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Basic structure of capacitive touch screen
- May 10, 2018 -

The basic structure of the capacitive touch screen is: organic glass substrate for a single, uniform forging respectively on internal and external surfaces of the organic glass on a layer of transparent conductive film, respectively in the outside surface of transparent conductive film on the four corners of a narrow electrodes on cone. Its working principle is: when the finger touch capacitive touch screen, in working face through high frequency signal, at this point a finger and touch screen face form a coupling capacitance, the equivalent of a conductor, because work surface has high frequency signal, the fingers in touch points suck a little current, the small current respectively from touch screen on the four corners of the electrode, through the four electrodes with the finger to the four corners of the current is proportional to the linear distance, the controller through the calculation of the four current ratio, can be concluded that the contact point coordinate values.

Capacitive touch screen can be simply regarded as composed of four layer composite panel screen: the outermost layer is glass coating, followed by a conductive layer, the third layer is not conductive glass screen, the most in the fourth floor is the conductive layer. Within the most conductive layer is the shielding layer, have the effect of shielding internal electrical signal, in the middle of the conductive layer is the key part of the touch screen, four corners or four side there is a direct lead, responsible for the touch point location detection.

The top layer is tempered glass or polyethylene terephthalate (PET). The advantage of PET is that the touch screen can be thinner, and on the other hand, it is cheaper than existing plastic and glass. Insulation layer is glass (0.4 ~ 1mm), organic film (10 ~ 100um), adhesive, air layer. One of the most important is the ITO layer, the typical thickness of ITO is 50 ~ 100nm, and its resistance is about 100 ~ 300 ohms. ITO process three-dimensional structure on the influence of the capacitive touch screen is very big, it is directly related to two important capacitance parameter of the touchscreen: induction capacitance (fingers and upper ITO) and parasitic capacitance (on the lower ITO, between between the lower ITO and display screen).

Capacitive touch screen structure is mainly in glass layer coated with a layer of transparent film on the screen, and then in the conductor layer and a protective glass, double glass design can completely protect the conductor layer and sensor, light transmittance is higher at the same time, also can better support multi-touch.

The capacitive touch screen is coated with long and narrow electrodes on the four sides of the touch screen, forming a low voltage ac electric field in the conductive body. When touching the screen, the human electric field will form between the fingers and the conductor layer.

Into a coupling capacitance, quadrilateral electrode current will flow to the contact, and the current strength and finger to the electrode is inversely proportional to the distance, the touch screen behind the controller can calculate the current ratio and strength, accurately calculate the position of the touch point. The double glass not only can protect the conductor and capacitive touch screen sensors, more effectively prevent external environmental factors affect the touch screen, even if the screen is stained with filth, dust, or oily be soiled, capacitive touch screen is still can accurately calculate the touch location

Because the capacitor varies with the contact area and dielectric of the medium, the stability of the capacitor is poor, and the drift phenomenon is often produced. This kind of touch screen is suitable for the debugging stage of system development.

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