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The difference between capacitive screen and resistive screen-main structure

The capacitive touch screen can be simply viewed as a screen composed of four layers of composite screens: the outermost layer is a protective glass layer, followed by a conductive layer, the third layer is a non-conductive glass screen, and the fourth innermost layer It is also a conductive layer. The innermost conductive layer is the shielding layer, which plays the role of shielding the internal electrical signals. The middle conductive layer is the key part of the entire touch screen. There are direct leads on the four corners or sides to detect the position of the touch point. Capacitive screens use the current induction of the human body to work. When a finger touches the metal layer, due to the electric field of the human body, a coupling capacitor is formed between the user and the touch screen surface. For high-frequency current, the capacitor is a direct conductor, so the finger draws 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 by accurately calculating the ratio of these four currents. .
Advantages: There are currently several types of touch screens, which are: resistive (double-layer), surface capacitive and inductive capacitive, surface acoustic wave, infrared, and bending wave, active digitizer and optical Imaging style. They can be divided into two types. One type requires ITO, such as the first three touch screens, and the other type of structure does not require ITO, such as the latter types of screens. Currently on the market, resistive touch screens and capacitive touch screens using ITO materials are the most widely used. ITO is the English abbreviation for indium tin oxide, which is a transparent electrical conductor. The properties of this substance can be adjusted by adjusting the ratio of indium to tin, the deposition method, the degree of oxidation and the size of the crystal grains. Thin ITO materials have good transparency, but high impedance; thick ITO materials have low impedance, but transparency will deteriorate. When depositing on PET polyester film, the reaction temperature should drop below 150 degrees, which will cause incomplete oxidation of ITO. In subsequent applications, ITO will be exposed to air or air barriers, and its unit area impedance will vary due to self-oxidation. Change of time. This makes resistive touch screens need frequent calibration. The multilayer structure of the resistive touch screen will cause a large light loss. For handheld devices, it is usually necessary to increase the backlight source to compensate for the problem of poor light transmission, but this will also increase battery consumption. The advantage of resistive touch screen is that its screen and control system are relatively cheap, and the response sensitivity is also very good. The surface capacitive touch screen only uses a single layer of ITO. When a finger touches the surface of the screen, a certain amount of electric charge will be transferred to the human body. In order to recover these charge losses, the charge is replenished from the four corners of the screen. The amount of charge added in each direction is proportional to the distance of the touch point, and we can calculate the position of the touch point from this. Surface capacitance ITO coating usually requires linearized metal electrodes on the periphery of the screen to reduce the influence of corner/edge effects on the electric field. Sometimes there is an ITO shielding layer under the ITO coating to block noise. The surface capacitive touch screen needs to be calibrated at least once before it can be used.



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