Surface acoustic wave
Surface acoustic wave touch screens work by sending an ultrasonic wave (ultra-sound wave) across the surface of the glass. Sensors detect the reflected wave and in some cases the attenuated wavefront that is caused by the pointer or finger. This is then translated into an X-Y coordinate for the touchpoint.
Traditional capacitive touch
Otherwise known as surface capacitive - work by detecting a change in capacitance of the field in front of the screen caused by a conductive entity of some sort. Usually a finger. Capacitive touch screens are commonly made of two layers - a surface insulator and a transparent conductive layer below it. As the human body is an electrical conductor when the touch panel is touched with a finger the electrostatic field of the panel is distorted. The touch screen controller then decodes the changes in capacitance and returns a touchpoint to the system. The advantages are that there is no membrane that needs to flex, so the touch-screen should last longer. Disadvantages include possible drift over time on large displays, which require periodic re-calibration. Because the sensor is a glass panel, there is less visual degradation than with resistive screens.
Projective capacitive touch
Instead of one capacitive sensor, there are many, usually on two layers of transparent conductors.
Projected Capacitive Technology (PCT) is fast becoming one of the most prevalent touch technologies for touchscreens. PCT technology is what allows us to tap, pinch, zoom, and scroll with various gesture controls and using multiple fingers, and can be used in a wide range of applications from consumer devices to commercial products.
PCT devices identify touch by measuring the capacitance at each addressable electrode in a dual-layer grid. When you touch the surface of a capacitive device, there is a disturbance in its electrical field (capacitance), which allows the device to determine when and where the touchpoint occurred.
PCT technology uses two main types of sensing methods, self-capacitance and mutual capacitance, each having its own advantages and disadvantages. In short, self-capacitance devices offer a higher signal strength and sensitivity to touch but does not support multi-touch (more than 2 touch-points) like mutual-capacitance devices.
“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” ( from 3M)
ACME’s addition of PCT technology to the MegaPAC results in a superior portable computing platform with a durable, UHD multi-touch touchscreen. The MegaPAC is a high performance, high-fidelity interactive solution that meets customers' expanding user interface requirements.
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