Front Screen Glass Lens For IphoneXR with OCA

                                                                             Capacitive touch screen principle

It works by using the current induction of the human body. The capacitive touch screen is a four-layer composite glass screen. The inner surface and the interlayer of the glass screen are coated with a layer of ITO, and the outermost layer is a thin layer of silica glass protective layer. The interlayer ITO coating is used as the working surface. Four electrodes, the inner ITO is the shielding layer to ensure a good working environment.

When a finger touches the metal layer, due to the electric field of the human body, a coupling capacitance is formed between the user and the surface of the touch screen. For high-frequency currents, the capacitance is a direct conductor, so the finger absorbs a small current from the contact point. This current flows from the electrodes on the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position of the touch point through accurate calculation of the four current ratios. .

Drawbacks of capacitive touch screens

The light transmittance and clarity of the capacitive touch screen is better than that of the four-wire resistive screen, but of course it cannot be compared with the surface acoustic wave screen and the five-wire resistive screen. The capacitive screen is seriously reflective, and the four-layer composite touch screen with capacitive technology has uneven light transmittance for each wavelength of light, and there is a problem of color distortion. Due to the reflection of light between layers, image characters are also blurred.

In principle, the capacitive screen uses the human body as an electrode of a capacitor element. When a conductor is close to the interlayer ITO working surface to couple a sufficient amount of capacitance, the flowing current is enough to cause the capacitive screen to malfunction. We know that although the capacitance value is inversely proportional to the distance between electrodes, it is directly proportional to the relative area, and is also related to the dielectric coefficient of the medium. Therefore, when a large area of the palm or a hand-held conductor is close to the capacitive screen instead of touching it, it can cause the malfunction of the capacitive screen. Within 15 cm of the display or the body is close to the display, it can cause the malfunction of the capacitive screen.

Another disadvantage of capacitive screens is that they do not respond when touched with gloved hands or holding non-conductive objects, because of the addition of a more insulating medium.

The main disadvantage of the capacitive screen is drift: when the ambient temperature and humidity change, or the environmental electric field changes, it will cause the capacitive screen to drift, resulting in inaccuracy.

The outermost silica protective glass of the capacitive touch screen is very scratch-resistant, but it is afraid of being knocked by nails or hard objects. If a small hole is knocked out, the interlayer ITO will be damaged, whether it is the interlayer ITO or the damage during installation and transportation. The ITO layer on the inner surface, the capacitive screen will not work properly.