They are a part of “capacitive sensing technology,” a technology in electrical engineering. Capacitive sensing can detect and measure anything that is conductive or has a dielectric constant different from the air, known as changes in capacitance.
In the case of capacitive switches, this sensing is based upon the constant monitoring of the electrical capacity of the touch area, which is changed by the touch of a human finger.
Generally under the umbrella of touch switches, capacitive switches are among the simplest kinds of tactile sensors. Some capacitive switches can work without actual touch, simply by detecting an object, such as a finger, in its field.
Touch surfaces of capacitive switches can be designed with virtually any material, as long as it is dielectric. This includes glass, plastic, polycarbonate, wood, marble or any rough or smooth surface less than 25 mm thick.
Some capacitive switches are designed to have adjustable surface sensitivity, so that whatever device they are supporting can be operated with or without gloves. This is an especially attractive quality in northern climates or in a setting where an operator needs to wear gloves for protection. Because capacitive switches work through sensing, they do not contain any mechanical components, which eliminates potential mechanical failure.
These switches consist of three main sections: the graphic overlay, the circuit and the backer, or back panel. The overlay displays graphics and can also feature windows, embossings, coatings, adhesives and selective texturing. Overlay materials may be air, formica, standard glass, ceramic glass, PET film, polycarbonate, plexiglass, ABS, wood or gypsum. The circuit is the switch itself, which may be a Flexible Printed Circuit (FPC) or a Printed Circuit Board (PCB).
Capacitive switches are utilized in the aerospace, defense, industrial, medical, telecommunications, data/communications and consumer industries. As interface types, they often work as: buttons, sliders, touch pads, touch screens and proximity settings. Some specific examples of where they may be found include: wireless handsets, PC peripherals, LCD monitors, TVs, laptops, digital cameras, and kiosks.
When considering the design of a capacitive switch, helpful things to consider are: environmental conditions, mechanical requirements, electrical requirements, appearance and certification.