CAPACITIVE TOUCHSCREEN

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Definition of "touchscreen"
A touchscreen display is one that is sensitive to touch. They are often used on smartphones and similar devices. The primary types of touchscreens are capacitive touchscreens and resistive touchscreens, but other types that use infrared light grids, sound, or optical sensors also exist, though they are not typically used in cell phones.

Definition of "capacitive touchscreen
In the cell phone industry there are two major categories of touchscreen displays: capacitive touchscreens and resistive touchscreens. Capacitive touchscreen displays rely on the electrical properties of the human body to detect when and where on a display the user touching. Because of this, capacitive displays can be controlled with very light touches of a finger and generally cannot be used with a mechanical stylus or a gloved hand. Examples of devices with capacitive touchscreens are the Apple iPhone and the T-Mobile G1.



CAPACITIVE SENSING

In electrical engineering, capacitive sensing is a technology based on capacitive coupling that is used in many different types of sensors, including those to detect and measure: proximity, position or displacement, humidity, fluid level, and acceleration. Capacitive sensing as ahuman interface device (HID) technology, for example to replace the computer mouse, is growing increasingly popular.[1] Capacitive touch sensors are used in many devices such as laptop trackpads, digital audio players, computer displays, mobile phones, mobile devices and others. More and more design engineers are selecting capacitive sensors for their versatility, reliability and robustness, unique human-device interface and cost reduction over mechanical switches.
Capacitive sensors detect anything which is conductive or has a dielectric different than that of air. While capacitive sensing applications can replace mechanical buttons with capacitive alternatives, other technologies such as multi-touch and gesture-based touchscreens are also premised on capacitive sensing.[2]

SENSOR DESIGN
Capacitive sensors can be constructed from many different media, such as copper, Indium tin oxide (ITO) and printed ink. Copper capacitive sensors can be implemented on standard FR4 PCBs as well as on flexible material. ITO allows the capacitive sensor to be up to 90% transparent (for one layer solutions). The size and spacing of the capacitive sensor are both very important to the sensor's performance. In addition to the size of the sensor, and its spacing relative to the ground plane, the type of ground plane used is very important. Since theparasitic capacitance of the sensor is related to the electric field's (e-field) path to ground, it is important to choose a ground plane that limits the concentration of e-field lines with no conductive object present.