<P> A simple parallel - plate capacitor has two conductors separated by a dielectric layer . Most of the energy in this system is concentrated directly between the plates . Some of the energy spills over into the area outside the plates, and the electric field lines associated with this effect are called fringing fields . Part of the challenge of making a practical capacitive sensor is to design a set of printed circuit traces which direct fringing fields into an active sensing area accessible to a user . A parallel - plate capacitor is not a good choice for such a sensor pattern . Placing a finger near fringing electric fields adds conductive surface area to the capacitive system . The additional charge storage capacity added by the finger is known as finger capacitance, or CF . The capacitance of the sensor without a finger present is known as parasitic capacitance, or CP . </P> <P> In this basic technology, only one side of the insulator is coated with a conductive layer . A small voltage is applied to the layer, resulting in a uniform electrostatic field . When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed . The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel . As it has no moving parts, it is moderately durable but has limited resolution, is prone to false signals from parasitic capacitive coupling, and needs calibration during manufacture . It is therefore most often used in simple applications such as industrial controls and kiosks . </P> <P> Projected capacitive touch (PCT; also PCAP) technology is a variant of capacitive touch technology . </P> <P> This technology was first developed by Ronald and Malcolm Binstead in 1984, when a simple 16 key capacitive touchpad was invented which could sense a finger through very thick glass, even though the signal to be sensed was significantly smaller than the capacitance changes caused by varying environmental factors such as humidity, dirt, rain and temperature . </P>

When did the first touch screen computer come out