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What are the different common types of touch screens?

Touch screen technology has the potential to replace most functions of the mouse and keyboard. The touchscreen interface is being used in a wide variety of applications to improve human-computer interaction. As the technology advances, people may be able to operate computers without mice and keyboards. Because of its convenience, touch screen technology solutions has been applied more and more to industries, applications, products and services, such as Kiosks, POS (Point-of-Sale), consumer electronics, tablet PC, moderate to harsh Machine Control, Process Control, System Control/Office Automation and Car, PC, etc.

The touch panels themselves are based around four basic screen technologies: Resistive, Capacitive, Infrared (IR), and Surface Acoustical Wave (SAW). Each of those designs has distinct advantages and disadvantages. Many of these are designed to comply with specific National Electrical Manufacturers Association (NEMA) standards to meet various installation requirements.

Resistive Touchscreen Panels

A resistive touchscreen panel comprises several layers, the most important of which are two thin, transparent electrically-resistive layers separated by a thin space. These layers face each other, with a thin gap between. One resistive layer is a coating on the underside of the top surface of the screen. Just beneath it is a similar resistive layer on top of its substrate. One layer has conductive connections along its sides, the other along top and bottom.

Resistive touchscreens respond to the pressure of a finger, a fingernail, or a stylus. They typically comprise a glass or acrylic base that is coated with electrically conductive and resistive layers. The thin layers are separated by invisible separator dots. When operating, an electrical current is constantly flowing through the conductive material. In the absence of a touch, the separator dots prevent the conductive layer from making contact with the resistive layer. When pressure is applied to the screen the layers are pressed together, causing a change in the electrical current. This is detected by the touchscreen controller, which interprets it as a vertical/horizontal coordinate on the screen (x- and y-axes) and registers the appropriate touch event.

Resistive type touchscreens are generally the most affordable. Although clarity is less than with other touchscreen types, they're durable and able to withstand a variety of harsh environments. This makes them particularly suited for use in POS environments, restaurants, control/automation systems and medical applications.

Resistive screens use a flexible membrane with a coating of transparent metal oxide and a grid of spacers to locate the touch point. The metal oxide coating and spacers may reduce the picture quality and brightness. The key advantage of resistive touch technology is the wide range of pointing devices e.g., a gloved finger, finger nails, credit card pens, etc. that can be used with it.

Capacitive Touchscreen Panels

Capacitive touchscreens consist of a glass panel with a capacitive (charge storing) material coating its surface. Unlike resistive touchscreens, where any object can create a touch, they require contact with a bare finger or conductive stylus. When the screen is touched by an appropriate conductive object, current from each corner of the touchscreen is drawn to the point of contact. This causes oscillator circuits located at corners of the screen to vary in frequency depending on where the screen was touched. The resultant frequency changes are measured to determine the x- and y- coordinates of the touch event.

Capacitive type touchscreens are very durable, and have a high clarity. They are used in a wide range of applications, from restaurant and POS use to industrial controls and information kiosks.

Capacitive touchscreens sense electrical signals to determine the presence and location of your finger as it makes contact with the surface of the touch screen. Strengths of capacitive technology include a fast response time, durability and a tolerance for surface contamination. Grease, water and dirt will not interfere with the capacitive screen's speed, accuracy or resolution like they can with surface acoustic wave or infrared touchscreens. Unfortunately, this technology only works with a conductive, grounded pointing device (like a finger) so in environments where gloves are required this is not an appropriate solution.

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