red light source. The light is emitted in a plane across the surface of the screen and can be either active (infra-red LED) or passive (special reflective surfaces).

Single Touch occurs when a finger or stylus creates a touch event on the surface of a touch sensor or within a touch field so it is detected by the touch controller and the application can determine the X,Y coordinates of the touch event.

These technologies have been integrated into millions of devices and typically do not have the ability to detect or resolve more than a single touch point at a time as part of their standard configuration.

Inactive pens enable the same input characteristics as a finger, but with greater pointing accuracy, while sophisticated, active pens can provide more control and uses for the touch system with drawing and palm rejection capabilities, and mouse event capabilities.

Since single touch systems can´t resolve the exact location of the second touch event, they rely on algorithms to interpret or anticipate the intended gesture event input. Common industry terms for this functionality are two-finger gestures, dual touch, dual control, and gesture touch.

The best demonstration of Two Touch capability is to draw two parallel lines on the screen at the same time. Two Touch systems can also support gesturing.

Multi-touch is considered by many to become a widely-used interface mainly because of the speed, efficiency and intuitiveness of the technology.